1. A handover f a i l u r e d e t e c t i o n d e v i c e c o m p r i s i n g : 5 d e t e c t i o n means f o r d e t e c t i n g at l e a s t one of handover f a i l u r e t y p e s r e g a r d i n g o u t g o i n g handover f r o m a f i r s t c e l l managed by a f i r s t b a s e s t a t i o n by observing ( a ) p r e s e n c e / a b s e n c e o f r e c e p t i o n by t h e f i r s t b a s e s t a t i o n o f a n acknowledgment r e s p o n s e t o a handover command r e g a r d i n g f i r s t handover of a mobile terminal f r o m t h e f i r s t c e l l t o a 10 s e c o n d c e l l managed by a s e c o n d b a s e s t a t i o n , and (b) p r e s e n c e / a b s e n c e of a r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t from the mobile t e r m i n a l t o the f i r s t c e l l , the r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n of t h e f i r s t h a n d o v e r . 15 2. The handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g t o Claim I , w h e r e i n t h e d e t e c t i o n m e a n s d e t e c t s a f i r s t handover f a i l u r e t y p e when t h e a c k n o w l e d g m e n t r e s p o n s e t o the handover command i s n o t r e c e i v e d w i t h i n a f i r s t p r e d e t e r m i n e d p e r i o d d e p e n d e n t o n i n i t i a t i o n o f t h e f i r s t handover and the r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t is also not 20 r e c e i v e d w i t h i n a s e c o n d p r e d e t e r m i n e d period d e p e n d e n t o n i n i t i a t i o n of the f i r s t handover.

3. The handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g t o Claim I or 2, wherein the d e t e c t i o n m e a n s d e t e c t s a second handover f a i l u r e type 25 when the r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t i s r e c e i v e d within a third p r e d e t e r m i n e d period d e p e n d e n t on i n i t i a t i o n of the f i r s t I ~ a n d o v e r .

4. The handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g to a n y o n e of 30 Claims 1 to 3, w h e r e i n t h e d e t e c t i o n m e a n s d e t e c t s a s e c o n d handover f a i l u r e t y p e when the r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t is r e c e i v e d b e f o r e receptioil of a I l a l ~ d o v e rc o n ~ p l e t i o nn o t i f i c a t i o n regardii-ig t h e f i r s t handover. 5 2

5. The handover f a i l u r e d e t e c t i o n d e v i c e accord.ing to any one of Claims 1 to 4, w h e r e i n t h e d e t e c t i o n m e a n s detects a secoild handover f a i l u r e t y p e w h e n the r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t is r e c e i v e d w i t h i n a f o u r t h p r e d e t e r m i n e d p e r i o d d e p e n d e n t on reception 5 of a handover c o m p l e t i o n n o t i f i c a t i o n r e g a r d i n g t h e f i r s t handover.

6. The handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g to Claim 4 o r 5 , wherein the handover c o m p l e t i o n n o t i f i c a t i o n is t r a n s m i t t e d to the f i r s t b a s e s t a t i o n f r o m t h e s e c o n d b a s e s t a t i o n or f r o m a n e t w o r k n o d e 10 belonging to a h i g h e r network t o w h i c h t h e f i r s t b a s e s t a t i o n is c o n n e c t e d .

7. The handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g t o a n y o n e o f Claims 4 to 6, w h e r e i n t h e handover completion n o t i f i c a t i o n i s a 15 m e s s a g e r e c e i v e d by the f i r s t b a s e s t a t i o n d u r i n g a handover procedure.

8. The handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g t o a n y o n e o f Claims 1 t o 7, wherein t h e d e t e c t i o n means d e t e c t s a t h i r d handover f a i l u r e t y p e when 20 t h e r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t i s n o t r e c e i v e d w i t h i n a f o u r t h p r e d e t e r m i n e d period d e p e n d e n t o n i n i t i a t i o n o f t h e f i r s t handover, but handover f a i l u r e i n f o r m a t i o n i s r e c e i v e d f r o m t h e s e c o n d b a s e s t a t i o n w i t h i n a f i f t h p r e d e t e r m i n e d period d e p e n d e n t o n i n i t i a t i o n o f the f i r s t handover, and 2 5 the t h i r d handover f a i l u r e t y p e c o r r e s p o n d s to a s i t u a t i o n where t h e m o b i l e t e r m i n a l t h a t has e x p e r i e n c e d a b n o r m a l discollllection i n t h e second cell d u r i n g e x e c u t i o n of t h e f i r s t handover o r a f t e r c o m p l e t i o ~ l of t h e f i r s t handover t r i e s c o n n e c t i o n r e - e s t a b l i s h m e n t t o a t h i r d c e l l d i f f e r e n t f r o m both the f i r s t and s e c o n d c e l l s . 3 0

9. The llal1dover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g to Claim 8, w h e r e i n t h e handover f a i l u r e i n f o r m a t i o n i n c l u d e s an i d e n t i f i e r o f t h e third cell t h a t is estimated by t h e s e c o n d b a s e s t a t i o n based on m e a s u r e m e n t i n f o r m a t i o n o f r a d i o q u a l i t y by the mobile terminal when 53 the m o b i l e t e r m i n a l i s c o n n e c t e d t o t h e s e c o n d c e l l w i t h o u t r e c e i v i n g i n f o r m a t i o n a t t h e s e c o n d b a s e s t a t i o n from a t h i r d b a s e s t a t i o n t h a t manages t h e t h i r d c e l l . 5 10. The h a n d o v e r f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g t o C l a i m 8 or 9, w h e r e i n t h e h a n d o v e r f a i l u r e i n f o r m a t i o n i s t r a n s m i t t e d w h e n t h e m o b i l e t e r m i n a l e x p e r i e n c e s t h e a b n o r m a l d i s c o n n e c t i o n in t h e second c e l l w i t h i n a s i x t h p r e d e t e r m i n e d p e r i o d d e p e n d e n t on c o n n e c t i o n of t h e m o b i l e t e r ~ n i n a lt o t h e s e c o n d c e l l b y t h e f i r s t h a n d o v e r . 10

11. The h a n d o v e r f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g to any one of C l a i m s 1 t o 7, w h e r e i n t h e d e t e c t i o n means d e t e c t s a t h i r d h a n d o v e r f a i l u r e t y p e when t h e r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t i s not r e c e i v e d w i t h i n a 15 f o u r t h p r e d e t e r m i n e d p e r i o d d e p e n d e n t on i n i t i a t i o n of t h e f i r s t h a n d o v e r , but h a n d o v e r f a i l u r e i n f o r m a t i o n i s r e c e i v e d from a t h i r d base s t a t i o n t h a t m a n a g e s a t h i r d c e l l d i f f e r e n t from b o t h t h e f i r s t a n d s e c o n d c e l l s w i t h i n a s e v e n t h p r e d e t e r m i n e d p e r i o d d e p e n d e n t o n i n i t i a t i o n o f t h e f i r s t h a n d o v e r , and 2 0 t h e t h i r d h a n d o v e r f a i l u r e t y p e c o r r e s p o n d s t o t h e s i t u a t i o n w h e r e t h e m o b i l e t e r m i n a l t h a t has e x p e r i e n c e d t h e a b n o r m a l d i s c o n n e c t i o n in t h e s e c o n d c e l l d u r i n g t h e e x e c u t i o n o f t h e f i r s t h a n d o v e r or a f t e r t h e c o m p l e t i o ~ lo f t h e f i r s t h a n d o v e r t r i e s t h e c o n n e c t i o n r e - e s t a b l i s h m e n t to t h e t h i r d c e l l d i f f e r e n t f r o m both the 25 f i r s t and s e c o n d c e l l s . 1 2 . The h a n d o v e r f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g to Claim 11. w h e r e i n the h a n d o v e r f a i l u r e i n f o r m a t i o n i s t r a n s m i t t e d when the t h i r d base s t a t i o n d e t e c t s p r e s e ~ l c e of a b a s e s t a t i o n t h a t h a s r e q u e s t e d 30 h a n d o v e r of the n l o b i l e t e r m i n a l to t h e second cell within an e i g h t h p r e d e t e r m i n e d p e r i o d b e f o r e t h e c o n n e c t i o n r e - e s t a b l i s h m e n t of the mobile t e r m i n a l in t h e t h i r d c e l l .

13. The h a n d o v e r f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g t o any one 5 4 of Claims 1 to 1 2 , w h e r e i n t h e d e t e c t i o n m e a n s g e n e r a t e s feedback i n f o r m a t i o n on handover f r o m t h e f i r s t c e l l b a s e d on a d e t e c t i o n r e s u l t of the a t l e a s t one of the handover f a i l u r e t y p e s . 1 4 . T h e handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g t o Claim 1 3 , wherein the f e e d b a c k i n f o r m a t i o n i n d i c a t e s thc n u m b e r o f o c c u r r e n c e s or a n o c c u r r e n c e r a t e of the at l e a s t one of the handover f a i l u r e t y p e s .

15. The handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g to any one 10 of Claims 1 to 1 4 , w h e r e i n t h e a c k n o w l e d g m e n t r e s p o n s e t o the handover command is t r a n s m i t t e d to the f i r s t base s t a t i o n f r o m t h e mobile t e r m i n a l . 1 6 . T h e handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g to any one 15 of Claims 1 to 1 5 , w h e r e i n the a c k n o w l e d g m e n t r e s p o n s e t o t h e handover command is a n a c k n o w l e d g m e n t r e s p o n s e to b e t r a n s m i t t e d to the f i r s t b a s e s t a t i o n by t h e m o b i l e t e r m i n a l in o r d e r t o control a ret r a n s m i s s i o n of a m e s s a g e t r a n s m i t t e d t o the mobile terminal from the f i r s t base s t a t i o n d u r i n g a handover p r o c e d u r e . 2 0

17. A handover p a r a m e t e r a d j u s t m e n t d e v i c e c o m p r i s i n g : adjustment means f o r a d j u s t i n g a handover parameter for c o n t r o l l i n g o u t g o i n g handover from a f i r s t cell managed by a f i r s t base s t a t i o n based o n ( a ) p r e s e n c e l a b s e n c e o f r e c e p t i o n by the f i r s t base 25 s t a t i o n of an a c k n o w l e d g m e n t r e s p o n s e t o a handover command r e g a r d i n g f i r s t handover of a mobile terminal fro111 t h e f i r s t c e l l t o a second cell managed by a second base s t a t i o n , and (b) p r e s e n c e l a b s e n c e of a request f o r c o n n e c t i o n r e - e s t a b l i s h m e n t from the mobile terminal to t h e f i r s t c e l l , the r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n 30 of t h e f i r s t handover. 1 8 . T h e handover parameter a d j u s t m e n t d c v i c c a c c o r d i n g to Claim 17, wherein the a d j u s t m e n t m e a n s r e c e i v e s f e e d b a c k information based on a 55 d e t e c t i o n r e s u l t of at l e a s t o n e o f handover f a i l u r e t y p e s r e g a r d i n g the outgoing handover f r o m t h e f i r s t c e l l , and t h e d e t e c t i o n r e s u l t of the at l e a s t one of the handover f a i l u r e types is obtained by o b s e r v a t i o n o f t h e p r e s e n c e l a b s e n c e of the 5 r e c e p t i o n o f t h e a c k n o w l e d g m e n t r e s p o n s e to the handover command, and the p r e s e n c e l a b s e n c e o f t h e r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t .

19. The handover p a r a m e t e r a d j u s t m e n t d e v i c e a c c o r d i n g to 10 Claim 18, w h e r e i n t h e a d j u s t m e n t means a d j u s t s the handover parameter by a n a l y z i n g t h e f e e d b a c k i n f o r m a t i o n .

20. The handover p a r a m e t e r a d j u s t m e n t d e v i c e a c c o r d i n g t o Claim 18 or 1 9 , w h e r e i n 15 t h e a d j u s t m e n t means: makes each of the at l e a s t one of the handover f a i l u r e t y p e s c o r r e s p o n d t o any o f a p l u r a l i t y o f a d j u s t m e n t d i r e c t i o n s of the handover p a r a m e t e r ; c a l c u l a t e s a t o t a l sum of t h e n u m b e r o f o c c u r r e n c e s or an 20 o c c u r r e n c e r a t e o f t h e handover f a i l u r e t y p e made to correspond to the each a d j u s t m e n t d i r e c t i o n , a s f o r e a c h o f t h e p l u r a l i t y o f a d j u s t m e n t d i r e c t i o n s ; and a d j u s t s t h e handover p a r a m e t e r t o the adjustment d i r e c t i o n w h e r e t h e t o t a l sum o f t h e n u m b e r of o c c u r r e n c e s o r t h e o c c u r r e n c e 25 r a t e is t h e l a r g e s t .

21. The handover p a r a m e t e r a d j u s t m e n t d e v i c e a c c o r d i n g to any one of Claims 17 t o 20, w h e r e i n t h e handover parameter i n c l u d e s at l e a s t one o f a f i r s t o f f s e t t h a t a c t s o n r a d i o q u a l i t y o f t h e f i r s t c e l l , a 30 second o f f s e t that acts on radio q u a l i t y o f t h e s e c o n d c e l l , and a guard time for t r i g g e r i n g t r a n s m i s s i o n o f a m e a s u r e m e n t report by t h e m o b i l e terminal connected to the f i r s t c e l l .

22. A handover f a i l u r e i n f o r m a t i o n generation device 56 c o m p r i s i n g : g e n e r a t i o n m e a n s f o r g e n e r a t i n g handover f a i l u r e i n f o r m a t i o n to be t r a n s m i t t e d to a f i r s t b a s e s t a t i o n , the handover f a i l u r e information being used to d e t e c t a handover f a i l u r e type t h a t c o r r e s p o n d s t o a 5 s i t u a t i o n w h e r e a m o b i l e t e r m i n a l , has e x p e r i e n c e d a b n o r m a l d i s c o n n e c t i o n in a s e c o n d c e l l m a n a g e d by a second b a s e s t a t i o n during e x e c u t i o n of f i r s t handover f r o m a f i r s t c e l l managed by the f i r s t base s t a t i o n t o t h e s e c o n d cell or a f t e r c o m p l e t i o n o f t h e f i r s t handover, and then t r i e s c o n n e c t i o n r e - e s t a b l i s h m e n t to a third cell d i f f e r e n t from 10 both the f i r s t a n d s e c o n d c e l l s .

23. The handover f a i l u r e i n f o r m a t i o n g e n e r a t i o n d e v i c e according to C l a i m 2 2 , w h e r e i n t h e g e n e r a t i o n m e a n s is c o u p l e d t o t h e second b a s e s t a t i o n , and the handover f a i l u r e i n f o r m a t i o n i n c l u d e s a n i d e n t i f i e r o f the t h i r d c e l l t h a t is e s t i m a t e d by t h e g e n e r a t i o n m e a n s based o n a m e a s u r e m e n t r e p o r t o f r a d i o q u a l i t y by the m o b i l e t e r m i n a l when the mobile t e r m i n a l is connected to the second c e l l w i t h o u t r e c e i v i n g i n f o r m a t i o n at the g e n e r a t i o n m e a n s f r o m a third base s t a t i o n that m a n a g e s t h e third c e l l .

24. The handover f a i l u r e illformation g e n e r a t i o n d e v i c e a c c o r d i n g t o Claim 2 3 , w h e r e i n t h e g e n e r a t i o n means t r a n s m i t s the handover f a i l u r e i n f o r m a t i o n when the mobile terminal e x p e r i e n c e s the 25 a b n o r m a l d i s c o n n e c t i o n in the s e c o n d c e l l w i t h i n a p r e d e t e r m i n e d period dependent on c o n n e c t i o n o f the mobile terminal to the second cell by t h e f i r s t handover.

25. The handover f a i l u r e i ~ l f o r n ~ a t i ogi le neration device 30 a c c o r d i n g t o Claim 2 3 or 2 4 , w h e r e i n t h e generation m e a n s e s t i m a t e s as thc third ccll a cell having the b e s t r a d i o quality i l l the n ~ e a s u r e m e n t r e p o r t .

26. The kandover r a i l u s e i n f ' o r ~ ~ ~ a t igoenn e r a t i o n d e v i c e according to Claim 22, wherein t h e g e n e r a t i o n m e a n s is c o u p l e d t o a t h i r d base s t a t i o n t h a t manages the t h i r d c e l l , a n d t h e g e n e r a t i o n means t r a n s m i t s the handover f a i l u r e i n f o r m a t i o n in r e s p o n s e t o d e t e c t i n g p r e s e n c e o f a b a s e s t a t i o n t h a t h a s r e q u e s t e d handover o f t h e m o b i l e t e r m i n a l to the second c e l l w i t h i n a p r e d e t e r m i n e d p e r i o d b e f o r e c o n n e c t i o n r e - e s t a b l i s h m e n t o f t h e m o b i l e terminal i n t h e t h i r d c e l l . 10 27. The handover f a i l u r e i n f o r m a t i o n g e n e r a t i o n d e v i c e according to Claim 26, w h e r e i n t h e g e n e r a t i o n m e a n s d e t e c t s , from base s t a t i o n s t h a t manage c e l l s to which handover c a n b e performed from the t h i r d c e l l , the b a s e s t a t i o n t h a t has r e q u e s t e d t h e handover of the m o b i l e t e r m i n a l t o t h e s e c o n d c e l l .

28. A system for handover o p t i m i z a t i o n c o m p r i s i n g : d e t e c t i o n means f o r d e t e c t i n g at l e a s t one of handover f a i l u r e t y p e s r e g a r d i n g o u t g o i n g handover from a f i r s t cell managed by a f i r s t base s t a t i o n by o b s e r v i n g ( a ) p r e s e n c e l a b s e n c e o f reception by the f i r s t 20 base s t a t i o n of a n a c k n o w l e d g m e n t r e s p o n s e t o a handover command r e g a r d i n g f i r s t handover of a m o b i l e t e r m i n a l f r o m t h e f i r s t c e l l to a second cell managed by a s e c o n d b a s e s t a t i o n , and (b) p r e s e n c e l a b s e n c e of a r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m t h e mobile t e r m i n a l to the f i r s t c e l l , the r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n 25 of the f i r s t h a n d o v e r ; and a d j u s t m e n t m e a n s for a d j u s t i n g a handover parameter for c o n t r o l l i n g tlie outgoing handover from the f i r s t cell based on a d e t e c t i o n r e s u l t of the at l e a s t o n e of the handover f a i l u r e t y p e s . 2 9 . The system according to Claim 28. wherein the detection n ~ e a n sd e t e c t s a f i r s t handover f a i l u r e t y p e when t h e acknowledgment response t o t h e handover command is not received within a f i r s t p r e d e t e r m i n e d period dependent on i n i t i a t i o n of the f i r s t handover and the request f o r c o n n e c t i o n r e - e s t a b l i s h m e n t is also not received within 5 8 a s e c o n d p r e d e t e r m i n e d p e r i o d d e p e n d e n t o n i n i t i a t i o n of the f i r s t handover. 3 0 . T h e s y s t e m a c c o r d i n g t o Claim 28 or 29, wherein the 5 d e t e c t i o n m e a n s d e t e c t s a s e c o n d handover f a i l u r e t y p e when the r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t is r e c e i v e d w i t h i n a third p r e d e t e r m i n e d period dependent on i n i t i a t i o n o f t h e f i r s t h a n d o v e r .

31. The s y s t e m a c c o r d i n g t o any one o f C l a i m s 2 8 to 30, wherein 10 the d e t e c t i o n means d e t e c t s a s e c o n d handover f a i l u r e t y p e when t h e r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t is r e c e i v e d b e f o r e r e c e p t i o n of a handover c o m p l e t i o n n o t i f i c a t i o n r e g a r d i n g t h e f i r s t handover.

32. The s y s t e m a c c o r d i n g to any one of C l a i m s 2 8 t o 3 1 , wherein 15 t h e d e t e c t i o n means d e t e c t s a s e c o n d handover f a i l u r e t y p e when the r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t is r e c e i v e d w i t h i n a fourth p r e d e t e r m i n e d p e r i o d d e p e n d e n t on r e c e p t i o n o f a handover completion n o t i f i c a t i o n r e g a r d i n g t h e f i r s t h a n d o v e r . 2 0 3 3 . T h e s y s t e m a c c o r d i n g to any one of C l a i m s 2 8 to 32, f u r t h e r c o m p r i s i n g g e n e r a t i o n m e a n s f o r g e n e r a t i n g handover f a i l u r e i n f o r m a t i o n and n o t i f y i n g t h e d e t e c t i o n m e a n s o f the handover f a i l u r e i n f o r m a t i o n , w h e r e i n the d e t e c t i o n means d e t e c t s a t h i r d handover f a i l u r e type when 25 t h e r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t is not r e c e i v e d w i t h i n a f o u r t h p r e d e t e r m i n e d period d e p e n d e n t o n i n i t i a t i o n o f the f i r s t handover, but the handover f a i l u r e informati011 is received within a f i f t h p r e d e t e r m i n e d period dependent on i n i t i a t i o n o f the f i r s t handover, and 3 0 the third handover f a i l u r e type c o r r e s p o n d s to a s i t u a t i o n where the mobile terminal t h a t h a s e x p e r i e ~ l c e d abnormal disconnection in the second cell d u r i n g e x e c u t i o n of the f i r s t handover or a f t e r c o m p l e t i o l ~ of t h e f i r s t handover t r i e s c o n n e c t i o n r e - e s t a b l i s h m e n t to a third cell d i f f e r e n t from both the f i r s t a n d s e c o n d c e l l s .

34. The s y s t e m a c c o r d i n g to Claim 3 3 , w h e r e i n t h e g e n e r a t i o n m e a n s is c o u p l e d t o the s e c o n d b a s e s t a t i o n , and the handover f a i l u r e i n f o r m a t i o n i n c l u d e s a n i d e n t i f i e r of the 5 third c e l l t h a t is e s t i m a t e d by the g e n e r a t i o n m e a n s based on m e a s u r e m e n t i n f o r m a t i o n of r a d i o q u a l i t y by t h e m o b i l e terminal when t h e m o b i l e t e r m i n a l is connected to t h e s e c o n d c e l l without r e c e i v i n g i n f o r m a t i o n at t h e g e n e r a t i o n m e a n s f r o m a t h i r d b a s e s t a t i o n that manages the third c e l l .

35. The s y s t e m a c c o r d i n g t o C l a i m 3 3 o r 34, wherein the g e n e r a t i o n m e a n s i s c o u p l e d t o the second base s t a t i o n , and t h e g e n e r a t i o n means t r a n s m i t s t h e handover f a i l u r e i n f o r m a t i o n when the m o b i l e t e r m i n a l e x p e r i e n c e s t h e a b n o r m a l d i s c o n n e c t i o n in 15 t h e s e c o n d c e l l w i t h i n a s i x t h p r e d e t e r m i n e d period dependent on connection of the mobile t e r m i n a l to the s e c o n d c e l l by t h e f i r s t handover.

36. The s y s t e m a c c o r d i n g t o C l a i m 3 3 , w h e r e i n 2 0 the generatioll m e a n s i s coupled to a third base s t a t i o n that m a n a g e s t h e third c e l l , a n d t h e g e n e r a t i o n means t r a n s m i t s t h e handover f a i l u r e i ~ ~ f o r m a t i o n in r e s p o n s e t o d e t e c t i n g p r e s e n c e o f a base s t a t i o n t h a t h a s r e q u e s t e d handover o f t h e m o b i l e t e r m i n a l t o the second c e l l w i t h i n an eighth 25 p r e d e t e r m i n e d period b e f o r e c o n n e c t i o n r e - c s t a b l i s l ~ m e n t of the mobile terminal in the third c e l l .

37. The system a c c o r d i n g t o Claim 36, w h e r e i n t h e g e n e r a t i o n m e a n s d e t e c t s , f r o m b a s e s t a t i o n s that manage c e l l s to which handover 30 can b e p e r f o r m e d f r o m t h e t h i r d c e l l , the base s t a t i o n that has r e q u e s t e d o f the m o b i l e t e r m i n a l t h e handover to the s e c o n d c e l l . 3 8 . T h e s y s t e m a c c o r d i n g t o any one o f C l a i m s 28 to 37, wherein the handover p a r a m e t e r i n c l u d e s a t l e a s t one of a f i r s t o f f s e t that acts 60 o n r a d i o q u a l i t y of t h e f i r s t c e l l , a s e c o n d o f f s e t that acts on radio q u a l i t y of t h e s e c o n d c e l l , and a g u a r d t i m e f o r t r i g g e r i n g t r a n s m i s s i o n of a m e a s u r e m e n t r e p o r t by the m o b i l e t e r m i n a l c o n n e c t e d to t h e f i r s t c e l l . 5

39. The s y s t e m a c c o r d i n g to Claim 3 8 d e p e n d i n g f r o m Claim 29, w h e r e i n when an o c c u r r e n c e r a t e o f t h e f i r s t handover f a i l u r e t y p e exceeds a p r e d e t e r m i n e d v a l u e , t h e a d j u s t m e n t m e a n s e x e c u t e s at l e a s t one of decrease in t h e f i r s t o f f s e t , i n c r e a s e in the s e c o n d o f f s e t , and 10 decrease in t h e g u a r d t i m e .

40. The s y s t e m a c c o r d i n g to Claim 3 8 d e p e n d i n g from C l a i m 3 0 , 31, or 3 2 , w h e r e i n when a n o c c u r r e n c e r a t e of t h e s e c o n d handover f a i l u r e t y p e e x c e e d s a p r e d e t e r m i n e d v a l u e , t h e a d j u s t m e n t m e a n s 15 executes at l e a s t one of the i n c r e a s e in the f i r s t o f f s e t , the decrease in t h e s e c o n d o f f s e t , a n d the i n c r e a s e in the guard time.

41. The s y s t e m a c c o r d i n g to Claim 3 8 d e p e n d i n g f r o m a n y one of Claims 3 3 t o 3 7 , w h e r e i n 20 the handover p a r a m e t e r i n c l u d e s t h e s e c o n d o f f s e t and a third o f f s e t that a c t s o n radio q u a l i t y of t h e t h i r d c e l l , and when an occurrence rate of the third handover f a i l u r e t y p e exceeds a p r e d e t e r m i n e d v a l u e , the adjustment means d e c r e a s e s the s e c o n d o f f s e t and i n c r e a s e s t h e third o f f s e t .

42. A b a s e s t a t i o n c o m p r i s i n g t h e I ~ a n d o v e r f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g t o any one of Claims 1 to 16.

43. A handover f a i l u r e d e t e c t i o n method c o m p r i s i n g : d e t e c t i n g at least o n e o f handover f a i l u r e t y p e s regarding outgoing handover fro111 a f i r s t cell managed by a f i r s t b a s e s t a t i o n by o b s e r v i n g ( a ) p r e s e n c c / a b s e n c e of reception by the f i r s t base s t a t i o n o f an a c k n o w l e d g m e n t r e s p o n s e t o a handover command regarding f i r s t handover of a m o b i l e terminal from t h e f i r s t c e l l to a second cell managed by a s e c o n d base s t a t i o n , a n d ( b ) p r e s e n c e l a b s e n c e o f a r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m t h e mobile terminal to the f i r s t c e l l , the r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n of the f i r s t h a n d o v e r . 5 44. A handover p a r a m e t e r a d j u s t m e n t m e t h o d c o m p r i s i n g : a d j u s t i n g a handover p a r a m e t e r f o r c o n t r o l l i n g o u t g o i n g handover f r o m a f i r s t c e l l managed by a f i r s t b a s e s t a t i o n based on (a) p r e s e n c e / a b s e n c e o f r e c e p t i o n by the f i r s t b a s e s t a t i o n of an a c k n o w l e d g m e n t r e s p o n s e t o a handover command r e g a r d i n g f i r s t 10 handover of a m o b i l e t e r m i n a l f r o m the f i r s t c e l l t o a s e c o n d cell managed by a s e c o n d b a s e s t a t i o n , a n d ( b ) p r e s e n c e l a b s e n c e o f a r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m t h e mobile terminal to the f i r s t c e l l , t h e r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n of the f i r s t h a n d o v e r . 15 45. A n o n - t r a n s i t o r y c o m p u t e r r e a d a b l e medium s t o r i n g a program f o r c a u s i n g a c o m p u t e r t o p e r f o r m a m e t h o d for handover f a i l u r e d e t e c t i o n , wherein the method i n c l u d e s d e t e c t i n g at l e a s t one of handover f a i l u r e t y p e s r e g a r d i n g o u t g o i n g handover f r o m a f i r s t c e l l managed by a f i r s t 20 base s t a t i o n by observing ( a ) p r e s e n c e l a b s e n c e of r e c e p t i o n by t h e f i r s t base s t a t i o n of an a c k n o w l e d g ~ n e n t response to a handover command r e g a r d i n g f i r s t handover of a m o b i l e terminal from the f i r s t cell t o a second c e l l managed by a s e c o n d base s t a t i o n , and (b) p r e s e n c e l a b s e n c e o f a r e q u e s t for c o ~ l n e c t i o i l r e - e s t a b l i s h m e n t from the 25 mobile terminal to the f i r s t c e l l , the r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n of t h e f i r s t handover.

46. A n o n - t r a n s i t o r y computer readable medium s t o r i n g a program f o r c a u s i n g a c o m p u t e r to perform a m e t h o d f o r handover 30 p a r a m e t e r a d j u s t m e n t . wherein the method i n c l u d e s a d j u s t i n g a handover parameter for c o n t r o l l i n g o u t g o i n g handover from a f i r s t cell managed by a f i r s t base s t a t i o n based on ( a ) p r e s e n c e l a b s e n c e o f r e c e p t i o n by the f i r s t base s t a t i o n of a11 a c k n o w l e d g m e n t r e s p o n s e to a handover command 62 r e g a r d i n g f i r s t haildoves of a mobile terminal f r o m t h e f i r s t c e l l to a second cell managed by a second b a s e s t a t i o n , and (b) p r e s e n c e / a b s e n c e of a r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t from the mobile terminal to the f i r s t c e l l , the request o c c u r r i n g a f t e r i n i t i a t i o n 5 of the f i r s t handover. Dated this 08th Day of July 2015 Of Anand And Anand Advocates Agents for the Applicant 63 ABSTRACT HANDOVER FAILURE DETECTION DEVICE, HANDOVER PARAMETER ADJUSTMENT DEVICE, AND HANDOVER OPTIMIZATION SYSTEM A handover f a i l u r e d e t e c t i o n d e v i c e (121) d e t e c t s a t l e a s t one of handover f a i l u r e t y p e s r e g a r d i n g o u t g o i n g handover f r o m a f i r s t cell (13 1) managed by a f i r s t base s t a t i o n (1 11) by o b s e r v i n g : ( a ) p r e s e n c e l a b s e n c e of r e c e p t i o n by the f i r s t base s t a t i o n (1 1 1 ) o f an 10 acknowledgment response to a handover command r e g a r d i n g f i r s t handover of a m o b i l e t e r m i n a l (101) from t h e f i r s t c e l l ( 1 3 1 ) to a s e c o n d c e l l ( 1 3 2 ) managed by a s e c o n d base s t a t i o n (1 12); and (b) p r e s e n c e l a b s e n c e of a r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t from the m o b i l e t e r m i n a l (101) to the f i r s t c e l l ( 1 3 1 ) , the r e q u e s t occurring 15 a f t e r i n i t i a t i o n of the f i r s t h a n d o v e r . As a r e s u l t , i t c o n t r i b u t e s to improvement of handover f a i l u r e d e t e c t i o n o r r e d u c t i o n of handover f a i l u r e in a s i t u a t i o n w h e r e exchange of i n f o r m a t i o n b e t w e e n base s t a t i o n s is r e s t r i c t e d .

DESCRIPTION
HANDOVER F A I L U R E D E T E C T I O N DEVICE, HANDOVER
PARAMETER ADJUSTMENT DEVICE, AND HANDOVER
OPTIMIZATION SYSTEM
T e c h n i c a l Field
[OOOI]
The p r e s e n t a p p l i c a t i o n r e l a t e s to d e t e c t i o n of h a n d o v e r f a i l u r e ,
10 or t o a d j u s t m e n t o f an HO ( h a n d o v e r ) p a r a m e t e r based on t h e d e t e c t i o n
of t h e HO ( h a n d o v e r ) f a i l u r e .
Background Art
[0002]
In a r a d i o c o m m u n i c a t i o n s y s t e m , i n moving f r o m a s e r v i n g c e l l
15 ( s o u r c e c e l l ) to a n o t h e r c e l l , a m o b i l e t e r m i n a l p e r f o r m s s w i t c h i n g
p r o c e s s i n g o f t h e s e r v i n g c e l l c a l l e d h a n d o v e r , a n d c o n t i n u e s
c o m m u n i c a t i o n . I n o r d e r to a c h i e v e h a n d o v e r of t h e m o b i l e t e r m i n a l , a
base s t a t i o n t h a t m a n a g e s t h e s o u r c e c e l l i n s t r u c t s t h e m o b i l e t e r m i n a l
to t r a n s m i t a m e a s u r e m e n t r e p o r t w h e n a p r e d e t e r m i n e d event o c c u r s .
20 The p r e d e t e r m i n e d e v e n t i s , f o r e x a m p l e , d e t e r i o r a t i o n of r a d i o q u a l i t y
of the s o u r c e c c l l . The m e a s u r e m e n t r e p o r t g e n e r a t e d by t h e m o b i l e
t e r m i n a l i n c l u d e s m e a s u r e m e n t r e s u l t s of r a d i o q u a l i t y of t h e s o u r c e
c e l l a n d i t s n e i g h b o r i n g c e l l s . In r e s p o n s e t o r e c e i v i n g the
m e a s u r e m e n t r e p o r t f r o m t h e m o b i l e t e r m i n a l , t h e b a s e s t a t i o n of t h e
25 s o u r c e c e l l d e t e r m i n e s a c e l l ( t a r g e t c e l l ) to which a r a d i o link
c o n n e c t i o n s w i t c h e s b a s e d o n t h e m e a s u r e m e n t r e p o r t , and i n i t i a t e s a
h a n d o v e r p r o c e d u r e i n c l u d i n g s i g n a l i n g with the mobile t e r m i n a l and
t h e t a r g e t c e l l .
[ 0 0 0 3 ]
3 0 H e r e , i n t r o d u c e d i s one of t r a n s m i s s i o n e v e n t s of the
m e a s u r e m e n t r e p o r t d e f i n e d by 3GPP TS 3 6 . 3 3 1 V 9 . 3 . 0 ( 2 0 1 0 - 0 6 ) ,
which is a t e c h n i c a l s p e c i f i c a t i o n r e g a r d i n g L T E ( L o n g Term
E v o l u t i o n ) / E - U T R A N ( E v o l v e d U T R A N ) . An e s s e n t i a l p o r t i o n o f a
r e p o r t i n g e v e n t d e f i n e d as E v e n t A 3 ( N e i g h b o r bccomes o f f s e t b e t t e r
than s e r v i n g ) i n t h e a b o v e - d e s c r i b e d l i t e r a t u r e is expressed by the
f o l l o w i n g E x p r e s s i o n ( 1 ) .
Ps + Os < PT + OT (1)
[0 0 0 41
5 Ps in Expression (1) is a m e a s u r e m e n t r e s u l t of r a d i o q u a l i t y of
a s o u r c e c e l l , a n d PT t h e r e i n is a m e a s u r e m e n t r e s u l t of radio q u a l i t y
o f a n e i g h b o r i n g c e l l . In a c a s e o f LTE, Ps and PT are downlink RSRP
( R e f e r e n c e S i g n a l R e c e i v e d P o w e r ) or RSRQ ( R e f e r e n c e Signal
R e c e i v e d Q u a l i t y ) . The RSRQ i s a r a t i o of the RSRP to t o t a l r e c e i v e d
10 power ( R S S I : R e c e i v e d S i g n a l S t r e n g t h I n d i c a t o r ) .
[ 0 0 0 5 ]
Os in Expression (1) is an o f f s e t value t h a t a c t s o n radio q u a l i t y
of a d o w n l i n k r e f e r e n c e s i g n a l of t h e s o u r c e c e l l , and i s an HO
p a r a m e t e r g e n e r a l l y c a l l e d a n a 3 - o f f s e t ( o r h y s t e r e s i s ) . Meanwhile, OT
15 in Expression ( 1 ) i s an o f f s e t value that a c t s on radio q u a l i t y of a
d o w n l i n k r e f e r e n c e s i g n a l of t h e n e i g h b o r i n g c e l l , and is an HO
p a r a m e t e r g e n e r a l l y c a l l e d a CIO ( C e l l I n d i v i d u a l O f f s e t ) . A value of
the CIO ( i . e . , OT) may be s e t t o b e d i f f e r e n t f o r e a c h neighboring c e l l .
T h e C I O i s included in a n e i g h b o r i n g l i s t ( a l s o called a neighboring
20 c e l l l i s t ) of w h i c l ~t he b a s e s t a t i o n n o t i f i e s nlobile t e r m i n a l s c o n n e c t e d
to a c e l l m a n a g e d by the b a s e s t a t i o n i t s e l f .
[ 0 0 0 6 ]
When a n o p e r a t i n g c o n d i t i o n of Expression ( 1 ) is s e t t o t h e base
s t a t i o n , the base s t a t i o n i n f o r m s a mobile t e r m i n a l , c o n n e c t e d to the
25 c e l l managed by the b a s e s t a t i o n , about the o p e r a t i n g condition of
E x p r e s s i o n ( 1 ) . When a p e r i o d in which the c o n d i t i o n of Expression
( 1 ) is s a t i s f i e d c o n t i n u e s e x c e e d i n g a p r e d e t e r m i n e d p e r i o d d e f i n e d as
a guard time (TT?': Time t o T r i g g e r ) , the mobile t e r m i n a l t r a n s m i t s a
m e a s u r e m e n t r e p o r t t o the b a s e s t a t i o n that manages the s o u r c e c e l l .
30 In r e s p o n s e t o r e c e i v i n g t h e m e a s u r e m e n t r e p o r t f r o m the mobile
t e r m i n a l , the base s t a t i o n d e c i d e s a t a r g e t c e l l based on the
measurement r e p o r t , and i n i t i a t e s handover to the t a r g e t c e l l .
10 0 0 71
I l o w e v e r , wllen the i n i t i a t i o n of the handover is too late or too
3
e a r l y , a c o n n e c t i o n f a i l u r e i n v o l v i n g a b n o r m a l d i s c o n n e c t i o n o f a radio
l i n k ( h e r e i n a f t e r r e f e r r e d to as RLF ( R a d i o L i n k F a i l u r e ) ) occurs. In
the p r e s e n t d e s c r i p t i o n , t h e c o n n e c t i o n f a i l u r e i n v o l v i n g RLF caused
by i n a p p r o p r i a t e handover i s c a l l e d " h a n d o v e r f a i l u r e " . Handover
5 o p t i m i z a t i o n o r MRO ( M o b i l i t y R o b u s t n e s s O p t i m i z a t i o n ) is a
technology of reducing handover f a i l u r e s by d e t e c t i n g them and
a d j u s t i n g HO p a r a m e t e r s , a n d is one of m a j o r u s e c a s e s o f SON ( S e l f -
O r g a n i z i n g N e t w o r k ) .
[0008]
1 0 F o r e x a m p l e , P a t e n t L i t e r a t u r e 1 d i s c l o s e s a t e c h n o l o g y of
c o n t r o l l i n g a n i n i t i a t i o n t i m i n g of handover by a d j u s t i n g HO
p a r a m e t e r s , s u c h as a 3 - o f f s e t , CIO and TTT in o r d e r t o s u p p r e s s
handover f a i l u r e and t o i n c r e a s e a s u c c e s s rate of t h e h a n d o v e r . I n
a d d i t i o n , N o n - P a t e n t L i t e r a t u r e 1 d e f i n e s three t y p e s of handover
1 5 f a i l u r e i n v o l v i n g R L F , i . e . , "Too L a t e H a n d o v e r " , " T o o Early
Handover", and " H a n d o v e r t o Wrong C e l l " , and d i s c l o s e s a detection
t e c h n i q u e t h e r e o f .
[0009]
Too Late Handover c o r r e s p o n d s to a s i t u a t i o n w h e r e a mobile
20 t e r m i n a l t h a t has e x p e r i e n c e d RLF in a s o u r c e cell during execution of
a handover p r o c e d u r e t r i e s c o n n e c t i o n r e - e s t a b l i s h m e n t (including ree
s t a b l i s h n ~ e n t o f a radio l i n k ) t o a t a r g e t c e l l , o r a s i t u a t i o n where a
mobile t e r m i n a l t h a t h a s e x p e r i e n c e d RLF in a s o u r c e c e l l b e f o r e
i n i t i a t i o n of handover t r i e s c o n n e c t i o n r e - e s t a b l i s h m e n t t o a cell
25 d i f f e r e n t from the s o u r c e c e l l .
[OO l o ]
Too Early Handover c o r r e s p o n d s to a s i t u a t i o n w h e r e a mobile
t e r m i n a l t h a t has e x p e r i e n c e d RLF in a t a r g e t cell during executioil of
a handover p r o c e d u r e o r imnlediately a f t e r c o m p l e t i o n of handover
30 t r i e s c o n n e c t i o n r e - e s t a b l i s h m e n t to a s o u r c e c e l l .
[OOl I ]
I-Iandover to Wrong Cell c o r r e s p o n d s to a s i t u a t i o n where a
mobile terminal that h a s e x p e r i e n c e d KL,F in a s o u r c e cell o r a target
cell during execution o f a handover procedure or immediately a f t e r
4
c o m p l e t i o n o f handover t r i e s c o n n e c t i o n r e - e s t a b l i s h m e n t t o a cell
d i f f e r e n t f r o m both the s o u r c e c e l l a n d the t a r g e t c e l l .
[OO 121
N o n - P a t e n t L i t e r a t u r e 1 d i s c l o s e s a t e c h n i q u e in which t h e b a s e
5 s t a t i o n of the source cell d e t e c t s a p l u r a l i t y o f handover f a i l u r e t y p e s
by r e f e r r i n g t o i n f o r m a t i o n ( i . e . , a HANDOVER REPORT message and
an RLF INDICATION message) t r a n s m i t t e d l r e c e i v e d between base
s t a t i o n s t h r o u g h an i n t e r - b a s e - s t a t i o n i n t e r f a c e ( i . e . , an X2 i n t e r f a c e ) .
[00 131
10 T h e RLF INDICATION m e s s a g e i s t r a n s m i t t e d f r o m a base
s t a t i o n B t o a base s t a t i o n A , w h e n a mobile terminal t r i e s connection
r e - e s t a b l i s h m e n t to t h e b a s e s t a t i o n B a f t e r RLF f a i l u r e i n t h e base
s t a t i o n A. The RLF INDICATION m e s s a g e i n c l u d e s the f o l l o w i n g
i n f o r m a t i o n :
15 - F a i l u r e C e l l I D : an i d e n t i f i e r ( P h y s i c a l C e l l I d e n t i t y (PCI)) of a cell
to which t h e m o b i l e t e r m i n a l h a d b e e n connected before o c c u r r e n c e o f
c o n n e c t i o n f a i l u r e ;
- R e e s t a b l i s h m e n t Cell I D : a n i d e n t i f i e r (E-UTRAN C e l l G l o b a l
I d e n t i f i e r ( E C G I ) ) of a cell t o w h i c h t h e m o b i l e t e r m i n a l t r i e d
20 conllection r e - e s t a b l i s h m e n t ; and
- C-RNI'I: an i d e n t i f i e r (C-RNTI) of the mobile terminal in the cell to
which the mobile t e r m i n a l had c o n n e c t e d b e f o r e t h e o c c u r r e n c e of the
c o n n e c t i o n f a i l u r e .
[00 141
2 5 The HANDOVER REPORT message i s g e n e r a t e d r e g a r d i n g
recently c o m p l e t e d h a n d o v e r . The HANDOVER REPORT message i s
t r a n s m i t t e d when handover f a i l u r e i s d e t e c t e d in a t a r g e t cell
i m m e d i a t e l y a f t e r a base s t a t i o n of the t a r g e t c e l l t r a n s m i t s a handover
c o n ~ p l e t i o n n o t i f i c a t i o n ( i . e . , a UE C o n t e x t R e l e a s e m e s s a g e ) to a base
30 s t a t i o n of a s o u r c e c e l l . The HANDOVER REPORT message includes
the f o l l o w i n g i n f o r m a t i o n :
- 'I'ype o l ' d e t e c t e d handover f a i l u r e ( i . e . , Too Early I-Iandover or
I-Iandovcr t o Wrong C e l l ) ;
- I d e n t i f i e r s (ECGIs) of the s o u r c e cell and t h e t a r g e t c e l l ;
5
- Cell t o w h i c h c o n n e c t i o n r e - e s t a b l i s h m e n t w a s t r i e d ( i n a case of
Handover to Wrong C e l l ) ; a n d
- Handover cause (a c o n t e n t s e n t f r o m t h e b a s e s t a t i o n o f t h e s o u r c e
c e l l d u r i n g handover p r e p a r a t i o n ) .
5 [0015]
As w i l l b e d e s c r i b e d b e l o w , N o n - P a t e n t L i t e r a t u r e 1 d i s c l o s e s an
o u t l i n e of a t e c h n i q u e of d e t e c t i n g the p l u r a l i t y of handover f a i l u r e
types ( i . e . , Too L a t e H a n d o v e r , Too E a r l y H a n d o v e r , and Handover to
Wrong Cell) by a b a s e s t a t i o n of a s o u r c e c e l l .
10 [0016]

A b a s e s t a t i o n of a s o u r c e cell c a n d e t e c t Too Late Handover by
r e c e i v i n g an RLF INDICATION m e s s a g e f r o m a t a r g e t c e l l (when
handover is i n i t i a t e d ) or a c e l l d i f f e r e n t f r o m the source cell (when
15 handover is n o t i n i t i a t e d ) .
[00 171

A b a s e s t a t i o n of a t a r g e t cell c a n d e t e c t Too Early Handover by
r e c e i v i n g , w i t h i n a p r e d e t e r m i n e d p e r i o d (Tstore-UE-cntxt) a f t e r
20 completion of incoming handover o f a mobile t e r m i n a l ( i . e . , a f t e r
t r a n s m i t t i n g a UE CONTEXT RELEASE m e s s a g e ) , o r w h i l e preparing
the handover of the mobile t e r m i n a l , an RLF INDICATION message
r e g a r d i n g the m o b i l e t e r m i n a l from t h e s o u r c e c e l l . In a d d i t i o n , the
base s t a t i o n o f t h e s o u r c e cell can d e t e c t Too Early Handover by
25 r e c e i v i n g , f r o m the b a s e s t a t i o n o f t h e t a r g e t c e l l , a HANDOVER
REPORT m e s s a g e i n d i c a t i n g Too Early Handover.
[00 I S ]

T h e b a s e s t a t i o n of the t a r g e t c e l l c a n d e t e c t Handover to Wrong
30 Cell by r e c e i v i n g , within a p r c d e t c r m i n e d period (Tstore-UE-cntxt)
a f t e r c o m p l e t i o n o f illconling handover of a m o b i l e termillal ( i . e . , a f t e r
t r a n s m i t t i n g a UE CONTEXT RELEASE message), or while prcparing
the handover of t h e m o b i l e t e r i ~ ~ i n aaln. RL,F INDICATION message
r e g a r d i n g t h e m o b i l e t e r m i n a l from a cell d i f f e r e n t fror7n the source cell
6
I n a d d i t i o n , the b a s e s t a t i o n of the source c e l l c a n d e t e c t Handover to
Wrong C e l l by r e c e i v i n g , f r o m t h e base s t a t i o n o f the t a r g e t c e l l , a
HANDOVER REPORT m e s s a g e i n d i c a t i n g Handover to Wrong Cell.
[00 191
5 A l t e r n a t i v e l y , when r e c e i v i n g an attempt for connection ree
s t a b l i s h m e n t f r o m a m o b i l e t e r m i n a l t h a t h a s experienced RLF in a
source cell during handover from the source cell t o a t a r g e t c e l l , a base
s t a t i o n of a n e i g h b o r i n g c e l l d i f f e r e n t f r o m both t h e s o u r c e cell and
t h e t a r g e t c e l l may t r a n s m i t an RLF INDICATION m e s s a g e to the base
10 s t a t i o n o f t h e s o u r c e c e l l . C o n s e q u e n t l y , the base s t a t i o n of t h e s o u r c e
c e l l c a n d e t e c t I-Iandover to Wrong Cell by r e c e i v i n g the RLF
INDICATION message from the n e i g h b o r i n g c e l l .
Citation List
Patent Literature
15 [0020]
[ P a t e n t L i t e r a t u r e 11 I n t e r n a t i o n a l A p p l i c a t i o n P u b l i c a t i o n N o . WO
20 101002926
N o n P a t e n t Literature
[0021]
20 [ N o n - P a t e n t L i t e r a t u r e 11 3GPP 'TS 3 6 . 3 0 0 V 9 . 7 . 0 ( 2 0 1 1 - 0 3 ) , section
2 2 . 4 . 2 , March 2 0 1 1
Summary of Invention
T e c h n i c a l Problem
[0022]
2 5 A s m e n t i o n e d a b o v e , N o n - P a t e n t L i t e r a t u r e 1 u s e s information
( i . e . , HANDOVER REPORT and RLF INDICATION m e s s a g e s )
t r a n s m i t t e d l r e c e i v e d b e t w e e n t h e b a s e s t a t i o n s t h r o u g h t h e i n t e r - b a s e -
s t a t i o n i n t e r f a c e in o r d e r t h a t the source cell d e t e c t s t h e p l u r a l i t y of
handover f a i l u r e t y p e s . H o w e v e r , a s i t u a t i o n can b e c o n t e m p l a t e d
30 where i l ~ f o r m a t i o n ( i . e . , HANDOVER REPORT and RLF INDICATION
messages) cannot be t r a n s l n i t t e d between a t l e a s t some of the base
s t a t i o n s for some r e a s o n . F o r e x a m p l e , when t h e i n t e r - b a s e - s t a t i o n
i n t e r f a c e cannot be u t i l i z e d between at l e a s t some of the base s t a t i o n s ,
t h e s e base s t a t i o n s c a n n o t t r a n s m i t / r e c e i v e a NANDOVER REPORT or
7
RLF INDICATION message. A s t h e s i t u a t i o n where t h e i n t e r - b a s e -
s t a t i o n i n t e r f a c e c a n n o t b e u t i l i z e d , for example, it can b e c o n s i d e r e d
t h a t t h e i n t e r - b a s e - s t a t i o n i n t e r f a c e c a n n o t b e u t i l i z e d between two
base s t a t i o n s m a n u f a c t u r e d by d i f f e r e n t m a n u f a c t u r e r s . In a d d i t i o n , it
5 c a n be c o n s i d e r e d t h a t the i n t e r - b a s e - s t a t i o n i n t e r f a c e c a n n o t be
u t i l i z e d between at l e a s t some of t h e b a s e s t a t i o n s b e c a u s e of an
o p e r a t i o n p o l i c y of a n e t w o r k o p e r a t o r .
[0023]
I f t h e b a s e s t a t i o n o f t h e t a r g e t c e l l cannot t r a n s m i t l r e c e i v e
10 i n f o r m a t i o n ( i . e . , HANDOVER REPORT and RLF INDICATION
messages) tolfrom the b a s e s t a t i o n of the source cell and a neighboring
b a s e s t a t i o n , it is d i f f i c u l t f o r the b a s e s t a t i o n o f the source cell to
d e t e c t a n y of three handover f a i l u r e t y p e s ( i . e . , T o o L a t e H a n d o v e r ,
Too E a r l y H a n d o v e r , a n d Handover to Wrong C e l l ) e v e n w i t h t h e
15 t e c h n i q u e of N o n - P a t e n t L i t e r a t u r e 1. In a d d i t i o n , i f a t l e a s t o n e i n t e r -
b a s e - s t a t i o n i n t e r f a c e of t h e s e t h r e e b a s e s t a t i o n s c a n n o t be used, it is
d i f f i c u l t f o r the b a s e s t a t i o n of t h e s o u r c e cell to d e t e c t all the three
handover f a i l u r e t y p e s e v e n t h o u g h a p a r t o f them c a n b e d e t e c t e d e v e n
with the t e c h n i q u e d i s c l o s e d in Non-Patent L i t e r a t u r e 1. Accordingly,
20 there is a p o s s i b i l i t y t h a t a d j u s t m e n t o f HO paralneters in
c o n s i d e r a t i o n of handover f a i l u r e c a n n o t b e s u f f i c i e n t l y performed.
[0024]
One of o b j e c t s of t h e p r e s e n t i n v e n t i o n is to p r o v i d e a handover
f a i l u r e d e t e c t i o n d e v i c e , a handover p a r a m e t e r a d j u s t m e n t d e v i c e , a
25 f a i l u r e i n f o r m a t i o n g e n e r a t i o n d e v i c e , a handover optiillization system,
and method and programs regardirlg these that c o n t r i b u t e to
i m p r o v e m e n t o f handover f a i l u r e d e t e c t i o n o r reduction of handover
f a i l u r e in a s i t u a t i o n w h e r e exchange o f i n f o r m a t i o n between at least
some o f t h r e e base s t a t i o n s ( i . e . , a base s t a t i o n of a s o u r c e c e l l . a base
30 s t a t i o n of a t a r g e t c e l l , a n d t h e i r n e i g h b o r i n g base s t a t i o n ) is r e s t r i c t e d
( e . g . , a s i t u a t i o n where an i n t e r - b a s e - s t a t i o n i n t c r f a c c c a n n o t be
u t i l i z e d ) .
S o l u t i o n to Problem
COO251
8
In a f i r s t a s p e c t , a handover f a i l u r e d e t e c t i o n d e v i c e i n c l u d e s a
d e t e c t i o n u n i t . The d e t e c t i o n u n i t o p e r a t e s so a s t o detect at l e a s t one
of handover f a i l u r e t y p e s r e g a r d i n g o u t g o i n g handover f r o m a f i r s t c e l l
managed by a f i r s t b a s e s t a t i o n by o b s e r v i n g : ( a ) p r e s e n c e l a b s e n c e of
5 r e c e p t i o n by t h e f i r s t b a s e s t a t i o n o f a n a c k n o w l e d g m e n t r e s p o n s e t o a
handover command r e g a r d i n g f i r s t handover of a m o b i l e t e r m i n a l f r o m
the f i r s t cell t o a s e c o n d cell managed by a s e c o n d base s t a t i o n ; and
(b) p r e s e n c e / a b s e n c e o f a r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t from
the m o b i l e t e r m i n a l t o t h e f i r s t c e l l , t h e r e q u e s t o c c u r r i n g a f t e r
1 0 i n i t i a t i o n of t h e f i r s t h a n d o v e r .
[0026]
I n a s e c o n d a s p e c t , a handover p a r a m e t e r a d j u s t m e n t d e v i c e
i n c l u d e s a n a d j u s t m e n t u n i t . The adjustment unit o p e r a t e s so as to
adjust a handover p a r a m e t e r f o r c o n t r o l l i n g o u t g o i n g handover f r o m a
15 f i r s t c e l l managed by a f i r s t base s t a t i o n based on: (a)
p r e s e n c e l a b s e n c e of r e c e p t i o n by the f i r s t b a s e s t a t i o n o f a n
a c k n o w l e d g m e n t r e s p o n s e t o a handover i n s t r u c t i o n r e g a r d i n g f i r s t
handover o f a mobile terminal f r o m t h e f i r s t cell t o a s e c o n d cell
managed by a s e c o n d base s t a t i o n ; and (b) p r e s e n c e / a b s e n c e o f a
20 r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m the mobile terminal t o t h e
f i r s t c e l l , the r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n o f t h e f i r s t handover.
[0027]
In a third a s p e c t , a h a n d o v c r f a i l u r e i n f o r m a t i o n g e n e r a t i o n
d e v i c e i n c l u d e s a g e n e r a t i o n u n i t . 'The g e n e r a t i o n unit is c o u p l e d t o a
25 second base s t a t i o n and o p e r a t e s so as to g e n e r a t e handover f a i l u r e
i n f o r m a t i o n t o be t r a n s m i t t e d to a f i r s t b a s e s t a t i o n . T h e handover
f a i l u r e i n f o r m a t i o n is used t o detect a handover f a i l u r e t y p e t h a t
c o r r e s p o n d s t o a s i t u a t i o n where a m o b i l e terminal has e x p e r i e n c e d
abnormal d i s c o ~ ~ n e c t i oin a second cell managed by a s e c o n d base
30 s t a t i o n d u r i n g e x e c u t i o n o f f i r s t handover from a f i r s t c e l l managed by
t h e f i r s t b a s e s t a t i o n t o t h e s e c o n d cell or a f t e r completion of the f i r s t
handover, a n d t h e n t r i e s c o n n e c t i o n r e - e s t a b l i s h n ~ ~ ntot a third cell
d i f f e r e n t fronl both t h e f i r s t and s e c o n d c e l l s .
[ 0 0 2 8 ]
9
In a f o u r t h a s p e c t , a handover o p t i m i z a t i o n s y s t e m i n c l u d e s a
d e t e c t i o n unit and a n a d j u s t m e n t u n i t . The d e t e c t i o n unit o p e r a t e s so
as to detect at l e a s t one of handover f a i l u r e t y p e s r e g a r d i n g o u t g o i n g
handover from a f i r s t c e l l managed by a f i r s t b a s e s t a t i o n by
5 o b s e r v i n g : ( a ) p r e s e n c e l a b s e n c e o f r e c e p t i o n by the f i r s t base s t a t i o n
of a n a c k n o w l e d g m e n t r e s p o n s e to a handover command r e g a r d i n g f i r s t
handover o f a mobile t e r m i n a l from t h e f i r s t c e l l t o a s e c o n d cell
managed by a s e c o n d b a s e s t a t i o n ; and ( b ) p r e s e n c e l a b s e n c e o f a
r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m t h e m o b i l e terminal to the
10 f i r s t c e l l , the r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n of the f i r s t h a n d o v e r .
The adjustment unit o p e r a t e s s o as to a d j u s t a handover p a r a m e t e r f o r
c o n t r o l l i n g t h e o u t g o i n g handover from t h e f i r s t c e l l b a s e d o n a
d e t e c t i o n r e s u l t of the at l e a s t o n e of the handover f a i l u r e types.
[0029]
15 In a f i f t h a s p e c t , a b a s e s t a t i o n i n c l u d e s the handover f a i l u r e
d e t e c t i o n d e v i c e a c c o r d i n g to t h e f i r s t a s p e c t d e s c r i b e d a b o v e .
[0030]
I n a s i x t h a s p e c t , a handover f a i l u r e d e t e c t i o n m e t h o d i n c l u d e s
d e t e c t i n g at l e a s t o n e o f handover f a i l u r e t y p e s r e g a r d i n g o u t g o i n g
20 handover from a f i r s t c e l l managed by a f i r s t b a s e s t a t i o n by
o b s e r v i n g : ( a ) p r e s e n c e l a b s e n c e o f r e c e p t i o n by t h e f i r s t b a s e s t a t i o n
of a11 a c k n o w l e d g n ~ e n t r e s p o n s e t o a handover command r e g a r d i n g f i r s t
handover of a mobile t e r m i n a l from t h e f i r s t c e l l t o a s e c o n d cell
managed by a s e c o n d base s t a t i o n ; and (b) p r e s e n c e / a b s e n c e of a
25 r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m t h e m o b i l e terminal to the
f i r s t c e l l , the r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n of t h e f i r s t handover.
[003 1 1
In a s e v e n t h a s p e c t , a handover p a r a m e t e r a d j u s t m e n t method
i n c l ~ i d e sa d j u s t i n g a handover parameter for c o n t r o l l i n g o u t g o i n g
30 handover fro111 a f i r s t cell managed by a f i r s t b a s e s t a t i o n based on: ( a )
p r e s e n c e l a b s e n c e o f r e c e p t i o n by t h e f i r s t b a s e s t a t i o n o f a11
a c k n o w l e d g m e n t r e s p o n s e to a handover command regarding f i r s t
handover of a m o b i l e t e r n ~ i n a l from the f i r s t c e l l to a second cell
managed by a s e c o n d base s t a t i o n ; and ( b ) p r e s e n c e l a b s e n c e of a
r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m t h e m o b i l e terminal to the
f i r s t c e l l , the r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n of the f i r s t h a n d o v e r .
[0032]
In an e i g h t h a s p e c t , a p r o g r a m i n c l u d e s i n s t r u c t i o n s t o c a u s e a
5 computer to perform a m e t h o d f o r handover f a i l u r e d e t e c t i o n . The
m e t h o d i n c l u d e s d e t e c t i n g at l e a s t o n e o f handover f a i l u r e types
r e g a r d i n g o u t g o i n g handover f r o m a f i r s t cell managed by a f i r s t b a s e
s t a t i o n by o b s e r v i n g : ( a ) p r e s e n c e / a b s e n c e o f r e c e p t i o n by t h e f i r s t
b a s e s t a t i o n o f a n acknowledgment r e s p o n s e t o a handover command
10 r e g a r d i n g f i r s t handover of a m o b i l e t e r m i n a l f r o m t h e f i r s t c e l l t o a
second cell managed by a s e c o n d b a s e s t a t i o n ; and (b)
p r e s e n c e / a b s e n c e o f a r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t from the
mobile terminal to the f i r s t c e l l , t h e r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n
of the f i r s t handover.
15 [0033]
In a ninth a s p e c t , a p r o g r a m i n c l u d e s i n s t r u c t i o n s to c a u s e a
computer t o p e r f o r m a m e t h o d f o r handover p a r a m e t e r a d j u s t m e n t . The
m e t h o d i n c l u d e s a d j u s t i n g a handover p a r a m e t e r f o r c o n t r o l l i n g
o u t g o i n g handover from a f i r s t c e l l managed by a f i r s t b a s e s t a t i o n
20 based o n : ( a ) p r e s e n c e / a b s e n c e of r e c e p t i o n by the f i r s t b a s e s t a t i o n o f
an acknowledgment r e s p o n s e to a handover command r e g a r d i n g f i r s t
handover o f a mobile t e r m i n a l f r o m the f i r s t cell to a second cell
managed by a s e c o n d b a s e s t a t i o n ; a n d (b) p r e s e n c e l a b s e n c e o f a
recluest f o r c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m t h e m o b i l e terminal to the
25 f i r s t c e l l . the request o c c u r r i n g a f t e r i n i t i a t i o n o f t h e f i r s t handover.
A d v a n t a g e o u s E f f e c t s o f I n v e n t i o n
[0034]
According to t h e a b o v e - m e n t i o n e d a s p e c t s , i t is possible to
p r o v i d e a handover f a i l u r e d e t e c t i o n d e v i c e , a handover parameter
70 adjustment device. a handover o p t i m i z a t i o n s y s t e n l , and methods and
programs r e l a t e d t h e r e t o t h a t can c o n t r i b u t e t o i m p r o v e m e n t o f
handover f a i l u r e d e t e c t i o n or reduction of handover f a i l u r e in a
s i t u a t i o n w l ~ c r e exchange o f i n f o r m a t i o n b e t w e e n at l e a s t some of three
base s t a t i o n s ( i . e . . a b a s e s t a t i o n of a s o u r c e c e l l , a base s t a t i o n o f a
11
t a r g e t c e l l , and t h e i r n e i g h b o r i n g b a s e s t a t i o n ) is r e s t r i c t e d .
Brief Description of Drawings
[003 51
F i g . 1 is a block d i a g r a m s h o w i n g a c o n f i g u r a t i o n e x a m p l e of a
5 r a d i o c o m m u n i c a t i o n s y s t e m a c c o r d i n g to f i r s t t o f i f t h e m b o d i m e n t s .
Fig. 2 is a block d i a g r a m s h o w i n g a c o n f i g u r a t i o n e x a m p l e of a
r a d i o c o m m u n i c a t i o n s y s t e m a c c o r d i n g to the second embodiment.
F i g . 3 is a flow c h a r t s h o w i n g a f i r s t example of a Too Late
Handover d e t e c t i o n p r o c e d u r e a c c o r d i n g t o t h e s e c o n d e m b o d i m e n t .
10 F i g . 4 is a flow c h a r t s h o w i n g a s e c o n d e x a m p l e o f a Too Late
Handover d e t e c t i o n p r o c e d u r e a c c o r d i n g t o the s e c o n d e m b o d i m e n t .
Fig. 5 is a flow c h a r t s h o w i n g one example o f a n HO p a r a m e t e r
a d j u s t m e n t p r o c e d u r e a c c o r d i n g to the s e c o n d e m b o d i m e n t .
Fig. 6 is a b l o c k d i a g r a m s h o w i n g a c o n f i g u r a t i o n example of a
15 r a d i o c o m m u n i c a t i o n s y s t e m a c c o r d i n g t o the t h i r d embodiment.
Fig. 7 is a flow chart showing a f i r s t e x a m p l e o f a T o o Early
Handover d e t e c t i o n p r o c e d u r e a c c o r d i n g t o t h e third embodiment.
Fig. 8 is a flow c h a r t s h o w i n g a s e c o n d e x a m p l e o f a Too Early
Handover d e t e c t i o n p r o c e d u r e a c c o r d i n g to the third embodiment.
2 0 Fig. 9 is a flow c h a r t s h o w i n g a t h i r d e x a m p l e of a T o o Early
Handover d e t e c t i o n p r o c e d u r e a c c o r d i n g t o t h e third embodiment.
Fig. 10 is a flow c h a r t s h o w i n g a f o u r t h e x a m p l e o f a T o o Early
Handover d e t e c t i o n p r o c e d u r e a c c o r d i n g t o the third embodiment.
Fig. 11 is a flow c h a r t s h o w i n g one e x a m p l e o f an HO p a r a m e t e r
25 a d j u s t m e n t p r o c e d u r e a c c o r d i n g to t h e t h i r d embodiment.
Fig. 12 is a block diagram s h o w i n g a c o n f i g u r a t i o n e x a m p l e o f a
r a d i o c o m m u n i c a t i o n s y s t e n ~ a c c o r d i n g t o the fourth embodiment.
Fig. 13 is a flow c h a r t s h o w i n g a f i r s t e x a m p l e o f a Handover to
Wrong C e l l d e t e c t i o n p r o c e d u r e a c c o r d i n g t o t h e fourth embodiment.
3 0 Fig. 1 4 i s a f l o w c h a r t s h o w i n g a s e c o n d e x a m p l e of a Handover
to Wrong Cell d e t e c t i o n p r o c e d u r e a c c o r d i n g to t h e f o u r t h embodinlent.
Fig. 15 is a flow chart s l ~ o w i n ga third example of a Handover to
Wrong Cell d e t e c t i o n p r o c e d u r e according to t h e f o u r t h embodiment.
Fig. 16 is a flow c h a r t s h o w i n g a f o u r t h e x a m p l e of a Handover
t o Wrong Cell d e t e c t i o n p r o c e d u r e a c c o r d i n g t o the f o u r t h e m b o d i m e n t .
Fig. 17 is a flow c h a r t s h o w i n g a f i r s t e x a m p l e of a n o t i f i c a t i o n
procedure of handover f a i l u r e i n f o r m a t i o n a c c o r d i n g t o t h e f o u r t h
embodiment.
5 F i g . 18 is a flow c h a r t s h o w i n g a s e c o n d e x a m p l e of a
n o t i f i c a t i o n p r o c e d u r e o f handover f a i l u r e i n f o r m a t i o n according to the
fourth embodiment.
Fig. 19 is a flow c h a r t s h o w i n g one e x a m p l e o f a n HO p a r a m e t e r
a d j u s t m e n t p r o c e d u r e a c c o r d i n g to the f o u r t h e m b o d i m e n t .
10 Fig. 20 is a block d i a g r a m s h o w i n g a c o n f i g u r a t i o n e x a m p l e of a
radio communication system a c c o r d i n g t o the f i f t h e m b o d i m e n t .
Fig. 21 is a flow c h a r t s h o w i n g a f i r s t e x a m p l e o f a Handover to
Wrong C e l l d e t e c t i o n p r o c e d u r e a c c o r d i n g t o t h e f i f t h e m b o d i m e n t .
Fig. 22 is a flow c h a r t s h o w i n g a s e c o n d e x a m p l e o f a Handover
15 t o Wrong Cell d e t e c t i o n p r o c e d u r e a c c o r d i n g t o t h e f i f t h e m b o d i m e n t .
F i g . 2 3 i s a flow c h a r t s h o w i n g a t h i r d e x a m p l e o f a Handover
to Wrong Cell d e t e c t i o n p r o c e d u r e a c c o r d i n g t o t h e f i f t h e m b o d i m e n t .
F i g . 24 is a flow chart showing a f i r s t e x a m p l e o f a n o t i f i c a t i o n
procedure of handover f a i l u r e i n f o r m a t i o n a c c o r d i n g t o the f i f t h
2 0 e m b o d i m e n t .
F i g . 2 5 is a flow chart s l ~ o w i n ga s e c o n d e x a m p l e of a
n o t i f i c a t i o n p r o c e d u r e of handover f a i l u r e i n f o r m a t i o n according to the
f i f t h embodiment.
D e s c r i p t i o n of Embodiments
25 [0036]
H e r e i n a f t e r , s p e c i f i c e m b o d i m e n t s w i l l b e e x p l a i n e d in d e t a i l
with r e f e r e n c e to d r a w i n g s . T h r o u g l ~ o u t t h e d r a w i n g s , the identical
and c o r r e s p o n d i n g colnponents are denoted by the same reference
symbols, and overlappillg e x p l a n a t i o n is omitted as needed f o r c l a r i t y
30 o f e x p l a n a t i o n .
[0037]
F i r s t embodimeilt
Fig. 1 is a block diagram showing a c o n f i g u r a t i o n example o f a
radio c o n ~ m u n i c a t i o n system 100 a c c o r d i n g t o some e m b o d i n ~ e n t s
13
i n c l u d i n g t h e p r e s e n t e m b o d i m e n t . The r a d i o c o m m u n i c a t i o n s y s t e m
100 i n c l u d e s b a s e s t a t i o n s 11 1 to 11 3. The b a s e s t a t i o n s 11 1 to 11 3
manage c e l l s 13 1 to 1 3 3 , r e s p e c t i v e l y , and c o m m u n i c a t e with o n e o r
m o r e m o b i l e t e r m i n a l s ( e . g . , a m o b i l e t e r m i n a l 1 0 1 ) . The mobile
5 t e r m i n a l 101 can be c o n n e c t e d to a n y o n e o f t h e b a s e s t a t i o n s 11 1 to
113. It i s t o b e n o t e d t h a t t h e c o n f i g u r a t i o n e x a m p l e o f Fig. 1 may be
a p p r o p r i a t e l y c h a n g e d s i n c e it i s merely one e x a m p l e f o r e x p l a n a t i o n .
For e x a m p l e , t h e r a d i o c o m m u n i c a t i o n s y s t e m 1 0 0 m a y i n c l u d e f o u r or
m o r e b a s e s t a t i o n s . In a d d i t i o n , n e i g h b o r h o o d r e l a t i o n s of t h e c e l l s
10 13 1 t o 133 shown i n F i g . I a r e a l s o m e r e l y one e x a m p l e . F o r e x a m p l e ,
t h e r a d i o c o m m u n i c a t i o n s y s t e m 1 0 0 may have a h i e r a r c h i c a l cell
s t r u c t u r e in which a c e r t a i n c e l l ( e . g . , the c e l l 132) i s a r r a n g e d w i t h i n
a n o t h e r c e l l ( e . g . , t h e c e l l 1 3 3 ) .
[003 81
15 The b a s e s t a t i o n s 11 1 t o 113 a r e c o n n e c t e d t o a n e t w o r k 140
i n c l u d i n g a n e t w o r k node 141, a n d c a n c o m m u n i c a t e with t h e network
n o d e 1 4 1 . The network 140 i n c l u d e s , f o r e x a m p l e , a r a d i o a c c e s s
n e t w o r k o r a c o r e n e t w o r k , or both of t h e m . The n e t w o r k n o d e 141
i n c l u d e s a r a d i o a c c e s s n e t w o r k n o d e o r a c o r e n e t w o r k n o d e , o r b o t h
20 o f t h e m . The network node 141 m a y c o r r e s p o n d t o a p l u r a l i t y o f
n e t w o r k n o d e s . T h e n e t w o r k n o d e 141 may b e a u s e r p l a n e ( d a t a p l a n e )
n o d e , or m a y b e a c o n t r o l p l a n e n o d e . T h e n e t w o r k node 141 e x e c u t e s
at l e a s t one o f r a d i o r e s o u r c e m a n a g e m e n t , m o b i l i t y m a n a g e m e n t ,
b e a r e r m a n a g e m e n t , u s e r d a t a f o r w a r d i n g / r o u t i n g , and a gateway
25 f u n c t i o n with an e x t e r n a l n e t w o r k .
[ 0 0 3 9 ]
111 a d d i t i o n , t h e r a d i o c o m m u ~ ~ i c a t i osny stem 100 i n c l u d e s a
h a n d o v e r (HO) f a i l u r e d e t e c t i o n u n i t 121 and an HO p a r a m e t e r
a d j u s t m e n t u n i t 151. The 130 f a i l u r e d e t e c t i o n u n i t 121 and the HO
30 p a r a m e t e r a d j u s t m e n t u n i t 1 5 1 can be c a l l e d a s y s t e m f o r r e d u c i n g
h a n d o v e r f a i l u r e s ( i . e . , a l l a n d o v e r o p t i m i z a t i o n s y s t e m ) . 'I'he HO
f a i l u r e d e t e c t i o n u n i t 1 2 1 d e t e c t s at l e a s t o n e o f a p l u r a l i t y 01
h a n d o v e r f a i l u r e t y p e s ( e . g . , Too Late H a n d o v e r . Too Early I-Iandover,
and Handover to Wrong C e l l ) r e g a r d i n g o u t g o i n g h a n d o v e r from t h e
14
c e l l 131 ( b a s e s t a t i o n 11 1 ) . The HO f a i l u r e d e t e c t i o n u n i t 121 then
g e n e r a t e s f e e d b a c k i n f o r m a t i o n o n t h e o u t g o i n g h a n d o v e r f r o m t h e
s o u r c e c e l l 13 1, and s u p p l i e s t h e f e e d b a c k i n f o r m a t i o n t o t h e HO
p a r a m e t e r a d j u s t m e n t u n i t 15 1. The f e e d b a c k i n f o r m a t i o n i s g e n e r a t e d
5 based on d e t e c t i o n r e s u l t s o f t h e h a n d o v e r f a i l u r e t y p e s , a n d i n d i c a t e s
a d e t e c t i o n h i s t o r y o f t h e h a n d o v e r f a i l u r e t y p e s . F o r e x a m p l e , t h e
f e e d b a c k i n f o r m a t i o n may i n d i c a t e t h e number of h a n d o v e r a t t e m p t s
and t h e d e t e c t e d n u m b e r f o r e a c h h a n d o v e r f a i l u r e t y p e . The f e e d b a c k
i n f o r m a t i o n m a y i n d i c a t e a n o c c u r r e n c e r a t e f o r each h a n d o v e r f a i l u r e
1 0 t y p e .
[ 0 0 4 0 ]
The HO p a r a m e t e r a d j u s t m e n t u n i t 15 1 a d j u s t s an HO p a r a m e t e r
( e . g . , a t l e a s t one o f A 3 - o f f s e t , C 1 0 , and TTT) based on t h e f e e d b a c k
i n f o r m a t i o n f r o m t h e HO f a i l u r e d e t e c t i o n u n i t 121, i . e . , t h e d e t e c t i o n
15 r e s u l t o f t h e h a n d o v e r f a i l u r e by t h e HO f a i l u r e d e t e c t i o n u n i t 121.
The a d j u s t e d HO p a r a m e t e r i s a p p l i e d t o t h e c e l l 13 1.
[ 0 0 4 1 ]
In t h e e x a m p l e s h o w n in F i g . 1, the HO f a i l u r e d e t e c t i o n u n i t
121 i s a r r a n g e d i n t e g r a l l y w i t h t h e b a s e s t a t i o n 11 1 , a n d t h e HO
20 p a r a m e t e r a d j u s t m e n t u n i t 1 5 1 i s a r r a n g e d in a n e t w o r k m a n a g e m e n t
s y s t e m 150. T11e network n l a n a g e m e n t system 150 may be c a l l e d an
OAM ( O p e r a t i o n A d l n i n i s t r a t i o n a n d M a i n t e n a n c e ) s e r v e r , a n OMC
( O p e r a t i o n and M a i n t e n a n c e C e n t r e ) , an NM ( N e t w o r k M a n a g e r ) , or an
EM ( E l e m e n t Manager) in some c a s e s . H o w e v e r , t h e s e a r r a n g e m e n t s
25 a r e m e r e l y one e x a m p l e . The 1-10 f a i l u r e d e t e c t i o n u n i t 121 may be
a r r a n g e d away froln the b a s e s t a t i o n 1 1 1 and s o a s to be a b l e to
c o i n m u n i c a t e with the b a s e s t a t i o n 1 1 1 . The HO p a r a m e t e r a d j u s t m e n t
u n i t 15 1 inay be a r r a n g e d i n t e g r a l l y wit11 the b a s e s t a t i o n 1 1 1, or may
be a r r a n g e d in t h e n e t w o r k 1 4 0 .
30 [ 0 0 4 2 ]
I - l e r c i n a f t e r , d e t e c t i o n of a h a n d o v e r f a i l u r e t y p e r e g a r d i n g
h a n d o v e r o f t h e l n o b i l e t e r m i n a l 101 f'ro~n the c e l l 13 1 to the cell 132
is e x p l a i n e d . A c c o r d i n g l y , in some c a s e s b e l o w , t h e c e l l 1 3 1 i s c a l l e d
a " s o u r c e c e l l " , and the c e l l 132 i s c a l l e d a " t a r g e t c e l l " . The base
15
s t a t i o n 11 1 is c a l l e d a " s o u r c e b a s e s t a t i o n " , and t h e b a s e s t a t i o n 1 1 2
i s c a l l e d a " t a r g e t base s t a t i o n " . The c e l l 1 3 3 is c a l l e d a "neighboring
c e l l " o r a " r e - c o n n e c t i o n c e l l " . The b a s e s t a t i o n 1 1 3 is called a
" n e i g h b o r i n g b a s e s t a t i o n " or a " r e - c o n n e c t i o n b a s e s t a t i o n " . It is to
5 b e n o t e d t h a t t h e r e - c o n n e c t i o n c e l l means a c e l l t o w h i c h t h e mobile
t e r m i n a l 101 t h a t has e x p e r i e n c e d RLF during handover or immediately
a f t e r c o m p l e t i o n of the handover r e q u e s t s r e - e s t a b l i s h m e n t of radio
c o n n e c t i o n .
[0043]
10 A s a l r e a d y m e n t i o n e d , in t h e s i t u a t i o n w h e r e e x c h a n g e of
i n f o r m a t i o n b e t w e e n a t l e a s t some of t h r e e b a s e s t a t i o n s ( i . e . , the
s o u r c e s t a t i o n 11 1, the t a r g e t b a s e s t a t i o n 112, and t h e n e i g h b o r i n g
base s t a t i o n 1 1 3 ) is r e s t r i c t e d ( e . g . , a s i t u a t i o n w h e r e an i n t e r - b a s e -
s t a t i o n i n t e r f a c e c a n n o t be u t i l i z e d ) , t h e r e is a p o s s i b i l i t y t h a t
15 d e t e c t i o n o f o n e o r more handover f a i l u r e t y p e s r e g a r d i n g t h e o u t g o i n g
handover from the cell 131 becomes d i f f i c u l t . I n o r d e r to a d d r e s s t h i s
problem, the HO f a i l u r e d e t e c t i o n u n i t 1 2 1 of t h e p r e s e n t e m b o d i m e n t
d e t e c t s at l e a s t o n e o f handover f a i l u r e t y p e s ( e . g . , Too Late Handover,
Too Early Handover, and Handover to Wrong C e l l ) r e g a r d i n g t h e
2 0 o u t g o i n g handover from the c e l l 131 by o b s e r v i n g : (a)
p r e s e n c e l a b s e n c e of r e c e p t i o n f r o m the mobile t e r m i n a l 1 0 1 by the
source base s t a t i o n 1 1 1 of a n a c k n o w l e d g m e n t r e s p o n s e t o a handover
colnlnand r e g a r d i n g f i r s t handover of the mobile terminal 101 from t h e
s o u r c e cell 13 1 to t h e t a r g e t c e l l 132; and (b) p r e s e n c e / a b s e n c e of a
25 r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t t o the s o u r c e b a s e s t a t i o n 11 1
fronl the mobile terminal 101 occurrillg a f t e r i n i t i a t i o n of the f i r s t
handovcr.
100441
In a d d i t i o n , the 1-10 p a r a m e t e r a d j u s t m e n t unit 15 1 o f t h e present
30 embodiment a d j u s t s an 1-10 parameter based on a d e t e c t i o n r e s u l t by the
HO f a i l u r e d e t e c t i o n unit 1 2 1 . A c c o r d i n g l y , t h e MO parameter
adjustment unit 15 1 a d j u s t s t h e HO parameter for c o n t r o l l i n g the
outgoing handover from the cell 131 based o n : ( a ) the presencelabsence
o f t h e r e c e p t i o n f r o n ~th e m o b i l e t e r m i n a l 101 by the source base
16
s t a t i o n 11 1 of the a c k n o w l e d g m e n t r e s p o n s e t o the handover command
regarding the f i r s t handover of t h e m o b i l e t e r m i n a l 101 f r o m t h e source
c e l l 1 3 1 to t h e t a r g e t c e l l 132; and (b) the p r e s e n c e l a b s e n c e o f t h e
r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t t o t h e s o u r c e base s t a t i o n 11 1
5 from the mobile t e r m i n a l 101 o c c u r r i n g a f t e r t h e i n i t i a t i o n o f t h e f i r s t
handover.
[0045]
H e r e , t h e a c k n o w l e d g m e n t r e s p o n s e to the handover command
may be t r a n s m i t t e d f r o m the m o b i l e t e r m i n a l 101 to the source base
10 s t a t i o n 11 1 r e g a r d l e s s of a s i t u a t i o n i n which the i n t e r - b a s e - s t a t i o n
i n t e r f a c e c a n n o t b e u t i l i z e d or a s i t u a t i o n in w h i c h t h e i n t e r - b a s e -
s t a t i o n i n t e r f a c e can be u t i l i z e d .
[0046]
The acknowledgment response to the handover command is a
15 m e s s a g e ( s i g n a l ) t h a t t h e s o u r c e base s t a t i o n 11 1 r e c e i v e s f r o m the
m o b i l e t e r m i n a l 101 d u r i n g a handover p r o c e d u r e . The
acknowledgment r e s p o n s e t o t h e handover command may be a message
t h a t i s t r a n s m i t t e d a f t e r the m o b i l e t e r m i n a l 101 n o r m a l l y r e c e i v e s the
handover command.
20 [0047]
In an LTE s y s t e m , for e x a m p l e , the acknowledgment response to
the halldover command m a y be an acknowledgrncnt response (ACK) to
be t r a n s m i t t e d to the source base s t a t i o n 11 1 by t h e m o b i l e terminal
101 to c o n t r o l a r e - t r a n s m i s s i o n o f a n "HO Command" message (more
2 5 s p e c i f i c a l l y , a n "RRC C o n n e c t i o n R e c o n f i g u r a t i o n " m e s s a g e )
t r a n s m i t t e d t o t h e m o b i l e t e r m i n a l 1 0 1 f r o m t h e source base s t a t i o n 11 1
The a c k n o w l e d g m e n t r e s p o n s e may b e a signal i n d i c a t i n g t h a t t h e
mobile t e r m i n a l 1 0 1 h a s a c c u r a t e l y r e c e i v e d t h e "HO Command"
message in the r e - t r a n s m i s s i o n c o l ~ t r o l based on an Automatic Repeat
30 reQuest (ARQ). In a n o t h e r e x a m p l e , the acknowledgment response may
be a signal i n d i c a t i n g that the nlobile terminal 101 h a s a c c u r a t e l y
r e c e i v e d t h e "HO Command" message i n the r e - t r a n s n ~ i s s i o nc ontrol
based on a Hybrid Automatic Repeat reQuest (I-IARQ). The ret
r a l ~ s m i s s i o n c o ~ i t r o l and handover p r o c e d u r e s a r e defined by 3GPP TS
36.300.
[0048]
I n i t i a t i o n of handover may c o r r e s p o n d t o t r a n s m i t t i n g a
handover command from t h e s o u r c e b a s e s t a t i o n 1 1 1 t o t h e mobile
5 t e r m i n a l 101. The mobile t e r m i n a l 101 t h a t h a s r e c e i v e d the handover
command i n i t i a t e s a c o n n e c t i o n t o t h e t a r g e t b a s e s t a t i o n 112.
A l t e r n a t i v e l y , the i n i t i a t i o n of the handover may c o r r e s p o n d to
t r a n s m i t t i n g a handover r e q u e s t for handover p r e p a r a t i o n f r o m the
s o u r c e base s t a t i o n 11 1 to the t a r g e t b a s e s t a t i o n 1 1 2 or to the network
10 node 141. The t a r g e t b a s e s t a t i o n 1 12 or the network node 14 1 that has
r e c e i v e d the handover r e q u e s t i n i t i a t e s the handover p r e p a r a t i o n
i n c l u d i n g s e t u p of r a d i o r e s o u r c e s in t h e t a r g e t b a s e s t a t i o n 1 1 2 . Also,
a l t e r n a t i v e l y , the i n i t i a t i o n of the handover may c o r r e s p o n d to
r e c e i v i n g i n f o r m a t i o n t o t r i g g e r the handover ( e . g . , a m e a s u r e m e n t
15 r e p o r t ) a t the s o u r c e b a s e s t a t i o n 11 1 f r o m t h e m o b i l e t e r m i n a l 1 0 1 .
[O 0 4 91
For e x a m p l e , i n t h e LTE s y s t e m , t h e i n i t i a t i o n o f t h e handover
may c o r r e s p o n d to t r a n s m i s s i o n of a "130 Command" message from the
s o u r c e b a s e s t a t i o n 1 1 1 to t h e m o b i l e t e r m i n a l 1 0 1 . A l t e r n a t i v e l y , t h e
20 i n i t i a t i o n of the handover may c o r r e s p o n d t o t r a n s m i s s i o n o f a
" H a n d o v e r R e q u e s t " m e s s a g e f r o m t h e s o u r c e base s t a t i o n 11 1 to the
t a r g e t b a s e s t a t i o n 1 1 2 . A l s o , a l t e r n a t i v e l y , t h e i n i t i a t i o n of the
handover may c o r r e s p o n d to t r a n s m i s s i o n o f a " H a n d o v e r Required"
m e s s a g e f r o m t h e s o u r c e base s t a t i o n 11 1 to t h e n e t w o r k node 141
25 ( s p e c i f i c a l l y , t h e MME). F u r t h e r , a l t e r n a t i v e l y , t h e i n i t i a t i o n o f the
handover may correspond to r e c e p t i o i ~o f a M e a s u r e m e n t Report at the
s o u r c e b a s e s t a t i o n 1 1 1 from the mobile terminal 10 1. Handover
p r o c e d u r e s i n c l u d i n g t r a n s m i s s i o n o f the HO Command m e s s a g e , the
I-Iandover R e q u e s t m e s s a g e , a n d t h e M e a s u r e m e n t R e p o r t a r e defined by
3 0 3GPP TS 36.300.
[ 0 0 5 0 ]
As m e n t i o n e d a b o v e , t h e HO f a i l u r e d e t e c t i o n unit 121 according
t o t h e present embodiment d e t e c t s a handover f a i l u r e type based on ( a )
whether the a c k n o w l e d g m e n t r e s p o n s e to the handover command has
18
been r e c e i v e d f r o m the mobile t e r m i n a l 101, and ( b ) w h e t h e r the
r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t has been r e c e i v e d f r o m t h e
mobile t e r m i n a l 1 0 1 . A c c o r d i n g l y , t h e HO f a i l u r e d e t e c t i o n unit 121
can improve handover f a i l u r e d e t e c t i o n in a s i t u a t i o n where exchange
5 of i n f o r m a t i o n ( e . g . , the HANDOVER REPORT message and the RLF
INDICATION m e s s a g e ) b e t w e e n at l e a s t some of the t h r e e base s t a t i o n s
( i . e . , t h e s o u r c e base s t a t i o n 11 1, t h e t a r g e t base s t a t i o n 1 1 2 , and the
n e i g h b o r i n g base s t a t i o n 1 1 3 ) is r e s t r i c t e d . In a d d i t i o n , t h e HO
p a r a m e t e r a d j u s t m e n t unit 15 1 can c o n t r i b u t e to r e d u c t i o n o f the
10 handover f a i l u r e in t h e a b o v e - d e s c r i b e d s i t u a t i o n by u t i l i z i n g a
d e t e c t i o n r e s u l t f r o m the HO f a i l u r e d e t e c t i o n unit 12 1.
[005 I ]
In o n e e x a m p l e , t h e 130 f a i l u r e d e t e c t i o n u n i t 1 2 1 c a n d e t e c t Too
Late Handover or Too Early Handover r e g a r d i n g t h e o u t g o i n g handover
15 from t h e s o u r c e c e l l 13 1, or both of them without u s i n g i n f o r m a t i o n
f r o m t h e t a r g e t b a s e s t a t i o n 112 a n d t h e n e i g h b o r i n g b a s e s t a t i o n 113.
In a n o t h e r e x a m p l e , the HO f a i l u r e d e t e c t i o n unit 121 c a n d e t e c t
Handover t o Wrong Cell r e g a r d i n g the outgoing handover froin the
s o u r c e c e l l 131 in a s i t u a t i o n w h e r e i n f o r m a t i o n f r o m e i t h e r one of the
20 t a r g e t b a s e s t a t i o n 11 2 and t h e n e i g h b o r i n g base s t a t i o n 1 1 3 cannot be
u t i l i z e d . S p e c i f i c examples of o p e r a t i o n s of the HO f a i l u r e detection
unit 12 1 a n d t h e HO p a r a m e t e r a d j u s t m e n t unit 15 1 f o r d e t e c t i n g each
handover f a i l u r e t y p e (Too Late Handover, Too Early Handover, or
Handover t o Wrong C e l l ) will be e x p l a i n e d in second to f i f t h
25 e m b o d i m e n t s .
I00521
Second embodiment
I n t h e p r e s e n t embodiineilt, d e t e c t i o n o f Too Late Handovelr
e g a r d i n g handover froin the s o u r c e cell 131 to the t a r g e t c e l l 132 will
30 be e x p l a i n e d . A c o n f i g u r a t i o n e x a ~ n p l eo f the radio c o m m u l ~ i c a t i o n
system 100 a c c o r d i n g t o the p r e s e n t cmbodiinent is the same as Fig. 1 .
Fig. 2 shows a s i t u a t i o n w h e r e Too Late IIandover o c c u r s . I t is to be
n o t e d t h a t Fig. 2 assumes a s i t u a t i o n w h e r e information ( e . g . . the
HANDOVER REPORT message and t h e RLF INDICA'I'ION message)
19
c a n n o t b e t r a n s m i t t e d b e t w e e n t h e s o u r c e base s t a t i o n 11 1 and the
t a r g e t base s t a t i o n 1 1 2 . T h i s s i t u a t i o n c o r r e s p o n d s f o r e x a m p l e t o a
s i t u a t i o n t h a t t h e i n t e r - b a s e - s t a t i o n i n t e r f a c e ( e . g . , the X2 i n t e r f a c e )
between the s o u r c e b a s e s t a t i o n 1 1 1 and the t a r g e t b a s e s t a t i o n 112
5 c a n n o t be u t i l i z e d .
[0053]
In Fig. 2, at the b e g i n n i n g , the mobile terminal 101 i s c o n n e c t e d
to the s o u r c e b a s e s t a t i o n 11 1 ( s o u r c e c e l l 13 I ) , and performs
c o m m u n i c a t i o n t h r o u g h t h e s o u r c e b a s e s t a t i o n 11 1. S i m u l t a n e o u s l y ,
10 the mobile t e r m i n a l 10 1 is l o c a t e d n e a r the t a r g e t base s t a t i o n 11 2.
T h e m o b i l e t e r m i n a l 1 0 1 , f o r e x a m p l e , t r a n s m i t s to t h e s o u r c e base
s t a t i o n 11 1 a m e a s u r e m e n t report i n d i c a t i n g radio q u a l i t y of t h e s o u r c e
c e l l 131 and t h e t a r g e t cell 132 in r e s p o n s e t o a p r e d e t e r m i n e d
c o n d i t i o n ( e . g . , s a t i s f a c t i o n o f a n a p e r i o d i c or periodic c o n d i t i o n ) .
15 After t h a t , t h e s o u r c e b a s e s t a t i o n 11 1 d e c i d e s and i n i t i a t e s o u t g o i n g
handover of t h e m o b i l e t e r m i n a l 101 t o t h e t a r g e t c e l l 1 3 2 ( t a r g e t base
s t a t i o n 1 1 2 ) . In the example shown in Fig. 2, the s o u r c e b a s e s t a t i o n
11 1 t r a n s m i t s a handover command ( e . g . , the f - I 0 Command message) to
t h e m o b i l e t e r m i n a l 101 in o r d e r t o i n i t i a t e t h e h a n d o v e r . It is to be
20 noted that as a l r e a d y m e n t i o n e d a b o v e , the i n i t i a t i o n o f t h e handover
may correspond to t r a n s m i s s i o n of a handover request ( e . g . , the
" H a n d o v e r R e q u i r e d " m e s s a g e ) f r o m t h e s o u r c e base s t a t i o n 1 1 1 to the
n e t w o r k n o d e 141 ( e . g . , the MME). A l t e r n a t i v e l y , the i n i t i a t i o n of the
handover may c o r r e s p o n d t o r e c e p t i o n by the source base s t a t i o n 11 1
25 o f i n f o r m a t i o n ( e . g . , the M e a s u r e m e n t R e p o r t ) to t r i g g e r the handover.
(00541
However, the mobile t e r m i ~ l a l 101 o f F i g . 2 e x p e r i e n c e s RLF in
the s o u r c e cell 1 3 1 ( s o u r c e base s t a t i o n 1 1 1) before c o m p l e t i o n o f the
handover t o t h e t a r g e t cell 132. 'The mobile terminal 10 1 t h e n t r i e s
3 0 c o n n e c t i o n r e - e s t a b l i s h m e n t to the t a r g e t cell 132. I11 o t h e r w o r d s , the
illobile terminal 101 t r a n s m i t s a r e q u e s t f o r c o n n e c t i o n ree
s t a b l i s h m e n t t o the t a r g e t b a s e s t a t i o n 1 1 2 .
[0055]
The s o u r c e b a s e s t a t i o n 1 1 1 ( i . e . . the HO f a i l u r e d e t e c t i o n unit
20
121) of F i g . 2 d e t e c t s Too Late Handover w i t h o u t r e c e i v i n g
i n f o r m a t i o n ( e . g . , the HANDOVER REPORT message and the RLF
INDICATION m e s s a g e ) from t h e t a r g e t b a s e s t a t i o n 112. S p e c i f i c a l l y ,
the HO f a i l u r e d e t e c t i o n u n i t 1 2 1 may d e t e c t Too Late Handover when
5 n e i t h e r an acknowledgment response t o t h e handover command
r e g a r d i n g a n o u t g o i n g handover to the t a r g e t cell 132 nor a r e q u e s t for
c o n n e c t i o n r e - e s t a b l i s h m e n t to the s o u r c e c e l l 1 3 1 i s r e c e i v e d from the
mobile t e r m i n a l 1 0 1 w i t h i n a p r e d e t e r m i n e d period TI d e p e n d e n t o n
t h e i n i t i a t i o n of t h e o u t g o i n g liandover. It is to b e n o t e d t h a t a
10 p r e d e t e r m i n e d period f o r r e c e p t i o n d e t e r m i n a t i o n of the
a c k n o w l e d g m e n t r e s p o n s e t o the handover command may be d i f f e r e n t
f r o m a p r e d e t e r m i n e d p e r i o d for r e c e p t i o n d e t e r m i n a t i o n o f t h e request
for c o n n e c t i o n r e - e s t a b l i s h m e n t .
[0056]
15 Fig. 3 is a flow c h a r t s h o w i n g a f i r s t e x a m p l e o f a Too Late
Handover d e t e c t i o n p r o c e d u r e . In s t e p S 11, t h e s o u r c e b a s e s t a t i o n
11 1 i n i t i a t e s handover of the m o b i l e t e r m i n a l 1 0 1 f r o m t h e s o u r c e cell
131 to the t a r g e t cell 132. I n i t i a t i o n of the handover may b e
t r a n s m i s s i o n to the mobile terminal 101 of a handover command, may
20 be t r a n s m i s s i o n to t h e n e t w o r k node 141 o f a handover r e q u e s t , o r may
be r e c e p t i o n from the mobile t e r m i n a l 1 0 1 of i n f o r m a t i o n t o t r i g g e r the
handover. In step S12, the source base s t a t i o n 11 1 s t a r t s a timer for
measuring the p r e d e t e r m i n e d period '1-1 in response to the handover
i n i t i a t i o n . In step S 1 3 , t h e s o u r c e base s t a t i o n 11 1 ( i . e . , the HO
25 f a i l u r e d e t e c t i o n unit 1 2 1 ) d e t e c t s t h a t the liandover having been
attempted r e g a r d i n g the liiobile terminal 101 is Too Late Handover, in
response to r e c e i v i n g , b e f o r e e x p i r a t i o n of the t i m e r , n e i t h e r a n
a c k n o w l e d g ~ i ~ e iriet sponse from t h e mobile terminal 101 to the
handover command nor a r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t from
3 0 t h e mobile t e r m i n a l 101.
[0057]
Fig. 4 is a flow c h a r t s h o w i n g a s e c o n d e x a m p l e of a '1.00 Late
Handover d e t e c t i o n p r o c e d u r e . 111 s t e p S21, the HO f a i l u r e d e t e c t i o n
unit 121 d e t e r m i n e s w l ~ e t h e r o r n o t a handover command ( e . g . , the HO
2 1
Command m e s s a g e ) h a s b e e n t r a n s m i t t e d f r o m t h e s o u r c e c e l l 131
( s o u r c e b a s e s t a t i o n 1 1 1 ) t o t h e m o b i l e t e r m i n a l 101. If the handover
command is t r a n s m i t t e d (YES in step S21), the HO f a i l u r e d e t e c t i o n
u n i t 1 2 1 a c q u i r e s a n d h o l d s an i d e n t i f i e r ( e . g . , a C-RNTI) of the
5 mobile t e r m i n a l 1 0 1 ( i . e . , a t r a n s m i s s i o n d e s t i n a t i o n o f t h e handover
command) ( s t e p S22). In s t e p S23, the HO f a i l u r e d e t e c t i o n unit 121
d e t e r m i n e s whether or not t h e a c k n o w l e d g m e n t response t o t h e
handover command r e g a r d i n g the outgoing handover o f t h e mobile
t e r m i n a l 101 h a s b e e n r e c e i v e d . If the a c k n o w l e d g m e n t r e s p o n s e t o the
10 handover command is n o t r e c e i v e d ( Y E S i n s t e p S23), the HO f a i l u r e
d e t e c t i o n unit 121 d e t e r m i n e s whether or not the request for
c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m t h e m o b i l e t e r m i n a l 10 1 to t h e s o u r c e
c e l l 1 3 1 has been r e c e i v e d ( s t e p S24). If n e i t h e r the acknowledgment
response to the handover command nor t h e r e - e s t a b l i s h m e n t r e q u e s t i s
15 r e c e i v e d (NO in s t e p S24), the HO f a i l u r e d e t e c t i o n u n i t 1 2 1
d e t e r m i n e s whether or not the p r e d e t e r m i n e d p e r i o d T1 h a s e l a p s e d
s i n c e t r a n s m i s s i o n of the handover command ( e . g . , the HO Command
message) (step S25). S u b s e q u e n t l y , i f t h e p r e d e t e r m i n e d period TI has
elapsed (YES in step S25), the 1-10 f a i l u r e d e t e c t i o n unit 121 d e t e c t s
20 that the handover h a v i n g b e e n a t t e m p t e d r e g a r d i n g the mobile terminal
101 is Too Late Handover ( s t e p S26).
[0058]
F i g . 5 is a flow chart s h o w i n g o n e e x a m p l e of an HO parameter
a d j u s t m e n t p r o c e d u r e by the 1-10 p a r a m e t e r a d j u s t m e n t unit 15 1. In
25 step S3 1 , t h e IIO p a r a m e t e r a d j u s t m e n t u n i t 1 5 1 c a l c u l a t e s an
occurrence rate 1i - TL o f T o o Late Handover r e g a r d i n g h a n d o v e r s from
the s o u r c e cell 13 1 to t h e t a r g e t cell 132 based on feedback
i n f o r m a t i o n r e c e i v e d f r o m the 1-10 f a i l u r e d e t e c t i o n unit 121. The
f e e d b a c k i n f o r m a t i o n , f o r e x a m p l e , i n c l u d e s l ~ a n d o v e r s t a t i s t i c a l
30 i n f o r m a t i o n . such as t h e d e t e c t e d n u ~ n b e ro f 'Too Late IIandovers and
the n u m b e r o f handover a t t e m p t s f o r e a c h n e i g h b o r i n g cell i n c l u d i n g
the t a r g e t cell 132. The occurrence rate R-TL of Too Late IIandover
may be a v a l u e o b t a i n e d by d i v i d i n g t h e d e t e c t e d number of Too Late
Handovers by the number of a t t e m p t s o f o u t g o i n g handover from t h e
22
s o u r c e c e l l 131. When the o c c u r r e n c e r a t e R-TL of Too Late Handover
is l a r g e r than a p r e d e t e r m i n e d t h r e s h o l d v a l u e R-TH1, the HO
p a r a m e t e r a d j u s t m e n t unit 1 5 1 a d j u s t s an HO p a r a m e t e r in order to
reduce Too Late Handover ( s t e p s S 3 2 a n d S33). In t h e a d j u s t m e n t o f
5 the HO p a r a m e t e r o f s t e p S33, t h e C I O t h a t a c t s o n radio q u a l i t y of the
t a r g e t c e l l 1 3 2 m a y b e i n c r e a s e d by a p r e d e t e r m i n e d s t e p s i z e . In
a d d i t i o n or a l t e r n a t i v e l y , the TTT a p p l i e d t o t h e s o u r c e c e l l 1 3 1 may
be decreased by a p r e d e t e r m i n e d s t e p s i z e . In a d d i t i o n or a l t e r n a t i v e l y ,
t h e A 3 - o f f s e t t h a t a c t s on r a d i o q u a l i t y of the s o u r c e c e l l 1 3 1 may b e
10 decreased by a p r e d e t e r m i n e d s t e p s i z e .
lo0591
As i s understood from t h e a b o v e e x p l a n a t i o n , t h e HO f a i l u r e
d e t e c t i o n unit 1 2 1 a c c o r d i n g to the p r e s e n t e m b o d i m e n t can d e t e c t T o o
Late Handover w i t h o u t r e c e i v i n g i n f o r m a t i o n ( e . g . , the HANDOVER
15 REPORT m e s s a g e and the RLF INDICATION message) from the t a r g e t
b a s e s t a t i o n 1 1 2 . In a d d i t i o n , the HO p a r a m e t e r a d j u s t m e n t u n i t 1 5 1
can a d j u s t a n HO parameter for reducing Too Late Handover r e g a r d l e s s
o f r e c e p t i o n of the i n f o r m a t i o n ( e . g . , the HANDOVER REPORT
m e s s a g e a n d t h e RLF INDICATION m e s s a g e ) f r o m t h e t a r g e t base
20 s t a t i o n 11 2.
[0060]
It is to be n o t e d t h a t Too Late Handover detected by a t e c h n i q u e
e x p l a i n e d by t h e p r e s e n t e m b o d i m e n t c a n include a part of Handover to
Wrong C e l l . In o t h e r w o r d s , t h e t e c h n i q u e explained by t h e p r e s e n t
25 embodiment c a n n o t d i s t i n g u i s h b e t w e e n Too Late Handover and a part
of Handover to Wrong C e l l . H o w e v e r , t h e part of I-Iandover to Wrong
Cell c a n b e reduced by a d j u s t m e n t of an HO parameter ( e . g . , decrease
of the A 3 - o f f s e t a p p l i e d t o t h e s o u r c e cell 13 1 ) s i m i l a r l y t o the
adjustment f o r r e d u c i n g Too L a t e H a n d o v e r . I n this c a s e , even if the
30 part of I-Iandover lo Wrong C e l l c a n n o t be s t r i c t l y d i s t i n g u i s h e d ,
handover f a i l u r e i n c l u d i n g Handover to Wrong Cell call be
a p p r o p r i a t e l y r e d u c e d .
LO06 1 ]
In a d d i t i o n or a l t e r n a t i v e l y , when an occurrence rate of Too Late
23
Handover does not d e c r e a s e e v e n t h o u g h a d j u s t m e n t of an HO
parameter for reducing Too Late Handover has been performed, the HO
p a r a m e t e r a d j u s t m e n t u n i t 1 5 1 may p e r f o r m HO parameter adjustment
for reducing Handover t o Wrong C e l l . For e x a m p l e , t h e HO parameter
5 adjustment for reducing Handover to Wrong C e l l may i n c l u d e
adjustment in a n o p p o s i t e d i r e c t i o n of the HO p a r a m e t e r a d j u s t m e n t f o r
reducing Too Late H a n d o v e r , f o r e x a m p l e , d e c r e a s e i n t h e CIO t h a t
acts on t h e r a d i o quality. of the t a r g e t c e l l 132, i n c r e a s e in the TTT
a p p l i e d t o t h e s o u r c e cell 131, o r i n c r e a s e in the A3-offset t h a t a c t s on
10 t h e r a d i o q u a l i t y of t h e s o u r c e cell 13 1. In a d d i t i o n o r a l t e r n a t i v e l y ,
t h e HO p a r a m e t e r a d j u s t m e n t may i n c l u d e i n c r e a s e of the CIO t h a t a c t s
on r a d i o q u a l i t y of a n e i g h b o r i n g c e l l ( e . g . , the cell 133) of t h e s o u r c e
cell 13 1 e x c l u d i n g the t a r g e t c e l l 1 3 2 . C o n s e q u e n t l y , e v e n i f the part
of Handover to Wrong Cell c a n n o t b e s t r i c t l y d i s t i n g u i s h e d , handover
15 f a i l u r e i n c l u d i n g Handover t o Wrong C e l l c a n b e a p p r o p r i a t e l y r e d u c e d .
[0062]
As d e s c r i b e d a b o v e , t h e t e c h n i q u e e x p l a i n e d in t h e p r e s e n t
e m b o d i m e n t c a n s u f f i c i e n t l y c o n t r i b u t e t o r e d u c t i o n o f handover
f a i l u r e s , e v e n i f t h e part of Handover to Wrong C e l l c a n n o t be
20 d i s t i n g u i s h e d . H o w e v e r , when t h e s o u r c e base s t a t i o n 111 c a n
communicate with e i t h e r t h e t a r g e t b a s e s t a t i o n 1 1 2 o r the n e i g h b o r i n g
base s t a t i o n 11 3, the part of Handover to Wrong Cell can also be
d e t e c t e d in d i s t i n c t i o n f r o m Too Late Handover. This technique will
be e x p l a i n e d in f o u r t h and f i f t h embodiments l a t e r .
25 [0063]
Third embodiment
In the p r e s e n t e m b o d i m e n t , d e t e c t i o n of Too Early Handovcr
r e g a r d i n g handover from the s o u r c e cell 131 t o t h e t a r g e t cell 132 will
be e x p l a i n e d . A c o n f i g u r a t i o n e x a m p l e of the r a d i o communication
30 s y s t e m 1 0 0 a c c o r d i n g to the present embodiment i s t h e same as Fig. 1.
Fig. 6 shows a s i t u a t i o n w h e r e Too Early Handover o c c u r s . Too Early
Handover c o r r e s p o l l d s t o a s i t u a t i o n w h e r e t h e mobile t e r n ~ i n a l 101 that
has e x p e r i e n c e d RLF i l l t h e t a r g e t cell 132 (base s t a t i o n 112) during
e x e c u t i o n of the handover p r o c e d u r e o r ilnmcdiately a f t e r completion
24
of the handover t r i e s c o n n e c t i o n r e - e s t a b l i s h m e n t t o t h e s o u r c e c e l l
131 ( b a s e s t a t i o n 11 1 ) . It is to be noted t h a t F i g . 6 a s s u m e s a s i t u a t i o n
w h e r e i n f o r m a t i o n ( e . g . , the HANDOVER REPORT message and the
RLF INDICATION m e s s a g e ) c a n n o t b e t r a n s m i t t e d between t h e s o u r c e
5 b a s e s t a t i o n 1 1 1 and the t a r g e t b a s e s t a t i o n 1 1 2 . T h i s s i t u a t i o n , for
e x a m p l e , c o r r e s p o n d s t o a s i t u a t i o n that t h e i n t e r - b a s e - s t a t i o n
i n t e r f a c e ( e . g . , the X2 i n t e r f a c e ) b e t w e e n t h e s o u r c e b a s e s t a t i o n 11 1
and the t a r g e t b a s e s t a t i o n 1 1 2 c a n n o t be u t i l i z e d .
[0064]
10 In F i g . 6 , at the b e g i n n i n g , t h e m o b i l e t e r m i n a l 101 is connected
t o t h e s o u r c e b a s e s t a t i o n 11 1 ( s o u r c e cell 131), and performs
c o m m u n i c a t i o n t h r o u g h t h e s o u r c e base s t a t i o n 11 1. S i m u l t a n e o u s l y ,
t h e m o b i l e t e r m i n a l 101 is l o c a t e d near t h e t a r g e t b a s e s t a t i o n 11 2.
A f t e r t h a t , t h e s o u r c e b a s e s t a t i o n 11 1 d e c i d e s and i n i t i a t e s o u t g o i n g
15 handover of the m o b i l e t e r m i n a l 101 to t h e t a r g e t c e l l 1 3 2 ( t a r g e t base
s t a t i o n 1 1 2 ) . I n t h e example of Fig. 6, the source b a s e s t a t i o n 11 1
t r a n s m i t s a handover command ( e . g . , t h e HO Command message) t o t h e
mobile t e r m i n a l 1 0 1 i n o r d e r to i n i t i a t e t h e h a n d o v e r . A s already
mentioned, the i n i t i a t i o n of the handover may c o r r e s p o n d to
20 t r a n s m i s s i o n o f a handover r e q u e s t ( e . g . , the "Handover Required"
m e s s a g e ) f r o m t h e s o u r c e base s t a t i o n 11 1 t o the network node 141
( e . g . , the MME). A l t e r n a t i v e l y , t h e i n i t i a t i o n of the handover may
correspond to r e c e p t i o n by t h e s o u r c e base s t a t i o n 1 I 1 of information
( e . g . , the Measurement R e p o r t ) t o t r i g g e r t h e h a n d o v e r .
25 [0065]
S u b s e q u e n t l y , t h e s o u r c e base s t a t i o n 11 1 r e c e i v e s a handover
c o m p l e t i o n n o t i f i c a t i o n ( e . g . , the "IJE Context Release Comnlal~d"
message from the MME) t r a n s m i t t e d in response to completion of the
handover of the mobile t e r m i n a l 101 to t h e t a r g e t c e l l 1 3 2 . However,
30 the mobile t e r m i n a l 1 0 1 e x p e r i e n c e s RLF in the t a r g e t c e l l 132
i r n i ~ ~ c d i a t e layf t e r c o m p l e t i o n o f the handover. A f t e r t h a t , the nob bile
terminal 101 d e t e c t s t h a t radio q u a l i t y o f the s o u r c e cell 131 i s g o o d .
and t r a n s m i t s a r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t to the source
cell 131 (source base s t a t i o n 1 1 1). I t is to be noted that the mobile
2 5
t e r m i n a l 101 may e x p e r i e n c e KLF in the t a r g e t c e l l 1 3 2 d u r i n g t h e
e x e c u t i o n of the handover to the t a r g e t cell 132 in some c a s e s . In this
c a s e , t h e handover c o m p l e t i o n n o t i f i c a t i o n s h o w n in F i g . 6 is
t r a n s m i t t e d t o the s o u r c e b a s e s t a t i o n 11 1 a f t e r t h e c o n n e c t i o n re-
5 e s t a b l i s h m e n t of the mobile t e r m i n a l 101 t o t h e t a r g e t cell 132 is
completed.
[0066]
The source base s t a t i o n 1 1 1 ( i . e . , the HO f a i l u r e d e t e c t i o n unit
121) of Fig. 6 d e t e c t s Too Early Handover w i t h o u t r e c e i v i n g
10 i n f o r m a t i o n ( e . g . , the HANDOVER REPORT message and the RLF
INDICATION m e s s a g e ) f r o m t h e t a r g e t base s t a t i o n 1 1 2 . A s a f i r s t
e x a m p l e , the HO f a i l u r e d e t e c t i o n unit 121 may d e t e c t Too Early
Handover when a r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m the
mobile t e r m i n a l 1 0 1 to the s o u r c e c e l l 13 1 ( s o u r c e base s t a t i o n 11 1) is
15 r e c e i v e d w i t h i n a p r e d e t e r m i n e d p e r i o d T2 dependent on the i n i t i a t i o n
of the outgoing handover of t h e m o b i l e terminal 101. A s a second
e x a m p l e , t h e HO f a i l u r e d e t e c t i o n unit 121 may d e t e c t T o o Early
I-Iandover when a r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m t h e
mobile t e r m i n a l 101 to the s o u r c e cell 13 1 (source b a s e s t a t i o n 11 1) is
20 r e c e i v e d a f t e r t h e i n i t i a t i o n of the outgoing handover of the mobile
t e r m i n a l 1 0 1 a n d b e f o r e t h e c o m p l e t i o n of the handover ( e . g . , before
t h e r e c e p t i o n of the handover c o m p l e t i o n n o t i f i c a t i o n ) . A s a third
e x a m p l e , t h e HO f a i l u r e d e t e c t i o n unit 121 may d e t e c t T o o Early
Handover when a r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t from the
2 5 m o b i l e terminal 101 t o t h e s o u r c e cell 13 1 (source base s t a t i o n 11 1) is
received within a p r e d e t e r l n i n e d period T3 dependent on the
c o m p l e t i o n o f the handover ( e . g . , the reception of the handover
c o n ~ p l e t i o n n o t i f i c a t i o n ) .
100671
3 0 Fig. 7 is a f l o w chart showing a f i r s t exanlple o f a T o o Early
Handover d e t e c t i o n p r o c e d u r e . 111 s t e p S41. the s o u r c e basc s t a t i o n
1 1 1 i n i t i a t c s handover of the mobile ternlinal 101 from the source cell
13 1 to the t a r g e t cell 132. I n i t i a t i o l ~ of the handover 111ay be
t r a n s m i s s i o n t o t h e mobile t e r m i n a l 101 o f a handover c o n ~ m a n d . may
26
b e t r a n s m i s s i o n t o t h e network node 141 of a handover r e q u e s t , o r may
be r e c e p t i o n f r o m t h e m o b i l e t e r m i n a l 101 o f i n f o r m a t i o n to t r i g g e r the
liandover. In s t e p S 4 2 , t h e s o u r c e b a s e s t a t i o n 11 1 s t a r t s a timer for
measuring the p r e d e t e r m i n e d p e r i o d T2 in response to the handover
5 i n i t i a t i o n . In s t e p S43, the s o u r c e b a s e s t a t i o n 11 1 r e c e i v e s a request
for c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m the m o b i l e t e r m i n a l 1 0 1 t h a t has
e x p e r i e n c e d RLF i n t h e t a r g e t c e l l 132. In s t e p S 4 4 , t h e s o u r c e b a s e
s t a t i o n 11 1 ( i . e . , the HO f a i l u r e d e t e c t i o n unit 1 2 1 ) d e t e c t s t h a t t h e
handover having been attempted r e g a r d i n g t h e m o b i l e t e r m i n a l 101 is
10 Too E a r l y H a n d o v e r , in response to o c c u r r e n c e o f a c o n n e c t i o n ree
s t a b l i s h m e n t e v e n t o f the m o b i l e t e r m i n a l 1 0 1 i n t h e s o u r c e cell 13 1
( s o u r c e b a s e s t a t i o n 11 1 ) b e f o r e e x p i r a t i o n of t h e t i m e r .
[0068]
Fig. 8 is a flow chart showing a s e c o n d e x a m p l e of a Too Early
15 Handover d e t e c t i o n p r o c e d u r e . Step S51 is t o t h e same a s s t e p S41 of
Fig. 7. Namely, in s t e p S 5 1 , t h e s o u r c e base s t a t i o n 1 1 1 i n i t i a t e s
handover of t h e m o b i l e t e r m i n a l 101 from the s o u r c e c e l l 13 1 t o the
t a r g e t c e l l 1 3 2 . In s t e p S 5 2 , t h e s o u r c e base s t a t i o n 11 1 r e c e i v e s , a f t e r
i n i t i a t i o n o f the outgoing handover of t h e m o b i l e t e r m i n a l 101 and
20 b e f o r e c o m p l e t i o n t h e r e o f , a r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t
f r o m t h e m o b i l e terminal 101 t h a t h a s e x p e r i e n c e d RLF in t h e t a r g e t
c e l l 132. In s t e p S 5 3 , the s o u r c e b a s e s t a t i o n 1 1 1 ( i . e . , the HO f a i l u r e
d e t e c t i o n u n i t 12 1 ) d e t e c t s that the l i a ~ ~ d o v ehra ving b e e n a t t e m p t e d
r e g a r d i n g the mobile terminal 101 is 1'00 Early Handover, in response
25 to r e c e i v i n g t h e r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m the
m o b i l e t e r m i n a l 101 a f t e r the i n i t i a t i o n o f t h e o u t g o i n g liandover of the
mobile ter111i11al 101 and before the c o m p l e t i o n t h e r e o f .
[0069]
Fig. 9 is a f l o w chart showing a third e x a m p l e o f a T o o Early
30 Handover d e t e c t i o n p r o c e d u r e . In s t e p S61, handover of the mobile
t e r n ~ i l l a l 101 from t h e s o u r c e cell 13 1 to t h e t a r g e t cell 132 is
c o m p l e t e d . F o r e x a m p l e . the s o u r c e b a s e s t a t i o n 1 1 1 r e c e i v e s a
handover completion n o t i f i c a t i o n ( e . g . . the UE C o n t e x t R e l e a s e
Command m e s s a g e ) from the n e t w o r k n o d e 1 4 1 . I n s t e p S 6 2 , the
2 7
s o u r c e b a s e s t a t i o n 1 1 1 s t a r t s a t i m e r f o r m e a s u r i n g the predetermined
period T3 in response to the handover c o m p l e t i o n . In s t e p S 6 3 , t h e
s o u r c e b a s e s t a t i o n 11 1 r e c e i v e s a r e q u e s t f o r c o n n e c t i o n r e -
e s t a b l i s h m e n t f r o m the m o b i l e t e r m i n a l 101 t h a t h a s e x p e r i e n c e d RLF
5 in t h e t a r g e t c e l l 132. In step S64, the s o u r c e b a s e s t a t i o n 1 1 1 ( i . e . ,
t h e HO f a i l u r e d e t e c t i o n unit 121) d e t e c t s t h a t the handover having
been attempted r e g a r d i n g the m o b i l e t e r m i n a l 101 is Too Early
Handover, in r e s p o n s e t o o c c u r r e n c e of a c o n n e c t i o n r e - e s t a b l i s h m e n t
e v e n t o f the m o b i l e t e r m i n a l 1 0 1 i n the source c e l l 1 3 1 (source base
10 s t a t i o n 11 1 ) b e f o r e e x p i r a t i o n of the t i m e r .
[0070]
F i g . 1 0 i s a f l o w c h a r t s h o w i n g a f o u r t h e x a m p l e o f a Too Early
Handover d e t e c t i o n p r o c e d u r e . In s t e p S 7 1 , t h e HO f a i l u r e detection
u n i t 1 2 1 d e t e r m i n e s whether or not a handover command ( e . g . , the HO
15 Command message) h a s b e e n t r a n s m i t t e d f r o m the source c e l l 13 1
( s o u r c e b a s e s t a t i o n 11 1 ) t o t h e mobile t e r m i n a l 101. If the handover
command is t r a n s m i t t e d (YES in s t e p S21), the HO f a i l u r e detection
u n i t 1 2 1 a c q u i r e s a n d h o l d s a n i d e n t i f i e r ( e . g . , the C-RNTI) of the
m o b i l e t e r m i n a l 101 ( i . e . , a t r a n s m i s s i o n d e s t i n a t i o n of the handover
20 command) ( s t e p S72). In step S 7 3 , t h e HO f a i l u r e d e t e c t i o n unit 121
d e t e r l n i n e s whether or not a handover coinpletion n o t i f i c a t i o n
r e g a r d i n g t h e o u t g o i n g handover of the mobile terminal 101 has been
r e c e i v e d . If the handover c o m p l e t i o n n o t i f i c a t i o n is r e c e i v e d (YES in
step S73), the I10 f a i l u r e d e t e c t i o n u n i t 1 2 1 a c q u i r e s and holds an
2 5 i d e n t i f i e r ( e . g . , the C-RNTI) o f t h e mobile t e r m i n a l 1 0 1 in the target
cell 132 ( s t e p S74). T h e i d e n t i f i e r of the m o b i l e t e r m i n a l 101 in the
t a r g e t cell 132 ( i . e . , the i d e n t i f i e r a l l o c a t e d to t h e m o b i l e terminal 101
by the t a r g e t cell 132) can be a c q u i r e d , for example, by r e f e r r i n g to
the handover command ( e . g . , the MO Command message) that the
3 0 s o u r c e base s t a t i o n 1 1 1 has received from t h e n e t w o r k node 141
i m m e d i a t e l y b e f o r e s t e p S71.
[0071]
I n s t e p S75. the I 1 0 f a i l u r e d e t e c t i o n unit 121 determines
w l ~ c t h e r or not a r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t Srom the
2 8
m o b i l e t e r m i n a l 101 to the s o u r c e c e l l 131 has been r e c e i v e d . I f t h e
r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t is received (YES in step S75),
the HO f a i l u r e d e t e c t i o n unit 121 d e t e c t s t h a t the handover having been
a t t e m p t e d r e g a r d i n g t h e m o b i l e t e r m i n a l 101 is T o o E a r l y Handover
5 ( s t e p S76). Meanwhile, if the r e q u e s t for connection r e - e s t a b l i s h m e n t
is n o t r e c e i v e d (NO in s t e p S75), t h e HO f a i l u r e d e t e c t i o n unit 121
r e p e a t s r e c e p t i o n d e t e r m i n a t i o n o f t h e r e q u e s t f o r c o n n e c t i o n ree
s t a b l i s h m e n t u n t i l t h e p r e d e t e r m i n e d period T2 e l a p s e s s i n c e t h e
i n i t i a t i o n o f the handover ( s t e p S77).
10 [0072]
It is to b e n o t e d t h a t i n s t e p S75, the i d e n t i f i e r h e l d i n step S72
or S74 may j u s t b e c h e c k e d with a n i d e n t i f i e r i n c l u d e d i n the request
for c o n n e c t i o n r e - e s t a b l i s h m e n t in o r d e r t o d e t e r m i n e w h e t h e r the
mobile t e r m i n a l t h a t h a s s e n t t h e r e q u e s t f o r c o n n e c t i o n re-
15 e s t a b l i s h m e n t is i d e n t i c a l w i t h t h e m o b i l e terminal t h a t h a s attempted
t h e o u t g o i n g handover to the t a r g e t c e l l 132. As is understood from
t h i s , s t e p s S73 and S74 are p e r f o r m e d t o c h a n g e t h e t e r m i n a l i d e n t i f i e r
to be checked with t h e r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t before
and a f t e r c o m p l e t i o n o f t h e h a n d o v e r . A c c o r d i n g l y , when t h e terminal
20 i d e n t i f i e r t h a t does not c h a n g e b e f o r e and a f t e r the c o m p l e t i o n o f the
handover c a n b e u t i l i z e d f o r t h e c h e c k , p r o c e s s i n g of steps S73 and
S74 may be o m i t t e d .
COO731
Fig. 11 is a flow chart s h o w i n g o n e example of a n HO parameter
25 a d j u s t m e n t p r o c e d u r e p e r f o r m e d by t h e HO p a r a m e t e r a d j u s t m e n t unit
15 1. In the example of Fig. 11, t h e HO parameter adjustment unit 15 1
a d j u s t s a n NO parameter in response to d e t e c t i o n of Too Late Handover
and Too Early Handover. Too Late Handover may b e d e t e c t e d in
accordance with the a b o v e - m e n t i o n e d s e c o n d e m b o d i m e n t . In step S81,
30 the 110 p a r a ~ n e t e r adjustment unit 151 c a l c u l a t e s t h e o c c u r r e n c e rate
I<-TI, of Too Late Mandover r e g a r d i n g t h e handover from the source
cell 131 to the t a r g e t cell 132 s i m i l a r l y to s t e p S31 of Fig. 5 . In step
S82, the 130 p a r a m e t e r a d j u s t m e n t unit 15 1 c a l c u l a t e s t h e occurrence
rate R-TE of Too Early Handover r e g a r d i n g t h e handover from the
2 9
s o u r c e c e l l 13 1 to t h e t a r g e t c e l l 132 based on feedback i n f o r m a t i o n
received from the FIO f a i l u r e d e t e c t i o n unit 12 1. The feedback
i n f o r m a t i o n , for e x a m p l e , i n c l u d e s handover s t a t i s t i c a l i n f o r m a t i o n ,
such as the d e t e c t e d n u m b e r o f T o o Late Handovers, t h e d e t e c t e d
5 number of Too E a r l y H a n d o v e r s , and t h e n u m b e r o f handover attempts
f o r e a c h n e i g h b o r i n g cell i n c l u d i n g the t a r g e t cell 132. The occurrence
r a t e R - T E o f T o o Early Handover may be a value obtained by dividing
t h e d e t e c t e d n u m b e r o f Too E a r l y H a n d o v e r s by the number of attempts
of t h e o u t g o i n g handover from t h e s o u r c e cell 13 1.
10 COO741
The HO p a r a m e t e r a d j u s t m e n t unit 15 1 a d j u s t s a n HO parameter
when a sum of the R - TL a n d the R-TE is l a r g e r than a p r e d e t e r m i n e d
t h r e s h o l d v a l u e R-TH2 ( s t e p S83). S p e c i f i c a l l y , i f t h e occurrence rate
R-TL of Too Late I-Iandover is l a r g e r t h a n t h e o c c u r r e n c e r a t e R - TE of
15 Too Early Handover (YES in s t e p S84), HO parameter a d j u s t m e n t f o r
r e d u c t i o n o f Too Late Handover is performed (step S85). In c o n t r a s t
with t h i s , if t h e o c c u r r e n c e rate R-TE o f T o o Early Handover i s n o t
l e s s than t h e o c c u r r e n c e r a t e R - T L o f T o o Late Handover (NO in step
S84), t h e HO p a r a m e t e r a d j u s t m e n t for the reduction of Too Early
20 Handover is p e r f o r m e d ( s t e p S86). In the adjustment o f t h e HO
parameter in s t e p S 8 6 , t h e CIO t h a t a c t s o n radio q u a l i t y of the t a r g e t
c e l l 1 3 2 may be decreased by a p r e d e t e r m i n e d s t e p s i z e . In addition or
a l t e r n a t i v e l y , t h e 'TTT a p p l i e d t o t h e s o u r c e c e l l 131 may b e i n c r e a s e d
by a p r e d e t e r m i n e d s t e p s i z e . In a d d i t i o n or a l t e r n a t i v e l y , the A3-
25 o f f s e t t h a t a c t s o n radio q u a l i t y of t h e s o u r c e cell 131 may be
increased by a p r e d e t e r m i n e d s t e p s i z e . I t is to be noted t h a t in step
S 8 5 , a d j u s t m e n t may be performed so as to increase o r d e c r e a s e the tIO
parameter i n an o p p o s i t e d i r e c t i o n o f s t e p S 8 6 .
[0075]
3 0 As is understood from t h e a b o v e e x p l a n a t i o n , t h e HO f a i l u r e
d e t e c t i o n u n i t 1 2 1 according to the p r e s e n t e m b o d i m e n t call d e t e c t Too
Early Handover w i t h o u t r e c e i v i n g i l ~ f o r n ~ a t i o(ne . g . , the HANDOVER
REPORT message and the RLF INDICATION message) f r o m t h e target
base s t a t i o n 1 1 2. I n a d d i t i o n , the HO p a r a m e t e r a d j u s t m e n t unit 15 1
3 0
can a d j u s t the HO p a r a m e t e r for t h e r e d u c t i o n of Too E a r l y Handover
r e g a r d l e s s of r e c e p t i o n of i n f o r m a t i o n ( e . g . , the HANDOVER REPORT
message and the RLF INDICATION m e s s a g e ) f r o m the t a r g e t b a s e
s t a t i o n 112.
5 [0076]
F o u r t h e m b o d i m e n t
In t h e p r e s e n t e m b o d i m e n t , d e t e c t i o n of Handover t o Wrong Cell
r e g a r d i n g the handover from the s o u r c e c e l l 131 to the t a r g e t cell 132
will be e x p l a i n e d . A c o n f i g u r a t i o n example of t h e r a d i o
10 c o m m u n i c a t i o n s y s t e m 1 0 0 a c c o r d i n g t o the present embodiment is the
same as F i g . 1 . F i g . 12 shows a s i t u a t i o n w h e r e Handover to Wrong
Cell o c c u r s . It is t o b e noted t h a t Fig. 1 2 a s s u m e s a s i t u a t i o n where
the t a r g e t base s t a t i o n 1 1 2 c a n n o t t r a n s m i t or receive i n f o r m a t i o n ( e . g . ,
the I-IANDOVER REPORT message and the RLF INDICATION message)
15 to or from o t h e r t w o base s t a t i o n s ( i . e . , the source base s t a t i o n 1 1 1 and
t h e n e i g h b o r i n g b a s e s t a t i o n 113). Meanwhile, the s o u r c e b a s e s t a t i o n s
11 1 can communicate with t h e n e i g h b o r i n g b a s e s t a t i o n 113, and
r e c e i v e s handover (HO) f a i l u r e i n f o r m a t i o n f r o m the n e i g h b o r i n g base
s t a t i o n 113. T h e HO f a i l u r e i n f o r m a t i o n may be t r a n s m i t t e d v i a an
20 i n t e r - b a s e - s t a t i o n i n t e r f a c e ( e . g . , the X2 i n t e r f a c e ) between t h e source
base s t a t i o n 11 1 a n d t h e n e i g h b o r i n g b a s e s t a t i o n 113, or may be
t r a n s m i t t e d v i a t h e n e t w o r k 1 4 0 .
[0077]
In Fig. 12, a t t h e b e g i n n i n g , t h e mobile terminal 101 i s
25 c o n n e c t e d t o t h e s o u r c e base s t a t i o n 11 1 ( s o u r c e cell 131), and
performs c o n ~ m u n i c a t i o nt hrough the s o u r c e b a s e s t a t i o n 1 1 1 .
S i m u l t a n e o u s l y , the mobile terminal 101 is located near t h e t a r g e t base
s t a t i o n 1 1 2 and t h e n e i g h b o r i n g b a s e s t a t i o n 1 1 3. After t h a t , the
source base s t a t i o n 11 1 decides and i n i t i a t e s o u t g o i n g handover of the
30 mobile terminal 101 t o t h e t a r g e t cell 132 ( t a r g e t base s t a t i o n 1 1 2). In
the example of F i g . 1 2 , t h e s o u r c e base s t a t i o n 1 1 1 t r a n s m i t s a
handover command ( e . g . , t h e HO Command m e s s a g e ) to the mobile
terminal 101 in o r d e r to i n i t i a t e t h e handover. As already mentioned,
the i n i t i a t i o n of the I ~ a n d o v e rm ay c o r r e s p o n d t o transmission o f a
3 1
handover r e q u e s t ( e . g . , t h e " H a n d o v e r R e q u i r e d " message) f r o m t h e
source base s t a t i o n 1 1 1 t o t h e n e t w o r k n o d e 141 ( e . g . , t h e MME).
A l t e r n a t i v e l y , t h e i n i t i a t i o n o f the handover may c o r r e s p o n d t o
reception by t h e s o u r c e b a s e s t a t i o n 1 1 1 o f i n f o r m a t i o n ( e . g . , the
5 Measurement R e p o r t ) t o t r i g g e r the handover.
[0078]
S u b s e q u e n t l y , the source base s t a t i o n 1 1 1 receives a handover
completion n o t i f i c a t i o n ( e . g . , the "UE C o n t e x t Release Command"
message from the MME) t r a n s m i t t e d in response to completion of the
10 handover of t h e m o b i l e t e r m i n a l 101 to the t a r g e t cell 132. However,
t h e m o b i l e t e r m i n a l 101 e x p e r i e n c e s RLF in the t a r g e t c e l l 132
immediately a f t e r c o m p l e t i o n o f t h e h a n d o v e r . After t h a t , t h e m o b i l e
t e r m i n a l 1 0 1 d e t e c t s t h a t radio q u a l i t y of t h e n e i g h b o r i n g c e l l 133 is
good, and t r a n s m i t s a r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t t o t h e
15 n e i g h b o r i n g c e l l 1 3 3 ( n e i g h b o r i n g b a s e s t a t i o n 11 3). It is to b e n o t e d
t h a t t h e m o b i l e t e r m i n a l 1 0 1 may e x p e r i e n c e RLF in t h e t a r g e t c e l l 1 3 2
d u r i n g e x e c u t i o n of the handover to t h e t a r g e t cell 132 i n some c a s e s .
In this c a s e , the handover c o m p l e t i o n n o t i f i c a t i o n s h o w n in Fig. 12 is
t r a n s m i t t e d to t h e s o u r c e b a s e s t a t i o n 11 1 a f t e r t h e c o n n e c t i o n r e -
20 e s t a b l i s h m e n t of the mobile t e r m i n a l 1 0 1 to t h e n e i g h b o r i n g cell 133 is
completed.
[0079]
The s o u r c e b a s e s t a t i o n 1 1 1 and the n e i g h b o r i n g base s t a t i o n 113
of F i g . 1 2 c o o p e r a t i v e l y p e r f o r m p r o c e s s i n g to detect Handover to
25 Wrong Cell w i t h o u t r e c e i v i n g i n f o r m a t i o n ( e . g . , the HANDOVER
REPORT m e s s a g e and the RLF INDICATION m e s s a g e ) f r o m t h e t a r g e t
b a s e s t a t i o n 112. S p e c i f i c a l l y , in order to detect IIandover to Wrong
C e l l , t h e HO f a i l u r e d e t e c t i o n unit 121 uses 110 f a i l u r e i n f o r m a t i o n
received from the n e i g h b o r i n g base s t a t i o n 1 1 3 .
30 [0080]
As a f i r s t e x a m p l e , the HO f a i l u r e d e t e c t i o n unit 1 2 1 may detect
Handover to Wrong Cell when ( a ) a r e q u e s t f o r c o n n e c t i o n r e -
e s t a b l i s h m e n t f r o ~ nt he mobile terminal 10 1 to t h e s o u r c e cell 13 1 is
not r e c e i v e d w i t h i n a p r e d e t e r m i n e d period 7'4 dependent on the
32
i n i t i a t i o n of t h e o u t g o i n g h a n d o v e r o f the m o b i l e t e r m i n a l 1 0 1 , but (b)
t h e HO f a i l u r e i n f o r m a t i o n , w h i c h i n d i c a t e s t h a t t h e m o b i l e t e r m i n a l
101 has r e q u e s t e d c o n n e c t i o n r e - e s t a b l i s h m e n t t o t h e n e i g h b o r i n g c e l l
133 w i t h i n t h e p r e d e t e r m i n e d p e r i o d T4, i s r e c e i v e d . A p r e d e t e r m i n e d
5 p e r i o d to d e t e r m i n e a t i m i n g when t h e m o b i l e t e r m i n a l 101 r e q u e s t e d
t h e c o n n e c t i o n r e - e s t a b l i s h m e n t t o t h e n e i g h b o r i n g c e l l 1 3 3 m a y be
d i f f e r e n t f r o m a p r e d e t e r m i n e d p e r i o d f o r r e c e p t i o n d e t e r m i n a t i o n of
t h e r e - e s t a b l i s h m e n t r e q u e s t to the s o u r c e c e l l 1 3 1 .
[ 0 0 8 1 ]
10 As a s e c o n d e x a m p l e , t h e HO f a i l u r e d e t e c t i o n u n i t 1 2 1 m a y
d e t e c t Handover t o Wrong C e l l when ( a ) a r e q u e s t f o r c o n n e c t i o n r e -
e s t a b l i s h m e n t f r o m t h e m o b i l e t e r m i n a l 101 t o t h e s o u r c e c e l l 1 3 1 i s
not r e c e i v e d a f t e r t h e i n i t i a t i o n o f t h e o u t g o i n g h a n d o v e r o f t h e mobile
t e r m i n a l 1 0 1 a n d b e f o r e c o m p l e t i o n o f t h e h a n d o v e r ( e . g . , b e f o r e
15 r e c e p t i o n o f t h e h a n d o v e r c o m p l e t i o n n o t i f i c a t i o n ) , b u t ( b ) t h e HO
f a i l u r e i n f o r m a t i o n , w h i c h i n d i c a t e s t h a t t h e m o b i l e t e r m i n a l 101 has
r e q u e s t e d c o n n e c t i o n r e - e s t a b l i s h m e n t to t h e n e i g h b o r i n g c e l l 133
b e f o r e t h e c o m p l e t i o n o f t h e h a n d o v e r , i s r e c e i v e d .
[ 0 0 8 2 ]
2 0 As a t h i r d e x a m p l e , t h e HO f a i l u r e d e t e c t i o n u n i t 1 2 1 m a y d e t e c t
H a n d o v e r to Wrong Cell wllen ( a ) a r e q u e s t f o r c o n n e c t i o n ree
s t a b l i s h m e n t f r o m t h e m o b i l e t e r m i n a l 101 to t h e s o u r c e c e l l 1 3 1 is
n o t r e c e i v e d w i t h i n a p r e d e t e r m i l ~ e d period T5 d e p e n d e n t on t h e
c o m p l e t i o ~ l of the o u t g o i n g h a n d o v e r o f t h e m o b i l e t e r m i n a l 1 0 1 , but
25 ( b ) the HO f a i l u r e i n f o r m a t i o n , w h i c h i n d i c a t e s t h a t t h e mobile
t e r ~ n i n a l 101 has r e q u e s t e d c o n n e c t i o n r e - e s t a b l i s h m e n t to t h e
n e i g h b o r i n g c e l l 133 within t h e p r e d e t e r m i n e d period T 5 , i s r e c e i v e d .
A p r e d e t e r m i n e d p e r i o d t o d e t e r m i n e a t i m i n g w h e n t h e mobile
t e r m i n a l 101 r e q u e s t e d t h e c o n n e c t i o n r e - e s t a b l i s h m e n t to the
30 n e i g h b o r i n g cell 133 may b e d i f f e r e n t from a p r e d e t e r m i n e d period for
t h e r e c e p t i o n d e t e r m i n a t i o n o f t h e r e - e s t a b l i s h m e n t r e q u e s t to t h e
s o u r c e c e l l 1 3 1 .
[ 0 0 8 3 ]
I t i s t o be n o t e d t h a t for e x a m p l e , when t r a n s m i s s i o n of the HO
33
f a i l u r e i n f o r m a t i o n by t h e n e i g h b o r i n g base s t a t i o n 113 i s s u f f i c i e n t l y
p r o m p t l y p e r f o r m e d , t h e HO f a i l u r e d e t e c t i o n unit 121 may d e t e c t
Handover to Wrong C e l l b a s e d on whether or not t h e HO f a i l u r e
i n f o r m a t i o n is r e c e i v e d w i t h i n the p r e d e t e r m i n e d p e r i o d . For example,
5 in t h e a b o v e - m e n t i o n e d f i r s t e x a m p l e , the HO f a i l u r e d e t e c t i o n unit
121 may d e t e c t Handover to Wrong Cell when t h e r e q u e s t f o r
c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m t h e mobile terminal 101 to the source
cell 13 1 i s n o t r e c e i v e d within the p r e d e t e r m i n e d period T4, but the
HO f a i l u r e i n f o r m a t i o n is r e c e i v e d w i t h i n the p r e d e t e r m i n e d p e r i o d T4.
10 In the a b o v e - m e n t i o n e d s e c o n d e x a m p l e , the HO f a i l u r e d e t e c t i o n u n i t
121 may d e t e c t Handover to Wrong C e l l when t h e HO f a i l u r e
i n f o r m a t i o n is r e c e i v e d a f t e r t h e i n i t i a t i o n of t h e o u t g o i n g handover of
the mobile t e r m i n a l 101 and before the completion of t h e r e o f , without
the r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m t h e m o b i l e terminal
15 101 to the s o u r c e cell 1 3 1 b e i n g r e c e i v e d . In the above-mentioned
t h i r d e x a m p l e , t h e HO f a i l u r e d e t e c t i o n unit 121 may d e t e c t Handover
t o Wrong Cell when t h e r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m
the mobile t e r m i n a l 101 t o t h e s o u r c e c e l l 13 1 is n o t r e c e i v e d w i t h i n
t h e p r e d e t e r m i n e d period T5, but the HO f a i l u r e information is
20 received within the p r e d e t e r m i n e d p e r i o d T5. Also in t h e s e m o d i f i e d
e x a m p l e s , a p r e d e t e r m i n e d p e r i o d f o r r e c e p t i o n d e t e r m i n a t i o n o f t h e
I - I 0 f a i l u r e i n f o r i n a t i o n may b e d i f f e r e n t f r o m t h e p r e d e t e r m i n e d p e r i o d
f o r t h e reception d e t e r m i n a t i o n of t h e r e - e s t a b l i s h m e n t request to the
s o u r c e cell 13 1.
25 100841
An HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n unit 123 arranged in the
n e i g h b o r i n g base s t a t i o n 1 1 3 g e n e r a t e s the MO f a i l u r e information
w i t h o u t r e c e i v i n g i n f o r n ~ a t i o lf~ro m the t a r g e t base s t a t i o n 112, and
sends t h e HO f a i l u r e i n f o r m a t i o n to the source base s t a t i o n 1 1 1 . The
30 1 1 0 f a i l u r e i n f o r m a t i o n may i n c l u d e : an i d e n t i f i e r ( e . g . , a PCI) of the
s o u r c e cell ( i . e . , the cell 13 1) r e g a r d i n g the handover f a i l u r e ; an
i d e n t i f i e r ( e . g . . the PCI) o f t h e t a r g e t cell ( i . e . , the cell 132) regarding
the handover f a i l u r e ; an i d e n t i f i e r ( e . g . , the PCI) of t h e c e l l ( i . e . , the
cell 133) t o which the nob bile terminal 101 has t r i e d c o n n e c t i o n re34
e s t a b l i s h m e n t a f t e r RLF in t h e t a r g e t c e l l ; and an i d e n t i f i e r ( e . g . , the
C-RNTI) of t h e m o b i l e t e r m i n a l 101 t h a t has e x p e r i e n c e d the RLF in
t h e t a r g e t c e l l . Note t h a t , when ECGIs o f t h e s e c e l l s c a n b e o b t a i n e d ,
the HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n unit 1 2 2 may notify the source
5 base s t a t i o n 1 1 1 of the HO f a i l u r e i n f o r m a t i o n i n c l u d i n g the ECGIs
instead of the PCIs.
[OOS5]
The HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n u n i t 1 2 2 may detect
whether or n o t a s o u r c e base s t a t i o n is p r e s e n t that has requested,
10 w i t h i n a p r e d e t e r m i n e d p e r i o d b e f o r e t h e c o n n e c t i o n r e - e s t a b l i s h m e n t
o f t h e mobile t e r m i n a l 101 w i t h t h e n e i g h b o r i n g cell 133, the mobile
t e r m i n a l 101 to handover to the t a r g e t c e l l 1 3 2 . S u b s e q u e n t l y , if the
s o u r c e b a s e s t a t i o n is d e t e c t e d , t h e HO f a i l u r e information g e n e r a t i o n
unit 122 may t r a n s m i t the HO f a i l u r e i n f o r m a t i o n t o t h e s o u r c e b a s e
15 s t a t i o n . In o t h e r w o r d s , t h e HO f a i l u r e i n f o r m a t i o n may b e t r a n s m i t t e d
if the handover of t h e m o b i l e t e r m i n a l 101 has b e e n i n i t i a t e d within
the p r e d e t e r m i n e d p e r i o d b e f o r e the connection r e - e s t a b l i s h m e n t o f t h e
m o b i l e t e r m i n a l 101 w i t h t h e n e i g h b o r i n g cell 133. In order to detect
whether or n o t t h e s o u r c e base s t a t i o n is p r e s e n t , t h e HO f a i l u r e
20 i n f o r m a t i o n g e n e r a t i o n unit 122 may s e a r c h f o r the s o u r c e b a s e s t a t i o n
by a s k i n g o n e o r m o r e n e i g h b o r i n g b a s e s t a t i o n s (including t h e b a s e
s t a t i o n 11 I ) t h a t can communicate w i t h t h e n e i g h b o r i n g base s t a t i o n
1 1 3 . F o r e x a m p l e , t h e HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n u n i t 122 may
ask a b a s e s t a t i o n t h a t m a n a g e s a cell ( e . g . a c e l l r e g i s t e r e d in a
25 n e i g h b o r i n g c e l l l i s t ) t o w h i c h a handover from the n e i g h b o r i n g c e l l
133 can be performed. A l t e r n a t i v e l y , t h e I-I0 f a i l u r e information
g e n e r a t i o n unit 122 may r e c e i v e a movement history of the mobile
ternliilal 101 t h e r c f r o m . The Inovement h i s t o r y may i n d i c a t e base
s t a t i o n s t o w h i c h the mobile t e r ~ l l i l l a l 101 was connected in the p a s t , o r
30 a handover l ~ i s t o r y . T h e movement history may b e t r a n s m i t t e d from t h e
mobile terminal 101 to the base s t a t i o n 1 1 3 when the nlobile terminal
10 1 r e q u e s t s c o n n e c t i o n r e - e s t a b l i s h m e n t .
[0086]
Fig. 13 is a flow c h a r t s h o w i n g a f i r s t e x a m p l e o f a Handover to
Wrong Cell d e t e c t i o n p r o c e d u r e . I11 s t e p S 9 1 , t h e s o u r c e base s t a t i o n
11 1 i n i t i a t e s handover of t h e m o b i l e t e r m i n a l 1 0 1 f r o m t h e source cell
131 to the t a r g e t c e l l 1 3 2 . I n i t i a t i o n of the handover may b e
t r a n s m i s s i o n t o t h e mobile t e r m i n a l 101 of a handover command, may
5 b e t r a n s m i s s i o n to the n e t w o r k n o d e 141 of a handover r e q u e s t , or may
be r e c e p t i o n f r o m t h e mobile t e r m i n a l 101 o f i n f o r m a t i o n t o t r i g g e r t h e
h a n d o v e r . I n s t e p S 9 2 , the s o u r c e b a s e s t a t i o n 11 1 s t a r t s a timer for
measuring the p r e d e t e r m i n e d p e r i o d T 4 in r e s p o n s e t o the handover
i n i t i a t i o n . In step S93, the source base s t a t i o n 11 1 r e c e i v e s HO f a i l u r e
10 i n f o r m a t i o n f r o m t h e n e i g h b o r i n g b a s e s t a t i o n 1 1 3 w i t h o u t r e c e i v i n g a
r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m the mobile t e r m i n a l 1 0 1
t h a t has e x p e r i e n c e d RLF in the t a r g e t c e l l 132. I n s t e p S 9 4 , t h e
s o u r c e base s t a t i o n 1 1 1 ( i . e . , the HO f a i l u r e d e t e c t i o n u n i t 1 2 1 ) d e t e c t s
t h a t the handover h a v i n g b e e n a t t e m p t e d r e g a r d i n g t h e m o b i l e terminal
15 101 i s Handover to Wrong C e l l , in r e s p o n s e t o r e c e i v i n g , before
e x p i r a t i o n of the t i m e r , the HO f a i l u r e i n f o r m a t i o n f r o m t h e
n e i g h b o r i n g b a s e s t a t i o n 1 1 3 without r e c e i v i n g t h e r e q u e s t f o r
c o n n e c t i o n r e - e s t a b l i s h m e n t t o t h e s o u r c e c e l l 1 3 1 . T h a t i s , t h e HO
f a i l u r e d e t e c t i o n u n i t 1 2 1 d e t e c t s t h a t a n a p p r o p r i a t e handover
2 0 d e s t i n a t i o n of the mobile t e r m i n a l 101 w o u l d h a v e been the
n e i g h b o r i n g cell 133
[0087]
Fig. 1 4 i s a flow c h a r t s h o w i n g a s e c o n d e x a m p l e o f a Handover
to Wrong Cell d e t e c t i o n p r o c e d u r e . Step S l O l is s i m i l a r t o step S91 of
25 Fig. 13. Namely, in s t e p S101, the source base s t a t i o n 11 1 i n i t i a t e s
handover o f t h e mobile t e r m i n a l 10 1 f r o m t h e s o u r c e c e l l 13 1 t o t h e
t a r g e t cell 132. In s t e p S102, the s o u r c e b a s e s t a t i o n 11 1 r e c e i v e s ,
a f t e r i n i t i a t i o n of outgoing handover of the mobile terminal 101 and
before completion t h e r e o f , HO f a i l u r e i n f o r m a t i o n f r o m t h e
3 0 n e i g h b o r i n g base s t a t i o n 1 1 3 without r e c e i v i n g a request for
c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m t h e mobile terminal 101 that has
experienced RI,F in t h e t a r g e t cell 132. 111 step S103, the source base
s t a t i o n 1 1 1 ( i . e . , the HO f a i l u r e d e t e c t i o n unit 1 2 1 ) d e t e c t s that the
outgoing handover of the mobile terminal 101 is Handover to Wrong
36
C e l l , in r e s p o n s e t o r e c e i v i n g , a f t e r t h e i n i t i a t i o n of the outgoing
handover of the mobile t e r m i n a l 1 0 1 a n d b e f o r e t h e c o m p l e t i o n t h e r e o f ,
the HO f a i l u r e i n f o r m a t i o n f r o m t h e n e i g h b o r i n g base s t a t i o n 113
w i t h o u t r e c e i v i n g t h e r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t to the
5 s o u r c e c e l l 13 1.
[OOSS]
Fig. 15 is a flow c h a r t s h o w i n g a third example of a Handover to
Wrong C e l l d e t e c t i o n p r o c e d u r e . In s t e p S1 11, handover of t h e m o b i l e
t e r m i n a l 101 f r o m t h e s o u r c e c e l l 1 3 1 t o t h e t a r g e t c e l l 1 3 2 is
10 c o m p l e t e d . F o r e x a m p l e , t h e s o u r c e base s t a t i o n 11 1 r e c e i v e s a
handover c o m p l e t i o n n o t i f i c a t i o n ( e . g . , the UE C o n t e x t R e l e a s e
Command m e s s a g e ) f r o m t h e n e t w o r k n o d e 14 1. In s t e p S 11 2 , the
s o u r c e b a s e s t a t i o n 1 1 1 s t a r t s a t i m e r f o r m e a s u r i n g the predetermined
period T5 in r e s p o n s e t o t h e handover c o m p l e t i o n . In s t e p S1 13, the
15 s o u r c e b a s e s t a t i o n 1 1 1 r e c e i v e s HO f a i l u r e i n f o r m a t i o n f r o m t h e
n e i g h b o r i n g base s t a t i o n 1 1 3 w i t h o u t r e c e i v i n g a r e q u e s t f o r
c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m the m o b i l e t e r m i n a l 10 1 that has
e x p e r i e n c e d RLF in t h e t a r g e t c e l l 1 3 2 . In step S1 1 4 , t h e s o u r c e b a s e
s t a t i o n 11 1 ( i . e . , the HO f a i l u r e d e t e c t i o n unit 1 2 1 ) d e t e c t s t h a t t h e
20 handover having been a t t e m p t e d r e g a r d i n g t h e m o b i l e terminal 101 is
Mandover t o Wrong C e l l , in r e s p o n s e t o r e c e i v i n g , b e f o r e e x p i r a t i o n of
t h e t i m e r , the HO f a i l u r e i n f o r m a t i o n f r o m t h e n e i g h b o r i n g base s t a t i o n
1 1 3 w i t h o u t r e c e i v i n g the r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t to
the s o u r c e cell 13 1.
25 [0089]
F i g . 1 6 is a flow chart showing a f o u r t h e x a m p l e o f a Handover
to Wrong Cell d e t e c t i o n p r o c e d u r e . P r o c e s s i n g in stcps S121 to S124
of F i g . 16 may be the same as p r o c e s s i n g ~ I I steps S71 to S74 shown in
Fig. 10. In step S125, the HO f a i l u r e d e t e c t i o n u n i t 121 determines
30 w h e t h e r o r not a r e q u e s t f o r c o n n e c t i o l ~r e - e s t a b l i s h m e n t from the
mobile terminal 101 to the s o u r c e cell 131 has been r e c e i v e d . I f the
r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s l ~ m e l ~ist not received (NO in step
S 125), the HO f a i l u r e d e t e c t i o n unit 12 1 r e p e a t s receptio11
d e t e r ~ n i n a t i o n of the r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h ~ n e n t until the
3 7
p r e d e t e r m i n e d period T4 e l a p s e s s i n c e t h e i n i t i a t i o n of the handover
( s t e p S126). S u b s e q u e n t l y , if t h e r e q u e s t f o r c o n n e c t i o n ree
s t a b l i s h m e n t f r o m t h e m o b i l e t e r m i n a l 101 is not r e c e i v e d within the
p r e d e t e r m i n e d period T4 (YES in s t e p S126), the 130 f a i l u r e detection
5 u n i t 1 2 1 d e t e r m i n e s w h e t h e r or not HO f a i l u r e i n f o r m a t i o n o n the
mobile t e r m i n a l 1 0 1 has been r e c e i v e d f r o m t h e n e i g h b o r i n g base
s t a t i o n 1 1 3 ( s t e p S 127). S p e c i f i c a l l y , in s t e p S 1 2 7 , t h e HO f a i l u r e
d e t e c t i o n u n i t 1 2 1 may d e t e r m i n e w h e t h e r or n o t t h e HO f a i l u r e
d e t e c t i o n u n i t 1 2 1 has b e e n r e c e i v e d t h e HO f a i l u r e i n f o r m a t i o n
10 i n d i c a t i n g t h a t t h e m o b i l e t e r m i n a l 101 has requested the connection
r e - e s t a b l i s h m e n t t o t h e n e i g h b o r i n g c e l l 1 3 3 w i t h i n t h e p r e d e t e r m i n e d
period T4. If t h e HO f a i l u r e i n f o r m a t i o n o n t h e m o b i l e terminal 101 is
r e c e i v e d (YES in step S127), the HO f a i l u r e d e t e c t i o n u n i t 1 2 1 d e t e c t s
t h a t t h e handover having been a t t e m p t e d r e g a r d i n g the mobile terminal
15 101 is Handover t o Wrong C e l l ( s t e p S128).
[0090]
Fig. 17 is a flow chart showing a f i r s t example of a n o t i f i c a t i o n
procedure of handover f a i l u r e i ~ l f o r m a t i o n . In s t e p S 13 1 , t h e
n e i g h b o r i n g base s t a t i o n 11 3 r e c e i v e s from t h e m o b i l e terminal 101 a
20 r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s l ~ m e n t to the n e i g h b o r i n g cell 133.
T h i s r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t i n d i c a t e s t h a t t h e m o b i l e
terminal 101 has e x p e r i e n c e d RLF in the t a r g e t cell 132. In step S132,
the 1-10 f a i l u r e i n f o r n ~ a t i o l l g e n e r a t i o n unit 122 d e t e c t s a s o u r c e c e l l
( s o u r c e b a s e s t a t i o n ) that has r e q u e s t e d t h e rnobile ternlinal 101 to
25 handover t o t h e t a r g e t cell 132 within a p r e d e t e r m i n e d p e r i o d b e f o r e
r e c e p t i o n of the connection r e - e s t a b l i s h n ~ e n to f the mobile terminal
101. In step S133, the 1-10 f a i l u r e i n f o r m a t i o n g e n e r a t i o n u n i t 122
s e n d s t h e handover f a i l u r e i n f o r m a t i o n to t h e d e t e c t e d source base
s t a t i o n .
30 [0091]
F i g . 1 8 i s a f l o w chart showing a s e c o n d e x a m p l e of a
n o t i f i c a t i o n p r o c e d u r e o f t h e handover f a i l u r e i n f o r m a t i o n . In step
S 1 4 1 , the I 1 0 f a i l u r e i n f o r m a t i o n g e n e r a t i o n unit 122 d e t e r l ~ l i n e s
whether or not a r e q u e s t f o r connection re-establisllment from the
3 8
mobile t e r m i n a l 101 to the n e i g h b o r i n g cell 1 3 3 h a s been received. If
the r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t is r e c e i v e d (YES i n step
S 14 I ) , the HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n unit 1 2 2 a c q u i r e s and
h o l d s a n i d e n t i f i e r ( e . g . , the P C I ) o f a c e l l ( c e l l A) in which the
5 m o b i l e t e r m i n a l 101 had m o s t r e c e n t l y s t a y e d . The i d e n t i f i e r o f t h e
cell A may be included in t h e r e q u e s t for connection r e - e s t a b l i s h m e n t .
In s t e p S 1 4 3 , t h e HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n u n i t 1 2 2 s e a r c h e s
f o r a s o u r c e c e l l ( c e l l B) t h a t r e q u e s t e d the handover of the mobile
terminal 101 t o t h e cell A within a p r e d e t e r m i n e d p e r i o d b e f o r e t h e
10 c o n n e c t i o n r e - e s t a b l i s h m e n t o f t h e mobile t e r m i n a l ( o r b e f o r e the
r e c e p t i o n of t h e r e - e s t a b l i s h m e n t r e q u e s t ) . S u b s e q u e n t l y , i f t h e c e l l B
i s f o u n d (YES in s t e p S144), the HO f a i l u r e i n f o r m a t i o n generation
unit 122 sends the HO f a i l u r e i n f o r m a t i o n t o t h e c e l l B . In the
example of Fig. 12, t h e c e l l B c o r r e s p o n d s to t h e s o u r c e cell 13 1.
F i g . 1 9 is a flow c h a r t s h o w i n g a n example o f a n HO parameter
adjustment p r o c e d u r e performed by the HO p a r a m e t e r a d j u s t m e n t unit
15 1. In the example o f F i g . 11, the HO p a r a m e t e r a d j u s t m e n t unit 15 1
a d j u s t s a n HO p a r a m e t e r in r e s p o n s e t o d e t e c t i o n o f T o o Late Handover,
20 Too Early Handover, and Handover t o Wrong C e l l . Too Late Handover
and Too Early Handover may be d e t e c t e d in accordance with the abovem
e n t i o n e d s e c o n d a n d t h i r d e ~ ~ ~ b o d i m e n tIns .s t e p s S151 and 152, the
HO p a r a m e t e r a d j u s t m e n t unit 15 1 c a l c u l a t e s the occurrence rate R - TL
of Too Late Handover and the o c c u r r e n c e r a t e R-TE of Too Early
25 Handover r e g a r d i n g handover from the s o u r c e c e l l 131 to the t a r g e t
cell 132 s i m i l a r l y t o s t e p s S81 and S82 of Fig. 11.
[0093]
In s t e p S153, the 1-10 p a r a m e t e r a d j u s t m e n t u n i t 151 c a l c u l a t e s
an occurrence rate R - WCF of Handover to Wrong C e l l - F in which the
30 cell 1 3 2 i s an i n a p p r o p r i a t e t a r g e t c e l l , based on f e e d b a c k i n f o r m a t i o n
received from the I-IO f a i l u r e d e t e c t i o n unit 121. In a d d i t i o n , in step
S1 54, t h e 1-10 parameter adjustnlent unit 15 1 calculates an occurrence
rate R .- WCR of Handover to Wrong Cell-R in which the cell 132 is a
re-connection cell ( i . e . , a t r u e t a r g e t c e l l ) .
3 9
[0094]
The HO p a r a m e t e r a d j u s t m e n t unit 1 5 1 a d j u s t s an I-IO parameter
when a t o t a l sum of the R-TL, R-TE, R-WCF, and R-WCR i s l a r g e r
t h a n a p r e d e t e r m i n e d t h r e s h o l d value R-TH3 ( s t e p S 1 5 5 ) . S p e c i f i c a l l y ,
5 if (R-TL+R - WCR) is l a r g e r than (R-TE+R-WCF) (YES in step S156),
I-IO p a r a m e t e r a d j u s t m e n t for reducing Too Late Handover to the cell
132 and Handover to Wrong C e l l - R t o t h e cell 1 3 2 ( s t e p S157) is
performed. In c o n t r a s t with t h i s , if the (R - TE+R - WCF) is not less
t h a n t h e (R-TL+R - WCR) (NO in step S156), HO parameter adjustment
10 for reducing Too Early Handover to the c e l l 1 3 2 a n d Handover to
Wrong C e l l - F t o the c e l l 132 is p e r f o r m e d ( s t e p S158). In the
a d j u s t m e n t o f the HO parameter in step S158, t h e C I O that acts on
r a d i o q u a l i t y o f t h e t a r g e t c e l l 1 3 2 may b e d e c r e a s e d by a
p r e d e t e r m i n e d s t e p s i z e . In a d d i t i o n o r a l t e r n a t i v e l y , t h e TTT applied
15 t o t h e s o u r c e c e l l 1 3 1 may b e i n c r e a s e d by a p r e d e t e r m i n e d s t e p s i z e .
In a d d i t i o n o r a l t e r n a t i v e l y , the A 3 - o f f s e t t h a t a c t s o n r a d i o q u a l i t y of
the source cell 131 may b e i n c r e a s e d by a p r e d e t e r m i n e d s t e p s i z e . It
is to be noted t h a t i n s t e p S157, a d j u s t m e n t may b e p e r f o r m e d so as to
i n c r e a s e o r d e c r e a s e the HO parameter in an o p p o s i t e d i r e c t i o n o f s t e p
As is u n d e r s t o o d f r o m the a b o v e e x p l a n a t i o n , t h e 1-10 f a i l u r e
d e t e c t i o n unit 121 and the HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n unit 122
a c c o r d i n g t o the p r e s e n t e m b o d i m e n t c a n d e t e c t Handover t o Wrong
25 C e l l i n a s i t u a t i o n w h e r e n e i t h e r the s o u r c e base s t a t i o n 1 1 1 nor the
n e i g h b o r i n g base s t a t i o n 11 3 c a n r e c e i v e i n f o r m a t i o n ( e . g . , the
HANDOVER REPORT message and the RLF INDICATION message)
from the t a r g e t b a s e s t a t i o n 112. This Handover t o Wrong Cell means
that the t a r g e t c e l l 132 is a n i n a p p r o p r i a t e t a r g e t c e l l , and that the cell
3 0 1 3 3 managed by t h e n e i g h b o r i n g base s t a t i o n 1 1 3 is a re-connection
cell ( i . e . . a true t a r g e t c e l l ) . In a d d i t i o n , the 1-10 parameter adjustment
u n i t 151 c a n perform t h e a d j u s t m e n t o f t h e HO p a r a m e t e r f o r r e d u c i n g
Handover to Wrong Cell in t h a t s i t u a t i o n .
LO0961
40
F i f t h e m b o d i m e n t
In the present e m b o d i m e n t , d e t e c t i o n o f Handover to Wrong Cell
r e g a r d i n g the handover f r o m t h e s o u r c e c e l l 1 3 1 to t h e t a r g e t cell 132
will be e x p l a i n e d . Note t h a t , the a b o v e - m e n t i o n e d f o u r t h embodiment
5 has e x p l a i n e d the example where t h e t a r g e t base s t a t i o n 1 1 2 cannot
t r a n s m i t or r e c e i v e i n f o r m a t i o n t o or from the o t h e r two b a s e s t a t i o n s
(the s o u r c e base s t a t i o n 11 1 a n d t h e n e i g h b o r i n g base s t a t i o n 113). 111
c o n t r a s t , the p r e s e n t e m b o d i m e n t will e x p l a i n a n e x a m p l e w h e r e the
n e i g h b o r i n g b a s e s t a t i o n 113 c a n n o t t r a n s m i t o r r e c e i v e information to
10 or f r o m t h e o t h e r t w o b a s e s t a t i o n s ( t h e s o u r c e b a s e s t a t i o n 11 1 and the
t a r g e t b a s e s t a t i o n 1 1 2 ) . A c o n f i g u r a t i o n e x a m p l e of the radio
communication s y s t e m 1 0 0 a c c o r d i n g t o t h e p r e s e n t e m b o d i m e n t is the
same as Fig. 1.
[0097]
15 Fig. 20 shows a s i t u a t i o n w h e r e Handover t o Wrong C e l l occurs.
In Fig. 2 0 , t h e n e i g h b o r i n g b a s e s t a t i o n 113 c a n n o t t r a n s m i t or receive
i n f o r m a t i o n ( e . g . , the HANDOVER REPORT message and the RLF
INDICATION message) to or f r o m t h e o t h e r t w o b a s e s t a t i o n s (the
s o u r c e b a s e s t a t i o n 1 1 1 and the t a r g e t b a s e s t a t i o n 1 1 2 ) . Meanwhile,
2 0 t h e s o u r c e b a s e s t a t i o n s 11 1 can communicate with the t a r g e t b a s e
s t a t i o n 112, a n d r e c e i v e s handover (HO) f a i l u r e i n f o r m a t i o n from the
t a r g e t b a s e s t a t i o n 112. The HO f a i l u r e i n f o r m a t i o n may be
t r a n s m i t t e d via an i n t e r - b a s e - s t a t i o n i n t e r f a c e ( e . g . , t h e X2 i n t e r f a c e )
b e t w e e n t h e s o u r c e b a s e s t a t i o n 11 1 and the t a r g e t b a s e s t a t i o n 112, or
25 may b e t r a n s m i t t e d v i a the n e t w o r k 1 4 0 .
[0098]
In F i g . 2 0 , a t t h e b e g i n n i n g , the mobile terminal 101 is
c o n n e c t e d t o the source base s t a t i o n 1 1 1 (source cell 13 I ) , and
p e r f o r m s c o m m u n i c a t i o n t l ~ r o u g h the source base s t a t i o n 11 1.
30 S i n ~ u l t a n e o u s l y ,t he mobilc t e r n l i n a l 101 i s l o c a t e d n e a r t h e t a r g e t base
s t a t i o n 11 2 a n d t h e n e i g h b o r i n g base s t a t i o n 1 1 3. After t h a t , the
s o u r c e b a s e s t a t i o n 1 1 1 d e c i d e s and i n i t i a t e s o u t g o i n g handover of the
mobile terminal 101 t o t h e t a r g e t cell 1 3 2 ( t a r g e t b a s e s t a t i o n 1 1 2 ) . I n
the example o f F i g . 20; the s o u r c e base s t a t i o n 11 1 t r a n s m i t s a
4 1
handover command ( e . g . , the HO Command message) to t h e m o b i l e
t e r m i n a l 1 0 1 i n o r d e r t o i n i t i a t e h a n d o v e r . A s already mentioned, the
i n i t i a t i o n o f t h e handover may c o r r e s p o n d t o t r a n s m i s s i o n of a
handover r e q u e s t ( e . g . , the Handover R e q u e s t m e s s a g e ) f r o m t h e source
5 b a s e s t a t i o n 1 1 1 to t h e t a r g e t b a s e s t a t i o n 1 1 2 . A l t e r n a t i v e l y , the
i n i t i a t i o n o f the handover may c o r r e s p o n d to reception by the source
b a s e s t a t i o n 11 1 of i n f o r m a t i o n ( e . g . , the Measurement R e p o r t ) t o
t r i g g e r the handover.
[0099]
10 S u b s e q u e n t l y , t h e s o u r c e b a s e s t a t i o n 11 1 receives a handover
c o m p l e t i o n n o t i f i c a t i o n ( e . g . , the "UE C o n t e x t Release Command"
m e s s a g e ) t r a n s m i t t e d in response to completion of the handover of the
mobile t e r m i n a l 101 t o t h e t a r g e t c e l l 1 3 2 . H o w e v e r , t h e m o b i l e
t e r m i n a l 101 e x p e r i e n c e s RLF in t h e t a r g e t c e l l 1 3 2 immediately a f t e r
1 5 c o m p l e t i o n of t h e h a n d o v e r . A f t e r t h a t , t h e mobile t e r m i n a l 101
d e t e c t s t h a t r a d i o q u a l i t y o f the n e i g h b o r i n g cell 133 is good, and
t r a n s m i t s a r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t t o t h e n e i g h b o r i n g
c e l l 1 3 3 ( n e i g h b o r i n g b a s e s t a t i o n 1 1 3 ) . I t i s to b e n o t e d t h a t t h e
mobile t e r m i n a l 1 0 1 may e x p e r i e n c e RLF i n t h e t a r g e t c e l l 132 during
2 0 e x e c u t i o n of the handover to the t a r g e t cell 132 in some c a s e s . In this
c a s e , the handover c o m p l e t i o n n o t i f i c a t i o n s h o w n in Fig. 20 is
t r a n s m i t t e d to t h e s o u r c e base s t a t i o n 11 1 a f t e r the connection ree
s t a b l i s h m e n t of the mobile t e r m i n a l 101 to the n e i g h b o r i n g c e l l 133 is
completed.
25 [01 001
The s o u r c e b a s e s t a t i o n 11 1 and the t a r g e t base s t a t i o n 112 of
F i g . 2 0 c o o p e r a t i v e l y perform p r o c e s s i n g t o detect Handover to Wrong
C e l l w i t h o u t r e c e i v i n g i n f o r m a t i o n ( e . g . , the HANDOVER REPORT
message and the RLF 1NDICATION message) from t h e n e i g h b o r i n g
3 0 b a s e s t a t i o n 1 1 3 that manages the n e i g h b o r i n g cell 133 ( i . e . , the true
t a r g e t c e l l ) t o w h i c h the mobile t e r m i n a l 1 0 1 has been r e - c o n n e c t e d .
S p e c i f i c a l l y . in order to detect Handover to Wrong C e l l , t h e 110 f a i l u r e
d e t e c t i o n unit 121 arranged in t h e s o u r c e b a s e s t a t i o n 1 1 1 u s e s HO
f a i l u r e i n f o r m a t i o n received from the t a r g e t base s t a t i o n 112. A
42
s p e c i f i c e x a m p l e o f a d e t e c t i o n t e c h n i q u e by t h e HO f a i l u r e d e t e c t i o n
u n i t 121 i s s i m i l a r t o t h e f i r s t t o t h i r d e x a m p l e s d e s c r i b e d in t h e f o u r t h
e m b o d i m e n t e x c e p t t h a t a t r a n s m i s s i o n s o u r c e o f the HO f a i l u r e
i n f o r m a t i o n i s d i f f e r e n t f r o m t h e m .
5 [OIOI]
N a m e l y , as a f i r s t e x a m p l e , t h e 1-10 f a i l u r e d e t e c t i o n u n i t 121
m a y d e t e c t H a n d o v e r to Wrong Cell when ( a ) a r e q u e s t f o r c o n n e c t i o n
r e - e s t a b l i s h m e n t from t h e m o b i l e t e r m i n a l 101 to the s o u r c e c e l l 1 3 1 is
not r e c e i v e d w i t h i n t h e p r e d e t e r ~ n i n e d p e r i o d T4 d e p e n d e n t 011 the
10 i n i t i a t i o n o f t h e o u t g o i n g h a n d o v e r o f the m o b i l e t e r m i n a l 1 0 1 , but ( b )
t h e HO f a i l u r e i n f o r m a t i o n , which i n d i c a t e s t h a t t h e m o b i l e t e r m i n a l
10 1 h a s e x p e r i e n c e d RLF i n t h e t a r g e t c e l l 132 within t h e
p r e d e t e r m i i l e d p e r i o d T4, i s r e c e i v e d . A p r e d e t e r m i i l e d p e r i o d to
d e t e r m i n e a t i m i n g w h e n t h e m o b i l e t e r m i n a l 1 0 1 e x p e r i e n c e d RLF in
15 t h e t a r g e t c e l l 132 may b e d i f f e r e n t from a p r e d e t e r m i n e d p e r i o d f o r
r e c e p t i o n d e t e r m i n a t i o n o f t h e r e - e s t a b l i s h m e n t r e q u e s t t o t h e s o u r c e
c e l l 1 3 1 .
[O 1021
As a s e c o n d e x a m p l e , the HO f a i l u r e d e t e c t i o n u n i t 121 may
20 d e t e c t H a n d o v e r t o Wrong C e l l when ( a ) a r e q u e s t f o r c o n n e c t i o n ree
s t a b l i s h m e n t f r o m t h e m o b i l e t e r m i n a l 101 to the s o u r c e cell 13 1 is
not r e c e i v e d a f t e r t h e i i l i t i a t i o n o f t h e o u t g o i n g h a n d o v e r of t h e mobile
t e r n l i n a l 101 a n d b e f o r e t h e c o m p l e t i o n of t h e h a n d o v e r ( e . g . , b e f o r e
r e c e p t i o n o f t h e l l a n d o v e r c o m p l e t i o n n o t i f i c a t i o n ) , but ( b ) t h e HO
25 f a i l u r e i n f o r m a t i o n , w h i c h i n d i c a t e s t h a t t h e m o b i l e t e r m i n a l 101 has
e x p e r i e n c e d RLF in t h e t a r g e t c e l l 132 b e f o r e t h e c o n l p l e t i o n of the
h a n d o v e r , is r e c e i v e d .
101031
As a t h i r d e x a m p l e , thc 110 f a i l u r e d e t e c t i o n u n i t 121 m a y d e t e c t
30 Handover to Wrong Cell whel1 ( a ) the r e q u e s t f o r c o n n e c t i o n ree
s t a b l i s l ~ m e n t from t h e mobile t e r m i n a l 101 to the s o u r c e cell 13 1 is
not r e c e i v e d w i t h i n t h e p r e d e t e r m i n e d p e r i o d T5 d e p e n d e n t 011 the
c o m p l e t i o i ~o f t h e o u t g o i n g h a n d o v e r o f t h e mobile t e r m i n a l 101. but
( b ) the HO f a i l u r e i n f o r m a t i o n , w h i c h i n d i c a t e s t h a t the mobile
43
t e r m i n a l 101 h a s e x p e r i e n c e d RLF in t h e t a r g e t cell 1 3 2 w i t h i n the
p r e d e t e r m i n e d p e r i o d T 5 , i s r e c e i v e d . A p r e d e t e r m i n e d period to
d e t e r m i n e a t i m i n g when t h e m o b i l e t e r m i n a l 101 e x p e r i e n c e d RLF in
the t a r g e t cell 132 may b e d i f f e r e n t f r o m a p r e d e t e r m i n e d p e r i o d for
5 r e c e p t i o n d e t e r m i n a t i o n of t h e r e - e s t a b l i s h m e n t r e q u e s t t o t h e s o u r c e
c e l l 1 3 1 .
[O 1041
It is to be n o t e d t h a t for e x a m p l e , when t r a n s m i s s i o n of the HO
f a i l u r e i n f o r m a t i o n by the n e i g h b o r i n g base s t a t i o n 1 1 3 is s u f f i c i e n t l y
10 p r o m p t l y p e r f o r m e d , the HO f a i l u r e d e t e c t i o n unit 1 2 1 may d e t e c t
Handover to Wrong C e l l b a s e d 011 whether or not the HO f a i l u r e
i n f o r m a t i o n is r e c e i v e d w i t h i n a p r e d e t e r m i n e d p e r i o d . For example,
in the a b o v e - m e n t i o n e d f i r s t e x a m p l e , the HO f a i l u r e d e t e c t i o n unit
121 may detect Handover to Wrong C e l l when t h e r e q u e s t for
1 5 c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m the mobile t e r m i n a l 1 0 1 to the source
c e l l 1 3 1 i s n o t r e c e i v e d w i t h i n t h e p r e d e t e r m i n e d period T4, but the
HO f a i l u r e informati011 is r e c e i v e d w i t h i n the p r e d e t e r m i n e d p e r i o d T 4 .
I n t h e a b o v e - m e n t i o n e d s e c o n d e x a m p l e , the HO f a i l u r e d e t e c t i o n unit
121 may detect Handover to Wrong Cell when t h e HO f a i l u r e
20 i n f o r m a t i o n is r e c e i v e d a f t e r the i n i t i a t i o n o f t h e o u t g o i n g handover of
t h e m o b i l e t e r m i n a l 101 and before the c o l n p l e t i o n o f t h e r e o f , without
t h e r e q u e s t for connection r e - e s t a b l i s l ~ m e n t from the mobile terminal
101 to the source c e l l 1 3 1 b e i n g r e c e i v e d . In the above-mentioned
third e x a m p l e , t h e HO f a i l u r e d e t e c t i o n unit 121 may d e t e c t Handover
25 to Wrong Cell when the r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m
the mobile terrninal 101 t o t h e s o u r c e c e l l 131 is not r e c e i v e d w i t h i n
t h e p r e d e t e r m i n e d p e r i o d T5, but the HO f a i l u r e i n f o r m a t i o n i s
received within the p r e d e t e r m i n e d period T5. Also in t h e s e m o d i f i e d
e x a m p l e s , a p r e d e t e r m i n e d period for reception d e t e r m i n a t i o n o f t h e
30 HO f a i l u r e i n f o r m a t i o n may be dif'fercl~t f r o n ~a p r e d e t e r m i n e d p e r i o d
for t h e r e c e p t i o n deter111i11ation of the r e - e s t a b l i s h m e n t r e q u e s t to the
source cell 13 1.
[0 1051
The 1-10 f a i l u r e i n f o r m a t i o n g e n e r a t i o n unit 1 2 3 a r r a n g e d in the
44
t a r g e t base s t a t i o n 1 1 2 g e n e r a t e s the HO f a i l u r e i n f o r m a t i o n without
r e c e i v i n g i n f o r m a t i o n from the n e i g h b o r i n g b a s e s t a t i o n 1 1 3 , and sends
the HO f a i l u r e i n f o r m a t i o n t o t h e s o u r c e b a s e s t a t i o n 1 1 1. The HO
f a i l u r e i n f o r m a t i o n may i n c l u d e : a n i d e n t i f i e r ( e . g . , a P C I ) of the
5 s o u r c e cell ( i . e . , t h e c e l l 1 3 1 ) r e g a r d i n g the handover f a i l u r e ; a n
i d e n t i f i e r ( e . g . , the PCI) of t h e t a r g e t c e l l ( i . e . , t h e c e l l 1 3 2 ) r e g a r d i n g
the handover f a i l u r e ; a n i d e n t i f i e r ( e . g . , the PCI) of t h e c e l l ( i . e . , the
c e l l 133) to which t h e m o b i l e t e r m i n a l 1 0 1 h a s t r i e d c o n n e c t i o n r e -
e s t a b l i s h m e n t a f t e r RLF in the t a r g e t c e l l ; and a n i d e n t i f i e r ( e . g . , the
10 C-RNTI) o f t h e m o b i l e t e r m i n a l 101 t h a t has e x p e r i e n c e d t h e RLF in
t h e t a r g e t c e l l . N o t e t h a t , w h e n ECGIs of t h e s e c e l l s c a n b e o b t a i n e d ,
t h e HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n unit 123 may n o t i f y the source
b a s e s t a t i o n 11 1 of the HO f a i l u r e i n f o r m a t i o n i n c l u d i n g the ECGIs
i n s t e a d o f t h e PCIs.
15 [0106]
The HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n u n i t 1 2 3 may t r a n s m i t HO
f a i l u r e i n f o r m a t i o n when a l o s s o f s y n c h r o n i z a t i o n of t h e m o b i l e
t e r m i n a l 1 0 1 i s d e t e c t e d within a p r e d e t e r m i n e d p e r i o d a f t e r t h e m o b i l e
t e r m i n a l 101 is c o n n e c t e d t o t h e t a r g e t c e l l 132. T h e c o n n e c t i o n o f the
20 mobile t e r m i n a l 1 0 1 w i t h the t a r g e t c e l l 132 may b e d e t e c t e d , for
e x a m p l e , by r e c e i v i n g a t t h e t a r g e t b a s e s t a t i o n 1 1 2 a m e s s a g e ( e . g . , a
"Handover Confirm" 111essage) t r a n s m i t t e d f r o m t h e m o b i l e t e r m i n a l
101 to t h e t a r g e t cell 132 during the handover p r o c e d u r e . It is to be
n o t e d t h a t a s t a r t i n g point o f a p r e d e t e r m i n e d period f o r d e t e c t i n g the
25 loss of s y n c h r o n i z a t i o n c a n be a p p r o p r i a t e l y s e t . For example, the
s t a r t i n g point of the predetermined period may be a t i m e when a
handover of t11c mobile t e r m i n a l 101 is completed. In a d d i t i o n , the
l o s s o f s y n c l ~ r o n i z a t i o no f t h e m o b i l e t e r m i n a l 101 can also be
r e p r e s e n t e d a s a b n o r m a l d i s c o ~ ~ n e c t i o(ni n c l u d i n g RLF) of t h e m o b i l e
30 t e r n ~ i n a l1 01. The loss of s y ~ ~ c l ~ r o n i z a t iboentw een the t a r g e t cell 132
and the mobile t e r m i n a l 101 may be d e t e c t e d , for example, when a
r e s p o n s e m e s s a g e ( A C K ) from t h e mobile terminal 101 does not
r e c e i v e d w i t h i n a p r e d e t e r m i n e d period a f t e r t h e t a r g e t b a s e s t a t i o n
1 1 2 t r a n s m i t s a packet to the mobile terminal 101.
45
[0 1071
When t h e l o s s of s y n c h r o n i z a t i o n o f t h e m o b i l e t e r m i n a l 101
o c c u r s , the HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n u n i t 1 2 3 c a r r i e s out
p r o c e s s i n g t o e s t i m a t e a c e l l t o w h i c h t h e mobile t e r m i n a l 1 0 1 t r i e s
5 c o n n e c t i o n r e - e s t a b l i s h m e n t . S u b s e q u e n t l y , the HO f a i l u r e i n f o r m a t i o n
g e n e r a t i o n unit 123 i n c l u d e s a n i d e n t i f i e r of the e s t i m a t e d c e l l in the
1-10 f a i l u r e i n f o r m a t i o n . The 130 f a i l u r e i n f o r m a t i o n g e n e r a t i o n unit
1 2 3 may use t h e m e a s u r e m e n t r e p o r t t h a t h a s b e e n r e c e i v e d f r o m t h e
mobile t e r m i n a l 1 0 1 by the t a r g e t b a s e s t a t i o n 1 1 2 in order to e s t i m a t e
10 the cell to which t h e m o b i l e t e r m i n a l 1 0 1 t r i e s t h e c o n n e c t i o n r e -
e s t a b l i s h m e n t . The m e a s u r e m e n t r e p o r t i n c l u d e s measurement r e s u l t s
of radio q u a l i t y o f t h e t a r g e t c e l l 132 to which t h e m o b i l e t e r m i n a l 101
had been c o n n e c t e d , a n d r a d i o q u a l i t y of n e i g h b o r i n g c e l l s (the cell
13 1, the cell 133, e t c . ) . The m o b i l e t e r m i n a l 1 0 1 g e n e r a l l y s e l e c t s a
15 cell h a v i n g t h e b e s t r a d i o q u a l i t y , a n d t r i e s t h e c o n n e c t i o n r e -
e s t a b l i s h m e n t t o the s e l e c t e d c e l l . A c c o r d i n g l y , a n e i g h b o r i n g cell
i n d i c a t e d t o h a v e t h e b e s t r a d i o q u a l i t y e x c e p t for the t a r g e t c e l l 132
in the m e a s u r e m e n t r e p o r t may b e e s t i m a t e d a s t h e c e l l t o w h i c h t h e
c o n n e c t i o n r e - e s t a b l i s h m e n t is t r i e d . T h e HO f a i l u r e i n f o r m a t i o n
20 g e n e r a t i o n unit 1 2 3 m a y i n c l u d e , in the HO f a i l u r e i n f o r m a t i o n ,
i d e n t i f i e r s o f a p l u r a l i t y of c e l l s having r e l a t i v e l y good r a d i o q u a l i t y
among t h e c e l l s i n c l u d e d in the measurement r e p o r t .
yo 1081
I t is to be n o t e d t h a t a t r i g g e r c o n d i t i o n o f the measurement
25 report may be set so t h a t t h e m e a s u r e m e n t r e p o r t from the mobile
terminal 101 to the t a r g e t cell 132 is performed i m m e d i a t e l y b e f o r e t h e
a b n o r m a l d i s c o n n e c t i o n ( o r t h e l o s s of synchroniezation). F o r e x a m p l e ,
i t may be set as t h e t r i g g e r c o n d i t i o n of t h e m e a s u r e m e n t r e p o r t t h a t
radio q u a l i t y ( Q s ) o f t h e t a r g e t cell 1 3 2 t o which the m o b i l e t e r m i n a l
30 101 is connected and r a d i o q u a l i t y (Qn) o f a n e i g h b o r i n g cell s a t i s f y
the f o l l o w i n g E x p r e s s i o n ( 2 ) .
Qs < Q - t h l and Qn > Q - th2 (2)
Here. Q - t h l is a t h r e s h o l d v a l u e to Qs, and Q-th2 is a threshold
value to Qn. The t r i g g e r c o n d i t i o n l i k e E x p r e s s i o n (2) is, for example,
46
defined by 3GPP TS 36.331. The m e a s u r e m e n t r e p o r t is sent
i m m e d i a t e l y b e f o r e the a b n o r m a l d i s c o n n e c t i o n by u s i n g a s t r i c t e r
v a l u e c o m p a r e d with a r e q u i r e d v a l u e of t h e r a d i o q u a l i t y , i . e . , by
a d d i n g m a r g i n v a l u e s to the t h r e s h o l d v a l u e s Q-thl and Q-TH2. As
5 the radio q u a l i t y , f o r e x a m p l e , RSRP ( R e f e r e n c e S i g n a l R e c e i v e d
P o w e r ) o r RSRQ ( R e f e r e n c e Signal R e c e i v e d Q u a l i t y ) defined by 3GPP
TS 3 6 . 2 1 4 c a n be used.
[O 1091
F i g s . 21 to 2 3 a r e flow c h a r t s showing the f i r s t to third
10 examples of a Handover to Wrong Cell d e t e c t i o n p r o c e d u r e in the
p r e s e n t e m b o d i m e n t . It is to be noted t h a t the flow charts of Figs. 21
and 23 a r e s i m i l a r t o t h e f l o w c h a r t s o f F i g s . 13 to 15 e x p l a i n e d i n the
f o u r t h e m b o d i m e n t e x c e p t t h a t a t r a n s m i s s i o n s o u r c e o f t h e HO f a i l u r e
i n f o r m a t i o n is t h e t a r g e t b a s e s t a t i o n 112. A c c o r d i n g l y , d e t a i l e d
15 e x p l a n a t i o n r e g a r d i n g t h e s e f l o w c h a r t s is omitted h e r e . Namely, steps
S161 to S164 of F i g . 2 1 c o r r e s p o n d t o s t e p s S91 to S94 of F i g . 1 3 ,
r e s p e c t i v e l y . Steps S 1 7 1 t o S 1 7 3 o f F i g . 22 c o r r e s p o n d t o s t e p s S l 01
to S103 of Fig. 14, r e s p e c t i v e l y . In a d d i t i o n , s t e p s S181 t o S 1 8 4 o f
Fig. 23 correspond to s t e p s S 11 1 t o S 11 4 of F i g . 1 5 , r e s p e c t i v e l y .
20 Note t h a t , as is a p p a r e n t f r o m c o m p a r i s o n o f s t e p S163 of Fig. 21 and
s t e p S 9 3 of Fig. 13, a t r a n s m i s s i o n s o u r c e o f t h e HO f a i l u r e
i n f o r m a t i o n i s t h e t a r g e t b a s e s t a t i o n 112 in s t e p S163. This is
s i m i l a r l y a p p l i e d to s t e p S 1 7 2 of Fig. 22 and s t e p S 1 8 3 of Fig. 23.
[Ol l o ]
2 5 Fig. 24 is a flow chart showillg a f i r s t e x a m p l e o f a n o t i f i c a t i o n
procedure of the handover f a i l u r e infornlation in t h e p r e s e n t
embodiment. In s t e p S191, handover of the mobile terminal 101 fro111
the source c e l l 1 3 1 to the t a r g e t cell 132 is completed.
For e x a m p l e , the t a r g e t b a s e s t a t i o n 1 1 2 t r a n s m i t s a handover
30 c o m p l e t i o n n o t i f i c a t i o n ( e . g . the IJE C o n t e x t R e l e a s e message) to the
s o u r c e base s t a t i o n 11 1. In s t e p S192, the HO f a i l u r e informatioll
g e n e r a t i o n unit 1 2 3 d e t e c t s a loss of s y n c h r o n i z a t i o n o f the mobile
terminal 101 w i t l ~ i n a p r e d e t e r m i n e d period a f t e r t h e handover of the
mobile t e r m i n a l 1 0 1 to the t a r g e t cell 132 is completed. In step S193,
47
the HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n unit 123 e s t i m a t e s a cell to
w h i c h t h e m o b i l e t e r m i n a l 1 0 1 r e q u e s t s r e - e s t a b l i s h m e n t based on a
measurement report t h a t has b e e n r e c e i v e d f r o m t h e m o b i l e terminal
101. F o r e x a m p l e , the HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n u n i t 123 may
5 s e l e c t a c e l l h a v i n g t h e b e s t r a d i o q u a l i t y i n t h e m e a s u r e m e n t r e p o r t .
In s t e p S194, the HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n u n i t 1 2 3 s e n d s t h e
HO f a i l u r e i n f o r m a t i o n t o t h e source base s t a t i o n 11 1 ( i . e . , the HO
f a i l u r e d e t e c t i o n unit 12 1).
[ O l l l ]
10 F i g . 2 5 is a f l o w c h a r t s h o w i n g a s e c o n d e x a m p l e of a
n o t i f i c a t i o n p r o c e d u r e of the handover f a i l u r e i n f o r m a t i o n in the
p r e s e n t e m b o d i m e n t . In s t e p S201, t h e t a r g e t base s t a t i o n 112
d e t e r m i n e s whether or not the mobile t e r m i n a l 1 0 1 i s c o n n e c t e d to the
t a r g e t c e l l 1 3 2 . C o n n e c t i o n of the mobile t e r m i n a l 101 to t h e t a r g e t
15 c e l l 132 may be d e t e c t e d by a m e s s a g e ( e . g . , t h e " H a n d o v e r C o n f i r m "
message) t r a n s m i t t e d f r o m the m o b i l e t e r m i n a l 101 during the handover
p r o c e d u r e h a v i n g b e e n r e c e i v e d by t h e t a r g e t b a s e s t a t i o n 112. In step
S202, the t a r g e t b a s e s t a t i o n 1 1 2 i n s t r u c t s the mobile terminal 10 1 to
t r a n s m i t a m e a s u r e m e n t r e p o r t . In step S203, the HO f a i l u r e
20 i n f o r m a t i o n g e n e r a t i o n unit 123 d e t e r m i n e s w h e t h e r o r not handover of
the mobile terminal 101 has been i n i t i a t e d . For example, the t a r g e t
b a s e s t a t i o n 1 1 2 may confirm w h e t h e r o r not a handover command ( e . g . ,
the Handover Command message) has been t r a n s m i t t e d to the mobile
t e r m i n a l 1 0 1 . In s t e p S204, the HO f a i l u r e i n f o r m a t i o n generation unit
25 123 d e t e c t s whether or not a l o s s o f s y l ~ c h r o n i z a t i o n of t h e m o b i l e
t e r m i n a l 101 has occurred in a s i t u a t i o n where the handover is not
i n i t i a t e d . If the l o s s o f s y n c h r o n i z a t i o n o f t h e m o b i l e terminal 101
does not occur (NO in s t e p S 2 0 4 ) , the HO f a i l u r e information
g e n e r a t i o n unit 123 c o n t i n u o u s l y monitors the l o s s o f s y n c l ~ r o n i z a t i o n
30 of the mobile t e r m i n a l 1 0 1 in a situatioil where the handover is not
i n i t i a t e d , until a p r e d e t e r m i n e d time e l a p s e s since connection of the
mobile ternlinal 101 to the t a r g e t cell 132 ( i . e . , s t e p S201) ( s t e p S205)
[0112]
Meanwhile, if the l o s s o f s y n c h r o n i z a t i o n o f the m o b i l e t e r m i n a l
48
101 occurs ( Y E S i n step S204), the HO f a i l u r e i n f o r m a t i o n generation
unit 123 c o n f i r m s w h e t h e r o r n o t the ~ n e a s u r e m e n t r e p o r t f r o m the
m o b i l e t e r m i n a l 1 0 1 h a s b e e n r e c e i v e d ( s t e p S206). If the
m e a s u r e m e n t r e p o r t h a s b e e n r e c e i v e d f r o m t h e m o b i l e t e r m i n a l 1 0 1
5 (YES in step S206), the HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n unit 123
r e f e r s to the received m e a s u r e m e n t r e p o r t , and g e n e r a t e s handover
f a i l u r e i n f o r m a t i o n i n d i c a t i n g a c e l l h a v i n g the best r a d i o q u a l i t y . In
s t e p S208, the HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n unit 123 sends the
handover f a i l u r e informatioll t o t h e s o u r c e cell 13 1.
10 [0113]
As is understood from the a b o v e e x p l a n a t i o n , t h e HO f a i l u r e
d e t e c t i o n u n i t 1 2 1 a n d the HO f a i l u r e i n f o r m a t i o n g e n e r a t i o n unit 123
a c c o r d i n g t o t h e present embodiment can d e t e c t Handover to Wrong
Cell in a s i t u a t i o n w h e r e n e i t h e r t h e s o u r c e base s t a t i o n 11 1 nor the
15 t a r g e t b a s e s t a t i o n 112 c a n r e c e i v e i n f o r m a t i o n ( e . g . , the HANDOVER
REPORT message and the RLF INDICATION m e s s a g e ) f r o m t h e
n e i g h b o r i n g b a s e s t a t i o n 1 1 3 . This Handover to Wrong Cell means t h a t
t h e t a r g e t c e l l 132 is a n i n a p p r o p r i a t e t a r g e t c e l l , and t h a t t h e cell 133
managed by the n e i g h b o r i n g b a s e s t a t i o n 11 3 is a r e - c o n n e c t i o n cell
20 ( i . e . , a t r u e t a r g e t c e l l ) . In a d d i t i o n , t h e HO parameter adjustrnellt unit
15 1 call perform the a d j u s t m e n t o f the 1-10 parameter for reducing
Handover t o Wrong Cell in t h a t s i t u a t i o n .
[Ol 141
Othcr embodiments
2 5 The a b o v e - m e n t i o n e d f i r s t to f i f t h embodiments can be combined
a s a p p r o p r i a t e .
[Ol 151
The p r o c e s s e s p e r f o r m e d by the HO f a i l u r e detection unit 12 1,
t h e HO f a i l u r e illforlnatioil g c n e r a t i o i ~u nits 122 and 123, and the 1-10
30 parameter adjustmellt u n i t 1 5 1 t h a t h a v e bee11 e x p l a i n e d in t h e f i r s t t o
f i f t h embodiments may be iinplclnclltcd by using a s e m i c o n d u c t o r
p r o c e s s i n g d e v i c e i n c l u d i n g a n ASIC ( A p p l i c a t i o l ~S p e c i f i c I n t e g r a t e d
C i r c u i t ) . In a d d i t i o n . these p r o c e s s e s may be i n ~ p l e m e n t e d by causing
a c o m p u t e r s y s t e n ~ i n c l u d i n g a t l e a s t o n e p r o c e s s o r ( e . g . a
49
m i c r o p r o c e s s o r , a n MPU, a DSP ( D i g i t a l S i g n a l P r o c e s s o r ) ) t o e x e c u t e
a p r o g r a m . S p e c i f i c a l l y , o n e o r m o r e p r o g r a m s i n c l u d i n g i n s t r u c t i o n s
t o c a u s e a computer s y s t e m t o e x e c u t e t h e a l g o r i t h m r e g a r d i n g t h e HO
f a i l u r e d e t e c t i o n unit 121 ( o r t h e HO f a i l u r e i n f o r m a t i o n generation
5 unit 122 o r 1 2 3 , or t h e HO p a r a m e t e r a d j u s t m e n t unit 15 1) explained
with r e f e r e n c e t o t h e flow c h a r t s e t c . may be created and supplied the
program(s) to the computer.
[Ol 161
The program(s) can be s t o r e d and p r o v i d e d t o a c o m p u t e r u s i n g
1 0 a n y type of n o n - t r a n s i t o r y computer r e a d a b l e m e d i a . Non-transitory
c o m p u t e r r e a d a b l e m e d i a i n c l u d e any type of t a n g i b l e s t o r a g e media.
Examples of n o n - t r a n s i t o r y computer r e a d a b l e m e d i a i n c l u d e m a g n e t i c
s t o r a g e media (such as f l o p p y d i s k s , m a g n e t i c t a p e s , h a r d d i s k d r i v e s ,
e t c . ) , o p t i c a l m a g n e t i c s t o r a g e media ( e . g . , m a g n e t o - o p t i c a l d i s k s ) ,
15 CD-ROM ( R e a d O n l y M e m o r y ) , CD-R, CD-RIW, and semiconductor
memories (such as mask ROM, PROM ( P r o g r a m m a b l e ROM), EPROM
( E r a s a b l e PROM), f l a s h ROM, RAM ( r a n d o m a c c e s s m e m o r y ) , e t c . ) .
T h e p r o g r a m may be p r o v i d e d t o a c o m p u t e r u s i n g a n y type of
t r a n s i t o r y computer r e a d a b l e m e d i a . Examples of t r a n s i t o r y c o m p u t e r
20 r e a d a b l e m e d i a i n c l u d e e l e c t r i c s i g n a l s , o p t i c a l s i g n a l s , and
e l e c t r o m a g n e t i c w a v e s . T r a n s i t o r y computer r e a d a b l e m e d i a can
provide the p r o g r a m t o a c o ~ l l p u t e r via a wired communication l i n e ,
such as e l e c t r i c w i r e s and o p t i c a l f i b e r s , o r a radio c o m m u n i c a t i o n l i n e .
[Ol 171
2 5 F u r t h e r m o r e , the i n v e n t i o n is not limited to the embodiments
described above, and i t will be obvious that v a r i o u s m o d i f i c a t i o n s may
be made t h e r e i n without d e p a r t i n g fro111 the s p i r i t and s c o p e o f the
present illvention described above.
LO1 181
3 0 This a p p l i c a t i o l ~ is based upon and c l a i m s t h e b e n e f i t of p r i o r i t y
from J a p a n e s e patent a p p l i c a t i o n No. 2013-022846, f i l e d on February 8,
2 0 1 3 , t h e d i s c l o s u r e o f which i s i n c o r p o r a t e d herein in i t s e n t i r e t y by
r e f e r e n c e .
R e f e r e n c e S i g n s L i s t
50
[Ol 191
1 0 0 RADIO COMMUNICATION SYSTEM
101 MOBILE TERMINAL
111-113 BASE STATIONS
5 121 HANDOVER (130) FAILURE DETECTION UNIT
122, 123 I-IANDOVER (HO) FAILURE INFORMATION
GENERATION UNITS
131-133 CELLS
1 4 0 NETWORK
10 141 NETWORK NODE
1 5 0 NETWORK MANAGEMENT SYSTEM
15 1 HANDOVER (HO) PARAMETER ADJUSTMENT UNIT
WE CLAIM:
1. A handover f a i l u r e d e t e c t i o n d e v i c e c o m p r i s i n g :
5 d e t e c t i o n means f o r d e t e c t i n g at l e a s t one of handover f a i l u r e
t y p e s r e g a r d i n g o u t g o i n g handover f r o m a f i r s t c e l l managed by a f i r s t
b a s e s t a t i o n by observing ( a ) p r e s e n c e / a b s e n c e o f r e c e p t i o n by t h e f i r s t
b a s e s t a t i o n o f a n acknowledgment r e s p o n s e t o a handover command
r e g a r d i n g f i r s t handover of a mobile terminal f r o m t h e f i r s t c e l l t o a
10 s e c o n d c e l l managed by a s e c o n d b a s e s t a t i o n , and (b)
p r e s e n c e / a b s e n c e of a r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t from the
mobile t e r m i n a l t o the f i r s t c e l l , the r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n
of t h e f i r s t h a n d o v e r .
15 2. The handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g t o Claim I ,
w h e r e i n t h e d e t e c t i o n m e a n s d e t e c t s a f i r s t handover f a i l u r e t y p e when
t h e a c k n o w l e d g m e n t r e s p o n s e t o the handover command i s n o t r e c e i v e d
w i t h i n a f i r s t p r e d e t e r m i n e d p e r i o d d e p e n d e n t o n i n i t i a t i o n o f t h e f i r s t
handover and the r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t is also not
20 r e c e i v e d w i t h i n a s e c o n d p r e d e t e r m i n e d period d e p e n d e n t o n i n i t i a t i o n
of the f i r s t handover.
3. The handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g t o Claim I or
2, wherein the d e t e c t i o n m e a n s d e t e c t s a second handover f a i l u r e type
25 when the r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t i s r e c e i v e d within a
third p r e d e t e r m i n e d period d e p e n d e n t on i n i t i a t i o n of the f i r s t
I ~ a n d o v e r .
4. The handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g to a n y o n e of
30 Claims 1 to 3, w h e r e i n t h e d e t e c t i o n m e a n s d e t e c t s a s e c o n d handover
f a i l u r e t y p e when the r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t is
r e c e i v e d b e f o r e receptioil of a I l a l ~ d o v e rc o n ~ p l e t i o nn o t i f i c a t i o n
regardii-ig t h e f i r s t handover.
5 2
5. The handover f a i l u r e d e t e c t i o n d e v i c e accord.ing to any one of
Claims 1 to 4, w h e r e i n t h e d e t e c t i o n m e a n s detects a secoild handover
f a i l u r e t y p e w h e n the r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t is
r e c e i v e d w i t h i n a f o u r t h p r e d e t e r m i n e d p e r i o d d e p e n d e n t on reception
5 of a handover c o m p l e t i o n n o t i f i c a t i o n r e g a r d i n g t h e f i r s t handover.
6. The handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g to Claim 4 o r
5 , wherein the handover c o m p l e t i o n n o t i f i c a t i o n is t r a n s m i t t e d to the
f i r s t b a s e s t a t i o n f r o m t h e s e c o n d b a s e s t a t i o n or f r o m a n e t w o r k n o d e
10 belonging to a h i g h e r network t o w h i c h t h e f i r s t b a s e s t a t i o n is
c o n n e c t e d .
7. The handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g t o a n y o n e o f
Claims 4 to 6, w h e r e i n t h e handover completion n o t i f i c a t i o n i s a
15 m e s s a g e r e c e i v e d by the f i r s t b a s e s t a t i o n d u r i n g a handover procedure.
8. The handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g t o a n y o n e o f
Claims 1 t o 7, wherein
t h e d e t e c t i o n means d e t e c t s a t h i r d handover f a i l u r e t y p e when
20 t h e r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t i s n o t r e c e i v e d w i t h i n a
f o u r t h p r e d e t e r m i n e d period d e p e n d e n t o n i n i t i a t i o n o f t h e f i r s t
handover, but handover f a i l u r e i n f o r m a t i o n i s r e c e i v e d f r o m t h e s e c o n d
b a s e s t a t i o n w i t h i n a f i f t h p r e d e t e r m i n e d period d e p e n d e n t o n
i n i t i a t i o n o f the f i r s t handover, and
2 5 the t h i r d handover f a i l u r e t y p e c o r r e s p o n d s to a s i t u a t i o n where
t h e m o b i l e t e r m i n a l t h a t has e x p e r i e n c e d a b n o r m a l discollllection i n t h e
second cell d u r i n g e x e c u t i o n of t h e f i r s t handover o r a f t e r c o m p l e t i o ~ l
of t h e f i r s t handover t r i e s c o n n e c t i o n r e - e s t a b l i s h m e n t t o a t h i r d c e l l
d i f f e r e n t f r o m both the f i r s t and s e c o n d c e l l s .
3 0
9. The llal1dover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g to Claim 8,
w h e r e i n t h e handover f a i l u r e i n f o r m a t i o n i n c l u d e s an i d e n t i f i e r o f t h e
third cell t h a t is estimated by t h e s e c o n d b a s e s t a t i o n based on
m e a s u r e m e n t i n f o r m a t i o n o f r a d i o q u a l i t y by the mobile terminal when
53
the m o b i l e t e r m i n a l i s c o n n e c t e d t o t h e s e c o n d c e l l w i t h o u t r e c e i v i n g
i n f o r m a t i o n a t t h e s e c o n d b a s e s t a t i o n from a t h i r d b a s e s t a t i o n t h a t
manages t h e t h i r d c e l l .
5 10. The h a n d o v e r f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g t o C l a i m 8
or 9, w h e r e i n t h e h a n d o v e r f a i l u r e i n f o r m a t i o n i s t r a n s m i t t e d w h e n t h e
m o b i l e t e r m i n a l e x p e r i e n c e s t h e a b n o r m a l d i s c o n n e c t i o n in t h e second
c e l l w i t h i n a s i x t h p r e d e t e r m i n e d p e r i o d d e p e n d e n t on c o n n e c t i o n of
t h e m o b i l e t e r ~ n i n a lt o t h e s e c o n d c e l l b y t h e f i r s t h a n d o v e r .
10
11. The h a n d o v e r f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g to any one
of C l a i m s 1 t o 7, w h e r e i n
t h e d e t e c t i o n means d e t e c t s a t h i r d h a n d o v e r f a i l u r e t y p e when
t h e r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t i s not r e c e i v e d w i t h i n a
15 f o u r t h p r e d e t e r m i n e d p e r i o d d e p e n d e n t on i n i t i a t i o n of t h e f i r s t
h a n d o v e r , but h a n d o v e r f a i l u r e i n f o r m a t i o n i s r e c e i v e d from a t h i r d
base s t a t i o n t h a t m a n a g e s a t h i r d c e l l d i f f e r e n t from b o t h t h e f i r s t a n d
s e c o n d c e l l s w i t h i n a s e v e n t h p r e d e t e r m i n e d p e r i o d d e p e n d e n t o n
i n i t i a t i o n o f t h e f i r s t h a n d o v e r , and
2 0 t h e t h i r d h a n d o v e r f a i l u r e t y p e c o r r e s p o n d s t o t h e s i t u a t i o n
w h e r e t h e m o b i l e t e r m i n a l t h a t has e x p e r i e n c e d t h e a b n o r m a l
d i s c o n n e c t i o n in t h e s e c o n d c e l l d u r i n g t h e e x e c u t i o n o f t h e f i r s t
h a n d o v e r or a f t e r t h e c o m p l e t i o ~ lo f t h e f i r s t h a n d o v e r t r i e s t h e
c o n n e c t i o n r e - e s t a b l i s h m e n t to t h e t h i r d c e l l d i f f e r e n t f r o m both the
25 f i r s t and s e c o n d c e l l s .
1 2 . The h a n d o v e r f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g to Claim 11.
w h e r e i n the h a n d o v e r f a i l u r e i n f o r m a t i o n i s t r a n s m i t t e d when the t h i r d
base s t a t i o n d e t e c t s p r e s e ~ l c e of a b a s e s t a t i o n t h a t h a s r e q u e s t e d
30 h a n d o v e r of the n l o b i l e t e r m i n a l to t h e second cell within an e i g h t h
p r e d e t e r m i n e d p e r i o d b e f o r e t h e c o n n e c t i o n r e - e s t a b l i s h m e n t of the
mobile t e r m i n a l in t h e t h i r d c e l l .
13. The h a n d o v e r f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g t o any one
5 4
of Claims 1 to 1 2 , w h e r e i n t h e d e t e c t i o n m e a n s g e n e r a t e s feedback
i n f o r m a t i o n on handover f r o m t h e f i r s t c e l l b a s e d on a d e t e c t i o n r e s u l t
of the a t l e a s t one of the handover f a i l u r e t y p e s .
1 4 . T h e handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g t o Claim 1 3 ,
wherein the f e e d b a c k i n f o r m a t i o n i n d i c a t e s thc n u m b e r o f o c c u r r e n c e s
or a n o c c u r r e n c e r a t e of the at l e a s t one of the handover f a i l u r e t y p e s .
15. The handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g to any one
10 of Claims 1 to 1 4 , w h e r e i n t h e a c k n o w l e d g m e n t r e s p o n s e t o the
handover command is t r a n s m i t t e d to the f i r s t base s t a t i o n f r o m t h e
mobile t e r m i n a l .
1 6 . T h e handover f a i l u r e d e t e c t i o n d e v i c e a c c o r d i n g to any one
15 of Claims 1 to 1 5 , w h e r e i n the a c k n o w l e d g m e n t r e s p o n s e t o t h e
handover command is a n a c k n o w l e d g m e n t r e s p o n s e to b e t r a n s m i t t e d to
the f i r s t b a s e s t a t i o n by t h e m o b i l e t e r m i n a l in o r d e r t o control a ret
r a n s m i s s i o n of a m e s s a g e t r a n s m i t t e d t o the mobile terminal from the
f i r s t base s t a t i o n d u r i n g a handover p r o c e d u r e .
2 0
17. A handover p a r a m e t e r a d j u s t m e n t d e v i c e c o m p r i s i n g :
adjustment means f o r a d j u s t i n g a handover parameter for
c o n t r o l l i n g o u t g o i n g handover from a f i r s t cell managed by a f i r s t base
s t a t i o n based o n ( a ) p r e s e n c e l a b s e n c e o f r e c e p t i o n by the f i r s t base
25 s t a t i o n of an a c k n o w l e d g m e n t r e s p o n s e t o a handover command
r e g a r d i n g f i r s t handover of a mobile terminal fro111 t h e f i r s t c e l l t o a
second cell managed by a second base s t a t i o n , and (b)
p r e s e n c e l a b s e n c e of a request f o r c o n n e c t i o n r e - e s t a b l i s h m e n t from the
mobile terminal to t h e f i r s t c e l l , the r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n
30 of t h e f i r s t handover.
1 8 . T h e handover parameter a d j u s t m e n t d c v i c c a c c o r d i n g to
Claim 17, wherein
the a d j u s t m e n t m e a n s r e c e i v e s f e e d b a c k information based on a
55
d e t e c t i o n r e s u l t of at l e a s t o n e o f handover f a i l u r e t y p e s r e g a r d i n g the
outgoing handover f r o m t h e f i r s t c e l l , and
t h e d e t e c t i o n r e s u l t of the at l e a s t one of the handover f a i l u r e
types is obtained by o b s e r v a t i o n o f t h e p r e s e n c e l a b s e n c e of the
5 r e c e p t i o n o f t h e a c k n o w l e d g m e n t r e s p o n s e to the handover command,
and the p r e s e n c e l a b s e n c e o f t h e r e q u e s t for c o n n e c t i o n r e -
e s t a b l i s h m e n t .
19. The handover p a r a m e t e r a d j u s t m e n t d e v i c e a c c o r d i n g to
10 Claim 18, w h e r e i n t h e a d j u s t m e n t means a d j u s t s the handover
parameter by a n a l y z i n g t h e f e e d b a c k i n f o r m a t i o n .
20. The handover p a r a m e t e r a d j u s t m e n t d e v i c e a c c o r d i n g t o
Claim 18 or 1 9 , w h e r e i n
15 t h e a d j u s t m e n t means:
makes each of the at l e a s t one of the handover f a i l u r e
t y p e s c o r r e s p o n d t o any o f a p l u r a l i t y o f a d j u s t m e n t d i r e c t i o n s of the
handover p a r a m e t e r ;
c a l c u l a t e s a t o t a l sum of t h e n u m b e r o f o c c u r r e n c e s or an
20 o c c u r r e n c e r a t e o f t h e handover f a i l u r e t y p e made to correspond to the
each a d j u s t m e n t d i r e c t i o n , a s f o r e a c h o f t h e p l u r a l i t y o f a d j u s t m e n t
d i r e c t i o n s ; and
a d j u s t s t h e handover p a r a m e t e r t o the adjustment d i r e c t i o n
w h e r e t h e t o t a l sum o f t h e n u m b e r of o c c u r r e n c e s o r t h e o c c u r r e n c e
25 r a t e is t h e l a r g e s t .
21. The handover p a r a m e t e r a d j u s t m e n t d e v i c e a c c o r d i n g to any
one of Claims 17 t o 20, w h e r e i n t h e handover parameter i n c l u d e s at
l e a s t one o f a f i r s t o f f s e t t h a t a c t s o n r a d i o q u a l i t y o f t h e f i r s t c e l l , a
30 second o f f s e t that acts on radio q u a l i t y o f t h e s e c o n d c e l l , and a guard
time for t r i g g e r i n g t r a n s m i s s i o n o f a m e a s u r e m e n t report by t h e m o b i l e
terminal connected to the f i r s t c e l l .
22. A handover f a i l u r e i n f o r m a t i o n generation device
56
c o m p r i s i n g :
g e n e r a t i o n m e a n s f o r g e n e r a t i n g handover f a i l u r e i n f o r m a t i o n to
be t r a n s m i t t e d to a f i r s t b a s e s t a t i o n , the handover f a i l u r e information
being used to d e t e c t a handover f a i l u r e type t h a t c o r r e s p o n d s t o a
5 s i t u a t i o n w h e r e a m o b i l e t e r m i n a l , has e x p e r i e n c e d a b n o r m a l
d i s c o n n e c t i o n in a s e c o n d c e l l m a n a g e d by a second b a s e s t a t i o n during
e x e c u t i o n of f i r s t handover f r o m a f i r s t c e l l managed by the f i r s t base
s t a t i o n t o t h e s e c o n d cell or a f t e r c o m p l e t i o n o f t h e f i r s t handover, and
then t r i e s c o n n e c t i o n r e - e s t a b l i s h m e n t to a third cell d i f f e r e n t from
10 both the f i r s t a n d s e c o n d c e l l s .
23. The handover f a i l u r e i n f o r m a t i o n g e n e r a t i o n d e v i c e
according to C l a i m 2 2 , w h e r e i n
t h e g e n e r a t i o n m e a n s is c o u p l e d t o t h e second b a s e s t a t i o n , and
the handover f a i l u r e i n f o r m a t i o n i n c l u d e s a n i d e n t i f i e r o f the
t h i r d c e l l t h a t is e s t i m a t e d by t h e g e n e r a t i o n m e a n s based o n a
m e a s u r e m e n t r e p o r t o f r a d i o q u a l i t y by the m o b i l e t e r m i n a l when the
mobile t e r m i n a l is connected to the second c e l l w i t h o u t r e c e i v i n g
i n f o r m a t i o n at the g e n e r a t i o n m e a n s f r o m a third base s t a t i o n that
m a n a g e s t h e third c e l l .
24. The handover f a i l u r e illformation g e n e r a t i o n d e v i c e
a c c o r d i n g t o Claim 2 3 , w h e r e i n t h e g e n e r a t i o n means t r a n s m i t s the
handover f a i l u r e i n f o r m a t i o n when the mobile terminal e x p e r i e n c e s the
25 a b n o r m a l d i s c o n n e c t i o n in the s e c o n d c e l l w i t h i n a p r e d e t e r m i n e d
period dependent on c o n n e c t i o n o f the mobile terminal to the second
cell by t h e f i r s t handover.
25. The handover f a i l u r e i ~ l f o r n ~ a t i ogi le neration device
30 a c c o r d i n g t o Claim 2 3 or 2 4 , w h e r e i n t h e generation m e a n s e s t i m a t e s
as thc third ccll a cell having the b e s t r a d i o quality i l l the n ~ e a s u r e m e n t
r e p o r t .
26. The kandover r a i l u s e i n f ' o r ~ ~ ~ a t igoenn e r a t i o n d e v i c e
according to Claim 22, wherein
t h e g e n e r a t i o n m e a n s is c o u p l e d t o a t h i r d base s t a t i o n t h a t
manages the t h i r d c e l l , a n d
t h e g e n e r a t i o n means t r a n s m i t s the handover f a i l u r e i n f o r m a t i o n
in r e s p o n s e t o d e t e c t i n g p r e s e n c e o f a b a s e s t a t i o n t h a t h a s r e q u e s t e d
handover o f t h e m o b i l e t e r m i n a l to the second c e l l w i t h i n a
p r e d e t e r m i n e d p e r i o d b e f o r e c o n n e c t i o n r e - e s t a b l i s h m e n t o f t h e m o b i l e
terminal i n t h e t h i r d c e l l .
10 27. The handover f a i l u r e i n f o r m a t i o n g e n e r a t i o n d e v i c e
according to Claim 26, w h e r e i n t h e g e n e r a t i o n m e a n s d e t e c t s , from
base s t a t i o n s t h a t manage c e l l s to which handover c a n b e performed
from the t h i r d c e l l , the b a s e s t a t i o n t h a t has r e q u e s t e d t h e handover of
the m o b i l e t e r m i n a l t o t h e s e c o n d c e l l .
28. A system for handover o p t i m i z a t i o n c o m p r i s i n g :
d e t e c t i o n means f o r d e t e c t i n g at l e a s t one of handover f a i l u r e
t y p e s r e g a r d i n g o u t g o i n g handover from a f i r s t cell managed by a f i r s t
base s t a t i o n by o b s e r v i n g ( a ) p r e s e n c e l a b s e n c e o f reception by the f i r s t
20 base s t a t i o n of a n a c k n o w l e d g m e n t r e s p o n s e t o a handover command
r e g a r d i n g f i r s t handover of a m o b i l e t e r m i n a l f r o m t h e f i r s t c e l l to a
second cell managed by a s e c o n d b a s e s t a t i o n , and (b)
p r e s e n c e l a b s e n c e of a r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m t h e
mobile t e r m i n a l to the f i r s t c e l l , the r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n
25 of the f i r s t h a n d o v e r ; and
a d j u s t m e n t m e a n s for a d j u s t i n g a handover parameter for
c o n t r o l l i n g tlie outgoing handover from the f i r s t cell based on a
d e t e c t i o n r e s u l t of the at l e a s t o n e of the handover f a i l u r e t y p e s .
2 9 . The system according to Claim 28. wherein the detection
n ~ e a n sd e t e c t s a f i r s t handover f a i l u r e t y p e when t h e acknowledgment
response t o t h e handover command is not received within a f i r s t
p r e d e t e r m i n e d period dependent on i n i t i a t i o n of the f i r s t handover and
the request f o r c o n n e c t i o n r e - e s t a b l i s h m e n t is also not received within
5 8
a s e c o n d p r e d e t e r m i n e d p e r i o d d e p e n d e n t o n i n i t i a t i o n of the f i r s t
handover.
3 0 . T h e s y s t e m a c c o r d i n g t o Claim 28 or 29, wherein the
5 d e t e c t i o n m e a n s d e t e c t s a s e c o n d handover f a i l u r e t y p e when the
r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t is r e c e i v e d w i t h i n a third
p r e d e t e r m i n e d period dependent on i n i t i a t i o n o f t h e f i r s t h a n d o v e r .
31. The s y s t e m a c c o r d i n g t o any one o f C l a i m s 2 8 to 30, wherein
10 the d e t e c t i o n means d e t e c t s a s e c o n d handover f a i l u r e t y p e when t h e
r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t is r e c e i v e d b e f o r e r e c e p t i o n of
a handover c o m p l e t i o n n o t i f i c a t i o n r e g a r d i n g t h e f i r s t handover.
32. The s y s t e m a c c o r d i n g to any one of C l a i m s 2 8 t o 3 1 , wherein
15 t h e d e t e c t i o n means d e t e c t s a s e c o n d handover f a i l u r e t y p e when the
r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t is r e c e i v e d w i t h i n a fourth
p r e d e t e r m i n e d p e r i o d d e p e n d e n t on r e c e p t i o n o f a handover completion
n o t i f i c a t i o n r e g a r d i n g t h e f i r s t h a n d o v e r .
2 0 3 3 . T h e s y s t e m a c c o r d i n g to any one of C l a i m s 2 8 to 32, f u r t h e r
c o m p r i s i n g g e n e r a t i o n m e a n s f o r g e n e r a t i n g handover f a i l u r e
i n f o r m a t i o n and n o t i f y i n g t h e d e t e c t i o n m e a n s o f the handover f a i l u r e
i n f o r m a t i o n , w h e r e i n
the d e t e c t i o n means d e t e c t s a t h i r d handover f a i l u r e type when
25 t h e r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t is not r e c e i v e d w i t h i n a
f o u r t h p r e d e t e r m i n e d period d e p e n d e n t o n i n i t i a t i o n o f the f i r s t
handover, but the handover f a i l u r e informati011 is received within a
f i f t h p r e d e t e r m i n e d period dependent on i n i t i a t i o n o f the f i r s t handover,
and
3 0 the third handover f a i l u r e type c o r r e s p o n d s to a s i t u a t i o n where
the mobile terminal t h a t h a s e x p e r i e ~ l c e d abnormal disconnection in the
second cell d u r i n g e x e c u t i o n of the f i r s t handover or a f t e r c o m p l e t i o l ~
of t h e f i r s t handover t r i e s c o n n e c t i o n r e - e s t a b l i s h m e n t to a third cell
d i f f e r e n t from both the f i r s t a n d s e c o n d c e l l s .
34. The s y s t e m a c c o r d i n g to Claim 3 3 , w h e r e i n
t h e g e n e r a t i o n m e a n s is c o u p l e d t o the s e c o n d b a s e s t a t i o n , and
the handover f a i l u r e i n f o r m a t i o n i n c l u d e s a n i d e n t i f i e r of the
5 third c e l l t h a t is e s t i m a t e d by the g e n e r a t i o n m e a n s based on
m e a s u r e m e n t i n f o r m a t i o n of r a d i o q u a l i t y by t h e m o b i l e terminal when
t h e m o b i l e t e r m i n a l is connected to t h e s e c o n d c e l l without r e c e i v i n g
i n f o r m a t i o n at t h e g e n e r a t i o n m e a n s f r o m a t h i r d b a s e s t a t i o n that
manages the third c e l l .
35. The s y s t e m a c c o r d i n g t o C l a i m 3 3 o r 34, wherein
the g e n e r a t i o n m e a n s i s c o u p l e d t o the second base s t a t i o n , and
t h e g e n e r a t i o n means t r a n s m i t s t h e handover f a i l u r e i n f o r m a t i o n
when the m o b i l e t e r m i n a l e x p e r i e n c e s t h e a b n o r m a l d i s c o n n e c t i o n in
15 t h e s e c o n d c e l l w i t h i n a s i x t h p r e d e t e r m i n e d period dependent on
connection of the mobile t e r m i n a l to the s e c o n d c e l l by t h e f i r s t
handover.
36. The s y s t e m a c c o r d i n g t o C l a i m 3 3 , w h e r e i n
2 0 the generatioll m e a n s i s coupled to a third base s t a t i o n that
m a n a g e s t h e third c e l l , a n d
t h e g e n e r a t i o n means t r a n s m i t s t h e handover f a i l u r e i ~ ~ f o r m a t i o n
in r e s p o n s e t o d e t e c t i n g p r e s e n c e o f a base s t a t i o n t h a t h a s r e q u e s t e d
handover o f t h e m o b i l e t e r m i n a l t o the second c e l l w i t h i n an eighth
25 p r e d e t e r m i n e d period b e f o r e c o n n e c t i o n r e - c s t a b l i s l ~ m e n t of the mobile
terminal in the third c e l l .
37. The system a c c o r d i n g t o Claim 36, w h e r e i n t h e g e n e r a t i o n
m e a n s d e t e c t s , f r o m b a s e s t a t i o n s that manage c e l l s to which handover
30 can b e p e r f o r m e d f r o m t h e t h i r d c e l l , the base s t a t i o n that has
r e q u e s t e d o f the m o b i l e t e r m i n a l t h e handover to the s e c o n d c e l l .
3 8 . T h e s y s t e m a c c o r d i n g t o any one o f C l a i m s 28 to 37, wherein
the handover p a r a m e t e r i n c l u d e s a t l e a s t one of a f i r s t o f f s e t that acts
60
o n r a d i o q u a l i t y of t h e f i r s t c e l l , a s e c o n d o f f s e t that acts on radio
q u a l i t y of t h e s e c o n d c e l l , and a g u a r d t i m e f o r t r i g g e r i n g t r a n s m i s s i o n
of a m e a s u r e m e n t r e p o r t by the m o b i l e t e r m i n a l c o n n e c t e d to t h e f i r s t
c e l l .
5
39. The s y s t e m a c c o r d i n g to Claim 3 8 d e p e n d i n g f r o m Claim 29,
w h e r e i n when an o c c u r r e n c e r a t e o f t h e f i r s t handover f a i l u r e t y p e
exceeds a p r e d e t e r m i n e d v a l u e , t h e a d j u s t m e n t m e a n s e x e c u t e s at l e a s t
one of decrease in t h e f i r s t o f f s e t , i n c r e a s e in the s e c o n d o f f s e t , and
10 decrease in t h e g u a r d t i m e .
40. The s y s t e m a c c o r d i n g to Claim 3 8 d e p e n d i n g from C l a i m 3 0 ,
31, or 3 2 , w h e r e i n when a n o c c u r r e n c e r a t e of t h e s e c o n d handover
f a i l u r e t y p e e x c e e d s a p r e d e t e r m i n e d v a l u e , t h e a d j u s t m e n t m e a n s
15 executes at l e a s t one of the i n c r e a s e in the f i r s t o f f s e t , the decrease in
t h e s e c o n d o f f s e t , a n d the i n c r e a s e in the guard time.
41. The s y s t e m a c c o r d i n g to Claim 3 8 d e p e n d i n g f r o m a n y one of
Claims 3 3 t o 3 7 , w h e r e i n
20 the handover p a r a m e t e r i n c l u d e s t h e s e c o n d o f f s e t and a third
o f f s e t that a c t s o n radio q u a l i t y of t h e t h i r d c e l l , and
when an occurrence rate of the third handover f a i l u r e t y p e
exceeds a p r e d e t e r m i n e d v a l u e , the adjustment means d e c r e a s e s the
s e c o n d o f f s e t and i n c r e a s e s t h e third o f f s e t .
42. A b a s e s t a t i o n c o m p r i s i n g t h e I ~ a n d o v e r f a i l u r e d e t e c t i o n
d e v i c e a c c o r d i n g t o any one of Claims 1 to 16.
43. A handover f a i l u r e d e t e c t i o n method c o m p r i s i n g :
d e t e c t i n g at least o n e o f handover f a i l u r e t y p e s regarding
outgoing handover fro111 a f i r s t cell managed by a f i r s t b a s e s t a t i o n by
o b s e r v i n g ( a ) p r e s e n c c / a b s e n c e of reception by the f i r s t base s t a t i o n o f
an a c k n o w l e d g m e n t r e s p o n s e t o a handover command regarding f i r s t
handover of a m o b i l e terminal from t h e f i r s t c e l l to a second cell
managed by a s e c o n d base s t a t i o n , a n d ( b ) p r e s e n c e l a b s e n c e o f a
r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m t h e mobile terminal to the
f i r s t c e l l , the r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n of the f i r s t h a n d o v e r .
5 44. A handover p a r a m e t e r a d j u s t m e n t m e t h o d c o m p r i s i n g :
a d j u s t i n g a handover p a r a m e t e r f o r c o n t r o l l i n g o u t g o i n g
handover f r o m a f i r s t c e l l managed by a f i r s t b a s e s t a t i o n based on (a)
p r e s e n c e / a b s e n c e o f r e c e p t i o n by the f i r s t b a s e s t a t i o n of an
a c k n o w l e d g m e n t r e s p o n s e t o a handover command r e g a r d i n g f i r s t
10 handover of a m o b i l e t e r m i n a l f r o m the f i r s t c e l l t o a s e c o n d cell
managed by a s e c o n d b a s e s t a t i o n , a n d ( b ) p r e s e n c e l a b s e n c e o f a
r e q u e s t f o r c o n n e c t i o n r e - e s t a b l i s h m e n t f r o m t h e mobile terminal to the
f i r s t c e l l , t h e r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n of the f i r s t h a n d o v e r .
15 45. A n o n - t r a n s i t o r y c o m p u t e r r e a d a b l e medium s t o r i n g a
program f o r c a u s i n g a c o m p u t e r t o p e r f o r m a m e t h o d for handover
f a i l u r e d e t e c t i o n , wherein
the method i n c l u d e s d e t e c t i n g at l e a s t one of handover f a i l u r e
t y p e s r e g a r d i n g o u t g o i n g handover f r o m a f i r s t c e l l managed by a f i r s t
20 base s t a t i o n by observing ( a ) p r e s e n c e l a b s e n c e of r e c e p t i o n by t h e f i r s t
base s t a t i o n of an a c k n o w l e d g ~ n e n t response to a handover command
r e g a r d i n g f i r s t handover of a m o b i l e terminal from the f i r s t cell t o a
second c e l l managed by a s e c o n d base s t a t i o n , and (b)
p r e s e n c e l a b s e n c e o f a r e q u e s t for c o ~ l n e c t i o i l r e - e s t a b l i s h m e n t from the
25 mobile terminal to the f i r s t c e l l , the r e q u e s t o c c u r r i n g a f t e r i n i t i a t i o n
of t h e f i r s t handover.
46. A n o n - t r a n s i t o r y computer readable medium s t o r i n g a
program f o r c a u s i n g a c o m p u t e r to perform a m e t h o d f o r handover
30 p a r a m e t e r a d j u s t m e n t . wherein
the method i n c l u d e s a d j u s t i n g a handover parameter for
c o n t r o l l i n g o u t g o i n g handover from a f i r s t cell managed by a f i r s t base
s t a t i o n based on ( a ) p r e s e n c e l a b s e n c e o f r e c e p t i o n by the f i r s t base
s t a t i o n of a11 a c k n o w l e d g m e n t r e s p o n s e to a handover command
62
r e g a r d i n g f i r s t haildoves of a mobile terminal f r o m t h e f i r s t c e l l to a
second cell managed by a second b a s e s t a t i o n , and (b)
p r e s e n c e / a b s e n c e of a r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t from the
mobile terminal to the f i r s t c e l l , the request o c c u r r i n g a f t e r i n i t i a t i o n
5 of the f i r s t handover.
Dated this 08th Day of July 2015
Of Anand And Anand Advocates
Agents for the Applicant
63
ABSTRACT
HANDOVER FAILURE DETECTION DEVICE, HANDOVER
PARAMETER ADJUSTMENT DEVICE, AND HANDOVER
OPTIMIZATION SYSTEM
A handover f a i l u r e d e t e c t i o n d e v i c e (121) d e t e c t s a t l e a s t one of
handover f a i l u r e t y p e s r e g a r d i n g o u t g o i n g handover f r o m a f i r s t cell
(13 1) managed by a f i r s t base s t a t i o n (1 11) by o b s e r v i n g : ( a )
p r e s e n c e l a b s e n c e of r e c e p t i o n by the f i r s t base s t a t i o n (1 1 1 ) o f an
10 acknowledgment response to a handover command r e g a r d i n g f i r s t
handover of a m o b i l e t e r m i n a l (101) from t h e f i r s t c e l l ( 1 3 1 ) to a
s e c o n d c e l l ( 1 3 2 ) managed by a s e c o n d base s t a t i o n (1 12); and (b)
p r e s e n c e l a b s e n c e of a r e q u e s t for c o n n e c t i o n r e - e s t a b l i s h m e n t from the
m o b i l e t e r m i n a l (101) to the f i r s t c e l l ( 1 3 1 ) , the r e q u e s t occurring
15 a f t e r i n i t i a t i o n of the f i r s t h a n d o v e r . As a r e s u l t , i t c o n t r i b u t e s to
improvement of handover f a i l u r e d e t e c t i o n o r r e d u c t i o n of handover
f a i l u r e in a s i t u a t i o n w h e r e exchange of i n f o r m a t i o n b e t w e e n base
s t a t i o n s is r e s t r i c t e d .