[001]
FIELD OF INVENTION
[002]
The present invention generally relates to wireless
communication
systems. In particular, the present invention relat
es to channel switching and
scheduling of multimedia broadcasts and multicast s
ervices in such systems.
[003]
BACKGROUND
5
[004]
There is a growing desire to use multimedia broadca
sts/multicast services
(MBMS) in wireless communication systems. For a par
ticular MBMS, a given
cell in the network may have none, one or multiple
users, wireless
transmit/receive units (WTRUs), subscribed to that
MBMS. As users migrate
between cells, a cell that may originally have one
or no users subscribed to the
10
service may at a later point have multiple subscrib
ed users. Conversely, a cell that
may at one point have multiple subscribed users may
at another time have only
one or no users.
[005]
This migration of the users can create inefficient
use of radio resource. If
only one or a few users are subscribed to the MBMS
in the cell, it may be
15
desirable to support the service using dedicated ch
annels to the users. The
dedicated channels can utilize power control and be
am steering to reduce the
amount of radio resources utilized to support the M
BMS.
[006]
However, if many users are subscribed to the MBMS i
n the cell, the
multiple dedicated channels in total may use consid
erable radio resources. In such
20
a situation, a more optimal use of the radio resour
ces may be to send the MBMS
data over a common/shared channel to a set of users
subscribed to that MBMS.
Although the use of beamsteering and power control
in such situations is limited,
the reduction in the number of total channels may r
educe the used radio resources.
As the number of MBMS users in the cell changes, an
original choice of using
25
either a common/shared channel or a dedicated chann
el may not be optimal at a
later time.
3
INTL-706-IN-DIV
[007]
Another potential problem resulting from user migra
tion is MBMS
scheduling. As a MBMS user moves between cells, tha
t user needs to reconstruct
the MBMS service from information received from bot
h cells. If both cells
synchronize their MBMS transmissions, the MBMS user
can seamlessly move
between the cells. However, such a scenario is typi
cally not practical and
5
undesirable. At certain time intervals based on the
cell's loading and available
resources, a cell may have more available resources
to support the MBMS
transmission than at another time. As a result, at
that time, it is desirable for that
cell to transmit a large amount of the MBMS data. F
or another cell at that same
time interval, resources to support the same MBMS b
andwidth may not be
10
available. As a result, it may be desirable to sche
dule the MBMS transmissions
differently between the cells, to better utilize su
ch resources. As the MBMS user
moves between cells, the new cell that the user has
moved into may have
transmissions either ahead or behind the other cell
's transmissions. As a result, the
MBMS user may miss MBMS data or needlessly receive
redundant MBMS data.
15
[008]
Accordingly, it is desirable to have better resourc
e utilization for MBMS.
[009]
SUMMARY
[0010]
The present invention includes a radio access netwo
rk and a method for
sending a multimedia broadcasts/multicast services
(MBMS) using channel
switching. The channel switching is between dedicat
ed and shared/common
20
channels. The invention also includes MBMS receptio
n scheduling for use when a
wireless transmit/receive device receives an MBMS s
ervice from multiple
transmission sources. The sources transmitting the
MBMS service data in
differing orders. One embodiment uses in band segme
ntation information and
another embodiment uses out of band synchronization
information.
25
[0011]
BRIEF DESCRIPTION OF THE DRAWING(S)
[0012]
Figure 1 is a flow chart for use in MBMS channel sw
itching.
4
INTL-706-IN-DIV
[0013]
Figure 2 is a radio access network using MBMS chann
el switching.
[0014]
Figure 3 is a flow chart for coordinating reception
of a MSMS
transmissions from multiple sources using in band s
egmentation information.
[0015]
Figure 4 is a flow chart for coordinating reception
of a MSMS
transmissions from multiple sources using out of ba
nd segmentation information.
5
[0016]
Figure 5 is a WTRU for receiving MBMS information u
sing in band
segmentation information.
[0017]
Figure 6 is a WTRU for receiving MBMS information u
sing out of band
synchronization information.
[0018]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
10
[0019]
Although the preferred embodiments are described in
conjunction with a
third generation partnership program (3GPP) wideban
d code division multiple
access (W-CDMA) system, the embodiments are applica
ble to any wireless
system using MBMS. Hereafter, a wireless transmit/r
eceive unit (WTRU)
includes but is not limited to a user equipment, mo
bile station, fixed or mobile
15
subscriber unit, pager, or any other type of device
capable of operating in a
wireless environment.
[0020]
Figure 1 is a flow chart for channel switching for
a MBMS. In a particular
cell, the number of WTRUs subscribed to the service
is determined or estimated,
step 20. Typically, this information is known. Usin
g the number of WTRUs in the
20
cell and/or other cell information, such as informa
tion on cell conditions, available
cell resources, etc., a choice of whether dedicated
channels, a common shared
channel or both are used, step 22. After the channe
l choice is made, the MBMS
data is mapped to the corresponding channel(s), ste
p 24. One possible approach to
determine which type(s) of channels should be used
is a threshold test. If below a
25
certain threshold number of WTRUs is in the cell, d
edicated channels are used.
The dedicated channels allow for power control and
transmit diversity techniques
to be employed. These techniques are highly desirab
le when high data rate MBMS
transfers are made, to efficiently use the availabl
e resources.
5
INTL-706-IN-DIV
[0021]
If the number of WTRUs exceeds the threshold, a com
mon/shared channel
is used, such as a shared channel, a high speed sha
red channel or a secondary
common control physical channel (S-CCPCH). A shared
channel or high speed
shared channel can be used to transfer the MBMS dat
a to multiple WTRUs
simultaneously. The S-CCPCH can be used to broadcas
t the MBMS data to
5
multiple users. Typically, the shared/common channe
ls are less radio resource
efficient.
[0022]
In an alternate embodiment, a two threshold scheme
may be used. If the
number of MBMS subscribed WTRUs in the cell is belo
w a first threshold,
dedicated channels are used. If the number is betwe
en a first and second threshold,
10
a shared or high speed shared channel is used. If t
he number exceeds the second
threshold, a common channel is used to broadcast th
e MBMS.
[0023]
Under certain circumstances, it may be desirable to
use both shared and
dedicated channels to support an MBMS. To illustrat
e, many subscribing WRTUs
may be located together, such as at a train station
, and a few or a single WTRU
15
may be outside of the train station. In such a situ
ation, the most efficient use of
cell resources to support the MBMS may be to alloca
te a shared channel to the
train station WTRUs and a dedicated channel to the
other WTRU. As the number
of users in a cell changes, the cell conditions cha
nges or periodically, the channel
choice is repeated using the new information, step
26.
20
[0024]
Figure 2 is an illustration of a preferred radio ac
cess network (RAN) for
performing channel switching. The RAN is managed by
a serving radio network
controllers (S-RNC) 30 which manages the user's ser
vices and the controlling
radio network controller (C-RNC) 34 which manages t
he physical resources of the
cells. Signaling procedures which provide the coord
ination needed between the S-
25
RNCs 30 and the C-RNCs 34 for proper operation of t
he RAN are utilized.
[0025]
A channel switching entity (MBMS channel switching
device 36)
determines which channels to use, such as dedicated
, shared or the common, for
MBMS transmission and it also coordinates reception
of the MBMS with the
6
INTL-706-IN-DIV
WTRUs 40
1
to 40
N
(40). The MBMS data is sent to the WTRUs 40 via th
e Node-
B 38.
[0026]
A preferred implementation of the channel switching
is as follows. A first
WTRU 40 subscribed to the MBMS can enter and exit c
ells autonomously with
respect to the activation and distribution of the M
BMS service. When the MBMS
5
is first established for the first WTRU 40 or a sma
ll number of users within a
particular cell, dedicated channels are established
with a unique radio link (RL)
indicator that identifies the MBMS service. A secon
d WTRU 40 that wishes to
utilize another MBMS will have a different dedicate
d channel assigned to that
user. When the RL is established for each user, a u
nique MBMS indicator is
10
signaled from the S-RNC 30 to the C-RNC 34. This MB
MS indicator is unique to
each service provided to the user. The C-RNC 34 mai
ntains a database of all users
currently active for a particular MBMS service and
this group is known as the
MBMS user group.
[0027]
The data for each active MBMS service is distribute
d to the C-RNC 34
15
from the core network 28 via the MBMS data stream.
A unique identifier is
associated with each MBMS data stream allowing the
C-RNC 34 to associate the
data with the appropriate user or user group so the
data can be properly routed.
Depending on the number of active users for a parti
cular MBMS service and cell
conditions, the C-RNC 34 will determine if the serv
ice should be transmitted on
20
dedicated or shared/common channels.
[0028]
Since individual users autonomously enter and exit
the cell, the switching
between dedicated and common channels is dynamic an
d may occur during
ongoing transmissions. Dynamic switching can be app
lied to the downlink shared
channels (DSCH). Data can be sent on the DSCH to be
received by a single user is
25
referred to as dedicated DSCH (D-DSCH) or by multip
le users simultaneously is
referred to as common DSCH (C-DSCH). For a particul
ar MBMS when there is
only one user or a small number of users existing w
ithin the cell, the DSCH will
be a D-DSCH to the user or users. When the number o
f users associated with a
particular MBMS increases, a C-DSCH can be establis
hed for this MBMS user
30
group.
7
INTL-706-IN-DIV
[0029]
When the first WTRU 40 becomes active within the ce
ll, a D-DSCH is
established to this first user. The MBMS transmissi
on may not necessarily be
continuously active. The transmission of the MBMS o
n the DSCH is indicated to
the first WTRU 40 on an associated dedicated channe
l. This indication may be
turned on and off on a transmission time interval (
TTI) basis.
5
[0030]
The C-DSCH may be physically identical to the D-DSC
H. However, a
distinguishing characteristic is that the signaling
for the DSCH transmission for
the individual user associated with a dedicated cha
nnel within the MBMS user
group is that the transmission is synchronized. Thi
s allows all users in the MBMS
user group to receive the common DSCH transmission.
An indication may be
10
signaled along with MBMS transmissions to indicate
that the MBMS transmission
is either dedicated to a particular user or common
to the users in the MBMS user
group. This allows for proper operation of power co
ntrol techniques, transmit
diversity or any other unique physical transmission
attributes. The MBMS
transitions between dedicated and common DSCH is pr
eferably transparent to the
15
WTRU 40.
[0031]
In another embodiment, the channel switching is app
lied to the high speed
DSCH (HS-DSCH). A difference between using the HS-D
SCH instead of the
DSCH is that rather than applying synchronized allo
cations in the C-RNC 34 on
the associated dedicated channels, the synchronized
allocations are provided on
20
HS-DSCH control channels in Node-B 38.
[0032]
In another embodiment, switching may be performed b
etween the
dedicated physical channels and common physical cha
nnels without the use of the
associated dedicated channels. The channel switchin
g between the dedicated
channels to the common channels is explicitly signa
led to each user. The RAN
25
layer 3 protocols allow for procedures of signaling
the radio frame to transition
between the dedicated and the common channels. The
signaling is performed by
either signaling a radio frame for the transition o
r by signaling the transmission
scheduling information.
[0033]
Figures 3 and 4 are flow charts to allow for
different cells and
30
different inter-cell MBMS transmissions to be sch
eduled in different orders. To
8
INTL-706-IN-DIV
illustrate, a first cell may be able to transmit l
arge amounts of MBMS data to
WTRUs 40 in a radio frame that a second cell can no
t. As a result, MBMS
transmission in the first cell may be one or multip
le radio frames or TTIs ahead of
the second cell.
[0034]
To illustrate for inter-cell, within a cell, one gr
oup of users may be located
5
in a train station and serviced by a common DSCH an
d another user within the
same cell may be outside of the train station and b
e serviced by a dedicated
channel or dedicated DSCH to take full advantage of
beam forming and power
control. Based on the DSCH loading and other factor
s, it may be desirable for
transmissions to the train station WTRUs 40 to eith
er lead or lag the outside
10
WTRU transmissions. If a user of the outside WTRU 4
0 goes to the train station,
it would most likely be desirable to switch that WT
RU 40 to the common DSCH
and disestablish the dedicated channel. In this sce
nario, the outside WTRU 40
may need to catch up to the transmissions on the co
mmon DSCH or allow those
transmissions to catch up to the segments that the
WTRU 40 already received.
15
[0035]
To maintain continuous service distribution and mak
e more efficient use of
radio resources, the MBMS transmissions are prefera
bly either segmented or
scheduled so that users can receive elements of an
MBMS service transmission in
any order. As a result, the MBMS service transmissi
ons do not have to be
reinitiated in a cell upon a user entry to that cel
l or the user does not have to wait
20
to synchronize with an existing MBMS service transm
ission.
[0036]
Figure 3 is a flow chart for using in-band segmenta
tion information to
handle differing MBMS transmission orders either in
ter-cell or between cells.
Along with the MBMS transmissions, segmentation inf
ormation is sent along with
the MBMS data, step 42. This segmentation informati
on typically includes a
25
segment identifier so that each receiving WTRU is a
ware of which segments that
it has received. As a particular WTRU moves between
MBMS transmission
sources (between cells or switched channels), step
44, the WTRU can receive
segments from the new MBMS source and reassemble th
e transmissions to
recovery all the MBMS data, step 46.
30
9
INTL-706-IN-DIV
[0037]
Figure 5 is a simplified block diagram of a WTRU 40
for receiving the
differing MBMS transmissions. The WTRU 40 receives
the MBMS transmissions
using an antenna 54. A MBMS receiver 56 receives th
e MBMS transmissions
from the differing transmission sources, including
the in band segmentation
information. A segmentation information recovery de
vice 58 recovers the
5
segmentation information. Using the segmentation in
formation and received
MBMS segments, a MBMS segmentation reassembly devic
e 60 reassembles the
segments to recover the MBMS data.
[0038]
Figure 4 is a flow chart for using out of band tran
smission scheduling
information to handle differing MBMS transmission o
rders. A WTRU receives a
10
MBMS transmission from a particular source, step 48
. The WTRU also receives
out of band scheduling information, step 50. As the
WTRU moves to a different
source, the WTRU can receive MBMS data from the new
source and using that
source's out of band scheduling data reassemble the
MBMS received segments,
step 52.
15
[0039]
Figure 6 is a simplified block diagram of a WTRU 40
for receiving the
differing MBMS transmissions. The WTRU 40 receives
the MBMS transmissions
using an antenna 54. A MBMS receiver 64 receives th
e MBMS transmissions
from the differing transmission sources. An out of
band synchronization
information device 62 receives synchronization info
rmation from the multiple
20
transmission sources. Using the synchronization inf
ormation and received MBMS
segments, a MBMS segmentation reassembly device 66
reassembles the segments
to recover the MBMS data.
[0040]
Both the approaches of Figure 3 and 4 allow for use
rs existing within the
cell to just transition between dedicated and commo
n channels without
25
interruption or delay in the MBMS transmission. Add
itionally, WTRUs entering
the cell can maintain continuous reception of the M
BMS service, even though the
sequence of transmission between the new and old ce
ll are different. Once MBMS
transmission data is received the WTRU reorders the
information according to the
in band segmentation and/or out of band transmissio
n scheduling information.
30
10
INTL-706-IN-DIV
[0041]
Since either in band segmentation or out of band sc
heduling is provided,
lost or failed transmissions can be efficiently rec
overed by the WTRU's
knowledge of when retransmission is expected. The R
NC MBMS retransmission
scheduling can also be reduced by taking into accou
nt intelligent reception by the
WTRUs. To illustrate, if the RNC knows all the user
s have received a particular
5
MBMS segment, retransmission of that segment can be
prevented.

Claims:1. A method for transferring multimedia broadcasts/multimedia services (MBMS) in a wireless communication system, the wireless communication system comprising a memory and a processor, the method being performed by the processor, the method comprising:
determining by the processor, a number of users in a cell to receive the MBMS;
using by the processor, the determined number of users to determine whether a dedicated channel or a shared/common channel is to be used for the MBMS;
receiving by the processor, MBMS data; and
mapping by the processor, the MBMS data to the determined dedicated or shared/common channel.

2. The method as claimed in claim 1 wherein the determined dedicated or shared/common channel is based on a threshold test where if the determined number of users is below the threshold, a dedicated channel is used for the MBMS and if the determined number of users is above the threshold, a shared/common channel is used for the MBMS.

3. The method as claimed in claim 2 wherein the threshold test has the threshold and a second threshold and if the determined number of users is above the second threshold, a common channel is used for the MBMS and if the determined number is between the threshold and the second threshold, a shared channel is used for the MBMS.
, Description:[001] FIELD OF INVENTION
[002] The present invention generally relates to wireless communication systems. In particular, the present invention relates to channel switching and scheduling of multimedia broadcasts and multicast services in such systems.
[003] BACKGROUND
[004] There is a growing desire to use multimedia broadcasts/multicast services (MBMS) in wireless communication systems. For a particular MBMS, a given cell in the network may have none, one or multiple users, wireless transmit/receive units (WTRUs), subscribed to that MBMS. As users migrate between cells, a cell that may originally have one or no users subscribed to the service may at a later point have multiple subscribed users. Conversely, a cell that may at one point have multiple subscribed users may at another time have only one or no users.
[005] This migration of the users can create inefficient use of radio resource. If only one or a few users are subscribed to the MBMS in the cell, it may be desirable to support the service using dedicated channels to the users. The dedicated channels can utilize power control and beam steering to reduce the amount of radio resources utilized to support the MBMS.
[006] However, if many users are subscribed to the MBMS in the cell, the multiple dedicated channels in total may use considerable radio resources. In such a situation, a more optimal use of the radio resources may be to send the MBMS data over a common/shared channel to a set of users subscribed to that MBMS. Although the use of beamsteering and power control in such situations is limited, the reduction in the number of total channels may reduce the used radio resources. As the number of MBMS users in the cell changes, an original choice of using either a common/shared channel or a dedicated channel may not be optimal at a later time.