1. A communication device for communicating with a plurality of further communication devices in a cellular communication system, said communication device comprising: means for communicating, in at least one communication cell operated 5 ted by communication apparatus of said communication system, using a plurality of subframes, wherein each subframe comprises a plurality of communication resources; means for obtaining a respective measure of communication quality associated with each of said communication resources and for providing information identifying said measures 10 of communication quality to said communication apparatus; means for identifying a set comprising a number of said communication resources in which to search for control information transmitted by said communication apparatus wherein the presence of communication resources in said set is based on said measures of communication quality; and 15 means for searching for control information in said set of communication resources.

2. A device according to claim 1 wherein said identifying means is operable to identify communication resources for inclusion in said set based on said measures of communication quality obtained by said obtaining means.

3. A device according to claim 1 wherein said wherein said communication device is 20 operable to receive, from said communication apparatus, information identifying the communication resources of said set after providing, to said communication apparatus, said information identifying a respective measure of communication quality associated with each of said communication resources; and wherein said identifying means is operable to identify the communication resources of said set based on said information 25 identifying the communication resources of said set received from said communication apparatus.

4. A device according to claim 1 or 2 wherein said communication device is operable to signal information identifying the communication resources of said set to said communication apparatus.

5. A device according to claim 4 wherein said communication device is operable to signal said information identifying the communication resources of said set to said communication apparatus as part of said information identifying said measures of communication quality.

6. A device according to any preceding claim wherein: said set of communication resources comprises a first set; said device further comprises means for identifying, based on a predetermined criteria, a second set comprising a number of said communication resources in which to search for control information transmitted by said communication apparatus in the event that control information for said communication device is not found in said first set of communication resources; and said searching means is 5 operable to search for control information in said second set of communication resources if control information for said communication device is not found in said first set of communication resources.

7. A device according to any preceding claim wherein said identifying means is operable to 10 identify communication resources for inclusion in said set based on at least one of a cell identity associated with said at least one cell and a subframe number associated with at least one of said plurality of subframes.

8. A device according to claim 7 wherein said identifying means is operable to identify communication resources for inclusion in said set from a subset of said communications 15 resources that are contiguous in frequency which subset is selected based on said at least one of said cell identity and said subframe number.

9. A device according to claim 7 wherein said identifying means is operable to identify communication resources for inclusion in said set from a subset of said communications resources that are distributed in frequency which subset is selected based on said at least 20 one of said cell identity and said subframe number.

10. A device according to any preceding claim wherein said set comprising a number of said communication resources in which to search for control information transmitted by said communication apparatus comprises a search space.

11. A device according to any preceding claim wherein said control information transmitted 25 by said communication apparatus is transmitted in a control channel (e.g. a physical downlink control channel (PDCCH) or enhanced physical downlink control channel (ePDCCH)) and wherein said device is operable to locate said control channel by searching in said set of communication resources.

12. A device according to claim 11 wherein said control channel comprises at least one 30 control channel element (CCE).

13. A device according to any preceding claim wherein said information identifying said measures of communication quality comprise at least one carrier quality indication (CQI) report.

14. A device according to any preceding claim wherein said communication resources in which to search for control information are arranged in said set in order of decreasing quality based on said measures of communication quality.

15. A device according to any preceding claim comprising a mobile telephone.

16. Communication apparatus for communicating with a plurality of mobile communication devices in a cellular communication system, said communication apparatus comprising5 : means for operating at least one communication cell; means for communicating using a plurality of subframes with at least one mobile communication device within said at least one cell, wherein each subframe comprises a plurality of communication resources; 10 means for receiving, from said at least one mobile communication device, information identifying a respective measure of communication quality associated with each of said communication resources; means for identifying a set comprising a number of said communication resources for use in potential transmission of control information for the at least one mobile 15 communication device wherein the presence of communication resources in said set is based on said measures of communication quality; and means for transmitting control information for said at least one mobile communication device in at least a subset of said set of communication resources.

17. Apparatus according to claim 16 wherein said identifying means is operable to identify 20 communication resources for inclusion in said set based on said information identifying a respective measure of communication quality associated with each of said communication resources received from the communication device.

18. Apparatus according to claim 16 wherein said wherein said communication device is operable to receive, from said communication device and separately to said information 25 identifying a respective measure of communication quality associated with each of said communication resources, information identifying the communication resources of said set; and wherein said identifying means is operable to identify the communication resources of said set based on said information identifying the communication resources of said set received from said communication device.

19. Apparatus according to claim 16 or 17 wherein said communication apparatus is operable to signal information identifying the communication resources of said set to said communication apparatus.

20. Apparatus according to any of claims 16 to 19 wherein: said set of communication resources comprises a first set; said apparatus further comprises means for identifying a second set comprising a number of said communication resources for use in potential transmission of control information for the at least one mobile communication device based on a predetermined criteria in the event that said information identifying a respective measure of communication quality associated with each of said communication resources has not been successfully received and interpreted 5 d by said communication apparatus; and said transmitting means is operable to transmit control information for said at least one mobile communication device in at least a subset of said second set of communication resources if said information identifying a respective measure of communication quality associated with each of said communication resources 10 has not been successfully received and interpreted by said communication apparatus.

21. Apparatus according to any of claims 16 to 20 wherein said identifying means is operable to identify communication resources for inclusion in said set based on at least one of a cell identity associated with said at least one cell and a subframe number associated with at least one of said plurality of subframes.

22. Apparatus according to claim 21 wherein said identifying means is operable to identify communication resources for inclusion in said set from a subset of said communications resources that are distributed in frequency which subset is selected based on said at least one of said cell identity and said subframe number.

23. Apparatus according to claim 22 wherein said set comprising a number of said 20 communication resources for use in potential transmission of control information for the at least one mobile communication device comprises a search space.

24. Apparatus according to any of claims 16 to 22 wherein said apparatus is operable to transmit said control information in a control channel (e.g. a physical downlink control channel (PDCCH) or enhanced physical downlink control channel (ePDCCH)) in said set 25 of communication resources.

25. Apparatus according to claim 24 wherein said control channel comprises at least one control channel element (CCE) and wherein said apparatus is operable to transmit each said CCE using communication resources of said set.

26. Apparatus according to any of claims 16 to 25 comprising a base station.

27. A communication device for communicating with a plurality of further communication devices in a cellular communication system, said communication device comprising: means for communicating, in at least one communication cell operated by communication apparatus of said communication system, using a plurality of subframes, wherein each subframe comprises a plurality of communication resources; means for identifying, based on information transmitted to said communication apparatus, a first set comprising a number of said communication resources in which to search for control information transmitted by said communication apparatus; means for identifying, based on a predetermined criteria, a second set comprising a number of said communication resources in which to search for control informati5 on transmitted by said communication apparatus in the event that control information for said communication device is not found in said first set of communication resources; and means for searching for control information in said first set of communication resources and, if control information for said communication device is not found in said first set of 10 communication resources, for searching for control information in said second set of communication resources.

28. A communication device according to claim 27 wherein said communication resources of said second set are transmitted with frequency diversity.

29. A communication device according to claim 27 or 28 wherein said set comprising a 15 number of said communication resources in which said control information is transmitted by said communication apparatus comprises a search space.

30. A communication device according to any of claims 27 to 29 wherein said control information transmitted by said communication apparatus is transmitted in a control channel (e.g. a physical downlink control channel (PDCCH) or enhanced physical 20 downlink control channel (ePDCCH)) and wherein said device is operable to locate said control channel by searching in said set of communication resources.

31. A communication device according to any of claims 27 to 30 wherein said control channel comprises at least one control channel element (CCE).

32. A communication device according to any of claims 27 to 31 wherein said information 25 identifying said measures of communication quality comprise at least one carrier quality indication (CQI) report.

33. A communication device according to any of claims 27 to 32 wherein said communication resources in which to search for control information are arranged in said set in order of decreasing quality based on said measures of communication quality.

34. Communication apparatus for communicating with a plurality of mobile communication devices in a cellular communication system, said communication apparatus comprising: means for operating at least one communication cell; means for communicating using a plurality of subframes with at least one mobile communication device within said at least one cell, wherein each subframe comprises a plurality of communication resources; means for identifying a first set comprising a number of said communication resources for use in potential transmission of control information for the at least one mobile communication device based on information received from said mobile communication device, in the event that said information from said mobile communication device 5 has been successfully received and interpreted by said communication apparatus; means for identifying a second set comprising a number of said communication resources for use in potential transmission of control information for the at least one mobile communication device based on a predetermined criteria, in the event that said 10 information from said mobile communication device has not been successfully received and interpreted by said communication apparatus; and means for transmitting control information for said at least one mobile communication device: in at least a subset of said first set of communication resources, in the event that said information from said mobile communication device has been successfully received 15 and interpreted by said communication apparatus; and in at least a subset of said second set of communication resources, if said information from said mobile communication device has not been successfully received and interpreted by said communication apparatus.

35. Apparatus according to claim 33 wherein said communication resources of said second 20 set are transmitted with frequency diversity.

36. Apparatus according to any of claims 33 to 35 wherein said set comprising a number of said communication resources in which said control information is transmitted by said communication apparatus comprises a search space.

37. Apparatus according to any of claims 33 to 36 wherein said control information 25 transmitted by said communication apparatus is transmitted in a control channel (e.g. a physical downlink control channel (PDCCH) or enhanced physical downlink control channel (ePDCCH)) and wherein said device is operable to locate said control channel by searching in said set of communication resources.

38. Apparatus according to any of claims 33 to 37wherein said control channel comprises at 30 least one control channel element (CCE).

39. Apparatus according to any of claims 33 to 38 wherein said information identifying said measures of communication quality comprise at least one carrier quality indication (CQI) report.

40. Apparatus according to any of claims 33 to 39 wherein said communication resources in which to transmit said control information are arranged in said set in order of decreasing quality based on said measures of communication quality.

41. A communication device for communicating with a plurality of further communication devices in a cellular communication system, said communication device comprising: means for communicating, in at least one communication cell having an associated ce5 ll identity and operated by communication apparatus of said communication system, using a plurality of subframes, wherein each subframe comprises a plurality of communication resources and has an associated subframe number; means for identifying a set comprising a number of said communication resources in 10 which to search for control information transmitted by said communication apparatus wherein the presence of communication resources in said set is based on at least one of said cell identity and said subframe number; and means for searching for control information in said set of communication resources.

42. Communication apparatus for communicating with a plurality of mobile communication 15 devices in a cellular communication system, said communication apparatus comprising: means for operating at least one communication cell having a corresponding cell identity; means for communicating using a plurality of subframes with at least one mobile communication device within said at least one cell, wherein each subframe comprises a plurality of communication resources and has an associated subframe number; 20 means for identifying a set comprising a number of said communication resources for use in potential transmission of control information for the at least one mobile communication device wherein the presence of communication resources in said set is based on at least one of said cell identity and said subframe number; and means for transmitting control information for said at least one mobile communication 25 device in at least a subset of said set of communication resources.

43. Apparatus according to claim 42 wherein said identifying means is operable to identify communication resources for inclusion in said set from a subset of said communications resources that are contiguous in frequency, wherein said subset is selected based on said at least one of said cell identity and said subframe number.

44. Apparatus according to claim 42 wherein said identifying means is operable to identify communication resources for inclusion in said set from a subset of said communications resources that are distributed in frequency, wherein said subset is selected based on said at least one of said cell identity and said subframe number.

45. A communication system comprising at least one communication device according to any of claims 1 to 15 or claims 27 to 33 or claim 41 and communication apparatus according to any of claims 16 to 26 or claims 34 to 40 or claims 42 to 44.

46. A method performed by a communication device for communicating with a plurality of further communication devices in a cellular communication system, the method comprising5 : communicating, in at least one communication cell operated by communication apparatus of said communication system, using a plurality of subframes, wherein each subframe comprises a plurality of communication resources; obtaining a respective measure of communication quality associated with each of said 10 communication resources and for providing information identifying said measures of communication quality to said communication apparatus; identifying a set comprising a number of said communication resources in which to search for control information transmitted by said communication apparatus wherein the presence of communication resources in said set is based on said measures of 15 communication quality; and searching for control information in said set of communication resources.

47. A method performed by communication apparatus for communicating with a plurality of mobile communication devices in a cellular communication system, the method comprising: 20 operating at least one communication cell; communicating using a plurality of subframes with at least one mobile communication device within said at least one cell, wherein each subframe comprises a plurality of communication resources; receiving, from said at least one mobile communication device, information identifying a 25 respective measure of communication quality associated with each of said communication resources; identifying a set comprising a number of said communication resources for use in potential transmission of control information for the at least one mobile communication device wherein the presence of communication resources in said set is based on said 30 measures of communication quality; and transmitting control information for said at least one mobile communication device in at least a subset of said set of communication resources.

48. A method performed by a communication device for communicating with a plurality of further communication devices in a cellular communication system, the method comprising: communicating, in at least one communication cell operated by communication apparatus of said communication system, using a plurality of subframes, wherein each subframe comprises a plurality of communication resources; identifying, based on information transmitted to said communication apparatus, 5 tus, a first set comprising a number of said communication resources in which to search for control information transmitted by said communication apparatus; identifying, based on a predetermined criteria, a second set comprising a number of said communication resources in which to search for control information transmitted by said 10 communication apparatus in the event that control information for said communication device is not found in said first set of communication resources; and searching for control information in said first set of communication resources and, if control information for said communication device is not found in said first set of communication resources, for searching for control information in said second set of 15 communication resources.

49. A method performed by communication apparatus for communicating with a plurality of mobile communication devices in a cellular communication system, the method comprising: operating at least one communication cell; 20 communicating using a plurality of subframes with at least one mobile communication device within said at least one cell, wherein each subframe comprises a plurality of communication resources; identifying a first set comprising a number of said communication resources for use in potential transmission of control information for the at least one mobile communication 25 device based on information received from said mobile communication device, in the event that said information from said mobile communication device has been successfully received and interpreted by said communication apparatus; identifying a second set comprising a number of said communication resources for use in potential transmission of control information for the at least one mobile communication 30 device based on a predetermined criteria, in the event that said information from said mobile communication device has not been successfully received and interpreted by said communication apparatus; and transmitting control information for said at least one mobile communication device: in at least a subset of said first set of communication resources, in the event that said information from said mobile communication device has been successfully received and interpreted by said communication apparatus; and in at least a subset of said second set of communication resources, if said information from said mobile communication device has not been successfully received and interpreted by said communication apparatus.

50. A method performed by a communication device for communicating with a plurality 5 of further communication devices in a cellular communication system, the method comprising: communicating, in at least one communication cell having an associated cell identity and operated by communication apparatus of said communication system, using a plurality of 10 subframes, wherein each subframe comprises a plurality of communication resources and has an associated subframe number; identifying a set comprising a number of said communication resources in which to search for control information transmitted by said communication apparatus wherein the presence of communication resources in said set is based on at least one of said cell 15 identity and said subframe number; and searching for control information in said set of communication resources.

51. A method performed by communication apparatus for communicating with a plurality of mobile communication devices in a cellular communication system, the method comprising: 20 operating at least one communication cell having a corresponding cell identity; communicating using a plurality of subframes with at least one mobile communication device within said at least one cell, wherein each subframe comprises a plurality of communication resources and has an associated subframe number; identifying a set comprising a number of said communication resources for use in 25 potential transmission of control information for the at least one mobile communication device wherein the presence of communication resources in said set is based on at least one of said cell identity and said subframe number; and transmitting control information for said at least one mobile communication device in at least a subset of said set of communication resources.

52. A computer implementable instructions product comprising computer implementable instructions for causing a programmable computer device to perform the method of claim 46 or 51.

The present invention relates to mobile communications devices and networks,
particularly but not exclusively those operating according to the 3rd Generation Partnership
Project (3GPP) standards or equivalents or derivatives thereof. The invention has particular
10 although not exclusive relevance to the Long Term Evolution (LTE) of UTRAN (called Evolved
Universal Terrestrial Radio Access Network (E-UTRAN)).
Background Art:
In a mobile (cellular) communications network, mobile devices (also known as User
15 Equipment (UE) or mobile terminals, such as mobile telephones) communicate with remote
servers or with other mobile devices via base stations. In their communication with each other,
mobile devices and base stations use licensed radio frequencies, which are typically divided into
frequency bands and/or time blocks. Depending on various criteria (such as the amount of data
to be transmitted, radio technologies supported by the mobile device, expected quality of service,
20 subscription settings, etc.), each base station is responsible for controlling the transmission
timings, frequencies, transmission powers, modulations, etc. employed by the mobile devices
attached to the base station. The scheduling decision can be modified every transmission time
interval, e.g. as frequently as 1ms. In order to minimise disruption to the service and to
maximise utilisation of the available bandwidth, the base stations continuously adjust their own
25 transmission power and also that of the mobile devices. Base stations also assign frequency
bands and/or time slots to mobile devices, and also select and enforce the appropriate
transmission technology to be used between the base stations and the attached mobile devices.
By doing so, base stations also reduce or eliminate any harmful interference caused by mobile
devices to each other or to the base stations.
30 In order to be able to communicate via the base stations, mobile devices need to monitor
the control channels operated by the base stations. One of these control channels, the so-called
Physical Downlink Control Channel (PDCCH) carries the scheduling assignments and other
control information. The PDCCH serves a variety of purposes. Primarily, it is used to convey
the scheduling decisions to individual mobile devices, i.e. scheduling assignments for uplink and
3
downlink communication.
The information carried on the PDCCH is referred to as downlink control information
(DCI). The format of the DCI can vary depending on the purpose of the control message.
An additional Physical Control Format Indicator Channel (PCFICH) is transmitted by the
base station to indicate the size of the PDCCH (e.g. the number of orthogonal frequency-5 division
multiplexing (OFDM) symbols occupied by the PDCCH). Using OFDMA, the mobile devices
are allocated blocks comprising a specific number of subcarriers for a predetermined amount of
time. These are referred to as physical resource blocks (PRBs) in the LTE specifications. PRBs
thus have both a time and a frequency dimension. One PRB consists of 12 consecutive
10 subcarriers for one slot (0.5ms) in duration. The PRB is the smallest element of resource
allocation assigned by the base station. LTE radio frames are divided into 10 subframes, each
subframe being 1.0ms long. Each subframe is further divided into two slots, each of 0.5ms in
duration. Slots consist of either 6 or 7 ODFM symbols, depending on whether the normal or
extended cyclic prefix is employed.
15 Physical control channels, such as the PDCCH, are transmitted on an aggregation of one
or several consecutive Control Channel Elements (CCEs), where a control channel element
corresponds to nine Resource Element Groups (REGs). Each REG has four Resource Elements
(REs).
When a mobile device is first switched on or when it arrives in an area served by a base
20 station, it will look for the location of the control channels in the frequency band(s) used by that
base station. For example, the mobile device needs to check all possible combinations of
locations and formats of the PDCCH, and the DCI formats and act on those messages. Since the
decoding of all possible combinations would require the mobile device to make many PDCCH
decoding attempts, 3GPP defined an alternative approach for LTE, according to which, for each
25 mobile device served by the base station, a limited set of CCE locations are set where a PDCCH
may be placed. The set of CCE locations in which the mobile device may find its PDCCH can
be considered as a ‘search space’, for example, as described in section 9.1.1 of the 3GPP TR
36.213 standard.
In LTE the search space is a different size for each PDCCH format. Moreover, separate
30 dedicated and common search spaces are defined, where a dedicated search space is configured
for each UE individually, while all mobile devices are informed of the extent of the common
search space.
It has been decided, as part of the 3GPP standardisation process, that downlink operation
for system bandwidths beyond 20MHz will be based on the aggregation of a plurality of
4
component carriers at different frequencies. Such carrier aggregation (CA) can be used to
support operation in a system both with and without a contiguous spectrum (for example, a noncontiguous
system may comprise component carriers at 800MHz, 2GHz, and 3.5GHz). Whilst a
legacy mobile device may only be able to communicate using a single, backward compatible,
component carrier, a more advanced multi-carrier capable terminal would be 5 able to
simultaneously use the multiple component carriers.
Carrier aggregation can be particularly beneficial in a heterogeneous network (HetNet),
even when the system bandwidth is contiguous, and does not exceed 20 MHz because multiple
carriers enable interference management between different power class cells as well as open
10 access and closed subscriber group (CSG) cells. Long-term resource partitioning can be carried
out by exclusively dedicating carriers to a certain power class of cell (Macro/Pico/CSG).
3GPP have considered introducing a so-called Enhanced Physical Downlink Control
Channel (ePDCCH) which supports Carrier Aggregation (CA), including new carrier types (also
known as CA Enhancement), Coordinated Multiple Point Transmission/Reception (CoMP) and
15 Downlink Multiple In Multiple Out (DL MIMO) technologies. Advantageously, the ePDCCH
supports:
• increased control channel capacity;
• frequency-domain Inter-Cell Interference Control (ICIC);
• improved spatial reuse of control channel resource;
20 • beamforming and/or diversity;
• new carrier type(s);
• Multicast-Broadcast Single Frequency Network (MBSFN) subframes;
• legacy User Equipment (UE) coexisting on the same carrier;
• frequency-selective scheduling; and
25 • mitigation of inter-cell interference.
Disclosure of the Invention:
The introduction of a new control channel (ePDCCH), however, presents the challenge of
how and where to signal the control channel in associated radio frames and how to ensure that
30 user equipment can efficiently locate and interpret the control signalling.
The present invention seeks to provide systems, devices and methods which at least
partially address the above issues.
According to one aspect, the present invention provides a communication device for
communicating with a plurality of further communication devices in a cellular communication
5
system, the communication device comprising: means for communicating, in at least one
communication cell operated by communication apparatus of the communication system, using a
plurality of subframes, wherein each subframe comprises a plurality of communication
resources; means for obtaining a respective measure of communication quality associated with
each of the communication resources and for providing information identifying the measures 5 s of
communication quality to the communication apparatus; means for identifying a set comprising a
number of the communication resources in which to search for control information transmitted
by the communication apparatus wherein the presence of communication resources in the set is
based on the measures of communication quality; and means for searching for control
10 information in the set of communication resources.
The identifying means may identify communication resources for inclusion in the set
based on the measures of communication quality obtained by the obtaining means.
The communication device may receive, from the communication apparatus, information
identifying the communication resources of the set after providing, to the communication
15 apparatus, the information identifying a respective measure of communication quality associated
with each of the communication resources; and wherein the identifying means is operable to
identify the communication resources of the set based on the information identifying the
communication resources of the set received from the communication apparatus.
The communication device may signal information identifying the communication
20 resources of the set to the communication apparatus. The communication device may signal the
information identifying the communication resources of the set to the communication apparatus
as part of the information identifying the measures of communication quality.
In one possibility, the set of communication resources may comprise a first set; the
device may further comprise means for identifying, based on a predetermined criteria, a second
25 set comprising a number of the communication resources in which to search for control
information transmitted by the communication apparatus in the event that control information for
the communication device is not found in the first set of communication resources; and the
searching means may be operable to search for control information in the second set of
communication resources if control information for the communication device is not found in the
30 first set of communication resources.
The identifying means may identify communication resources for inclusion in the set
based on at least one of a cell identity associated with the at least one cell and a subframe
number associated with at least one of the plurality of subframes. The identifying means may
identify communication resources for inclusion in the set from a subset of the communications
6
resources that are contiguous in frequency which subset may be selected based on the at least
one of the cell identity and the subframe number. The identifying means may identify
communication resources for inclusion in the set from a subset of the communications resources
that are distributed in frequency which subset may be selected based on the at least one of the
cell identity and the subframe 5 me number.
The set comprising a number of the communication resources in which to search for
control information transmitted by the communication apparatus may comprise a search space.
The control information transmitted by the communication apparatus may be transmitted
in a control channel (e.g. a physical downlink control channel (PDCCH) or enhanced physical
10 downlink control channel (ePDCCH)) and the device may locate the control channel by
searching in the set of communication resources.
The control channel may comprise at least one control channel element (CCE). The
information identifying the measures of communication quality may comprise at least one carrier
quality indication (CQI) report. The communication resources in which to search for control
15 information may be arranged in the set in order of decreasing quality based on the measures of
communication quality.
The device may comprise a mobile telephone.
According to another aspect, the present invention provides communication apparatus for
communicating with a plurality of mobile communication devices in a cellular communication
20 system, the communication apparatus comprising: means for operating at least one
communication cell; means for communicating using a plurality of subframes with at least one
mobile communication device within the at least one cell, wherein each subframe comprises a
plurality of communication resources; means for receiving, from the at least one mobile
communication device, information identifying a respective measure of communication quality
25 associated with each of the communication resources; means for identifying a set comprising a
number of the communication resources for use in potential transmission of control information
for the at least one mobile communication device wherein the presence of communication
resources in the set is based on the measures of communication quality; and means for
transmitting control information for the at least one mobile communication device in at least a
30 subset of the set of communication resources.
The identifying means may identify communication resources for inclusion in the set
based on the information identifying a respective measure of communication quality associated
with each of the communication resources received from the communication device.
The communication device may receive, from the communication device and separately
7
to the information identifying a respective measure of communication quality associated with
each of the communication resources, information identifying the communication resources of
the set; and the identifying means may identify the communication resources of the set based on
the information identifying the communication resources of the set received from the
communication device5 .
The communication apparatus may signal information identifying the communication
resources of the set to the communication apparatus.
The set of communication resources may comprise a first set. The apparatus may further
comprise means for identifying a second set comprising a number of the communication
10 resources for use in potential transmission of control information for the at least one mobile
communication device based on a predetermined criteria in the event that the information
identifying a respective measure of communication quality associated with each of the
communication resources has not been successfully received and interpreted by the
communication apparatus, and the transmitting means may transmit control information for the
15 at least one mobile communication device in at least a subset of the second set of communication
resources if the information identifying a respective measure of communication quality
associated with each of the communication resources has not been successfully received and
interpreted by the communication apparatus.
The apparatus may comprise a base station.
20 According to another aspect, the present invention provides a communication device for
communicating with a plurality of further communication devices in a cellular communication
system, the communication device comprising: means for communicating, in at least one
communication cell operated by communication apparatus of the communication system, using a
plurality of subframes, wherein each subframe comprises a plurality of communication
25 resources; means for identifying, based on information transmitted to the communication
apparatus, a first set comprising a number of the communication resources in which to search for
control information transmitted by the communication apparatus; means for identifying, based
on a predetermined criteria, a second set comprising a number of the communication resources in
which to search for control information transmitted by the communication apparatus in the event
30 that control information for the communication device is not found in the first set of
communication resources; and means for searching for control information in the first set of
communication resources and, if control information for the communication device is not found
in the first set of communication resources, for searching for control information in the second
set of communication resources.
8
According to another aspect, the present invention provides communication apparatus for
communicating with a plurality of mobile communication devices in a cellular communication
system, the communication apparatus comprising: means for operating at least one
communication cell; means for communicating using a plurality of subframes with at least one
mobile communication device within the at least one cell, wherein each subframe comprises 5 omprises a
plurality of communication resources; means for identifying a first set comprising a number of
the communication resources for use in potential transmission of control information for the at
least one mobile communication device based on information received from the mobile
communication device, in the event that the information from the mobile communication device
10 has been successfully received and interpreted by the communication apparatus; means for
identifying a second set comprising a number of the communication resources for use in
potential transmission of control information for the at least one mobile communication device
based on a predetermined criteria, in the event that the information from the mobile
communication device has not been successfully received and interpreted by the communication
15 apparatus; and means for transmitting control information for the at least one mobile
communication device: in at least a subset of the first set of communication resources, in the
event that the information from the mobile communication device has been successfully received
and interpreted by the communication apparatus; and in at least a subset of the second set of
communication resources, if the information from the mobile communication device has not
20 been successfully received and interpreted by the communication apparatus.
According to another aspect, the present invention provides a communication device for
communicating with a plurality of further communication devices in a cellular communication
system, the communication device comprising: means for communicating, in at least one
communication cell having an associated cell identity and operated by communication apparatus
25 of the communication system, using a plurality of subframes, wherein each subframe comprises
a plurality of communication resources and has an associated subframe number; means for
identifying a set comprising a number of the communication resources in which to search for
control information transmitted by the communication apparatus wherein the presence of
communication resources in the set is based on at least one of the cell identity and the subframe
30 number; and means for searching for control information in the set of communication resources.
According to another aspect, the present invention provides communication apparatus for
communicating with a plurality of mobile communication devices in a cellular communication
system, the communication apparatus comprising: means for operating at least one
communication cell having a corresponding cell identity; means for communicating using a
9
plurality of subframes with at least one mobile communication device within the at least one cell,
wherein each subframe comprises a plurality of communication resources and has an associated
subframe number; means for identifying a set comprising a number of the communication
resources for use in potential transmission of control information for the at least one mobile
communication device wherein the presence of communication resources in the set is 5 s based on at
least one of the cell identity and the subframe number; and means for transmitting control
information for the at least one mobile communication device in at least a subset of the set of
communication resources.
Aspects of the invention extend to corresponding systems, methods, and computer
10 program products such as computer readable storage media having instructions stored thereon
which are operable to program a programmable processor to carry out a method as described in
the aspects and possibilities set out above or recited in the claims and/or to program a suitably
adapted computer to provide the apparatus recited in any of the claims.
Each feature disclosed in this specification (which term includes the claims) and/or
15 shown in the drawings may be incorporated in the invention independently (or in combination
with) any other disclosed and/or illustrated features. In particular but without limitation the
features of any of the claims dependent from a particular independent claim may be introduced
into that independent claim in any combination or individually.
20 Brief Description of Drawings:
Embodiments of the invention will now be described by way of example only with
reference to the attached figures in which:
Figure 1 schematically illustrates a telecommunication system;
Figure 2 illustrates a radio frame for the telecommunication system of Figure 1;
25 Figure 3 shows a simplified illustration of a resource grid used in the telecommunication
system of Figure 1;
Figure 4 shows an example of a CQI-based search space selection mechanism in the
telecommunication system of Figure 1;
Figure 5 shows an example of a fallback search space selection mechanism in the
30 telecommunication system of Figure 1;
Figure 6 shows a simplified block diagram of a base station for the telecommunication
system of Figure 1;
Figure 7 shows a simplified block diagram of a mobile communication device for the
telecommunication system of Figure 1;
10
Figure 8 is an exemplary flow diagram illustrating the steps performed by a mobile
communication device in the telecommunication system of Figure 1;
Figure 9 is an exemplary flow diagram illustrating the steps performed by a base station
in the telecommunication system of Figure 1;
Figure 10 is an exemplary flow diagram illustrating the steps of a fallback operati5 on
performed by a mobile communication device in the telecommunication system of Figure 1; and
Figure 11 is an exemplary flow diagram illustrating the steps of a fallback operation
performed by a base station in the telecommunication system of Figure 1.
10 Mode(s) for Carrying out the Invention:
Overview
Figure 1 schematically illustrates a mobile (cellular) telecommunication system 1 in
which users of mobile communication devices 3 can communicate with other users via base
stations 5. In the system illustrated in Figure 1, the base station 5 shown is an Evolved Universal
15 Terrestrial Radio Access Network (E-UTRAN) base station capable of operating in a multicarrier
environment. Such base stations are commonly referred to as eNBs (Evolved NodeBs).
In this embodiment, it will be assumed, for the sake of simplicity of explanation, that the mobile
device 3 is in communication with only one base station 5 at a time, although, in deployed
systems, a mobile device 3 might communicate with several base stations in parallel.
20 In Figure 1, the base station 5 operates in a plurality of cells using respective component
carriers (CCs) C1 and C2, of a component carrier set. In this embodiment, the base station 5
operates component carrier C1 as a primary component carrier on which a primary cell (PCell) is
provided, and component carrier C2 as a secondary component carrier on which a secondary cell
(SCell) is provided. The base station 5 operates carrier C1 for the PCell as a stand-alone carrier
25 having an ePDCCH, which can be used to schedule the resources of its own component carrier
C1. The ePDCCH of component carrier C1 can also be used to schedule the resources of
component carrier C2 (‘cross carrier scheduling’) to be used by a mobile device 3 when
communicating using the resources of component carrier C2. The ePDCCH is transmitted on an
aggregation of one or several enhanced control channel elements (eCCEs).
30 The mobile device 3 is configured to provide regular feedback to the base station 5 about
the perceived signal quality. The feedback is based on signal measurements performed during
the periods when the mobile device 3 is not scheduled to communicate with the base station 5.
Based on the result of measurements, the mobile device 3 generates and sends a report back to
the base station 5. This feedback mechanism is called channel quality indication (CQI) and, it is
11
employed to fine-tune the operation of the base station 5, including resource allocation,
scheduling and power of transmission. The mobile device 3 reports the channel state
information (CSI) such as CQI for each physical resource block (PRB) or group of PRBs in
frequency domain of the system bandwidth.
Advantageously, in this example, each mobile device 3 is provided with its 5 s own mobile
device specific search space comprising a mobile specific set of ePDCCHs in which to search for
control information. The search space is dynamically configured (and re-configured) based on
the CQI reports periodically transmitted to the base station. Specifically, the search space is
configured to comprise ePDCCHs transmitted using resources which have been reported to have
10 the best signal quality. Such a CQI-based search space can be advantageously determined by
both the mobile device 3 and the base station 5 using the CQI reports, without additional explicit
signalling, and thus both the mobile device 3 and the base station 5 will know, at any point in
time, the search space in which the mobile device will look for control information. The benefit
for the mobile device 3 and the base station 5 is that control information can be transmitted using
15 resources that have the highest quality signals (and thus the highest likelihood to transmit
without error) as indicated by the mobile device 3. Further, the search space can be minimised
thereby reducing the length of time taken and processing resources used for locating the control
signals.
Advantageously, the resources used to transmit the ePDCCHs in each cell are restricted
20 to alleviate ePDCCH interference between neighbouring or overlapping cells. Specifically,
different resources are used to transmit the ePDCCHs in different cells. This is achieved by
basing the dynamic search space configuration on the identity of the cell (e.g. Cell ID) such that
different resources are used by different cells for ePDCCH transmission. In a particularly
advantageous example, the cell specific search space design is based both on the identity of the
25 cell and the number of the sub-frame for the current communication such that the cell specific
resources available for transmission of the ePDCCH vary in time as well as in dependence on the
cell identity thereby ensuring that even though the range of resources in a specific subframe are
restricted, the entire range of resources will nevertheless be available for use over time.
The base station 5 is also beneficially configured to use a ‘fallback’ search space in the
30 event that the CQI report has not been received by the base station 5, or in case the CQI report
cannot be decoded due to an error. The mobile device 3 falls back to this fallback search space
in the event that it cannot find control signalling in the dynamically configured mobile device
specific search space. The use of a fallback search space therefore helps to ensure uninterrupted
transmission between the mobile device 3 and the base station 5.
12
In overview, therefore, the communication system advantageously allows exploitation of
the frequency selection gain available by transmitting ePDCCH in frequencies in which the
mobile device 3 has better channel conditions, thereby providing significant advantages over the
legacy PDCCH search space design.
Operat5 ion
Figure 2 illustrates a radio frame 140 for the telecommunication system 1 of Figure 1.
The resources of the radio frame 140 are divided into ten subframes 141, in each of which a first
part 142 of the sub-frame 141 may be used to carry a PDCCH (e.g. for legacy devices).
Historically, the remainder 143 of each sub-frame comprises resources used for transmitting a
10 Physical Downlink Shared Channel (PDSCH) and part of which, in the present embodiment,
may be used for transmitting an ePDCCH.
Figure 3 shows a simplified illustration of a typical resource grid of a PRB pair 151 used
in the telecommunication system 1 of Figure 1. The PRB pair comprises a number of resource
elements 157 defined in time (i.e. in columns corresponding to ‘symbols’ along the horizontal
15 axis of Figure 3) and frequency (i.e. in rows corresponding to each ‘sub-carrier’ along the
vertical axis of Figure 3). Each ePDCCH consists of an aggregation of control channel elements
(‘eCCEs’). Each eCCE occupies a predefined number of resource elements, e.g. the same
number as the legacy PDCCH CCEs. Each eCCE starts at a fixed location within the PRB pair
151. In this example, one PRB pair 151 supports three eCCEs 153-1, 153-2 and 153-3. If the
20 first resource elements of the three symbols are not used for a legacy PDCCH then the number of
potential eCCEs per PRB pair could be increased to four by using the first three symbols for a
fourth eCCE. The PDCCH 152 is carried in the first part of the subframe 151, as shown
generally in the left hand side area of the PRB pair 151 of Figure 3.
Some resource elements of the PRB pair 151 are also used to carry cell reference signals
25 (CRS) 154 and demodulation reference signals (DM RS) 155, both of which are transmitted by
the base station 5 periodically, at predetermined intervals and predetermined locations within a
PRB pair. These signals are used to provide reference signal levels and to inform the mobile
device 3 about the current operation of the base station 5. Resource elements can be transmitted
at varying energy levels but the CRS 154 resource elements are always transmitted at a known
30 (e.g. a default) energy level. The mobile device 3 can thus carry out signal quality measurements
over the CRS 154 resource elements and, based on these measurements, can indicate to the base
station 5 the perceived signal quality of a given frequency band (of a given cell) operated by the
base station 5.
Starting from the 4th symbol of the PRB pair, and extending to the last symbol (as seen in
13
Figure 3), the remaining resource blocks of the resource block pair 151 are divided into the three
eCCE areas 153-1 to 153-3.
A search space for a particular mobile device consists of a collection of ePDCCHs in
which to search for control information for that mobile device 3. The mobile device 3 monitors
all the ePDCCHs in its search space in every subframe to detect control information such 5 h as
scheduling grants from the base station 5. Ideally, the size of the search space should be as small
as possible to minimise the processing burden on the mobile device 3. However, smaller search
spaces also place greater restrictions on the base station’s scheduling algorithm.
The number of eCCEs making up one ePDCCH is called the aggregation level, and the
10 mobile device 3 search space contains ePDCCHs with a mixture of aggregation levels. Table 1
shows the typical size of the mobile device 3 search space, which is based on the size of the
legacy PDCCH search space. However the actual size of the ePDCCH search space is not yet
defined by 3GPP, and may even be configurable by higher layer signalling.
In order to place the ePDCCH for a mobile device 3 in the best location in frequency
15 domain when it is transmitted, dynamic configuration of each mobile device’s search space is
carried out based on the periodic CQI measurements performed by the given mobile device 3.
The following section describes a method for CQI-based search space selection in more detail.
In the following, ‘PRB’ will be used as shorthand for ‘PRB pair’.
Search space (L)
k S Number of
ePDCCH
candidates
(L) M
Number of
PRB-pairs n
(Localised
eCCE
allocation)
Number of
PRB-pairs n
(Distributed
eCCE
allocation)
Type Aggregation
level L
Size L N CCE,
[in eCCEs]
UEspecific
1 6 6 2 N/A
2 12 6 4 4
4 24 6 8 8
8 32 4 11 11
20 Table 1: ePDCCH candidates monitored by a mobile device (N=3)
CQI-based search space selection
In this example, eCCE N is the total number of eCCEs in the system bandwidth, and
eCCE 0  i  N is an index which uniquely identifies each eCCE. It is assumed that the eCCEs are
numbered in non-decreasing frequency order; specifically if 2 1 25 i  i then the PRB number of the
PRB containing eCCE number i2 is not less than the PRB number of the PRB containing eCCE
number 1 i .
For aggregation level L, the mth ePDCCH candidate consists of the contiguous set of L
14
eCCEs which satisfy the condition l L m i    , where L l   0 and 




 
L
N
m eCCE 0 .
The above defines a set of ePDCCH candidates for each aggregation level. The aim of
the CQI-based search space selection is to construct a search space for each mobile device 3
consisting of ePDCCHs taken from these sets, such that the ePDCCHs with the best channel
5 quality are selected.
Each mobile device 3 reports a CQI for each CQI reporting sub-band (referred to simply
as sub-bands in the following), where a CQI reporting sub-band is a block of contiguous PRBs.
The size and location of the sub-bands depends on the system bandwidth as specified in the
3GPP TR 36.213 standard.
10 Figure 4 shows an example of a CQI-based search space selection mechanism in the
telecommunication system 1 of Figure 1. For each mobile device 3 and at each aggregation
level, this procedure is performed by both the respective mobile device 3 and the base station 5
for determining the search space without explicit signalling.
Initially, in a first stage, the sub-band (or sub-bands) with the best CQI for the given
15 mobile device 3 is identified. This can be achieved, for example, by sorting the sub-bands
according to their CQI parameter, once the results of the CQI measurements are available at the
mobile device 3 or the base station 5, respectively.
In a second stage, all the ePDCCH candidates are found for the aggregation level L which
belongs to the sub-band or sub-bands identified in the first stage. An ePDCCH candidate m is
20 said to belong to a sub-band if more than half of the eCCEs in the ePDCCH candidate lie inside
the sub-band, or exactly half of the eCCEs of the ePDCCH candidate lie inside the sub-band
including the last eCCE (i.e. eCCE number i mL (L 1) ).
Then, in the third stage, the list of ePDCCH candidates found in the second stage is
sorted in ascending order of ePDCCH number m. Then, where K is the number of ePDCCH
25 candidates on the list, the first UE_ID mod K entries on the list are taken and moved to the end
(where the integer UE_ID may be any UE-specific identifier which is known to both the mobile
device 3 and base station 5).
In the fourth stage, the ePDCCH candidates are read from the sorted list generated in
stage three and are added to search space for that mobile device. This is repeated until either the
30 search space attains the required size or the list is exhausted. If the list is exhausted and the
search space has not reached the required size then the sub-band (or sub-bands) with the next
best CQI is found, and the procedure repeated from the second stage.
The first to fourth stages described above beneficially ensure a dynamic configuration of
15
the mobile device specific search space based on the CQI reports from the given mobile device
3. Advantageously, each mobile device specific search space comprises the best (or close to the
best) ePDCCHs from all ePDCCH candidates within the cell. The base station 5 allocates the
ePDCCH in decreasing order of channel quality based on the reported CQI. By employing the
same technique, the mobile device 3 searches for the ePDCCH in decreasing order of channe5 l
quality based on its CQI, therefore, both the base station 5 and the mobile device 3 are able to
identify the search space for a specific mobile device without the need for additional signalling
between them. Accordingly, the base station is able to identify appropriate resources of the
mobile device specific search space for transmitting an ePDCCH for the mobile device and the
10 mobile device is able to search efficiently for control information, such as scheduling
assignments or the like, within the search space. This technique also allows for dynamic
configuration (e.g. by higher layer signalling) of the size of the search space.
Inter-cell interference co-ordination
In order to reduce ePDCCH interference between cells operated by the base station 5 or
15 by neighbouring base stations, it is possible to restrict which PRBs are to be used to transmit
ePDCCH in each cell. Advantageously, base stations 5 are configured to avoid using the same
PRBs in neighbouring or overlapping cells.
Specifically, in this example, the eCCE numbering described above takes into account
only the PRBs that are available for ePDCCH transmission in the given cell. The other PRBs are
20 skipped (i.e. they do not contain any eCCEs). The rest of the CQI-based search space selection
procedure is performed as described in the previous section.
To control which PRBs may be used by each cell, each cell is given an assignment
identifier (‘Assignment ID’) which identifies a set of PRBs to use for search space definition.
One way to do this is to determine the Assignment ID from the cell ID, as follows:
25 AssignmentIDCell ID mod P where P is the number of PRB sets.
In a variation on this, the Assignment ID in a particular cell may be varied over time, for
example by using the current sub-frame number, as follows:
AssignmentIDCell IDSubframe_ Numbermod P
In this embodiment, two options are provided for the definition of the PRB sets selected
30 by the Assignment ID as follows:
• Type 0: Localised transmission, in which the PRB-pairs used in one cell are
localised (i.e. contiguous) in the frequency domain in the system bandwidth;
• Type 1: Distributed transmission, in which the PRB-pairs used in one cell are
distributed in frequency domain in the system bandwidth.
16
Table 2 illustrates an example of a cell specific search space design based on system
bandwidth of 50 PRBs and P=3.
Assignment ID PRB Number for
Localised Transmission
(Type 0)
PRB Number for
Distributed Transmission (Type
1)
0 0 to 15 0, 3, 6, 9, 12, 15, 18, 21, 24, 27,
30, 33, 36, 39, 42, 45
1 16 to 31 1, 4, 7, 10, 13, 16, 19, 22, 25, 28,
31, 34, 37, 40, 43, 46
2 32 to 47 2, 5, 8, 11, 14, 17, 20, 23, 26, 29,
32, 35, 38, 41, 44, 47
Table 2: Cell specific search space configured in a subframe in FDD system
5
Accordingly, a cell specific search space design based on the Cell ID and subframe
number can be used to achieve interference co-ordination between neighbouring cells. In this
example, a fraction of the bandwidth designated for ePDCCH allocation can be re-configured via
higher layer signalling, based on e.g. the number of co-ordinating cells.
10 Fallback operation
In the event when the base station 5 fails to decode the CQI report(s) transmitted by a
mobile device 3 correctly, the base station 5 will not be able to derive the CQI-based search
space assumed by the mobile device 3 (which of course will have its own CQI data). Therefore,
the base station 5 will not be able to send scheduling grants to the given mobile device 3.
15 Advantageously, therefore, to recover from this situation, a ‘fallback’ search space is provided,
which is monitored by the mobile device 3 in addition to its CQI-based search space. Such a
fallback search space has the added benefit that it can also be used by mobile devices 3 that do
not generate sub-band CQI reports.
Figure 5 shows an example of a fallback search space selection mechanism in the
20 telecommunication system 1 of Figure 1.
The fallback search space uses eCCEs which are also used for the CQI-based search
space. In any given sub-frame, any eCCE in the fallback search space that is not used to transmit
a fallback ePDCCH may be used to transmit a CQI-based ePDCCH (and vice-versa).
If L is the aggregation level used for the fallback search space, the size of the search
25 space may be any multiple of L eCCEs (i.e. a whole number of ePDCCHs), with the exact size
chosen on the basis of system bandwidth and expected traffic.
In order to ensure reliable transmission, each fallback ePDCCH is preferably transmitted
with frequency diversity, i.e. the eCCEs comprising the ePDCCH should be widely separated in
17
frequency. Furthermore, when a fallback ePDCCH is transmitted, any CQI-based ePDCCH
which is mapped to any of the same eCCEs as the transmitted fallback ePDCCH cannot also be
transmitted in the same sub-frame. Preferably, such restrictions on the scheduler algorithm
should be minimised. In particular, each fallback ePDCCH should overlap with as few CQIbased
ePDCCHs as possible5 .
A method for constructing the fallback search space is described as follows.
All eCCEs in the system bandwidth are divided into contiguous blocks of size B eCCEs.
A sub-set of these blocks is then selected such that it contains the fallback search space. If the
total number of eCCEs required for the fallback search space is FB N (which is a multiple of L,
the ePDCCH size) and the total number of eCCEs available in the cell is eCCE 10 N , then the blocks
used to carry the fallback space are selected, in this example, by using the blocks which start at
the eCCE numbers given by the following:




 





























  
B
N
k
N
B
N
B
i B k FB
FB
eCCE
0
where  denotes the ‘floor’ function and  denotes the ‘ceiling’ function. Advantageously,
15 this has the effect of distributing the fallback space blocks as evenly as possible throughout the
total available eCCEs.
For example, if B=4,  48 eCCE N and  32 FB N then the blocks beginning at eCCE
numbers 0, 4, 12, 16, 24, 28, 36 and 40 are used. This case is illustrated in Figure 5, which also
assumes interference co-ordination with P=3 cells.
20 Although any value of B may be used, blocking performance will generally be improved
if B is chosen to match one of the aggregation levels used for the CQI-based search space.
After having selected the eCCEs which comprise the fallback search space, the individual
ePDCCHs are mapped to these eCCEs. If j is the eCCE index into the list of FB N eCCEs
selected by the above procedure, the jth eCCE in the fallback search space can be assigned to the
25 mth ePDCCH, given by
FB
FB j N
L
N
S
j
m   








 mod 0
where S is a sub-multiple of L (for example, if L=8 then S may be 1, 2, 4 or 8). Effectively, the
value of S controls the degree of frequency distribution of the eCCEs belonging to each
ePDCCH. The case S=1 corresponds to fully distributed transmission and S=L corresponds to
18
fully localised transmission. Intermediate values can be regarded as ‘block distributed’.
S=1 provides the most advantageous frequency diversity, but only at the expense of
relatively poor blocking between the fallback search space and CQI-based search space. An
intermediate value of S represents a good trade-off between these two requirements. Some
further examples are also illustrated in Figure 55 .
Mobile communication device
Figure 6 is a block diagram illustrating the main components of the mobile
communication device 3 shown in Figure 1. The mobile communication device 3 comprises a
mobile (or ‘cell’ telephone) capable of operating in a multi-carrier environment. The mobile
10 communication device 3 comprises a transceiver circuit 601 which is operable to transmit signals
to, and to receive signals from, the base station 5 via at least one antenna 603. The mobile
device 3 also includes a user interface 605 which allows a user to interact with the mobile device
3.
The operation of the transceiver circuit 601 is controlled by a controller 607 in
15 accordance with software stored in memory 609. The software includes, among other things, an
operating system 611, a communication control module 613, a measurement module 615, a
control channel search space module 617, and a fallback module 619.
The communication control module 613 is operable for managing communication with
the base station 5 on the associated component carriers C1, C2. The measurement module 615
20 receives measurement configuration information from the base station 5 for the purposes of
configuring the mobile communication device 3 to take measurements of the CSI.
The measurement module 615 manages performance of the measurements of CSI,
generates associated measurement reports and transmits the generated reports to the base station
5. The measurement module 615 also determines reference signal received power (RSRP) for
25 the cells. In this embodiment, the measurement module 615 is operable to carry out signal
quality measurements during the periods when the mobile device 3 is not scheduled to
communicate with the base station 5. Based on the result of measurements, the measurement
module 615 generates and sends a CSI report (including the CQI) back to the base station 5.
The search space selection module 617 is operable to use the measurements of CSI, such
30 as the CQI to determine the eCCE resources carrying the ePDCCH for use by the mobile device
3. This determination can be carried out for each subframe 141 transmitted between the base
station 5 and the mobile device 3. Alternatively, the determination can be carried out whenever
the CQI values are updated.
The fallback module 619 is operable to select and monitor a fallback search space, in
19
case the measurements of CSI have not been received or correctly decoded by the base station 5.
The fallback module 619 is also operable to select the search space in case the sub-band CQI
reports have not been generated by the mobile device 3 (e.g. in the absence of instructions from
the base station 5 or due to technical limitations of the mobile device 3).
Base 5 ase Station
Figure 7 is a block diagram illustrating the main components of the base station 5 shown
in Figure 1. The base station 5 comprises an E-UTRAN multi-carrier capable base station
comprising a transceiver circuit 701 which is operable to transmit signals to, and to receive
signals from, the mobile device 3 via one or more antennas 703. The base station 5 is also
10 operable to transmit signals to and to receive signals from a core network 7 via a network
interface 705. The operation of the transceiver circuit 701 is controlled by a controller 707 in
accordance with software stored in memory 709.
The software includes, among other things, an operating system 711, a communication
control module 713, a measurement module 715, a control channel search space module 717, and
15 a fallback module 719.
The communication control module 713 is operable to control communication with the
mobile device 3 on the component carriers C1, C2, of its component carrier set. The
communication control module 713 is also responsible for scheduling the resources of the
primary and extension component carrier C1, C2 to be used by the mobile devices 3 served by
20 this base station 5.
The measurement module 715 is operable to communicate with the mobile device 3 for
configuring the mobile device 3 to initiate measurement of the CSI. The measurement module
715 is also operable to receive and analyse measurement reports from the mobile devices 3 in
order to assess the channel state for the purposes of search space selection. The measurement
25 module 715 also obtains, from the transceiver circuit 701, the current reference signal power
transmitted in the cells served by the base station 5.
The search space selection module 717 is operable to use the measurements of CSI, such
as the CQI to determine the eCCE resources for carrying the ePDCCH for the respective mobile
device(s) 3. This determination can be carried out for each subframe 141 transmitted between
30 the base station 5 and the mobile device 3. Alternatively, the determination can be carried out
whenever the CQI values are updated.
The fallback module 719 is operable to select a fallback search space, in case the
measurements of CSI have not been received or correctly decoded by the base station 5. The
fallback module 719 is also operable to locate the search space in case the sub-band CQI reports
20
have not been generated by the mobile device 3 (e.g. in the absence of instructions from the base
station 5 or due to technical limitations of the mobile device 3).
In the above description, the mobile device 3 and the base station 5 are described for ease
of understanding as having a number of discrete modules. Whilst these modules may be
provided in this way for certain applications, for example where an existing system has bee5 n
modified to implement the invention, in other applications, for example in systems designed with
the inventive features in mind from the outset, these modules may be built into the overall
operating system or code and so these modules may not be discernible as discrete entities.
Figure 8 is an exemplary flow diagram illustrating the steps performed by a mobile
10 communication device 3 in the telecommunication system 1 of Figure 1.
The procedure starts in step s801, in which the mobile device 3 obtains measures of
communication quality for the communication resources operated by the base station 5. The
measures can be, for example, the CQI values obtained by channel quality measurements (not
shown) performed over the reference signals transmitted by the base station 5. The
15 communication resources can be, for example, the cells or the sub-bands of the base station 5.
Next, in step s803, the mobile device 3 identifies the search space based on the obtained
measure, such as by selecting the sub-bands having the highest CQI values. In step s805, the
mobile device 3 is searching for control information, such as a mobile device specific control
channel, in the identified search space. As shown in step s807, once control information is
20 found, e.g. when it has been transmitted by the base station 5 to the mobile device 3 within the
identified search space, the mobile device 3 applies the control information. For example, the
mobile device 3 can send and receive user data according to the instructions carried in the
control channel (e.g. ePDCCH) within the search space.
Advantageously, the procedure is repeated from step s801 whenever the communication
25 quality for the communication resources changes and the mobile device 3 obtains new measures
of the changed communication quality (e.g. updated CQI).
Figure 9 is an exemplary flow diagram illustrating the steps performed by a base station 5
in the telecommunication system 1 of Figure 1.
The procedure starts in step s901, in which the base station 5 obtains measures of
30 communication quality for the communication resources operated by the given base station 5.
The measures can be, for example, the CQI values obtained through channel quality
measurements (not shown) performed by the mobile device 3 over the reference signals
transmitted by this base station 5. The communication resources can be, for example, the cells or
the sub-bands of the base station 5.
21
Next, in step s903, the base station 5 identifies the search space based on the obtained
measure, such as by selecting the sub-bands having the highest CQI values. Finally, in step
s905, the base station 5 transmits control information for the given mobile device 3, such as a
mobile device specific control channel e.g. ePDCCH), within the identified search space.
Advantageously, the procedure is repeated from step s901 whenever the communicati5 on
quality for the communication resources changes and the base station 5 obtains, from the mobile
device 3, new measures of the changed communication quality (e.g. updated CQI).
Figure 10 is an exemplary flow diagram illustrating the steps of a fallback operation
performed by a mobile communication device 3 in the telecommunication system 1 of Figure 1.
10 The procedure starts in step s1001, in which the mobile device 3 obtains measures of
communication quality (e.g. CQI) for the communication resources (e.g. sub-bands) operated by
the base station 5.
Next, in step s1002, the mobile device 3 defines a first set of communication resources
(e.g. a primary search space) specific to this mobile device 3. Advantageously, this first set is
15 defined based on the obtained measures, for example, by selecting the highest quality sub-bands
based on their CQI values. In step s1003, the mobile device 3 also defines a second set of
communication resources, for example, by selecting sub-bands that have been reserved for this
mobile device 3, such as fallback sub-bands.
In step s1004, the mobile device 3 searches for control information in the first set of
20 communication resources. In step s1005, the mobile device 3 determines whether of not control
information dedicated to this mobile device 3 can be found in the first set of communication
resources. The determination can be based on, for example, the control information transmitted
by the base station 5 and checking whether or not the transmitted control information has been
scrambled with an identification (e.g. UE-ID) specific to this mobile device 3.
25 If the result of the determination at step s1005 indicates that there is control information
for this mobile device 3 in the first set of communication resources, the mobile device 3 proceeds
to step s1007. If the result of the determination at step s1005 indicates that there is no control
information for this mobile device 3 in the first set of communication resources, the mobile
device 3 proceeds to step s1006, in which it is searching for control information in the second set
30 of communication resources.
Finally, in step s1007, the mobile device 3 applies the control information (if any) found
in either the first or the second set of communication resources.
Advantageously, the procedure is repeated from step s1001 whenever the communication
quality for the communication resources changes and the mobile device 3 obtains new measures
22
of the changed communication quality (e.g. updated CQI).
Figure 11 is an exemplary flow diagram illustrating the steps of a fallback operation
performed by a base station 5 in the telecommunication system 1 of Figure 1.
The procedure starts in step s1101, in which the base station awaits measures of
communication quality (e.g. CQI) from the mobile device 3, the measures concerning 5 the
communication resources (e.g. sub-bands) operated by the base station 5.
In step s1101, base station 5 checks whether or not the measures of communication
quality have been successfully received and interpreted. If yes, the base station 5 proceeds to
step s1103, in which it defines a first set of communication resources for the given mobile device
10 3. Next, in step s1005, the base station 5 transmits, within the first set of communication
resources, control information (e.g. ePDCCH) specific for the mobile device 3.
However, if in step s1101, the base station 5 determines that the measures of
communication quality have not been successfully received and interpreted, it proceeds to step
s1107. In step s1107, the base station 5 defines a second set of communication resources, for
15 example, by selecting sub-bands that have been reserved for the given mobile device 3, such as
fallback sub-bands. In this case, as shown in step s1109, the base station 5 transmits control
information to the mobile device 3 in the second set of communication resources.
Advantageously, the procedure is repeated from step s1101 whenever the communication
quality for the communication resources changes and the base station 5, from the mobile device
20 3, obtains new measures of the changed communication quality (e.g. updated CQI).
Modifications and alternatives
Detailed embodiments have been described above. As those skilled in the art will
appreciate, a number of modifications and alternatives can be made to the above embodiments
and variations whilst still benefiting from the inventions embodied therein.
25 It will be appreciated that although the communication system 1 is described in terms of
base stations 5 operating as E-UTRAN base stations, the same principles may be applied to base
stations operating as macro or pico base stations, femto base stations, relay nodes providing
elements of base station functionality, home base stations (HeNB), or other such communication
nodes.
30 Although in Figure 3, three eCCE areas are shown, it will be appreciated that there might
be a different number of eCCEs defined in one subframe, and that the number of eCCEs might
vary from subframe to subframe.
Whilst the example procedure shown on Figure 4 is described from a purely algorithmic
viewpoint, it will be appreciated that more efficient implementations may exist which attain the
23
same outcome. For example, in practice it is not necessary to store and manipulate the entire list
of K ePDCCH candidates as implied by the description in the third stage, since in general not all
of them will be included in the search space.
In the second stage, the criterion for deciding whether or not an ePDCCH candidate
belongs to a sub-band could be simplified to checking if the last (or alternatively first) eCCE 5 E of
the ePDCCH candidate lies inside the sub-band.
The purpose of the third stage is to try to prevent the mobile devices 3 that share the same
best CQI sub-bands from selecting the same ePDCCH candidates. This is achieved by reordering
the ePDCCH candidates according to a circular shift based on the UE_ID, but other re10
ordering methods could also be applied (for example a pseudo-random reordering based on the
UE_ID).
Whilst it is stated that the search space selection procedure is repeated for each
aggregation level, alternatively, the procedure may be applied for the highest aggregation level
only. Accordingly, once the ePDCCH candidates for the highest aggregation level are obtained,
15 they can be sub-divided to obtain the ePDCCH candidates for lower aggregation levels (retaining
only the number of ePDCCH candidates required at each level). This would advantageously
simplify the procedure, and also ensure that the same set of eCCEs is re-used for each
aggregation level, thereby reducing processing complexity in the mobile device 3.
Since the ePDCCHs in the search space are sorted in decreasing order of channel quality,
20 the base station 5 attempts to use first ePDCCHs in the search space whenever possible when
transmitting to the mobile device 3. Likewise, the mobile device 3 should attempt decoding in
the same order, in order to reduce the average decoding delay.
According to the procedure illustrated in Figure 4, the search space for a given mobile
device 3 may change when a new CQI report is generated. However since there is a finite delay
25 of a few sub-frames between measuring the CQI at the mobile device 3 and the CQI report being
received and processed at the base station 5, switching between the old search space and new
search space is synchronised such that both the base station 5 and the mobile device 3 perform
the switching in the same subframe 141. This can be done, for example, by both the base station
5 and the mobile device 3 applying the change at a scheduling round which is a fixed number of
30 subframes after the CQI report is transmitted to the base station 5. This delay can be configured
by separate (e.g. higher layer) signalling, or can be defined as a fixed value (e.g. specified in the
relevant standards).
In the CQI-based search space selection procedure described above, the search space is
calculated separately by the base station 5 and by the mobile device 3 based on the CQI report.
24
According to an alternative approach, a set of search spaces can be pre-defined, from which the
mobile device 3 can select its preferred search space and report the selected search space to the
base station 5. In this case, the mobile device 3 selects its preferred search space using e.g. the
results of its signal quality measurements or the like. The advantage of this method is that it
allows the pre-defined search spaces to be defined in such a way that blocking between 5 n mobile
devices 3 in different search spaces is less likely, whilst still providing for frequency selection
gain by allowing the mobile device 3 to choose the search space that is most favourable for its
current channel state.
This method would require new or modified uplink signalling. For example, if a set of
10 16 search spaces were defined then the choice could be indicated by transmission of a 4-bit value
from the mobile device 3 to the base station 5. One option would be to add this signalling to the
existing CQI report sent from the mobile device 3 to the base station 5.
According to a variation of this approach, instead of the mobile device explicitly
indicating its selection, a search space can be selected by both the mobile device 3 and the base
15 station 5 by applying the same algorithm for the selection of the best pre-defined search space
based on the CQI information.
In the description of Figure 10, step s1003 (defining a second set) has been described as
being performed by the mobile device 3 after defining the first set of communication resources.
It will be appreciated, that step s1003 can be performed before step s1002. Alternatively, step
20 s1003 can be performed only after step s1005.
In the above embodiments, the component carriers C1 and C2 are transmitted by the
same base station. However, it will be appreciated that component carriers might be transmitted
by different base stations. In this case, although both base stations might receive respective CQI
indications from the mobile device regarding their cells, only one of the base stations will be in
25 charge of the scheduling decisions and the search space allocation. The two (or more) base
stations can be arranged to exchange CQI reports between them, thus the base station allocating
the ePDCCH search space can obtain the CQI report(s) either directly from the mobile device or
via another base station (or via any additional network entity) between them.
The proposed ePDCCH search space design does not affect the support for carrier
30 aggregation because the existing UE monitoring procedure and DCI formats can be reused. For
the cross carrier scheduling case where the base station 5 schedules secondary component carrier
on the primary cell, the CQI feedback of the primary cell is used since ePDCCH is transmitted in
the primary cell. Similarly, only the cell ID of the primary cell is needed for the allocation of
cell specific search space. For this case, the number of ePDCCH candidates (i.e. the size of the
25
search space) monitored by the mobile device 3 configured with a carrier indication field can be
based on existing formula CI
m  mM(L) n as described in the 3GPP TR 36.213 standard.
In the above embodiments, a mobile telephone based telecommunications system was
described. As those skilled in the art will appreciate, the signalling techniques described in the
5 present application can be employed in other communications system. Other communications
nodes or devices may include user devices such as, for example, personal digital assistants,
laptop computers, web browsers, etc. As those skilled in the art will appreciate, it is not essential
that the above described relay system be used for mobile communications devices. The system
can be used to extend the coverage of base stations in a network having one or more fixed
10 computing devices as well as or instead of the mobile communicating devices.
In the embodiments described above, the base stations 5 and mobile communication
devices 3 each include transceiver circuitry. Typically, this circuitry will be formed by dedicated
hardware circuits. However, in some embodiments, part of the transceiver circuitry may be
implemented as software run by the corresponding controller.
15 In the above embodiments, a number of software modules were described. As those
skilled in the art will appreciate, the software modules may be provided in compiled or uncompiled
form and may be supplied to the base station or the relay station as a signal over a
computer network, or on a recording medium. Further, the functionality performed by part or all
of this software may be performed using one or more dedicated hardware circuits.
20 Various other modifications will be apparent to those skilled in the art and will not be
described in further detail here.
The following is a detailed description of the way in which the present inventions may be
implemented in the currently proposed 3GPP standard. Whilst various features are described as
being essential or necessary, this may only be the case for the proposed 3GPP standard, for
25 example due to other requirements imposed by the standard. These statements should not,
therefore, be construed as limiting the present invention in any way.
______________________________________________________________
1. Introduction
From [1], Working Assumption from RAN1#66bis, based on considerations from CA
30 Enhancement new carrier type, CoMP and DL MIMO is as following:
 Introduce an enhanced physical downlink control channel that is:
- able to support increased control channel capacity
- able to support frequency-domain ICIC,
- able to achieve improved spatial reuse of control channel resource
26
- able to support beamforming and/or diversity
- able to operate on the new carrier type and in MBSFN subframes
- able to coexist on the same carrier as legacy UEs
Desirable characteristics include ability to be scheduled frequency-selectively, and
ability to mitigate inter-cell interference5 .
In this contribution, we discuss the search space design for e-PDCCH that supports
frequency scheduling gain and inter-cell interference co-ordination, as well as its ‘Fallback’
operation.
2. Discussion
10 2.1. Considerations of frequency scheduling gain
For the legacy PDCCH, the UE shall monitor a set of PDCCH candidates, attempting to
decode each of the PDCCHs in the set according to the monitored DCI formats. The set of
PDCCH candidates to monitor are defined in terms of search spaces, as described in section
9.1.1 of [2].
15 One option is to reuse the legacy PDCCH search space design for ePDCCH. However,
since PDCCH REGs are interleaved and span across the whole bandwidth, it would not be
possible in this case to exploit frequency selection gain available by transmitting ePDCCH in
frequencies in which the UE has better channel conditions.
One ePDCCH consists of an aggregation of elements called eCCEs. Figure 3 shows an
20 example of eCCE allocation within a PRB pair (The exact method of eCCE allocation is yet to
be decided by 3GPP). Each eCCE occupies 36 REs, same as the legacy PDCCH CCE. Each
eCCE starts at a fixed location within a PRB pair. In this example, one PRB pair supports N=3
eCCEs. If the legacy PDCCH does not exist in the subframe, the number of eCCEs per PRB pair
could be N=4.
25 Although the example given here contains legacy PDCCH for normal subframe, the
deployment scenario of e-PDCCH in this design is considered to be generic, able to provide
support for MBSFN subframe, Secondary Component Carrier and new carrier type.
A search space consists of a collection of ePDCCHs. The UE must monitor all the
ePDCCHs in its search space in every subframe to detect scheduling grants from the eNB. The
30 size of the search space should therefore be as small as possible to minimise the processing
burden on the UE, but smaller search spaces also place greater restrictions on the eNB
scheduling algorithm.
The number of eCCEs making up one ePDCCH is called the aggregation level, and the
UE search space contains ePDCCHs with a mixture of aggregation levels. Table 1 shows the
27
typical size of the UE search space, which is based on the size of the legacy PDCCH search
space. However the actual size of the ePDCCH search space is not yet defined by 3GPP, and
may even be configurable by higher layer signalling.
In order to place the ePDCCH for a UE in the best location in frequency domain when it
is transmitted, dynamic configuration of each UE’s search space is necessary based 5 d on the
periodic CQI measurements performed by the UE. A method for achieving this is described in
the following section.
Note that in the following, ‘PRB’ will be used as a shorthand for ‘PRB pair’.
Search space (L)
k S Number of
ePDCCH
candidates
(L) M
Number
of PRBpairs
n
(Localised
eCCE
allocation)
Number of
PRB-pairs
n
(Distributed
eCCE
allocation)
Type
Aggregation
level L
Size
L N CCE,
[in
eCCEs]
UEspecific
1 6 6 2 N/A
2 12 6 4 4
4 24 6 8 8
8 32 4 11 11
10 Table 1 ePDCCH candidates monitored by a UE (N=3)
2.2. CQI-Based Search Space Selection
Let eCCE N be the total number of eCCEs in the system bandwidth, and let eCCE 0  i  N
be an index which uniquely identifies each eCCE. We assume that the eCCEs are numbered in
non-decreasing frequency order; specifically if 2 1 15 i  i then the PRB number of the PRB
containing eCCE number 2 i is not less than the PRB number of the PRB containing eCCE
number 1 i .
For aggregation level L, the mth ePDCCH candidate consists of the contiguous set of L
eCCEs which satisfy the condition l L m i    , where L l   0 and 




 
L
N
m eCCE 0 .
20 The above defines a set of ePDCCH candidates for each aggregation level. The aim of
CQI-Based Search Space Selection is to construct a search space for each UE consisting of
ePDCCHs taken from these sets, such that the ePDCCHs with the best channel quality are
selected. This is achieved by the following method.
We assume that each UE reports a channel quality indication (CQI) for each CQI
25 Reporting Sub-band (referred to simply as sub-bands in the following), where a CQI Reporting
28
Sub-band is a block of contiguous PRBs. The size and location of the sub-bands depends on the
system bandwidth according to the 3GPP specification [Ref. 36.213].
For each UE and each aggregation level, the following procedure is performed. (This
procedure is performed by both the UE and eNB so that both can determine the search space
without explicit signalling5 ).
1. Find the sub-band (or sub-bands) with the best CQI for this UE.
2. Find all the ePDCCH candidates for the aggregation level L which belong to the
sub-band or sub-bands selected in step 1. An ePDCCH candidate m is said to
belong to a sub-band if more than half of the eCCEs in the ePDCCH candidate lie
10 inside the sub-band, or exactly half of the eCCEs of the ePDCCH candidate lie
inside the sub-band including the last eCCE (i.e. eCCE number i mL (L 1) ).
3. Sort the list of ePDCCH candidates selected in step 2 in ascending order of
ePDCCH number m. Let K be the number of ePDCCH candidates on the list.
Take the first UE_ID mod K entries on the list and place them at the end, where
15 the integer UE_ID may be any UE-specific identifier which is known to both the
UE and eNB.
4. Read ePDCCH candidates from the sorted list generated in step 3 and add them to
the UE’s search space. Continue until either the search space attains the required
size or the list is exhausted. If the list is exhausted and the search space has not
20 reached the required size then find the sub-band (or sub-bands) with the next best
CQI, and repeat from step 2.
An example of this procedure is shown in Figure 4.
Note that the procedure above is described from a purely algorithmic viewpoint and more
25 efficient implementations may exist which attain the same outcome. For example, in practice it
is not necessary to store and manipulate the entire list of K ePDCCH candidates as implied by
the description in step 3, since in general not all of them will be included in the search space.
In step 2, the criterion for deciding that an ePDCCH candidate belongs to a sub-band
could optionally by simplified to checking if the last (or alternatively first) eCCE of the
30 ePDCCH candidate lies inside the sub-band.
The purpose of step 3 is to try to prevent UEs that share the same best CQI sub-bands
from selecting the same ePDCCH candidates. This is achieved by re-ordering the ePDCCH
candidates according to a circular shift based on the UE_ID, but other re-ordering methods could
also be applied (for example a pseudo-random reordering based on the UE_ID).
29
Above it is stated that the search space selection procedure is repeated for each
aggregation level. Alternatively, the procedure may be applied for the highest aggregation level
only. Once the ePDCCH candidates for the highest aggregation level are obtained, they are then
sub-divided to obtain the ePDCCH candidates for lower aggregation levels (retaining only the
number of ePDCCH candidates required at each level). This simplifies the procedure slightly5 ,
and also ensures that the same set of eCCEs is re-used for each aggregation level, which may
reduce processing complexity in the UE.
Since the ePDCCHs in the search space are sorted in decreasing order of channel quality,
the eNB should attempt to use first ePDCCHs in the search space whenever possible when
10 transmitting to the UE. Likewise, the UE should attempt decoding in the same order, in order to
reduce the average decoding delay.
Note that according to the above procedure, the search space for a given UE may change
when a new CQI report is generated. However since there is a finite delay of a few sub-frames
between measuring the CQI at the UE and the CQI report being received and processed at the
15 eNB, care must be taken to synchronise the switching between the old search space and new
search space such that both eNB and UE perform the switch in the same sub-frame. This can be
done by both eNB and UE agreeing to apply the change a fixed number of sub-frames after the
CQI report is transmitted to the eNB. This delay could be configured by separate (higher layer)
signalling, or fixed as a constant in the specification.
20
Proposal 1: Consider dynamic configuration of UE specific search space based on the CQI
reports from the UE. Each UE specific search space consists of the best ePDCCHs from all
ePDCCH candidates within the cell. UE searches ePDCCH in decreasing order of channel
quality (CQI). The size of the search space can be higher layer re-configurable.
25 2.3. Inter-Cell Interference Co-ordination
In order to reduce ePDCCH interference between cells, we may choose to restrict which
PRBs may be used to transmit ePDCCH in each cell in order to avoid the same PRBs being used
in closely neighbouring cells.
In this case, the eCCE numbering described in the previous section is performed taking
30 into account only the PRBs that are available for ePDCCH transmission in the given cell. The
other PRBs are skipped (i.e. they do not contain any eCCEs). The remainder of the CQI-Based
search space selection procedure is then performed exactly as described in the previous section.
To control which PRBs may be used by each cell, each cell may be given an Assignment
ID which identifies a set of PRBs. One way to do this is to determine the Assignment ID from
30
the cell ID, as follows
AssignmentIDCell ID mod P
where P is the number of PRB sets.
Furthermore, the Assignment ID in a particular cell may be varied over time, for example
5 by using the current sub-frame number, as follows
AssignmentIDCell IDSubframe_ Numbermod P
Two options exist for the definition of the PRB sets selected by the Assignment ID, as
follows
• Type 0: Localised transmission, in which the PRB-pairs used in one cell are
10 localised (i.e. contiguous) in frequency domain in the system bandwidth.
• Type 1: Distributed transmission, in which the PRB-pairs used in one cell are
distributed in frequency domain in the system bandwidth.
Table 2 gives an example of cell specific search space design based on system bandwidth
of 50 PRBs and P=3.
15
Assignment ID PRB Number for Localised
Transmission (Type 0)
PRB Number for
Distributed Transmission
(Type 1)
0 0 to 15 0, 3, 6, 9, 12, 15, 18, 21, 24,
27, 30, 33, 36, 39, 42, 45
1 16 to 31 1, 4, 7, 10, 13, 16, 19, 22, 25,
28, 31, 34, 37, 40, 43, 46
2 32 to 47 2, 5, 8, 11, 14, 17, 20, 23, 26,
29, 32, 35, 38, 41, 44, 47
Table 2 Cell Specific Search Space configured in a subframe in FDD system
Proposal 2: Consider cell specific search space design based on the Cell ID and subframe
number to achieve interference co-ordination. Fraction of bandwidth designated for
20 ePDCCH allocation can be higher layer re-configurable based on the number of coordinating
cells.
2.4. Fallback Operation
The eNB may sometimes fail to decode the CQI Reports transmitted by the UE correctly.
In this case, the eNB will not know the CQI-Based search space being assumed by the UE, and
25 so will be unable to send scheduling grants to the UE. To recover from this situation, it is
necessary to introduce a ‘fallback’ search space, which every UE must monitor continually in
addition to its CQI-Based search space.
The fallback search space can also be used for UEs that do not generate sub-band CQI
31
reports.
The fallback search space uses eCCEs which are also used for the CQI-Based search
space. In any given sub-frame, any eCCE in the fallback search space that is not used to transmit
a fallback ePDCCH may be used to transmit a CQI-Based ePDCCH (and vice-versa).
Let L be aggregation level used for the fallback search space. We assume that the 5 size of
the search space may be any multiple of L eCCEs (i.e. a whole number of ePDCCHs), with the
exact size chosen on the basis of system bandwidth and expected traffic.
There are two important design considerations for the fallback search space, as follows.
1. For reliable transmission it is preferable if each fallback ePDCCH is transmitted
10 with frequency diversity, i.e. the eCCEs comprising the ePDCCH should be
widely separated in frequency.
2. When a fallback ePDCCH is transmitted, any CQI-Based ePDCCH which is
mapped to any of the same eCCEs as that fallback ePDCCH cannot also be
transmitted in the same sub-frame, placing restrictions on the scheduler algorithm.
15 Such blocking should be minimised. In particular, this suggests that each fallback
ePDCCH should overlap with as few CQI-Based ePDCCHs as possible.
One method for constructing the fallback search space is described as follows.
We divide all eCCEs in the system bandwidth into contiguous blocks of size B eCCEs.
We then select a sub-set of these blocks to contain the fallback search space. If the total number
of eCCEs required for the fallback search space is FB 20 N (which will be a multiple of L, the
ePDCCH size) and the total number of eCCEs available in the cell is eCCE N , then one way to
select the blocks used to carry the fallback space is to use the blocks which start at the eCCE
numbers given by the following.




 





























  
B
N
k
N
B
N
B
i B k FB
FB
eCCE
0
25 where  denotes the ‘floor’ function and  denotes the ‘ceiling’ function. This has the effect
of distributing the fallback space blocks as evenly as possible throughout the total available
eCCEs.
(For example, if B=4,  48 eCCE N and  32 FB N then the blocks beginning at eCCE
numbers 0, 4, 12, 16, 24, 28, 36 and 40 are used. This case is illustrated in Figure 5. This figure
30 also assumes interference co-ordination with P=3 cells).
Although any value of B may be used, blocking performance will generally be improved
32
if B is chosen to match one of the aggregation levels used for the CQI-Based search space.
Having selected the eCCEs which comprise the fallback search space, it remains to map
the individual ePDCCHs to these eCCEs. Let j be a eCCE index into the list of FB N eCCEs
selected by the above procedure. Then we may assign the jth eCCE in the fallback search space
to the mth ePDCCH, given 5 n by
FB
FB j N
L
N
S
j
m   








 mod 0
Where S may be any sub-multiple of L (for example, if L=8 then S may be 1, 2, 4 or 8).
The value of S controls the degree of frequency distribution of the eCCEs belonging to each
ePDCCHs. The case S=1 corresponds to fully distributed, and S=L is fully localised.
10 Intermediate values are ‘block distributed’.
S=1 provides the best frequency diversity, but at the expense of relatively poor blocking
between the fallback search space and CQI-Based search space. An intermediate value of S
represents a good trade-off between these two requirements.
Some examples are shown in Figure 5.
15
Proposal 3: Provide a fallback search space common to all UEs to allow recovery from CQI
decoding failure.
2.5. UE Search Space Selection with Uplink Notification to eNB
In the CQI-Based search space selection procedure described above, the search space is
20 calculated separately at eNB and UE based on the CQI report. An alternative approach would
be to pre-define a set of search spaces, and allow the UE to select its preferred search space from
this set and report its choice to the eNB. In this case the precise method of search space
selection may be left for the UE designers to decide.
The advantage of this method is that it allows the pre-defined search spaces to be defined
25 in such a way that blocking between UEs in different search spaces is less likely, whilst still
providing for frequency selection gain by allowing the UE to choose the search space that is
most favourable for its current channel state.
This method would require some new uplink signalling. For example, if a set of 16
search spaces were defined then the choice could be indicated by transmission of a 4-bit value
30 from UE to eNB. One option would be to add this signalling to the existing CQI report sent
from UE to eNB.
2.6. Other Issues
Note that the proposed e-PDCCH search space design shall not affect the support of
33
carrier aggregation scenario. Existing UE monitoring procedure and DCI formats can be reused.
For the cross carrier scheduling case where eNB schedules secondary component carrier on the
primary cell, the CQI feedback of the primary cell should be used since ePDCCH is transmitted
in the primary cell. Similarly, only the cell ID of the primary cell should be needed for the
allocation of Cell Specific Search Space. For this case, the number of ePDCCH candidates 5 s (ie.
the size of search space) monitored by UE configured with a carrier indication field can be based
on existing formula CI
L m  mM( ) n as described in [2].
______________________________________________________________
References
10 [1] RAN1 Chairman’s Notes, RAN1#66bis
[2] 3GPP, TR36.213 (V10.5.0), “E-UTRA; Physical layer procedures”, March 2012.
This application is based upon and claims the benefit of priority from United Kingdom
patent application No. 1208236.8, filed on May 10, 2012, the disclosure of which is incorporated
15 herein in its entirety by reference.

WE CLAIM:
1. A communication device for communicating with a plurality of further communication
devices in a cellular communication system, said communication device comprising:
means for communicating, in at least one communication cell operated 5 ted by
communication apparatus of said communication system, using a plurality of subframes,
wherein each subframe comprises a plurality of communication resources;
means for obtaining a respective measure of communication quality associated with each
of said communication resources and for providing information identifying said measures
10 of communication quality to said communication apparatus;
means for identifying a set comprising a number of said communication resources in
which to search for control information transmitted by said communication apparatus
wherein the presence of communication resources in said set is based on said measures of
communication quality; and
15 means for searching for control information in said set of communication resources.
2. A device according to claim 1 wherein said identifying means is operable to identify
communication resources for inclusion in said set based on said measures of
communication quality obtained by said obtaining means.
3. A device according to claim 1 wherein said wherein said communication device is
20 operable to receive, from said communication apparatus, information identifying the
communication resources of said set after providing, to said communication apparatus,
said information identifying a respective measure of communication quality associated
with each of said communication resources; and wherein said identifying means is
operable to identify the communication resources of said set based on said information
25 identifying the communication resources of said set received from said communication
apparatus.
4. A device according to claim 1 or 2 wherein said communication device is operable to
signal information identifying the communication resources of said set to said
communication apparatus.
5. A device according to claim 4 wherein said communication device is operable to signal
said information identifying the communication resources of said set to said
communication apparatus as part of said information identifying said measures of
communication quality.
6. A device according to any preceding claim wherein: said set of communication resources
comprises a first set; said device further comprises means for identifying, based on a
predetermined criteria, a second set comprising a number of said communication
resources in which to search for control information transmitted by said communication
apparatus in the event that control information for said communication device is not
found in said first set of communication resources; and said searching means is 5 operable
to search for control information in said second set of communication resources if control
information for said communication device is not found in said first set of
communication resources.
7. A device according to any preceding claim wherein said identifying means is operable to
10 identify communication resources for inclusion in said set based on at least one of a cell
identity associated with said at least one cell and a subframe number associated with at
least one of said plurality of subframes.
8. A device according to claim 7 wherein said identifying means is operable to identify
communication resources for inclusion in said set from a subset of said communications
15 resources that are contiguous in frequency which subset is selected based on said at least
one of said cell identity and said subframe number.
9. A device according to claim 7 wherein said identifying means is operable to identify
communication resources for inclusion in said set from a subset of said communications
resources that are distributed in frequency which subset is selected based on said at least
20 one of said cell identity and said subframe number.
10. A device according to any preceding claim wherein said set comprising a number of said
communication resources in which to search for control information transmitted by said
communication apparatus comprises a search space.
11. A device according to any preceding claim wherein said control information transmitted
25 by said communication apparatus is transmitted in a control channel (e.g. a physical
downlink control channel (PDCCH) or enhanced physical downlink control channel
(ePDCCH)) and wherein said device is operable to locate said control channel by
searching in said set of communication resources.
12. A device according to claim 11 wherein said control channel comprises at least one
30 control channel element (CCE).
13. A device according to any preceding claim wherein said information identifying said
measures of communication quality comprise at least one carrier quality indication (CQI)
report.
14. A device according to any preceding claim wherein said communication resources in
which to search for control information are arranged in said set in order of decreasing
quality based on said measures of communication quality.
15. A device according to any preceding claim comprising a mobile telephone.
16. Communication apparatus for communicating with a plurality of mobile communication
devices in a cellular communication system, said communication apparatus comprising5 :
means for operating at least one communication cell;
means for communicating using a plurality of subframes with at least one mobile
communication device within said at least one cell, wherein each subframe comprises a
plurality of communication resources;
10 means for receiving, from said at least one mobile communication device, information
identifying a respective measure of communication quality associated with each of said
communication resources;
means for identifying a set comprising a number of said communication resources for use
in potential transmission of control information for the at least one mobile
15 communication device wherein the presence of communication resources in said set is
based on said measures of communication quality; and
means for transmitting control information for said at least one mobile communication
device in at least a subset of said set of communication resources.
17. Apparatus according to claim 16 wherein said identifying means is operable to identify
20 communication resources for inclusion in said set based on said information identifying a
respective measure of communication quality associated with each of said
communication resources received from the communication device.
18. Apparatus according to claim 16 wherein said wherein said communication device is
operable to receive, from said communication device and separately to said information
25 identifying a respective measure of communication quality associated with each of said
communication resources, information identifying the communication resources of said
set; and wherein said identifying means is operable to identify the communication
resources of said set based on said information identifying the communication resources
of said set received from said communication device.
19. Apparatus according to claim 16 or 17 wherein said communication apparatus is operable
to signal information identifying the communication resources of said set to said
communication apparatus.
20. Apparatus according to any of claims 16 to 19 wherein: said set of communication
resources comprises a first set; said apparatus further comprises means for identifying a
second set comprising a number of said communication resources for use in potential
transmission of control information for the at least one mobile communication device
based on a predetermined criteria in the event that said information identifying a
respective measure of communication quality associated with each of said
communication resources has not been successfully received and interpreted 5 d by said
communication apparatus; and said transmitting means is operable to transmit control
information for said at least one mobile communication device in at least a subset of said
second set of communication resources if said information identifying a respective
measure of communication quality associated with each of said communication resources
10 has not been successfully received and interpreted by said communication apparatus.
21. Apparatus according to any of claims 16 to 20 wherein said identifying means is operable
to identify communication resources for inclusion in said set based on at least one of a
cell identity associated with said at least one cell and a subframe number associated with
at least one of said plurality of subframes.
22. Apparatus according to claim 21 wherein said identifying means is operable to identify
communication resources for inclusion in said set from a subset of said communications
resources that are distributed in frequency which subset is selected based on said at least
one of said cell identity and said subframe number.
23. Apparatus according to claim 22 wherein said set comprising a number of said
20 communication resources for use in potential transmission of control information for the
at least one mobile communication device comprises a search space.
24. Apparatus according to any of claims 16 to 22 wherein said apparatus is operable to
transmit said control information in a control channel (e.g. a physical downlink control
channel (PDCCH) or enhanced physical downlink control channel (ePDCCH)) in said set
25 of communication resources.
25. Apparatus according to claim 24 wherein said control channel comprises at least one
control channel element (CCE) and wherein said apparatus is operable to transmit each
said CCE using communication resources of said set.
26. Apparatus according to any of claims 16 to 25 comprising a base station.
27. A communication device for communicating with a plurality of further communication
devices in a cellular communication system, said communication device comprising:
means for communicating, in at least one communication cell operated by
communication apparatus of said communication system, using a plurality of subframes,
wherein each subframe comprises a plurality of communication resources;
means for identifying, based on information transmitted to said communication
apparatus, a first set comprising a number of said communication resources in which to
search for control information transmitted by said communication apparatus;
means for identifying, based on a predetermined criteria, a second set comprising a
number of said communication resources in which to search for control informati5 on
transmitted by said communication apparatus in the event that control information for
said communication device is not found in said first set of communication resources; and
means for searching for control information in said first set of communication resources
and, if control information for said communication device is not found in said first set of
10 communication resources, for searching for control information in said second set of
communication resources.
28. A communication device according to claim 27 wherein said communication resources
of said second set are transmitted with frequency diversity.
29. A communication device according to claim 27 or 28 wherein said set comprising a
15 number of said communication resources in which said control information is transmitted
by said communication apparatus comprises a search space.
30. A communication device according to any of claims 27 to 29 wherein said control
information transmitted by said communication apparatus is transmitted in a control
channel (e.g. a physical downlink control channel (PDCCH) or enhanced physical
20 downlink control channel (ePDCCH)) and wherein said device is operable to locate said
control channel by searching in said set of communication resources.
31. A communication device according to any of claims 27 to 30 wherein said control
channel comprises at least one control channel element (CCE).
32. A communication device according to any of claims 27 to 31 wherein said information
25 identifying said measures of communication quality comprise at least one carrier quality
indication (CQI) report.
33. A communication device according to any of claims 27 to 32 wherein said
communication resources in which to search for control information are arranged in said
set in order of decreasing quality based on said measures of communication quality.
34. Communication apparatus for communicating with a plurality of mobile communication
devices in a cellular communication system, said communication apparatus comprising:
means for operating at least one communication cell;
means for communicating using a plurality of subframes with at least one mobile
communication device within said at least one cell, wherein each subframe comprises a
plurality of communication resources;
means for identifying a first set comprising a number of said communication resources
for use in potential transmission of control information for the at least one mobile
communication device based on information received from said mobile communication
device, in the event that said information from said mobile communication device 5 has
been successfully received and interpreted by said communication apparatus;
means for identifying a second set comprising a number of said communication resources
for use in potential transmission of control information for the at least one mobile
communication device based on a predetermined criteria, in the event that said
10 information from said mobile communication device has not been successfully received
and interpreted by said communication apparatus; and
means for transmitting control information for said at least one mobile communication
device: in at least a subset of said first set of communication resources, in the event that
said information from said mobile communication device has been successfully received
15 and interpreted by said communication apparatus; and in at least a subset of said second
set of communication resources, if said information from said mobile communication
device has not been successfully received and interpreted by said communication
apparatus.
35. Apparatus according to claim 33 wherein said communication resources of said second
20 set are transmitted with frequency diversity.
36. Apparatus according to any of claims 33 to 35 wherein said set comprising a number of
said communication resources in which said control information is transmitted by said
communication apparatus comprises a search space.
37. Apparatus according to any of claims 33 to 36 wherein said control information
25 transmitted by said communication apparatus is transmitted in a control channel (e.g. a
physical downlink control channel (PDCCH) or enhanced physical downlink control
channel (ePDCCH)) and wherein said device is operable to locate said control channel by
searching in said set of communication resources.
38. Apparatus according to any of claims 33 to 37wherein said control channel comprises at
30 least one control channel element (CCE).
39. Apparatus according to any of claims 33 to 38 wherein said information identifying said
measures of communication quality comprise at least one carrier quality indication (CQI)
report.
40. Apparatus according to any of claims 33 to 39 wherein said communication resources in
which to transmit said control information are arranged in said set in order of decreasing
quality based on said measures of communication quality.
41. A communication device for communicating with a plurality of further communication
devices in a cellular communication system, said communication device comprising:
means for communicating, in at least one communication cell having an associated ce5 ll
identity and operated by communication apparatus of said communication system, using
a plurality of subframes, wherein each subframe comprises a plurality of communication
resources and has an associated subframe number;
means for identifying a set comprising a number of said communication resources in
10 which to search for control information transmitted by said communication apparatus
wherein the presence of communication resources in said set is based on at least one of
said cell identity and said subframe number; and
means for searching for control information in said set of communication resources.
42. Communication apparatus for communicating with a plurality of mobile communication
15 devices in a cellular communication system, said communication apparatus comprising:
means for operating at least one communication cell having a corresponding cell identity;
means for communicating using a plurality of subframes with at least one mobile
communication device within said at least one cell, wherein each subframe comprises a
plurality of communication resources and has an associated subframe number;
20 means for identifying a set comprising a number of said communication resources for use
in potential transmission of control information for the at least one mobile
communication device wherein the presence of communication resources in said set is
based on at least one of said cell identity and said subframe number; and
means for transmitting control information for said at least one mobile communication
25 device in at least a subset of said set of communication resources.
43. Apparatus according to claim 42 wherein said identifying means is operable to identify
communication resources for inclusion in said set from a subset of said communications
resources that are contiguous in frequency, wherein said subset is selected based on said
at least one of said cell identity and said subframe number.
44. Apparatus according to claim 42 wherein said identifying means is operable to identify
communication resources for inclusion in said set from a subset of said communications
resources that are distributed in frequency, wherein said subset is selected based on said
at least one of said cell identity and said subframe number.
45. A communication system comprising at least one communication device according to
any of claims 1 to 15 or claims 27 to 33 or claim 41 and communication apparatus
according to any of claims 16 to 26 or claims 34 to 40 or claims 42 to 44.
46. A method performed by a communication device for communicating with a plurality of
further communication devices in a cellular communication system, the method
comprising5 :
communicating, in at least one communication cell operated by communication
apparatus of said communication system, using a plurality of subframes, wherein each
subframe comprises a plurality of communication resources;
obtaining a respective measure of communication quality associated with each of said
10 communication resources and for providing information identifying said measures of
communication quality to said communication apparatus;
identifying a set comprising a number of said communication resources in which to
search for control information transmitted by said communication apparatus wherein the
presence of communication resources in said set is based on said measures of
15 communication quality; and
searching for control information in said set of communication resources.
47. A method performed by communication apparatus for communicating with a plurality of
mobile communication devices in a cellular communication system, the method
comprising:
20 operating at least one communication cell;
communicating using a plurality of subframes with at least one mobile communication
device within said at least one cell, wherein each subframe comprises a plurality of
communication resources;
receiving, from said at least one mobile communication device, information identifying a
25 respective measure of communication quality associated with each of said
communication resources;
identifying a set comprising a number of said communication resources for use in
potential transmission of control information for the at least one mobile communication
device wherein the presence of communication resources in said set is based on said
30 measures of communication quality; and
transmitting control information for said at least one mobile communication device in at
least a subset of said set of communication resources.
48. A method performed by a communication device for communicating with a plurality of
further communication devices in a cellular communication system, the method
comprising:
communicating, in at least one communication cell operated by communication
apparatus of said communication system, using a plurality of subframes, wherein each
subframe comprises a plurality of communication resources;
identifying, based on information transmitted to said communication apparatus, 5 tus, a first set
comprising a number of said communication resources in which to search for control
information transmitted by said communication apparatus;
identifying, based on a predetermined criteria, a second set comprising a number of said
communication resources in which to search for control information transmitted by said
10 communication apparatus in the event that control information for said communication
device is not found in said first set of communication resources; and
searching for control information in said first set of communication resources and, if
control information for said communication device is not found in said first set of
communication resources, for searching for control information in said second set of
15 communication resources.
49. A method performed by communication apparatus for communicating with a plurality of
mobile communication devices in a cellular communication system, the method
comprising:
operating at least one communication cell;
20 communicating using a plurality of subframes with at least one mobile communication
device within said at least one cell, wherein each subframe comprises a plurality of
communication resources;
identifying a first set comprising a number of said communication resources for use in
potential transmission of control information for the at least one mobile communication
25 device based on information received from said mobile communication device, in the
event that said information from said mobile communication device has been
successfully received and interpreted by said communication apparatus;
identifying a second set comprising a number of said communication resources for use in
potential transmission of control information for the at least one mobile communication
30 device based on a predetermined criteria, in the event that said information from said
mobile communication device has not been successfully received and interpreted by said
communication apparatus; and
transmitting control information for said at least one mobile communication device: in at
least a subset of said first set of communication resources, in the event that said
information from said mobile communication device has been successfully received and
interpreted by said communication apparatus; and in at least a subset of said second set
of communication resources, if said information from said mobile communication device
has not been successfully received and interpreted by said communication apparatus.
50. A method performed by a communication device for communicating with a plurality 5 of
further communication devices in a cellular communication system, the method
comprising:
communicating, in at least one communication cell having an associated cell identity and
operated by communication apparatus of said communication system, using a plurality of
10 subframes, wherein each subframe comprises a plurality of communication resources and
has an associated subframe number;
identifying a set comprising a number of said communication resources in which to
search for control information transmitted by said communication apparatus wherein the
presence of communication resources in said set is based on at least one of said cell
15 identity and said subframe number; and
searching for control information in said set of communication resources.
51. A method performed by communication apparatus for communicating with a plurality of
mobile communication devices in a cellular communication system, the method
comprising:
20 operating at least one communication cell having a corresponding cell identity;
communicating using a plurality of subframes with at least one mobile communication
device within said at least one cell, wherein each subframe comprises a plurality of
communication resources and has an associated subframe number;
identifying a set comprising a number of said communication resources for use in
25 potential transmission of control information for the at least one mobile communication
device wherein the presence of communication resources in said set is based on at least
one of said cell identity and said subframe number; and
transmitting control information for said at least one mobile communication device in at
least a subset of said set of communication resources.
52. A computer implementable instructions product comprising computer implementable
instructions for causing a programmable computer device to perform the method of claim 46 or 51.