U.S. patent application number 13/818294 was filed with the patent office on 2013-06-20 for communication system.
The applicant listed for this patent is Yassin Aden Awad, Yasushi Maruta, Toshifumi Sato. Invention is credited to Yassin Aden Awad, Yasushi Maruta, Toshifumi Sato.
Application Number | 20130157660 13/818294 |
Document ID | / |
Family ID | 44652264 |
Filed Date | 2013-06-20 |
United States Patent
Application |
20130157660 |
Kind Code |
A1 |
Awad; Yassin Aden ; et
al. |
June 20, 2013 |
COMMUNICATION SYSTEM
Abstract
A communication system is presented in which a base station is
provided for communicating with a plurality of mobile communication
devices in a cellular communication system. The base station
operates one of more communication cells and communicates
subframes, with each of the plurality of communication devices
within the cell(s), each comprising the communication resources of
a control region for communicating a control channel and the
communication resources of a data region for communicating a
respective data channel. The base station communicates a control
channel having a first DMRS sequence in a control region of some
subframes and a control channel having a second DMRS sequence in a
control region of other subframes. The second control channel may
be transmitted in a radio beam focussed spatially in a direction of
a communication device. The first control channel may be
transmitted omnidirectionally throughout the cell(s).
Inventors: |
Awad; Yassin Aden;
(Minato-ku, JP) ; Maruta; Yasushi; (Minato-ku,
JP) ; Sato; Toshifumi; (Minato-ku, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Awad; Yassin Aden
Maruta; Yasushi
Sato; Toshifumi |
Minato-ku
Minato-ku
Minato-ku |
|
JP
JP
JP |
|
|
Family ID: |
44652264 |
Appl. No.: |
13/818294 |
Filed: |
July 25, 2012 |
PCT Filed: |
July 25, 2012 |
PCT NO: |
PCT/JP2012/069523 |
371 Date: |
February 21, 2013 |
Current U.S.
Class: |
455/435.1 ;
455/450 |
Current CPC
Class: |
H04W 72/0406 20130101;
H04W 72/042 20130101; H04W 72/046 20130101; H04W 16/28 20130101;
H04W 72/0453 20130101 |
Class at
Publication: |
455/435.1 ;
455/450 |
International
Class: |
H04W 72/04 20060101
H04W072/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 25, 2011 |
GB |
1112752.9 |
Claims
1. 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, via a
plurality of antenna ports, a plurality of subframes with each of a
plurality of communication devices within said at least one cell,
wherein: each sub-frame comprises a plurality of communication
resources defining a control region for communicating a respective
control channel and a plurality of communication resources defining
a data region for communicating a respective data channel; and said
communicating means is operable to communicate: first control
information using a first reference signal pattern and using a
first antenna port; and second control information using a second
reference signal pattern and using a second antenna port.
2. A communication device for communicating with communication
apparatus of a cellular communication system said communication
device comprising: means for registering said communication device
in at least one communication cell operated by said communication
apparatus; means for receiving a plurality of sub-frames
transmitted from said communication apparatus via a plurality of
antenna ports, wherein: each sub-frame comprises a plurality of
communication resources defining a control region for communicating
a respective control channel and a plurality of communication
resources defining a data region for communicating a respective
data channel; and said receiving means is operable: first control
information communicated using a first reference signal pattern and
using a first antenna port by said communication apparatus; and
second control information communicated using a second reference
signal pattern and using a second antenna port by said
communication apparatus; and means for interpreting said control
information communicated using said first reference signal pattern,
and for interpreting control information communicated using said
second reference signal pattern.
3. 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 a plurality
of subframes with each of a plurality of communication devices
within said at least one cell, wherein: each sub-frame comprises a
plurality of communication resources defining a control region for
communicating a respective control channel and a plurality of
communication resources defining a data region for communicating a
respective data channel; and said communicating means is operable
to communicate: a first control channel having a first reference
signal pattern in a control region of a first of said subframes;
and a second control channel having a second reference signal
pattern in a control region of a second of said subframes, wherein
said second reference signal pattern is different from said first
reference signal pattern.
4. Communication apparatus according to claim 3 wherein said means
for operating at least one communication cell is operable to
operate a first cell using a first component carrier and a second
cell using a second component carrier, and wherein said first
subframe is provided using said first component carrier and said
second subframe is provided using said second component
carrier.
5. Communication apparatus according to claim 4 wherein said second
component carrier is operated as an extension carrier.
6. Communication apparatus according to claim 4 wherein said first
component carrier is operated as a stand-alone carrier.
7. Communication apparatus according to claim 3 wherein said
communicating means is operable to focus said second control
channel spatially in a direction of a specific communication
device.
8. Communication apparatus according to claim 3 wherein said
communicating means is operable to transmit said first control
channel omnidirectionally throughout said at least one cell.
9. Communication apparatus according to claim 3 further comprising
means for determining whether a specific communication device
should receive a first control channel having said first reference
signal pattern, or a second control channel having said second
reference signal pattern.
10. Communication apparatus according to claim 9 wherein said
determining means is operable to determine whether said specific
communication device should receive said first control channel
having said first reference signal pattern, or said second control
channel having said second reference signal pattern, based on a
location of said communication device.
11. Communication apparatus according to claim 10 wherein said
determining means is operable to determine whether said specific
communication device should receive said first control channel
having said first reference signal pattern, or said second control
channel having said second reference signal pattern, based on the
location of said communication device relative to further
communication apparatus.
12. Communication apparatus according to claim 11 wherein said
determining means is operable to determine the location of said
communication device relative to said further communication
apparatus based on a result of a measurement of a parameter
representing a distance of said communication device from said
further communication apparatus.
13. Communication apparatus according to claim 12 wherein said
parameter representing a distance of said communication device from
said further communication apparatus comprises a reference signal
received power (RSRP) of a signal transmitted by said further
communication apparatus.
14. Communication apparatus according to claim 9 wherein said
determining means is operable to determine that said specific
communication device should receive said first control channel
having said first reference signal pattern if a predefined message
has been received from the specific communication device.
15. Communication apparatus according to claim 9 wherein said
determining means is operable to determine that said specific
communication device should receive said second control channel
having said second reference signal pattern if a further predefined
message has been received from the specific communication
device.
16. Communication apparatus according to claim 9 wherein said
determining means is operable to determine whether said specific
communication device should receive a said first control channel
having said first reference signal pattern, or said second control
channel having said second reference signal pattern, in dependence
on a measurement report received from the specific communication
device.
17. Communication apparatus according to claim 3 wherein said
communication apparatus comprises a plurality of distributed
antennas.
18. Communication apparatus according to claim 17 wherein said
communicating means is operable to communicate said first control
channel having a first reference signal pattern using any of said
plurality of antennas.
19. Communication apparatus according to claim 17 wherein said
communicating means is operable to communicate said second control
channel having a second reference signal pattern using a subset
comprising at least one, but not all, of said plurality of
antennas.
20. Communication apparatus according to claim 17 wherein said
communicating means is operable to communicate a control channel
having a third reference signal pattern in a third of said
subframes using a subset comprising at least one, but not all, of
said plurality of antennas, wherein said third reference signal
pattern is different from first reference signal pattern and said
second reference signal pattern.
21. Communication apparatus according to claim 3 wherein said
communicating means is operable to communicate radio frames
comprising a plurality of subfames, each subframe having a
different respective subframe location, and wherein said
communicating means is operable: to communicate said first control
channel having a first reference signal pattern in a subframe at a
subframe location, within a radio frame, selected from a first set
of subframe location(s) comprising at least one subframe location;
and to communicate said second control channel having a second
reference signal pattern in a subframe at a subframe location,
within a radio frame, selected from a second set of subframe
location(s) comprising at least one subframe location; wherein said
first set of subframe location(s) does not comprise the same
subframe location(s) as said second set of subframe
location(s).
22. Communication apparatus according to claim 3 wherein said first
control channel having a first reference signal pattern is not
communicated in a subframe at a subframe location of a multi-media
broadcast over a single frequency network (MBSFN) subframe and/or
is not communicated in a subframe at a subframe location of an
almost blank subframe (ABS).
23. Communication apparatus according to claim 3 wherein said
second control channel having a second reference signal pattern is
communicated in a subframe at a subframe location of a multi-media
broadcast over a single frequency network (MBSFN).
24. Communication apparatus according to claim 3 wherein said
second control channel having a second reference signal pattern is
communicated in a subframe of an almost blank subframe (ABS).
25. Communication apparatus according to claim 3 wherein control
information communicated using said first and/or said second
represents a resource allocation for a communication device.
26. Communication apparatus according to claim 3 wherein each said
reference signal pattern comprises a demodulation reference signal
pattern `DMRS`.
27. A communication device for communicating with communication
apparatus of a cellular communication system said communication
device comprising: means for registering said communication device
in at least one communication cell operated by said communication
apparatus; means for receiving a plurality of sub-frames from said
communication apparatus, wherein: each sub-frame comprises a
plurality of communication resources defining a control region for
communicating a respective control channel and a plurality of
communication resources defining a data region for communicating a
respective data channel; and said receiving means is operable: to
receive a first control channel having a first reference signal
pattern in a control region of a first of said subframes; and to
receive a second control channel having a second reference signal
pattern in a in a control region of a second of said subframes,
wherein said second reference signal pattern is different from said
first reference signal pattern; and means for interpreting control
information communicated in said first control channel having a
first reference signal pattern, and for interpreting control
information communicated in said second control channel having a
second reference signal pattern.
28. A communication device according to claim 27 wherein said
receiving means is operable to receive said first subframe on a
first component carrier of a first frequency band and said second
subframe on a said second component carrier of a second frequency
band.
29. A communication device according to claim 28 wherein said
second component carrier is operated as an extension carrier.
30. A communication device according to claim 28 wherein said first
component carrier is operated as a stand-alone carrier.
31. A communication device according to claim 27 wherein said
receiving means is operable to receive said second control channel
in a radio beam focussed spatially in a direction of said
communication device.
32. A communication device according to claim 27 wherein said
receiving means is operable to receive said first control channel
in a radio communication transmitted omnidirectionally throughout
said at least one cell.
33. A communication device according to claim 27 further comprising
means for measuring a parameter representing a distance of said
communication device from further communication apparatus.
34. A communication device according to claim 33 wherein said
parameter representing a distance of said communication device from
said further communication apparatus comprises a reference signal
received power (RSRP) of a signal transmitted by said further
communication apparatus.
35. A communication device according to claim 33 further comprising
means for transmitting a predefined message to said communication
apparatus operating said cell in dependence on a result of said
measurement of said parameter representing a distance of said
communication device from said further communication apparatus.
36. A communication device according to claim 35 wherein said
predefined message comprises a measurement report including said
result of said measurement.
37. A communication device according to claim 35 wherein said
predefined message comprises information representing an identity
of said further communication apparatus and/or of a cell operated
by said further communication apparatus.
38. A communication device according to claim 35 further comprising
means for comparing said parameter against a predetermined
threshold value.
39. A communication device according to claim 38 wherein said
transmitting means is operable to transmit said predefined message
if said comparison indicates that said parameter has risen above
said threshold value.
40. A communication device according to claim 38 wherein said
transmitting means is operable to transmit a further predefined
message if said comparison indicates that said parameter has fallen
below said threshold value.
41. A communication device according to claim 23 wherein said
receiving means is operable to receive radio frames comprising a
plurality of subfames, each subframe having a different respective
subframe location within the radio frame, and wherein said
receiving means is operable: to receive a first control channel
having a first reference signal pattern in a subframe at a subframe
location, within a radio frame, selected from a first set of
subframe location(s) comprising at least one subframe location; and
to receive a second control channel having a second reference
signal pattern in a subframe at a subframe location, within a radio
frame, selected from a second set of subframe location(s)
comprising at least one subframe location; wherein said first set
of subframe location(s) does not comprise the same subframe
location(s) as said second set of subframe location(s).
42. A communication device according to claim 27 wherein said first
control channel having a first reference signal pattern is not
received in a subframe at a subframe location of a multi-media
broadcast over a single frequency network (MBSFN) and/or is not
received in a subframe at a subframe location of an almost blank
subframe (ABS).
43. A communication device according to claim 27 wherein said
second control channel having a second reference signal pattern is
received in a subframe at a subframe location of a multi-media
broadcast over a single frequency network (MBSFN).
44. A communication device according to claim 27 wherein said
second control channel having a second reference signal pattern is
received in a subframe of an almost blank subframe (ABS).
45. A communication device according to claim 27 wherein said
control information communicated using said first and/or said
second represents a resource allocation for the communication
device.
46. A communication device according to claim 27 wherein each said
reference signal pattern comprises a demodulation reference signal
pattern `DMRS`.
47. 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; communicating, via a plurality of
antenna ports, a plurality of subframes with each of a plurality of
communication devices within said at least one cell, wherein each
sub-frame comprises a plurality of communication resources defining
a control region for communicating a respective control channel and
a plurality of communication resources defining a data region for
communicating a respective data channel; communicating first
control information using a first reference signal pattern and
using a first antenna port; and communicating second control
information using a second reference signal pattern and using a
second antenna port.
48. A method, performed by a communication device for communicating
with communication apparatus of a cellular communication system,
the method comprising: registering said communication device in at
least one communication cell operated by said communication
apparatus; receiving a plurality of sub-frames transmitted from
said communication apparatus via a plurality of antenna ports,
wherein each sub-frame comprises a plurality of communication
resources defining a control region for communicating a respective
control channel and a plurality of communication resources defining
a data region for communicating a respective data channel;
receiving first control information communicated using a first
reference signal pattern and using a first antenna port by said
communication apparatus; interpreting said control information
communicated using said first reference signal pattern; receiving
second control information communicated using a second reference
signal pattern and using a second antenna port by said
communication apparatus; and interpreting control information
communicated using said second reference signal pattern.
49. A method, performed by communication apparatus, of
communicating with a plurality of mobile communication devices in a
cellular communication system said method comprising: operating at
least one communication cell; communicating a plurality of
subframes with each of a plurality of communication devices within
said at least one cell, wherein each sub-frame comprises a
plurality of communication resources defining a control region for
communicating a respective control channel and a plurality of
communication resources defining a data region for communicating a
respective data channel; communicating control information using a
first control channel having a first reference signal pattern in a
control region of a first of said subframes; and communicating
control information using a second control channel having a second
reference signal pattern in a control region of a second of said
subframes, wherein said second reference signal pattern is
different from said first reference signal pattern.
50. A method, performed by a communication device, of communicating
with communication apparatus of a cellular communication system
said method: registering said communication device in at least one
communication cell operated by said communication apparatus;
receiving a plurality of sub-frames from said communication
apparatus, wherein each sub-frame comprises a plurality of
communication resources defining a control region for communicating
a respective control channel and a plurality of communication
resources defining a data region for communicating a respective
data channel; receiving a first control channel having a first
reference signal pattern in a control region of a first of said
subframes; interpreting control information communicated in said
first control channel having a first reference signal pattern;
receiving a second control channel having a second reference signal
pattern in a in a control region of a second of said subframes,
wherein said second reference signal pattern is different from said
first reference signal pattern; and interpreting control
information communicated in said second control channel having a
second reference signal pattern.
51. A computer program product comprising instructions operable to
program a programmable processor to implement communication
apparatus according to claim 3.
52. 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 a plurality
of subframes with each of a plurality of communication devices
within said at least one cell, wherein: each sub-frame comprises a
plurality of communication resources defining a control region for
communicating a respective control channel and a plurality of
communication resources defining a data region for communicating a
respective data channel; and said communicating means is operable
to communicate: control information using a first control channel
having a first reference signal pattern in a control region of a
first of said subframes; and control information using a second
control channel having a second reference signal pattern in one of
said control and data regions of a second of said subframes,
wherein said second reference signal pattern is different from said
first reference signal pattern.
53. A communication device for communicating with communication
apparatus of a cellular communication system said communication
device comprising: means for registering said communication device
in at least one communication cell operated by said communication
apparatus; means for receiving a plurality of sub-frames from said
communication apparatus, wherein: each sub-frame comprises a
plurality of communication resources defining a control region for
communicating a respective control channel and a plurality of
communication resources defining a data region for communicating a
respective data channel; and said receiving means is operable: to
receive a first control channel having a first reference signal
pattern in a control region of a first of said subframes; and to
receive a second control channel having a second reference signal
pattern in at least one of a control region and a data region of a
second of said subframes, wherein said second reference signal
pattern is different from said first reference signal pattern; and
means for interpreting control information communicated in said
first control channel having a first reference signal pattern, and
for interpreting control information communicated in said second
control channel having a second reference signal pattern.
54. 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 a plurality
of subframes with each of a plurality of communication devices
within said at least one cell, wherein: said communicating means is
operable to communicate: control information using a first control
channel omnidirectionally throughout said cell; and control
information using a second control channel in a direction spatially
focussed towards a communication device for which the control
information is intended.
55. A communication device for communicating with communication
apparatus of a cellular communication system said communication
device comprising: means for registering said communication device
in at least one communication cell operated by said communication
apparatus; means for receiving a plurality of sub-frames from said
communication apparatus, wherein: said receiving means is operable:
to receive a first control channel omnidirectionally by the
communication apparatus throughout said cell; and to receive a
second control channel transmitted in a direction spatially
focussed towards said communication device; and means for
interpreting control information communicated in said first control
channel, and for interpreting control information communicated in
said second control channel.
56. Communication apparatus for communicating with a plurality of
mobile communication devices in a cellular communication system
said communication apparatus comprising: a cell controller adapted
to operate at least one communication cell; a transceiver operable
to communicate a plurality of subframes with each of a plurality of
communication devices within said at least one cell, wherein: each
sub-frame comprises a plurality of communication resources defining
a control region for communicating a respective control channel and
a plurality of communication resources defining a data region for
communicating a respective data channel; and said transceiver is
further operable to communicate: control information using a first
control channel having a first reference signal pattern in a
control region of a first of said subframes; and control
information using a second control channel having a second
reference signal pattern in at least one of said control and data
regions of a second of said subframes, wherein said second
reference signal pattern is different from said first reference
signal pattern.
57. A communication device for communicating with communication
apparatus of a cellular communication system said communication
device comprising: a cell registration module operable to register
said communication device in at least one communication cell
operated by said communication apparatus; a transceiver operable to
receive a plurality of sub-frames from said communication
apparatus, wherein: each sub-frame comprises a plurality of
communication resources defining a control region for communicating
a respective control channel and a plurality of communication
resources defining a data region for communicating a respective
data channel; and said transceiver is further operable: to receive
a first control channel having a first reference signal pattern in
a control region of a first of said subframes; and to receive a
second control channel having a second reference signal pattern in
at least one of said control region and said data region of a
second of said subframes, wherein said second reference signal
pattern is different from said first reference signal pattern; and
a processor operable to interpret control information communicated
in said first control channel having a first reference signal
pattern, and to interpret control information communicated in said
second control channel having a second reference signal
pattern.
58. A computer program product comprising instructions operable to
program a programmable processor to implement a communication
device according to claim 27.
Description
TECHNICAL FIELD
[0001] The present invention relates to mobile communications
devices and networks, particularly but not exclusively those
operating according to the 3.sup.rd Generation Partnership Project
(3GPP) standards or equivalents or derivatives thereof. The
invention has particular although not exclusive relevance to the
Long Term Evolution (LTE) of UTRAN (called Evolved Universal
Terrestrial Radio Access Network (E-UTRAN)).
BACKGROUND ART
[0002] It has been decided, as part of the 3GPP standardisation
process, that downlink operation for system bandwidths beyond 20
MHz will be based on the aggregation of a plurality of component
carriers at different frequencies. Such carrier aggregation can be
used to support operation in a system both with and without a
contiguous spectrum (for example, a non-contiguous system may
comprise component carriers at 800 MHz, 2 GHz, and 3.5 GHz). 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 able to simultaneously use
the multiple component carriers.
[0003] 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 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).
[0004] Further, the need for interference management between
different cells operating on component carriers of the same
frequency in co-incident or overlapping geographic areas has led to
the development of extension carriers (which are not backwards
compatible with legacy devices). Extension carriers may be used as
a tool for carrier aggregation based HetNet operation and improved
spectral efficiency. A multi-carrier capable base station is able
to operate at least one of its carriers as an extension carrier, on
which a control channel (e.g. a channel carrying resource
scheduling information such as the Physical Downlink Control
Channel (PDCCH)), a Common reference Signal (CRS) (sometimes
referred to as a Cell-specific Reference Signal), and other
information cannot be transmitted. More specifically, an extension
carrier may not be used for transmission of any of the following:
[0005] a Physical Downlink Control Channel (PDCCH); [0006] a
Physical Hybrid ARQ Indicator Channel (PHICH); [0007] a Physical
Control Format Indicator Channel (PCFICH); [0008] a Physical
Broadcast Channel (PBCH); [0009] a Primary Synchronization Signal
(PSS); [0010] a Secondary Synchronization Signal (SSS); or [0011] a
Common Reference Signal/Cell-specific Reference Signal (CRS).
[0012] An extension carrier therefore comprises a carrier that
cannot be operated as a single carrier (stand-alone) carrier, but
must be a part of a component carrier set where at least one of the
carriers in the set is a stand-alone-capable carrier, which can be
used to transmit the scheduling information (and other control
information) for the extension carrier.
[0013] Thus, when a first base station is operating a component
carrier as an extension carrier, another base station may operate a
component carrier of the same frequency to transmit a control
channel, a CRS and other such information more reliably, in the
same general geographic area as the first base station, without
significant interference because there is no corresponding control
channel, CRS and other such information on the extension carrier
operated by the first base station.
[0014] However, in communication systems in which extension
carriers are employed, the cross-carrier scheduling from the
stand-alone (legacy) component carrier can cause an increase in
control channel (PDCCH) blocking and control channel (PDCCH)
capacity can become a limiting factor of system performance. This
is because of the additional control channel signalling required to
schedule resources on multiple component carriers.
DISCLOSURE OF INVENTION
[0015] The invention therefore aims to provide a mobile
communication system, a mobile communication device, a
communication node and associated methods which overcomes or at
least mitigates the above issues.
[0016] According to one aspect of the present invention, there is
provided 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 a plurality
of subframes with each of a plurality of communication devices
within the at least one cell, wherein: each sub-frame comprises a
plurality of communication resources defining a control region for
communicating a respective control channel and a plurality of
communication resources defining a data region for communicating a
respective data channel; and the communicating means is operable to
communicate: a first control channel having a first reference
signal pattern (which may also referred to as a `sequence`) in a
control region of a first of the subframes; and a second control
channel having a second reference signal pattern (sequence) in a
control region of a second of the subframes, wherein the second
reference signal pattern (sequence) is different from the first
reference signal pattern (sequence).
[0017] The means for operating at least one communication cell may
be operable to operate a first cell using a first component carrier
and a second cell using a second component carrier, and the first
subframe may be provided using the first component carrier and the
second subframe may be provided using the second component
carrier.
[0018] The second component carrier may be operated as an extension
carrier. The first component carrier may be operated as a
stand-alone carrier. The communicating means may be operable to
focus the second control channel spatially in a direction of a
specific communication device.
[0019] The communicating means may be operable to transmit the
first control channel omnidirectionally throughout the at least one
cell.
[0020] The communication apparatus may further comprise means for
determining whether a specific communication device should receive
a first control channel having the first reference signal pattern,
or a second control channel having the second reference signal
pattern.
[0021] The determining means may be operable to determine whether
the specific communication device should receive the first control
channel having the first reference signal pattern, or the second
control channel having the second reference signal pattern, based
on a location of the communication device.
[0022] The determining means determining means may be operable to
determine whether the specific communication device should receive
the first control channel having the first reference signal
pattern, or the second control channel having the second reference
signal pattern, based on the location of the communication device
relative to further communication apparatus.
[0023] The determining means may be operable to determine the
location of the communication device relative to the further
communication apparatus based on a result of a measurement of a
parameter representing a distance of the communication device from
the further communication apparatus.
[0024] The parameter representing a distance of the communication
device from the further communication apparatus may comprise a
reference signal received power (RSRP) of a signal transmitted by
the further communication apparatus.
[0025] The determining means may be operable to determine that the
specific communication device should receive the first control
channel having the first reference signal pattern if a predefined
message has been received from the specific communication
device.
[0026] The determining means may be operable to determine that the
specific communication device should receive the second control
channel having the second reference signal pattern if a further
predefined message has been received from the specific
communication device.
[0027] The determining means may be operable to determine whether
the specific communication device should receive a the first
control channel having the first reference signal pattern, or the
second control channel having the second reference signal pattern,
in dependence on a measurement report received from the specific
communication device.
[0028] The communication apparatus may comprise a plurality of
distributed antennas.
[0029] The communicating means may be operable to communicate the
first control channel having a first reference signal pattern using
any of the plurality of antennas.
[0030] The communicating means may be operable to communicate the
second control channel having a second reference signal pattern
using a subset comprising at least one, but not all, of the
plurality of antennas.
[0031] The communicating means may be operable to communicate a
control channel having a third reference signal pattern in a third
of the subframes using a subset comprising at least one, but not
all, of the plurality of antennas, wherein the third reference
signal pattern may be different from first reference signal pattern
and the second reference signal pattern.
[0032] The communicating means may be operable to communicate radio
frames comprising a plurality of subfames, each subframe having a
different respective subframe location, and wherein the
communicating means may be operable: to communicate the first
control channel having a first reference signal pattern in a
subframe at a subframe location, within a radio frame, selected
from a first set of subframe location(s) comprising at least one
subframe location; and may be operable to communicate the second
control channel having a second reference signal pattern in a
subframe at a subframe location, within a radio frame, selected
from a second set of subframe location(s) comprising at least one
subframe location; wherein the first set of subframe location(s)
may not comprise the same subframe location(s) as the second set of
subframe location(s).
[0033] The first control channel having a first reference signal
pattern may not be communicated in a subframe at a subframe
location of a multi-media broadcast over a single frequency network
(MBSFN) subframe and/or may not be communicated in a subframe at a
subframe location of an almost blank subframe (ABS).
[0034] The second control channel having a second reference signal
pattern may be communicated in a subframe at a subframe location of
a multi-media broadcast over a single frequency network (MBSFN).
The second control channel having a second reference signal pattern
may be communicated in a subframe of an almost blank subframe
(ABS).
[0035] Control information communicated using the first and/or the
second may represent a resource allocation for a communication
device. Each reference signal pattern may comprise a demodulation
reference signal pattern `DMRS`.
[0036] According to one aspect of the present invention, there is
provided a communication device for communicating with
communication apparatus of a cellular communication system said
communication device comprising: means for registering said
communication device in at least one communication cell operated by
said communication apparatus; means for receiving a plurality of
sub-frames from said communication apparatus, wherein: each
sub-frame comprises a plurality of communication resources defining
a control region for communicating a respective control channel and
a plurality of communication resources defining a data region for
communicating a respective data channel; and said receiving means
is operable: to receive a first control channel having a first
reference signal pattern in a control region of a first of said
subframes; and to receive a second control channel having a second
reference signal pattern in a in a control region of a second of
said subframes, wherein said second reference signal pattern may be
different from said first reference signal pattern; and means for
interpreting control information communicated in said first control
channel having a first reference signal pattern, and for
interpreting control information communicated in said second
control channel having a second reference signal pattern.
[0037] The receiving means may be operable to receive the first
subframe on a first component carrier of a first frequency band and
the second subframe on a the second component carrier of a second
frequency band. The second component carrier may be operated as an
extension carrier. The first component carrier may be operated as a
stand-alone carrier.
[0038] The receiving means may be operable to receive the second
control channel in a radio beam focussed spatially in a direction
of the communication device.
[0039] The receiving means may be operable to receive the first
control channel in a radio communication transmitted
omnidirectionally throughout the at least one cell.
[0040] The communication device may further comprise means for
measuring a parameter representing a distance of the communication
device from further communication apparatus.
[0041] The parameter representing a distance of the communication
device from the further communication apparatus may comprise a
reference signal received power (RSRP) of a signal transmitted by
the further communication apparatus.
[0042] The communication device may further comprise means for
transmitting a predefined message to the communication apparatus
operating the cell in dependence on a result of the measurement of
the parameter representing a distance of the communication device
from the further communication apparatus.
[0043] The predefined message may comprise a measurement report
including the result of the measurement.
[0044] The predefined message may comprise information representing
an identity of the further communication apparatus and/or of a cell
operated by the further communication apparatus.
[0045] The communication device may further comprise means for
comparing the parameter against a predetermined threshold
value.
[0046] The transmitting means may be operable to transmit the
predefined message if the comparison indicates that the parameter
has risen above the threshold value.
[0047] The transmitting means may be operable to transmit a further
predefined message if the comparison indicates that the parameter
has fallen below the threshold value.
[0048] The receiving means may be operable to receive radio frames
comprising a plurality of subfames, each subframe having a
different respective subframe location within the radio frame, and
wherein the receiving means may be operable: to receive a first
control channel having a first reference signal pattern in a
subframe at a subframe location, within a radio frame, selected
from a first set of subframe location(s) comprising at least one
subframe location; and may be operable to receive a second control
channel having a second reference signal pattern in a subframe at a
subframe location, within a radio frame, selected from a second set
of subframe location(s) comprising at least one subframe location;
wherein the first set of subframe location(s) may not comprise the
same subframe location(s) as the second set of subframe
location(s).
[0049] The first control channel having a first reference signal
pattern may not be received in a subframe at a subframe location of
a multi-media broadcast over a single frequency network (MBSFN)
and/or may not be received in a subframe at a subframe location of
an almost blank subframe (ABS). The second control channel having a
second reference signal pattern may be received in a subframe at a
subframe location of a multi-media broadcast over a single
frequency network (MBSFN). The second control channel having a
second reference signal pattern may be received in a subframe of an
almost blank subframe (ABS).
[0050] The control information communicated using the first and/or
the second may represent a resource allocation for the
communication device.
[0051] The reference signal pattern may comprise a demodulation
reference signal pattern `DMRS`.
[0052] According to one aspect of the present invention, there is
provided a method, performed by communication apparatus, of
communicating with a plurality of mobile communication devices in a
cellular communication system the method comprising: operating at
least one communication cell; communicating a plurality of
subframes with each of a plurality of communication devices within
the at least one cell, wherein each sub-frame comprises a plurality
of communication resources defining a control region for
communicating a respective control channel and a plurality of
communication resources defining a data region for communicating a
respective data channel; communicating control information using a
first control channel having a first reference signal pattern in a
control region of a first of the subframes; and communicating
control information using a second control channel having a second
reference signal pattern in a control region of a second of the
subframes, wherein the second reference signal pattern is different
from the first reference signal pattern.
[0053] According to one aspect of the present invention, there is
provided a method, performed by a communication device, of
communicating with communication apparatus of a cellular
communication system the method:
[0054] registering the communication device in at least one
communication cell operated by the communication apparatus;
[0055] receiving a plurality of sub-frames from the communication
apparatus, wherein each sub-frame comprises a plurality of
communication resources defining a control region for communicating
a respective control channel and a plurality of communication
resources defining a data region for communicating a respective
data channel; receiving a first control channel having a first
reference signal pattern in a control region of a first of the
subframes; interpreting control information communicated in the
first control channel having a first reference signal pattern;
receiving a second control channel having a second reference signal
pattern in a in a control region of a second of the subframes,
wherein the second reference signal pattern is different from the
first reference signal pattern; and interpreting control
information communicated in the second control channel having a
second reference signal pattern.
[0056] According to one aspect of the present invention, there is
provided a computer program product comprising instructions
operable to program a programmable processor to implement
communication apparatus or a communication device according as
recited above.
[0057] According to one aspect of the present invention, there is
provided 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 a plurality
of subframes with each of a plurality of communication devices
within the at least one cell, wherein: each sub-frame comprises a
plurality of communication resources defining a control region for
communicating a respective control channel and a plurality of
communication resources defining a data region for communicating a
respective data channel; and the communicating means may be
operable to communicate: control information using a first control
channel having a first reference signal pattern in a control region
of a first of the subframes; and control information using a second
control channel having a second reference signal pattern in one of
the control and data regions of a second of the subframes, wherein
the second reference signal pattern is different from the first
reference signal pattern.
[0058] According to one aspect of the present invention, there is
provided a communication device for communicating with
communication apparatus of a cellular communication system the
communication device comprising: means for registering the
communication device in at least one communication cell operated by
the communication apparatus; means for receiving a plurality of
sub-frames from the communication apparatus, wherein: each
sub-frame comprises a plurality of communication resources defining
a control region for communicating a respective control channel and
a plurality of communication resources defining a data region for
communicating a respective data channel; and the receiving means is
operable: to receive a first control channel having a first
reference signal pattern in a control region of a first of the
subframes; and to receive a second control channel having a second
reference signal pattern in at least one of a control region and a
data region of a second of the subframes, wherein the second
reference signal pattern may be different from the first reference
signal pattern; and means for interpreting control information
communicated in the first control channel having a first reference
signal pattern, and for interpreting control information
communicated in the second control channel having a second
reference signal pattern.
[0059] According to one aspect of the present invention, there is
provided a 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 a plurality of subframes with each of a plurality of
communication devices within the at least one cell, wherein: the
communicating means is operable to communicate: control information
using a first control channel omnidirectionally throughout the
cell; and control information using a second control channel in a
direction spatially focussed towards a communication device for
which the control information is intended.
[0060] According to one aspect of the present invention, there is
provided a communication device for communicating with
communication apparatus of a cellular communication system the
communication device comprising: means for registering the
communication device in at least one communication cell operated by
the communication apparatus; means for receiving a plurality of
sub-frames from the communication apparatus, wherein: the receiving
means may be operable: to receive a first control channel
omnidirectionally by the communication apparatus throughout the
cell; and to receive a second control channel transmitted in a
direction spatially focussed towards the communication device; and
means for interpreting control information communicated in the
first control channel, and for interpreting control information
communicated in the second control channel.
[0061] According to one aspect of the present invention, there is
provided communication apparatus for communicating with a plurality
of mobile communication devices in a cellular communication system
the communication apparatus comprising: a cell controller adapted
to operate at least one communication cell; a transceiver operable
to communicate a plurality of subframes with each of a plurality of
communication devices within the at least one cell, wherein: each
sub-frame comprises a plurality of communication resources defining
a control region for communicating a respective control channel and
a plurality of communication resources defining a data region for
communicating a respective data channel; and the transceiver is may
be further operable to communicate: control information using a
first control channel having a first reference signal pattern in a
control region of a first of the subframes; and control information
using a second control channel having a second reference signal
pattern in at least one of the control and data regions of a second
of the subframes, wherein the second reference signal pattern is
different from the first reference signal pattern.
[0062] According to one aspect of the present invention, there is
provided a communication device for communicating with
communication apparatus of a cellular communication system the
communication device comprising: a cell registration module
operable to register the communication device in at least one
communication cell operated by the communication apparatus; a
transceiver operable to receive a plurality of sub-frames from the
communication apparatus, wherein: each sub-frame comprises a
plurality of communication resources defining a control region for
communicating a respective control channel and a plurality of
communication resources defining a data region for communicating a
respective data channel; and the transceiver is further operable:
to receive a first control channel having a first reference signal
pattern in a control region of a first of the subframes; and to
receive a second control channel having a second reference signal
pattern in at least one of the control region and the data region
of a second of the subframes, wherein the second reference signal
pattern is different from the first reference signal pattern; and a
processor operable to interpret control information communicated in
the first control channel having a first reference signal pattern,
and to interpret control information communicated in the second
control channel having a second reference signal pattern.
[0063] Aspects of the invention extend to computer 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.
[0064] Each feature disclosed in this specification (which term
includes the claims) and/or 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0065] Embodiments of the invention will now be described by way of
example only with reference to the attached figures in which:
[0066] FIG. 1 schematically illustrates a telecommunication
system;
[0067] FIG. 2 illustrates a possible subframe configuration for
component carriers for the telecommunication system of FIG. 1;
[0068] FIG. 3 shows a simplified illustration of a resource grid
for demodulation reference signals in the telecommunication system
of FIG. 1;
[0069] FIG. 4 shows a simplified block diagram of a first base
station for the telecommunication system of FIG. 1;
[0070] FIG. 5 shows a simplified block diagram of a second base
station for the telecommunication system of FIG. 1;
[0071] FIG. 6 shows a simplified block diagram of a mobile
communication device for the telecommunication system of FIG.
1;
[0072] FIG. 7 shows a simplified flow chart illustrating operation
of the telecommunication system of FIG. 1;
[0073] FIG. 8 schematically illustrates another telecommunication
system;
[0074] FIG. 9 illustrates a possible subframe configuration for
component carriers for the telecommunication system of FIG. 8;
[0075] FIG. 10 illustrates another possible subframe configuration
for component carriers for the telecommunication system of FIG.
8;
[0076] FIG. 11 schematically illustrates another telecommunication
system;
[0077] FIG. 12 illustrates a possible subframe configuration for
component carriers for the telecommunication system of FIG. 10;
[0078] FIG. 13 schematically illustrates another telecommunication
system;
[0079] FIG. 14 illustrates a radio frame for the telecommunication
system of FIG. 13;
[0080] FIG. 15 illustrates a number of possible subframe
configurations for component carriers for the telecommunication
system of FIG. 13;
[0081] FIG. 16 schematically illustrates another telecommunication
system; and
[0082] FIG. 17 illustrates a number of possible subframe
configurations for component carriers for the telecommunication
system of FIG. 16.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
Overview
[0083] FIG. 1 schematically illustrates a mobile (cellular)
telecommunication system 1 in which a user of any of a plurality of
mobile communication devices 3-1 to 3-7 can communicate with other
users via one or more of a plurality of base stations 5-1, 5-2 and
5-3. In the system illustrated in FIG. 1, each base station 5 shown
is an Evolved Universal Terrestrial Radio Access Network (E-UTRAN)
base station capable of operating in a multi-carrier
environment.
[0084] In FIG. 1, the base station labelled 5-1 comprises a so
called `macro` base station operating a plurality of relatively
geographically large `macro` cells 7, 8 using respective component
carriers (CCs) C1, C2, of a component carrier set. In this
embodiment, the macro base station 5-1 operates component carrier
C1 as a primary component carrier on which a primary cell (PCell) 7
is provided, and component carrier C2 as a secondary component
carrier on which a secondary cell (SCell) 8 is provided. The PCell
7 has a larger geographical coverage than the SCell 8. The
difference in the size of the PCell 7 and SCell 8 may be by design
(e.g. as a result of using a lower transmit power for component
carrier C2) or may result from one or more radio environmental
factors affecting the primary carrier C1 and secondary carrier C2
to different extents (e.g. path loss affecting a lower frequency
primary carrier C1 to a lesser extent than a higher frequency
secondary carrier C2).
[0085] The other base stations 5-2, 5-3 shown in FIG. 1 each
comprises a so called `pico` base station operating a plurality of
`pico` cells 9-2, 9-3, 10-2, 10-3, using a component carrier set
having component carriers (CCs) C1, C2 corresponding in frequency
to those used by the macro-base station 5-1. Each pico base station
5-2, 5-3 operates a respective pico primary cell (PCell) 9-2, 9-3
on component carrier C2 and a respective pico secondary cell
(SCell) 10-2, 10-3 on component carrier C1. Thus, the pico Pcells 9
share substantially the same frequency band as the macro Scell 8,
and the pico Scells 10 share substantially the same frequency band
as the macro Pcell 7. As seen in FIG. 1, the power of the carriers
C1, C2 used to provide the pico cells 9, 10 is set such that the
geographical coverage of the pico PCells 9, of this example, are
substantially co-incident with the geographical coverage of the
pico SCells 10.
[0086] The power used to provide pico cells 9, 10 is low relative
to the power used for the macro cells 7, 8 and the pico cells 9, 10
are therefore small relative to the macro cells 7, 8. As shown in
FIG. 1, in this example the geographical coverage of each of the
pico cells 9, 10 falls completely within the geographical coverage
of the macro PCell 7 and overlaps partially with the geographical
coverage of the macro SCell 8.
[0087] Referring to FIG. 2, in which the subframe configuration for
the component carriers for each of the cells is illustrated, it
will be apparent that there is a potential for relatively high
communication interference between the macro PCell 7 and each of
the pico SCells 10. The risk of interference is high because the
macro PCell 7 and pico SCells 10 operate in co-incident
geographical regions and use a common component carrier frequency.
Further, the strength of communication signals from the macro base
station 5-1, in the geographical area covered by each pico Scell
10, may be comparable to communication signals from the respective
pico base station 5-2, 5-3 because of the relatively high power
used by the macro base station 5-1 compared to that used by the
pico base stations 5-2, 5-3. Whilst there is also the potential for
some interference between the macro SCell 8 and each of the pico
PCells 9, any such interference is likely to be relatively small
and restricted to the relatively small geographical region in which
the macro SCell 8 and pico PCells 9 overlap.
[0088] In order to alleviate the issue of interference, the
component carrier C2 used for the macro Scell 8 is operated by the
macro base station 5-1 as an extension carrier on which the nature
of information that may be transmitted is restricted. Specifically,
the component carrier, when operating as the extension carrier may
not be used for transmission of any of the following: [0089] a
Physical Downlink Control Channel (PDCCH); [0090] a Physical Hybrid
ARQ Indicator Channel (PHICH); [0091] a Physical Control Format
Indicator Channel (PCFICH); [0092] a Physical Broadcast Channel
(PBCH); [0093] a Primary Synchronization Signal (PSS); [0094] a
Secondary Synchronization Signal (SSS); or [0095] a Common
Reference Signal/Cell-specific Reference Signal (CRS).
[0096] The macro base station 5-1 operates carrier C1 for the PCell
7 as a stand-alone carrier having a Physical Downlink Control
Channel (PDCCH), which can be used to schedule the resources of its
own component carrier C1 (as shown by arrow X). The PDCCH of
component carrier C1 can also be used to schedule the resources of
component carrier C2 ('cross carrier scheduling') to be used for
communication purposes by a mobile communication device 3 when
operating in the macro Scell 8 (as shown by arrow Y). The PDCCH is
transmitted omnidirectionally throughout the cell.
[0097] The respective component carrier C1 used for each of the
pico SCells 10 is also operated as an extension carrier by the
associated pico base station 5-2, 5-3. The respective component
carrier C2 used for each of the pico Pcells 9 is operated, by the
associated pico base station 5-2, 5-3, as a stand-alone carrier
having an associated PDCCH for scheduling resources within its own
component carrier C2 (as shown by arrow X'). This PDCCH can also be
used for cross carrier scheduling resources of component carrier C1
to be used for communication purposes by a mobile communication
device 3 when operating in the associated pico Scell 10 (as shown
by arrow Y').
[0098] As illustrated in FIGS. 1 and 2, in this embodiment whilst a
conventional PDCCH is not provided on the extension carriers, a
dedicated Beamformed Physical Downlink Control Channel (BFed PDCCH)
4-1, 4-2, 4-5 is provided using the extension component carrier C2
of the macro SCell 8. The BFed PDCCH 4-1, 4-2, 4-5 is directional
and can be used selectively to schedule resources of the extension
component carrier C2 for the macro SCell 8 (as shown by arrow Z)
for specific mobile communication devices 3. The BFed PDCCH is used
in conjunction with frequency selective scheduling in which the
mobile communication device reports the channel state information
(CSI) such as channel quality indicator (CQI) for each resource
block (RB) or group of RBs in frequency domain of the system
bandwidth and the base station selects the best resource blocks to
use to schedule the BFed PDCCH for each terminal.
[0099] In this exemplary embodiment, a BFed PDCCH is not provided
for the extension component carrier C1 of the pico SCells 10-2,
10-3. Instead each pico base station 5-2, 5-3 operates its
respective extension component carrier C1 as a completely
PDCCH-less component carrier as shown in FIG. 2.
[0100] The PDCCH of the primary component carrier C1, operated by
the macro base station 5-1, can thus be used for scheduling
resources (e.g. as shown by arrow Y) for a mobile communication
device 3-7, located in the macro SCell 8, but which is in
geographical close proximity to a pico PCell 9-2 being operated on
the same component carrier C2 as the macro SCell 8. Accordingly,
interference between the macro SCell 8 and the pico PCell 9-2 is
avoided because, although the macro SCell 8 and the pico PCell 9-2
are being operated using same component carrier frequency band
(C2), the control information for each cell is transmitted using a
different respective component carrier frequency band.
[0101] The BFed PDCCH 4-1, 4-2, 4-5 of the extension component
carrier C2 for macro SCell 8 can be used selectively to schedule
resources for a respective mobile communication device 3-1, 3-2,
3-5, operating within the macro SCell 8, but which is not
geographically close to one of the pico PCells 9-2, 9-3.
Accordingly, where interference is not such a significant risk, the
capacity of the PDCCH of the component carrier C1 used for the
macro Pcell 7 can, beneficially, be conserved without significantly
affecting interference.
[0102] For the smaller pico cells in which control channel capacity
is not such an issue, the PDCCH of the respective component carrier
C2 operated by each pico base station 5-2, 5-3, can be used for the
cross carrier scheduling of resources for any mobile communication
device 3-3, 3-4 located in the respective pico SCell 10-2, 10-3. As
described above, the pico cells are geographically located entirely
within the region covered by the macro PCell 7. Accordingly, the
absence of a BFed PDCCH, for the component carrier C1 operated by
each pico base station 5-2, 5-3, avoids the interference that could
otherwise potentially result with the PDCCH of the macro PCell's
component carrier C1.
Beamformed Physical Downlink Control Channel (BFed PDCCH)
[0103] A possible implementation of a BFed PDCCH will now be
described, in more detail.
[0104] The beamforming of the BFed PDCCH 4-1, 4-2, 4-5 is achieved
using a multi-layer beamforming approach that is suitable for a
multiple input multiple output (MIMO) based communication system in
which the transmitters and the receivers of the signals have
multiple antennas. Beamforming is achieved using a precoding
technique in which the phase (and possibly gain) of each stream of
signals transmitted from each of a plurality of antennas is
independently weighted such that the power of each signal stream is
focussed in the direction of interest (e.g. that of the mobile
communication device for which the BFed PDCCH is intended) to
maximise the signal level. Similarly, the power of each stream of
signals is minimised in other directions, including directions in
which interference is a potential issue (e.g. that of the pico
cells 9, 10).
[0105] In order to beamform successfully, the state of the channel
is analysed based on Channel State Information (CSI) measured by
the mobile communication devices 3 and reported to the macro base
station 5-1. The CSI comprises information such as a rank indicator
(RI), precoding matrix indicator (PMI), a channel quality indicator
(CQI) and/or the like. Based on this information, an appropriate
type of beamforming is selected. For example, where full CSI is
reliably available a statistical eigenvector beamforming technique
may be used. In situations where a more limited CSI is available,
an interpolation technique may be used estimate the CSI for
beamforming. In situations where no CSI is available the CSI may be
estimated blindly at the base station, for example from received
signal statistics or uplink signals received from the terminal.
[0106] FIG. 3 shows a resource grid for an orthogonal frequency
division multiplexing (OFDM) subframe 30 for the communication
system 1 of FIG. 1, in which a BFed PDCCH is provided. The resource
grid shown is for a resource block (RB) pair each RB having, for
example, a resource grid similar to that described in section 6.2
of the 3.sup.rd Generation Partnership Project (3GPP) Technical
Standard (TS) 36.211 V10.2.0 and shown in FIG. 6.2.2-1 of that
standard.
[0107] As seen in FIG. 3, the BFed PDCCH transmission is provided
in a set of resource elements 35 in a control region 31 of the
subframe 30. The control region 31 comprises resource elements 35
of the first three OFDM symbols of the first slot of the subframe
30, and spans all twelve subcarrier frequencies of one resource
block (RB). The remaining resource elements 35 of the first slot
and the resource elements 35 of the second slot form a data region
33 in which the Physical Downlink Shared Channel (PDSCH) is
transmitted. A set of UE specific PDSCH demodulation reference
signals (DMRS) and UE specific BFed PDCCH DMRS are provided in the
data region 33 and control region 31 respectively as
illustrated.
[0108] The DMRS pattern for the BFed PDCCH is different to that
used for a legacy PDCCH. In the DMRS pattern shown in FIG. 3, PDSCH
DMRS for antenna ports 7 and 8 are transmitted in resource elements
35 at three evenly distributed subcarrier frequencies, in each of
the last two symbols of the first slot and in each of the last two
symbols of the second slot. PDSCH DMRS for antenna ports 9 and 10
are also transmitted in resource elements 35 at three evenly
distributed subcarrier frequencies (different to those used for
ports 7 and 8), in each of the last two symbols of the first slot
and in each of the last two symbols of the second slot. BFed PDCCH
DMRS for antenna ports x1 and x2 are transmitted in resource
elements 35 at three evenly distributed subcarrier frequencies, in
each of the first two symbols of the first slot. BFed PDCCH DMRS
for antenna ports x3 and x4 are transmitted in resource elements 35
at three evenly distributed subcarrier frequencies (different to
those used for ports x3 and x4), in each of the first two symbols
of the first slot.
Macro Base Station
[0109] FIG. 4 is a block diagram illustrating the main components
of the macro base station 5-1 shown in FIG. 1. The macro base
station 5-1 comprises an E-UTRAN multi-carrier capable base station
comprising a transceiver circuit 431 which is operable to transmit
signals to, and to receive signals from, the mobile communication
devices 3 via a plurality of antennas 433. The base station 5-1 is
also operable to transmit signals to and to receive signals from a
core network via a network interface 435. The operation of the
transceiver circuit 431 is controlled by a controller 437 in
accordance with software stored in memory 439.
[0110] The software includes, among other things, an operating
system 441, a communication control module 442, a component carrier
management module 443, a measurement management module 445, a
control channel management module 446, a direction determination
module 447, a resource scheduling module 448, and a beamforming
module 449.
[0111] The communication control module 442 is operable to control
communication with the mobile communication devices 3 on the
component carriers (CCs) C1, C2, of its component carrier set. The
component carrier management module 443 is operable to manage the
use of the component carriers C1, C2 and, in particular, the
configuration and operation of the macro PCell 7 and macro SCell 8
and the operation of the secondary component carrier C2 for the
SCell 8 as an extension carrier. The measurement management module
445 communicates with the mobile communication device 3 to
configure the mobile communication device 3 to initiate measurement
of the CSI and to receive and analyse measurement reports received
from the mobile communication devices 3 to assess the channel state
for the purposes of beamforming. The direction determination module
447 determines the directional position of a mobile communication
device 3, relative to the base station 5-1, for beamforming
purposes, from the uplink signals that the base station 5-1
receives from that mobile communication device 3. The resource
scheduling module 448 is responsible for scheduling the resources
of the primary and extension component carrier C1, C2 to be used by
the mobile communication devices 3 operating in the macro cells 7,
8. The beamforming module 449 manages the formation of the
directional `beam` via which the BFed PDCCH 4-1, 4-2, 4-5 is
provided to the respective mobile communication devices 3-1, 3-2,
3-5.
[0112] In this exemplary embodiment, the control channel management
module 446 determines which control channel to use for scheduling
resources of the extension carrier C2 of the macro SCell 8 based on
trigger messages received from the mobile communication device 3.
These trigger messages indicate either that a mobile communication
device is within range of a pico base station 5-2, 5-3 or that a
mobile communication device 3 is no longer within range of a pico
base station 5-2, 5-3.
[0113] Specifically, if a mobile communication device 3 has not
issued a trigger message indicating that it is within range of a
pico base station 5-2, 5-3, or if it has issued a trigger message
indicating that it is no longer within range of a pico base station
5-2, 5-3, then the control channel management module 446 determines
that the mobile communication device 3 should receive resource
scheduling for the extension carrier C2 of the macro SCell 8 via a
BFed PDCCH provided on the extension carrier C2.
[0114] If a mobile communication device 3 has issued a trigger
message indicating that it is within range of a pico base station
5-2, 5-3, then the control channel management module 446 determines
that the mobile communication device 3 should receive resource
scheduling for the extension carrier C2 of the macro SCell 8 via a
PDCCH provided on the primary component carrier C1 of the macro
PCell 7.
[0115] In the above description, the base station 5-1 is 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 been
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.
Pico Base Station
[0116] FIG. 5 is a block diagram illustrating the main components
of a pico base station 5-2, 5-3 shown in FIG. 1. Each pico base
station 5-2, 5-3 comprises an E-UTRAN multi-carrier capable base
station comprising a transceiver circuit 531 which is operable to
transmit signals to, and to receive signals from, the mobile
communication devices 3 via at least one antenna 533.
[0117] The base station 5-2, 5-3 is also operable to transmit
signals to and to receive signals from a core network via a network
interface 535. The operation of the transceiver circuit 531 is
controlled by a controller 537 in accordance with software stored
in memory 539.
[0118] The software includes, among other things, an operating
system 541, a communication control module 542, a component carrier
management module 543, a cell type identifier module 547 and a
resource scheduling module 548.
[0119] The communication control module 542 is operable to control
communication with the mobile communication devices 3 on the
component carriers (CCs) C1, C2, of its component carrier set. The
component carrier management module 543 is operable to manage the
use of the component carriers C1, C2 and in particular the
configuration and operation of the pico PCell 9 and pico SCell 10
and the operation of the secondary component carrier C1 for the
SCell 10 as an extension carrier. The cell type identifier module
547 provides information for identifying the cells controlled by
the base station 5-2, 5-3 as pico cells 9, 10. This information is
provided to mobile communication devices 3 that come within (or
close to) the coverage area of the pico Pcell 9. In this exemplary
embodiment, for example, the cell type identifier module 547
broadcasts information identifying the cells it controls to be pico
cells. The resource scheduling module 548 is responsible for
scheduling the resources of the primary and extension component
carrier C2, C1 to be used by the mobile communication devices 3
operating in the pico cells 9, 10.
[0120] In the above description, the base station 5-2, 5-3 is
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 been
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.
Mobile Communication Device
[0121] FIG. 6 is a block diagram illustrating the main components
of the mobile communication devices 3 shown in FIG. 1. Each mobile
communication device 3 comprises a mobile (or `cell` telephone)
capable of operating in a multi-carrier environment. The mobile
communication device 3 comprises a transceiver circuit 651 which is
operable to transmit signals to, and to receive signals from, the
base stations 5 via at least one antenna 653. The operation of the
transceiver circuit 651 is controlled by a controller 657 in
accordance with software stored in memory 659.
[0122] The software includes, among other things, an operating
system 661, a communication control module 662, a measurement
module 665, and a cell identification module 667, a cell proximity
detection module 668, and a resource determination module 669.
[0123] The communication control module 662 is operable for
managing communication with the base stations 5 on the associated
component carriers (CCs) C1, C2. The measurement module 665
receives measurement configuration information from the base
station 5-1 for the purposes of configuring the mobile
communication device 3 to take measurements of the CSI. The
measurement module 665 manages performance of the measurements of
CSI (e.g. for the macro cells 7, 8), generates associated
measurement reports and transmits the generated reports to the
macro base station 5-1. The measurement module 665 also determines
reference signal received power (RSRP) for the pico cells 9, 10 for
use in determining the proximity of the mobile communication device
3 to the pico cells. The cell identification module 667 is operable
to determine the type of cell, which the mobile communication
device 3 enters, or comes geographically close to, from information
provided by the base station 5-2, 5-3, controlling that cell. In
this exemplary embodiment, for example, the cell identification
module 667 is operable to receive the information for identifying
the cell type that is broadcast by a pico base station 5-2, 5-3,
and to identify the cell type to be a pico cell from the received
information.
[0124] The cell proximity detection module 668 uses the
measurements of RSRP from the pico Pcells 9 to determine the
proximity of the mobile communication device 3 to the pico Pcells 9
by comparing the RSRP measurement to a predetermined `trigger`
threshold 663. The trigger threshold is set such that an RSRP above
the trigger threshold indicates that the mobile communication
device 3 is in a geographical location that is close enough to a
pico Pcell 9 for there to be a risk of associated control channel
interference between the PDCCH on the primary carrier (C2) of the
pico PCell 9 and the BFed PDCCH on the extension carrier C2 of the
macro SCell 8
[0125] Hence, if the RSRP measurement exceeds the threshold value,
then the mobile communication device 3 is deemed to be sufficiently
close to (or within) the pico cell for there to be a risk of
interference between any BFed PDCCH transmitted on the extension
carrier C2 of the macro SCell 8 with the PDCCH of transmitted on
the extension carrier C2 of the pico PCell 9. When the trigger
threshold 663 is exceeded, the cell proximity detection module 668
triggers a message to the macro base station 5-1 indicating that
the mobile communication device is within range of a pico base
station 5-2, 5-3. When the RSRP measurement drops below the trigger
threshold 663, the cell proximity detection module 668 triggers a
message to the macro base station 5-1 indicating that the mobile
communication device is no longer within range of a pico base
station 5-2, 5-3.
[0126] The resource determination module 669 determines the
resources scheduled for use by the mobile communication devices 3
for communication purposes by decoding the PDCCH and/or BFed PDCCH
appropriately.
[0127] In the above description, the mobile communication device 3
is 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
been 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.
Operation
[0128] FIG. 7 is a flow chart illustrating typical operation of the
communication system 1 to schedule resources for use by a mobile
communication device (MCD) 3 during communications.
[0129] In FIG. 7, the exemplary operation scenario begins (at S1)
when a mobile communication device 3 starts operating in the Scell
8 of the macro base station 5-1, in a geographical location that is
sufficiently far from the pico Pcells 9 for there to be little risk
of associated control channel to control channel interference. The
base station 5-1 determines the direction of the mobile
communication device 3 relative to the base station at S2 and
identifies an appropriate precoding matrix (also referred to as a
precoding vector) for use in beamforming the BFed PDCCH for that
mobile communication device 3 in the determined direction. The
macro base station 5-1 schedules the resources for the extension
carrier C2 of the macro SCell 8 using within-carrier scheduling via
the BFed PDCCH (at S3).
[0130] In this example, each pico base station broadcasts
information for identifying itself to be a pico base station 5-2,
5-3 at S4 and the mobile communication device 3 determines, from
this broadcast identity information, that the base station 5-2, 5-3
is a pico base station (at S5). The mobile communication device 3
identifies the reference signals that it receives from the pico
base stations 5-2, 5-3 and then monitors the reference signal
received power (RSRP) of these reference signals relative to the
predetermined trigger threshold (at S6).
[0131] In this example, while the RSRP remains below the trigger
threshold, the process in steps S2 to S6 is repeated via loop L1.
When the RSRP increases above the trigger threshold it sends a
`trigger` message to the macro base station 5-1 to indicate that it
is in sufficient range of a pico base station 5-2, 5-3, for control
channel interference to be a significant risk at S7. On receipt of
the trigger message, the macro base station 5-1 determines that it
should no longer use a BFed PDCCH for that mobile communication
device 3 and schedules the resources for the extension carrier C2
of the macro SCell 8 using cross-carrier scheduling via the PDCCH
of the macro PCell's primary component carrier C1 at S8.
[0132] The mobile communication device 3 continues to monitor the
reference signal received power (RSRP) of the reference signals
from the pico base station 5-3, 5-3 relative to the predetermined
trigger threshold at S6 (via loop L2). While the RSRP remains above
the trigger threshold, the process in step S8 is repeated via loop
L4. When the RSRP drops below the trigger threshold it sends
another `trigger` message to the macro base station 5-1 to indicate
that it is no longer in sufficient range of a pico base station
5-2, 5-3 for control channel interference to be a significant risk
(at S9 via loop IA). On receipt of the further trigger message, the
macro base station 5-1 determines that it can start to use a BFed
PDCCH for that mobile communication device 3 again and schedules
the resources for the extension carrier C2 of the macro SCell 8
using within-carrier scheduling via the BFed PDCCH of the macro
SCell's extension component carrier C2 (at S3) following
appropriate direction finding and beamforming (at S2).
Application in a Communication System in which Macro PCell and Pico
PCell Use Same Carrier
[0133] FIG. 8 schematically illustrates a further mobile (cellular)
telecommunication system 81. The telecommunication system 81 is
similar to that of FIG. 1 and corresponding parts are given the
same reference numerals.
[0134] In the telecommunication system 81, a plurality of mobile
communication devices 3-1 to 3-7 can communicate with other users
via one or more of a plurality of base stations 5-1, 5-2 and 5-3.
In the system illustrated in FIG. 1, each base station 5 shown is
an Evolved Universal Terrestrial Radio Access Network (E-UTRAN)
base station capable of operating in a multi-carrier
environment.
[0135] In FIG. 8, the base station labelled 5-1 comprises a macro
base station operating a plurality of relatively geographically
large macro cells 7, 8 using respective component carriers (CCs)
C1, C2, of a component carrier set. In this embodiment, the macro
base station 5-1 operates component carrier C1 as a primary
component carrier on which a primary cell (PCell) 7 is provided,
and component carrier C2 as a secondary component carrier on which
a secondary cell (SCell) 8 is provided. The PCell 7 has a larger
geographical coverage than the SCell 8.
[0136] The other base stations 5-2, 5-3 shown in FIG. 8, each
comprises a pico base station operating a plurality of `pico` cells
9-2, 9-3, 10-2, 10-3, using a component carrier set having
component carriers (CCs) C1, C2 corresponding in frequency to those
used by the macro-base station 5-1. In this exemplary embodiment,
unlike that shown in FIG. 1, each pico base station 5-2, 5-3
operates a respective pico primary cell (PCell) 9-2, 9-3 on
component carrier C1 and a respective pico secondary cell (SCell)
10-2, 10-3 on component carrier C2.
[0137] Thus, unlike the system of FIG. 1, the pico Pcells 9 share
substantially the same frequency band as the macro Pcell 7, and the
pico Scells 10 share substantially the same frequency band as the
macro Scell 8. The geographical coverage of each of the pico cells
9, 10 falls completely within the geographical coverage of the
macro PCell 7. However, the overlap between the pico cells 9 and 10
and the macro SCell 8 is relatively small.
[0138] Referring to FIG. 9, in which the subframe configuration for
the component carriers for each of the cells is illustrated, it
will be apparent that there is a potential for relatively high
communication interference between the PDCCH of the macro PCell 7
and the PDCCH of each of the pico PCells 9. In this exemplary
embodiment, however, this interference is avoided by using a time
domain solution in which the macro base station 5-1 transmits a
PDCCH only in certain subframes and the pico base stations 5-2, 5-3
transmits a PDCCH in other subframes that do not overlap in time
with the subframes used by the base station 5-1.
[0139] More specifically, the macro base station 5-1 uses a first
predetermined set of subframes of a radio frame (in this example
even numbered subframes) to transmit a PDCCH and each pico base
station 5-2, 5-3 uses a second predetermined set of subframes of a
radio frame (in this example odd numbered subframes) to transmit a
respective PDCCH. Accordingly, because the PDCCH provided by the
macro base station 5-1 and the pico base stations 5-2, 5-3, do not
overlap the risk of control channel to control channel interference
is avoided. The subframes in which a particular base station 5 does
not transmit a PDCCH are also not used for data (e.g. PDSCH)
transmission by that base station and, accordingly, are referred to
as almost blank subframes (ABS). These ABS may, however, be used
for transmission of common/cell-specific reference signals
(CRS).
[0140] The potential for any interference between the macro SCell 8
and each of the pico SCells 10 is relatively small.
[0141] Each base station 5 operates carrier C1 for its PCell 7, 9
as a stand-alone carrier having a Physical Downlink Control Channel
(PDCCH), which can be used to schedule the resources of its own
component carrier C1 (as shown by arrows X and X'). The PDCCH of
each component carrier C1 can also be used to schedule the
resources of component carrier C2 (`cross carrier scheduling`) to
be used for communication purposes by a mobile communication device
3 when operating in the corresponding Scell 8, 10 (e.g. as shown by
arrow Y).
[0142] The respective component carrier C2 used for each of the
Scells 8, 10 is operated, by the associated base station 5, as an
extension carrier (as described previously) on which a BFed PDCCH
4-1, 4-2, 4-3, 4-5, 4-8 can be provided. The BFed PDCCH 4-1, 4-2,
4-3, 4-5, 4-8 is directional and can be used selectively to
schedule resources of the extension component carrier C2 for each
SCell 8, 10 (e.g. as shown by arrows Z and Z') for specific mobile
communication devices 3. The BFed PDCCH of each extension component
carrier C2 can also be used to schedule the resources of the
related primary component carrier C1 (`cross carrier scheduling`)
to be used for communication purposes by a mobile communication
device 3 when operating in the corresponding Pcell 7, 9 (e.g. as
shown by arrow W').
[0143] The BFed PDCCH 4-1, 4-2, 4-3, 4-5, 4-8 of the extension
component carrier C2 for each SCell 8, 10 can be used selectively
to schedule resources for a respective mobile communication device
3-1, 3-2, 3-3, 3-5, 3-8 operating within in the corresponding SCell
8, 10. Accordingly, the risk of interference in the region in which
the macro SCell 8 and pico SCell 10 does overlap is significantly
reduced because of the geographically localised nature of the BFed
PDCCH. The DMRS pattern for the BFed PDCCH is different to that
used for a legacy PDCCH.
[0144] FIG. 10 shows another possible subframe configuration for
the component carriers for the system of FIG. 8. In the
configuration shown in FIG. 10, the control region of the subframes
provided using component carrier C2 used for each SCell 8, 10 is
partitioned into a BFed PDCCH region in which the BFed PDCCH is
provided, and a PDCCH-less region in which no PDCCH or BFed PDCCH
is provided. The regions are generally equal sized and are
partitioned such that the BFed PDCCH region for the macro SCell 8
does not overlap with the BFed PDCCH region for the pico SCell 10,
thereby reducing the small risk of control channel to control
channel interference even further.
Application in a Communication System in which Only the Pico Base
Stations Use a BFed PDCCH
[0145] FIG. 11 schematically illustrates a further mobile
(cellular) telecommunication system 111 and FIG. 12 shows a
possible subframe configuration for the component carriers for the
system of FIG. 11. The telecommunication system 111 is similar to
that of FIG. 8 and corresponding parts are given the same reference
numerals.
[0146] The communication system is, essentially, the same as that
shown in FIG. 8 except that only the pico base stations 5-2, 5-3
provide a BFed PDCCH and, unlike the system of FIG. 8, the macro
base station 5-1 provides all resource scheduling for the macro
SCell 8 via a PDCCH provided in the primary component carrier C1
for the macro PCell 7 (e.g. as shown by arrow Y in FIG. 12).
[0147] More specifically, each base station 5 operates carrier C1
for its PCell 7, 9 as a stand-alone carrier having a PDCCH that can
be used to schedule the resources of its own component carrier C1
(as shown by arrows X and X'). The PDCCH of each component carrier
C1 can also be used to schedule the resources of component carrier
C2 (`cross carrier scheduling`) to be used for communication
purposes by a mobile communication device 3 when operating in the
corresponding Scell 8, 10 (e.g. as shown by arrow Y).
[0148] The respective component carrier C2 used for each of the
Scells 8, 10 is operated, by the associated base station 5, as an
extension carrier as described previously. However, the component
carrier C2 used for the macro Scell 8 is not provided with a PDCCH
or a BFed PDCCH and so can only be scheduled using the PDCCH
provided on the primary component carrier C1. The component carrier
C2 used for each pico Scell 10 operated by the associated pico base
station 5-2, 5-3 can be provided with a BFed PDCCH 4-3, 4-8.
[0149] The BFed PDCCH 4-3, 4-8 is directional and can be used
selectively to schedule resources of the extension component
carrier C2 for each pico SCe1110 (e.g. as shown by arrow Z') for
specific mobile communication devices 3. The BFed PDCCH of the
extension component carrier C2 for each pico SCell 10 can also be
used to schedule the resources of the related primary component
carrier C1 (`cross carrier scheduling`) to be used for
communication purposes by a mobile communication device 3 (e.g. as
shown by arrow W').
[0150] The BFed PDCCH 4-3, 4-8 of the extension component carrier
C2 for each pico SCell 10 can thus be used selectively to schedule
resources for a respective mobile communication device 3-3, 3-8
operating within the corresponding SCell 10. Accordingly, the risk
of control channel to control channel interference in the region in
which the macro SCell 8 and pico SCell 10 overlaps is significantly
reduced.
Application in a Single Carrier Communication System
[0151] FIG. 13 schematically illustrates a further mobile
(cellular) telecommunication system 131, FIG. 14 shows the
configuration of a radio frame for the system 131 of FIG. 13, and
FIG. 15 shows a number of possible subframe configurations for the
system of FIG. 13. The telecommunication system 131 has
similarities to those described earlier and corresponding parts are
given the same reference numerals. In the system illustrated in
FIG. 13, each base station 5 shown is an Evolved Universal
Terrestrial Radio Access Network (E-UTRAN) base station capable of
operating in a single-carrier environment.
[0152] A major difference between the system 131 shown in FIG. 13
and those described earlier is that the telecommunication system
131 is a single component carrier system which has been adapted in
a manner that allows legacy mobile communication devices to use the
system as normal (e.g. those defined by the 3.sup.rd Generation
Partnership Project (3GPP) release 8, 9 and 10 standards) whilst
more advanced mobile communication device can advantageously be
scheduled using a BFed-PDCCH.
[0153] In FIG. 13, the base station labelled 5-1 comprises a macro
base station operating a relatively geographically large macro cell
7 using a single component carrier C1 (e.g. a backwards compatible
or `legacy` component carrier). The other base stations 5-2, 5-3
shown in FIG. 13 each comprises a pico base station operating a
pico cell 9-2, 9-3, using a component carrier C1 of the same
frequency as the component carrier used by the macro base station
5-1.
[0154] The power used to provide pico cells 9 is low relative to
the power used for the macro cell 7 and the pico cells 9 are
therefore small relative to the macro cell 7. As shown in FIG. 13,
in this example the geographical coverage of each of the pico cells
9 falls completely within the geographical coverage of the macro
cell 7.
[0155] Referring to FIG. 14, the configuration of a radio frame 140
for the communication system 113 is shown. As seen in FIG. 14, and
as those skilled in the art will readily understand, each radio
frame comprises an E-UTRA radio frame comprising ten subframes 142,
144, a number of which are reserved for Multi-Media Broadcast over
a Single Frequency Network (MBSFN). In FIG. 14, the subframes
reserved for MBSFN are referred to as MBSFN subframes 144.
[0156] To allow legacy mobile communication devices to communicate
successfully in the system 131, the non-MBSFN subframes 142
comprise legacy E-UTRA subframes having a legacy PDCCH (e.g. as
defined in the relevant 3GPP release 8, 9 or 10 standards). Thus,
older (e.g. release 8, 9 and 10) mobile communication devices are
advantageously able to monitor the legacy PDDCH in the non-MBSFN
subframes 142.
[0157] The MBSFN subframes 144 are configured with a BFed PDCCH
with a corresponding new DMRS pattern, as described previously.
Newer (e.g. release 11 and beyond) mobile communication devices 3,
such as those shown in FIG. 13, are advantageously able to monitor
both the legacy PDDCH in the non-MBSFN subframes 142 and the BFed
PDCCH in the MBSFN subframes 144.
[0158] Referring to FIG. 15, there are a number of different
options (labelled (a) to (c) in FIG. 15) for MBSFN subframe
configuration for the system of FIG. 13. In the first option (a),
the MBSFN subframes 144 of both the macro base station 5-1 and the
pico base stations 5-2, 5-3 are provided with the BFed PDCCH. This
option has the advantage of simplicity and the fact that beamformed
control channels 4-1, 4-2, 4-3, 4-5, 4-8 can be used in both the
pico and macro cells 7, 9.
[0159] In the second option (b), the MBSFN subframes 144 of both
the macro base station 5-1 and the pico base stations 5-2, 5-3 are
provided with a partitioned BFed PDCCH region and PDCCH-less region
(similar to that described with reference to FIG. 10). The regions
are generally equal sized and are partitioned such that the BFed
PDCCH region for the macro cell 7 does not overlap with the BFed
PDCCH region for the pico cell 8. This option reduces the risk of
interference and allows beamformed control channels 4-1, 4-2, 4-3,
4-5, 4-8 to be used in both the pico and macro cells 7, 9.
[0160] In the third option (c), the MBSFN subframes 144 of the of
the pico base stations 5-2, 5-3 are provided with a BFed PDCCH
region, whilst the MBSFN subframes 144 of the macro base station
5-1 are not. This option reduces the risk of interference and
allows beamformed control channels 4-3, 4-8 to be advantageously
used in the pico cells 9 (for this option, the macro base station
5-1 does not use the beamformed control channels labelled 4-1, 4-2,
4-5 shown in FIG. 13).
Application in a Distributed Antenna System
[0161] FIG. 16 schematically illustrates a mobile (cellular)
telecommunication system 161 in which a user of any of a plurality
of mobile communication devices 3-1 to 3-7 can communicate with
other users via a macro base station and a local antenna 15-0 at
the base station and a plurality of geographically distributed
antennas 15-1, 15-2 and 15-3. Each distributed antenna 15-1 to 15-3
is connected to the base station (for example by a fibre optic
link) and the base station 5 controls reception and transmission
via the antenna 15. The base station 5 uses a common cell identity
for communications via each antenna 15 and hence a mobile
communication device 3 being served by any one of the antenna 15
behaves as if it is operating in a single cell.
[0162] In FIG. 16, the base station effectively operates, on a
first component carrier C1, a single `common` primary cell (PCell)
7 that comprises a plurality of primary sub-cells 7-0 to 7-3 each
provided using a different respective antenna 15-0 to 15-3. The
base station operates, on a second component carrier C2, an
effective secondary cell (SCell) 8 that comprises a plurality of
secondary sub-cells 8-0 to 8-3 each provided using a different
respective antenna 15-0 to 15-3.
[0163] In the example shown, the `local` or `master` primary
sub-cell 7-0 operated via the local antenna 15-0 has a larger
geographical coverage than the `local` or `master` secondary
sub-cell 8-0 operated via the local antenna 15-0. The geographical
coverage of each of the `distributed` sub-cells 7-1 to 7-3 and 8-1
to 8-3 operated via the distributed antennas 15-1 to 15-3 falls
completely within the geographical coverage of the local primary
sub-cell 7-0 and overlaps partially with the geographical coverage
of the local secondary sub-cell 8-0. The power of the carriers C1,
C2 used to provide the distributed sub-cells 7-1 to 7-3 and 8-1 to
8-3 is set such that the geographical coverage of the distributed
primary sub-cells 7-1 to 7-3 (of this example) are substantially
co-incident with the geographical coverage of the distributed
secondary sub-cells 8-1 to 8-3. In the example shown the
distributed sub-cell 7-2, 8-2 provided using distributed antenna
15-2 partially overlaps with the distributed sub-cells 7-1, 7-3,
8-1, 8-3 respectively provided using the other distributed antennas
15-1, 15-3. It will be apparent, therefore, that there is a
potential for relatively high control channel to control channel
interference between the sub-cells 7, 8 where they overlap with one
another.
[0164] In this exemplary embodiment, PDCCH to PDCCH interference on
the primary component carrier C2 may be avoided by appropriate time
domain separation of the sub-frames used to communicate the PDCCH
(e.g. with ABS for the other sub-frames as described
previously).
[0165] Referring to FIG. 17, in which the subframe configuration
for the component carriers for the distributed cells is
illustrated, control channel to control channel interference on the
secondary carrier C2 is avoided by providing a different control
channel (DMRS based PDCCH), each having a different respective DMRS
sequence, in the control regions of respective subframes for
overlapping distributed secondary subcells 8-1 to 8-3. The DMRS
sequence selected for the different DMRS based PDCCHs is selected
to be substantially orthogonal.
[0166] As shown in FIG. 17, a DMRS based PDCCH having a first DMRS
sequence (DMRS based PDCCH 1) is provided in the control region of
subframes communicated in the non-overlapping secondary subcells
8-1 and 8-3 provided via antennas 15-1 and 15-3. A DMRS based PDCCH
having a second DMRS sequence (DMRS based PDCCH 2) is provided in
the control region of subframes communicated in the secondary
subcell 8-2, provided via antenna 15-2, that overlaps with the
other secondary subcells 8-1 and 8-2, thereby helping to avoid
control channel to control channel interference in the regions in
which the secondary subcells 8 overlap.
[0167] The structure of each DMRS based PDCCH is, therefore,
similar to that of the BFed PDCCH of earlier examples. However, in
this embodiment, the new PDCCH is transmitted from a single antenna
and is omnidirectional rather than beamformed. The structure of the
DMRS based PDCCH is, therefore similar to the BFed PDCCH as
transmitted from a single antenna port.
Other Modifications and Alternatives
[0168] 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.
[0169] It will be appreciated that although the macro and the pico
base stations 5 have each been described with particular reference
to a different set of modules (as shown in FIGS. 4 and 5) to
highlight the particularly relevant features of the different base
stations 5, the macro and the pico base stations 5 are similar and
may include any of the modules described for the other. For
example, each pico base station 5-2, 5-3 may include a measurement
management module 445, a direction determination module 447 and/or
a beamforming module 449 as described with reference to FIG. 4.
Similarly, the macro base station 5-1 may include a cell type
identifier module 547 as described with reference to FIG. 5.
[0170] It will be appreciated that although the communication
system 1 is described in terms of base stations 5 operating as
macro or pico base stations, the same principles may be applied to
base stations operating as femto base stations, relay nodes
providing elements of base station functionality, home base
stations (HeNB), or other such communication nodes.
[0171] In the above embodiments, the cell type identifier module
has been described as providing information for identifying the
cells controlled by the base station 5-2, 5-3 as pico cells 9, 10
and that this information is broadcast to mobile communication
devices 3 that come within or close to the coverage area of the
pico Pcell 9. It will be appreciated that the information for
identifying the cells provided by the base station 5-2, 5-3 may
comprise any suitable information such as a specific cell type
identifier information element, or a cell identity (Cell ID) from
which cell type can be derived. For example, if a HeNB, rather than
a pico base station, operates the low power cells 9, 10, the cell
type can be identified from comparing the cell identity provided by
the HeNB to a range of Cell IDs known to be allocated to HeNBs.
[0172] Further, whilst in the above description it is the mobile
communication device that determines whether a particular cell is a
pico cell for which control channel interference is a risk, the
macro base station could also do this. For example, the macro base
station may mandate any mobile communication device configured with
a BFed PDCCH, to carry out RSRP measurements and to compare the
results with predefined threshold value (e.g. similar to the
`trigger` threshold as described). If the results are found to be
above that threshold value, the mobile communication device simply
reports the measurement to the base station with cell identity
information (e.g. the Cell ID) for the cell to which the
measurements relate. On receipt of the report, the macro base
station (which has access to information identifying the cell IDs
for the pico cells in its coverage area) can avoid using a BFed
PDCCH for a mobile communication device that is close to a pico
cell within its coverage area. In the case of HeNBs, the macro base
station is able to identify them, based on their cell IDs, so that
the macro base station can avoid using the BFed PDCCH for a mobile
communication device that is close to an identified HeNB cell.
[0173] Referring to the embodiment described with reference to FIG.
1, whilst a BFed PDCCH is not provided for the extension component
carrier C1 of the pico SCells 10-2, 10-3, it will be appreciated
that such a BFed PDCCH could potentially be provided, albeit at the
possible expense of interference between the PDCCH of the macro
PCell 7 and the BFed PDCCH of the pico SCell 9. It will also be
appreciated that whilst it has not been described in significant
detail above, a BFed PDCCH of any of the communication systems
could potentially be used for cross carrier scheduling for any
component carrier of that system regardless of whether or not a
control channel is provided for that component carrier.
[0174] Whilst a particular DMRS pattern has been described for the
BFed PDCCH any suitable DMRS pattern may be used that is different
to that used for a legacy PDCCH.
[0175] It will be appreciated that the predetermined trigger
threshold may be reconfigurable. Further, the trigger threshold may
be adaptive, for example to allow it to change automatically, or
semi-automatically, based on prevailing radio conditions. The
threshold value, and timing of the trigger message, may vary in
dependence on the implementation. The optimum threshold value for
different situations may be arrived at based on simulation.
[0176] Where a flow chart shows discrete sequential blocks, this is
for the purposes of clarity only and, it will be appreciated that
many of the steps may occur in any logical order, may be repeated,
omitted, and/or may occur in parallel with other steps. For
example, referring to step S4 of the flow chart of FIG. 7, the pico
base stations may broadcast identification periodically, in
parallel with the other of the steps shown. Similarly, steps S4 and
S5 need not be repeated every iteration of loops L1 and L4.
Further, the mobile communication device 3 may monitor the RSRP of
received reference signals continuously in parallel with the other
steps.
[0177] Although the provision a beamformed PDCCH has been described
in detail it will be appreciated that other information,
deliberately omitted from transmission on an extension carrier, may
also be provided in a beamformed manner on extension carriers. For
example a new beamformed Physical Hybrid ARQ Indicator Channel
(BFed PHICH) may also be provided on the extension carrier.
[0178] Although the terminology used refers to a beamformed PDCCH
(BFed PDCCH), any similar terminology may be used appropriately to
refer to a new beamformed PDCCH and/or a PDCCH having a modified
DMRS (for example `Precoded PDCCH`, `DMRS-based PDCCH`, `Codebook
based beamforming PDCCH`).
[0179] The beamforming may be codebook based in which a `precoding`
vector (for weighting the transmissions from respective antennas)
is selected from a set of predefined precoding vectors (the
`codebook`). In this case the mobile communication device either
knows, or is informed of, the precoding vector used. The
beamforming may be non-codebook based in which the network applies
arbitrary beamforming at the transmitter and the mobile
communication device has no immediate means for determining the
nature of the beamforming that has been applied. In this case a
mobile communication device specific reference signal to which the
same beamforming has been applied is transmitted to allow
estimation of the channel experienced by the beamformed
transmission. The pico and macro base stations may respectively use
different beamforming techniques (e.g. the pico base station may
use codebook based beamforming or and the macro base station may
use non-codebook based beamforming or vice versa).
[0180] In the example described with reference to FIG. 13, the BFed
PDCCH was described as being provided in the MBSFN subframes of a
radio frame whilst the legacy PDCCH was placed in other subframes.
It will be appreciated that whilst using the MBSFN subframes is
advantageous in terms of simplicity of implementation, any
appropriate predetermined subframes may be used (for example ABS
subframes). In a particularly advantageous scenario for example,
the subframes used for BFed PDCCH transmission use MBSFN subframes
that are also configured to be ABS subframes. The benefits of this
arise because MBSFN subframes are standardised for 3GPP, Release 8
mobile communication devices, and ABS subframes are standardised
for 3GPP Release 10 mobile communication devices. Thus, for
backward compatibility, Release 8 mobile communication devices are
able to interpret MBSFN subframes, and Release 10 mobile
communication devices are able to interpret both MBSFN and ABS
subframes. Accordingly, having MBSFN subframes carrying the new
BFed control channel as a subset of subframes configured for Almost
Blank Subframes (ABS) means that the legacy Release 10 mobile
communication devices will be able to effectively ignore them as
ABS subframes carrying no data, Release 8 mobile communication
devices will be able to treat them as MBSFN subframes and newer
mobile communication devices, as described for the above
embodiments, will be able to treat them as BFed PDCCH carrying
sub-frames.
[0181] Furthermore, in the example described with reference to FIG.
13, by using co-ordinated scheduling in which the macro base
station 5-1 and pico base station 5-2, 5-3 exchange information on
when the BFed PDCCH is to be scheduled, collision between the BFed
PDCCHs transmitted by those base stations 5 can be avoided.
[0182] In yet another advanced variation of the example described
with reference to FIG. 13, the macro base station 5-1 and pico base
station 5-2, 5-3 can use the same resource for BFed PDCCHs where
orthogonal communication streams are applied based on CSI
information exchanged between the macro base station 5-1 and pico
base station 5-2, 5-3.
[0183] In the exemplary embodiments described above, each new
control channel having a new DMRS pattern has been described as
being provided in a control region of a subframe. It will be
appreciated that whilst this is particularly beneficial, the
control channel could be provided in a data region of a subframe or
partially in a control region and partially in a data region whilst
still benefiting from many of the advantages provided by the
invention. Nevertheless, despite the fact that there may be a
reluctance to reuse a region normally reserved for the existing
PDCCH because of the perceived technical difficulties in doing so,
providing the new control channel(s) having the new DMRS in the
control region, as opposed to the data region does provide some
notable advantages. Firstly, for example, decoding a control
channel in the region of a subframe reserved as a control region is
significantly quicker than decoding a control channel in the region
of a subframe reserved as a data region because mobile
communication devices look at the control region before the data
region. Secondly, for similar reasons, decoding a control channel
in the region of a subframe reserved as a control region uses less
battery power than decoding a control channel in the region of a
subframe reserved as a data region. Further, when no data resources
are allocated by the control channel, having the control channel in
the control region allows the mobile communication device to ignore
the data region completely, with the power and speed advantages
that follow from such an arrangement.
[0184] In the above exemplary embodiments, a mobile telephone based
telecommunications system was described. As those skilled in the
art will appreciate, the signalling techniques described in the
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
computing devices as well as or instead of the mobile communicating
devices.
[0185] In the exemplary 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 exemplary
embodiments, part of the transceiver circuitry may be implemented
as software run by the corresponding controller.
[0186] In the above exemplary 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
un-compiled 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.
[0187] Various other modifications will be apparent to those
skilled in the art and will not be described in further detail
here.
[0188] This application is based upon and claims the benefit of
priority from United Kingdom patent application No. 1112752.9,
filed on Jul. 25, 2011, the disclosure of which is incorporated
herein in its entirety by reference.
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