DESCRIPTION
RELAY COMMUNICATION SYSTEM
TECHNICAL FIELD:
The present invention relates to a communication system and to components thereof for
providing relay services to mobile or fixed communication devices. The invention has particular
but not exclusive relevance to relay services used in LTE-Advanced as currently defined in 3GPP
standards documentation TR 36.814 VI. 5.0.
BACKGROUND ART:
Relaying is considered for LTE-Advanced as a tool to improve, for example, the
coverage of high data rates for User Equipment (UE), group mobility, temporary network
deployment, the cell edge throughput and/or to provide coverage in new cell areas. The relay
node is wirelessly connected to the radio-access network via a donor cell. With respect to the
relay node's usage of spectrum, its operation can be classified into:
• inband, in which case the base station-to-relay link shares the same carrier
frequency with relay-to-UE links. Rel-8 UEs (see 3GPP specifications TS 36.21 1
V8.6.0, TS 36.212 V8.6.0 and TS 36.213 V8.6.0) should be able to connect to the
donor cell in this case.
• outband, in which case the base station-to-relay link does not operate in the same
carrier frequency as relay-to-UE links.
A Type 1 relay is an inband relay that controls cells of its own. The relay controls one or
several cells and a unique physical-layer cell identity is provided in each of the cells controlled
by the relay. The same RRM (Radio Resource Management) mechanisms are available and from
a UE perspective there is no difference in accessing cells controlled by a relay and cells
controlled by a "normal" eNodeB (LTE base station). The cells controlled by the relay should
support also LTE Rel-8 (legacy) UEs.
For inband relaying, the eNodeB-to-relay link operates in the same frequency spectrum
as the relay-to-UE link. Due to the relay transmitter causing interference to its own receiver,
simultaneous eNodeB-to-relay and relay-to-UE transmissions on the same frequency resource
may not be feasible unless sufficient isolation of the outgoing and incoming signals is provided
e.g. by means of specific, well separated and well isolated antenna structures. Similarly, at the
relay it may not be possible to receive UE transmissions simultaneously with the relay
transmitting to the eNodeB.
One possibility to handle the interference problem is to operate the relay such that the
relay is not transmitting to UEs when it is supposed to receive data from the donor eNodeB, i.e.
to create "gaps" in the relay-to-UE transmission. These "gaps" during which UEs (including
Rel-8 UEs) are not supposed to expect any relay transmission can be created by configuring
MBSFN (Multi-media Broadcast over a Single Frequency Network) sub-frames. Similarly,
Relay-to-eNodeB transmissions can be facilitated by not allowing any UE-to-relay transmissions
in some sub-frames. However, the use of the MBSFN sub-frame introduces some design
restrictions for the relay control structure as the relay can not read the PDCCH (Physical
Downlink Control Channel) of the donor cell. Hence a new control channel (R-PDCCH) is
required solely for the relay stations.
Various issues surrounding the new relay node control channel have been discussed since
the last RANl#58Bis meeting held from the 12th to the 16th of October 2009. Some of the open
issues include R-PDCCH multiplexing including Interleaving; R-PDCCH placement in the
frequency domain; and R-PDCCH region size in the time domain.
SUMMARY:
The inventors believe that early deployments of LTE-Advanced Release 10 will be
mainly based on fixed relay nodes and that in later deployments mobile relay nodes will also be
used. Therefore, the inventors consider it important to clarify the necessity of supporting both
frequency diversity R-PDCCH transmission for mobile relay nodes and frequency selective RPDCCH
transmissions for fixed relay nodes in the backhaul sub-frame to the donor base station
and their impact on the choice of the open issues discussed above.
The present application discusses these issues and ways of supporting both frequency
diversity and frequency selective R-PDCCH transmissions with the same donor base station.
According to one aspect, the present invention provides a communications station
operable to communicate with a number of communications devices, including a number of relay
stations, wherein the communications station is operable to transmit a sequence of sub-frames,
and transmits relay control data for different relay stations using both frequency selective
transmission and frequency diversity transmission in the same sub-frame. It can do this by
frequency division multiplexing the frequency selective transmission and the frequency diversity
transmission.
In one embodiment, the communications station transmits respective configuration data
in advance to each relay station, identifying if the relay station is to monitor frequency selective
transmissions or frequency diversity transmissions. The configuration data may include data
defining one or more subsets of Physical Resource Blocks that may carry the control data.
Different subsets may be defined for different groups of relay stations within the cell. Different
subsets may also be defined for FD relays and for FS relays.
For frequency diversity transmission, the communications station transmits relay control
data for a first subset of said relay stations on plural Physical Resource Blocks, such that the
relay control data for the relay stations in said first subset are carried on the same Physical
Resource Blocks in an interleaved manner. For frequency selective transmission, the
communications station transmits relay control data for a second subset of said relay stations on
a respective plurality of Physical Resource Blocks, such that the relay control data for each relay
station in said second subset is carried on a respective different Physical Resource Block.
Separate Physical Resource Blocks are used to carry the frequency selective transmission and the
frequency diversity transmission.
The communications station may also transmit relay control data for different groups of
relay stations in different sub-frames. In this way, the communications station can share the
resources between a plurality of relay stations in a time division way as well. This is useful
when there are many relay stations in the same cell.
According to another aspect, the present invention provides a communications station
comprising: a communications controller that generates a sub-frame comprising an initial part
including control data and a subsequent part including user data for devices served by the
communications station; and a transceiver operable to use communications resources to transmit
the generated sub-frame for receipt by the devices served by the communications station;
wherein the communications controller includes relay control data for a plurality of relay stations
served by the communications station within the subsequent part of the generated sub-frame;
wherein the communications controller transmits relay control data for different relay stations
using both a frequency selective transmission and a frequency diversity transmission in the same
sub-frame of the cell.
According to another aspect, the present invention provides a relay station operable to
communicate with a remote communications device that communicates using a communication
cell, wherein the relay station receives, within the cell, a sequence of sub-frames, wherein at least
one sub-frame includes relay control data for different relay stations using a frequency selective
transmission and a frequency diversity transmission; wherein the relay station is operable to
receive configuration data identifying if its relay control data will be transmitted using frequency
diversity transmission or configuration data identifying if its relay control data will be
transmitted using frequency selective transmission and wherein the relay station is operable to
use the received configuration data to recover its relay control data from the at least one subframe.
The relay station may receive the configuration data in advance of receiving the at least
one sub-frame and may use the received configuration data to recover its relay control data from
plural sub-frames until the relay station receives new configuration data. In this way, the relay
station can be semi-statically assigned (in other words it can be changed at a later time point if
desired) to receive its relay control data on a frequency selective transmission or on a frequency
diversity transmission.
The configuration data may identify a plurality of Physical Resource Blocks that are used
for carrying relay control data and the relay station can attempt a plurality of blind decodings of
the Physical Resource Blocks identified by the configuration data, in order to find out the actual
Physical Resource Blocks used to carry the control data for the relay station. The configuration
data may include data defining a plurality of subsets of Physical Resource Blocks that are used
for carrying relay control data and the relay station may limit the number of blind decodings that
it performs using the data defining the plurality of subsets.
The relay station may receive a plurality of sub-frames and may perform blind decodings
on predetermined Physical Resource Blocks of each sub-frame to identify if the sub-frame
includes control data for the relay station. If the relay station is unable to decode any of the
predetermined Physical Resource Blocks of a sub-frame, then the sub-frame does not include
any data for the relay station; and if the relay station is able to decode one or more of the
Physical Resource Blocks to recover the relay control data, then the relay station uses the relay
control data to identify resources used within the sub-frame that carries other data for the relay
station and is operable to recover this other relay data from the identified resources.
According to another aspect, the present invention provides a communications station
operable to communicate with a number of communications devices, including a number of relay
stations, wherein the communications device transmits a sequence of sub-frames in a
communications cell, and transmits relay control data for different relay stations only using a
frequency selective transmission in some sub-frames of the cell and transmits relay control data
for different relay stations only using a frequency diversity transmission in other sub-frames of
the cell.
According to another aspect, the present invention provides a relay station that
communicates with a remote communications device using a communications cell, wherein the
relay station receives, within the cell, a sequence of sub-frames, wherein some sub-frames
include relay control data for different relay stations only using a frequency selective
transmission and other sub-frames include relay control data for different relay stations only
using a frequency diversity transmission; wherein the relay station receives configuration data
identifying if its relay control data will be transmitted in a sub-frame that uses frequency
diversity transmission or configuration data identifying if its relay control data will be
transmitted in a sub-frame that uses frequency selective transmission and wherein the relay
station is operable to use the received configuration data to recover its relay control data from the
corresponding sub-frame.
According to another aspect, the present invention provides a communications station
that communicates with a number of communications devices, including a number of relay
stations, using a plurality of communication cells, wherein the communications device transmits,
in at least one of said cells, relay control data for different relay stations only using a frequency
selective transmission and transmits, in at least one other of said communications cells, relay
control data for different relay stations only using a frequency diversity transmission.
The invention also provides corresponding methods and computer software products that
may be provided on a carrier signal or on a recording medium.
BRIEF DESCRIPTION OF THE DRAWINGS:
These and other features and aspects of the invention will be apparent from the following
embodiments of the invention which are described by way of example only with reference to the
attached figures in which:
Figure 1 schematically illustrates a mobile telecommunication system of a type to which
the described embodiments are applicable;
Figure 2a schematically illustrates a generic frame structure used in communications over
the wireless links of the system shown in Figure 1;
Figure 2b schematically illustrates the way in which the frequency subcarriers are divided
into resource blocks and the way that a time slot is divided into a number of OFDM symbols;
Figure 3 shows a base station sub-frame and a relay station sub-frame and illustrates a
problem caused when the two sub-frames are time synchronised;
Figure 4a illustrates one way in which relay nodes can receive R-PDCCH control data
from the base station by using Frequency Division Multiplexing;
Figure 4b illustrates another way in which relay nodes can receive R-PDCCH control
data from the base station by using a Hybrid Time Division Multiplexing and Frequency
Division Multiplexing;
Figure 5a illustrates one way in which R-PDCCH control data for the relay nodes can be
interleaved with each other to achieve frequency diversity gain;
Figure 5b illustrates another way in which R-PDCCH control data for the relay nodes is
placed within the sub-frame to achieve a frequency selective gain;
Figure 6 illustrates the way in which R-PDCCH control data for relay nodes can be sent
within the same sub-frame using both Frequency diversity and Frequency selective transmission;
Figure 7 schematically illustrates how R-PDCCH data for a number of different relay
stations can be multiplexed together in sub-frame;
Figure 8 is a block diagram illustrating the main components of the base station
illustrated in Figure 1; and
Figure 9 is a block diagram illustrating the main components of a relay station illustrated
in Figure 1.
FigurelO is examples of FD and FS R-PDCCH transmissions. (A-D means each Relay,
"+" means being interleaved)
Figurel 1 is an example of co-existence of FD and FS R-PDCCH transmissions in the
same sub-frame. (A-E means each Relay, "+" means being interleaved)
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS:
Overview
Figure 1 schematically illustrates a mobile (cellular) telecommunication system 1 in
which users of mobile telephones 3-1, 3-2, 3-3 and 3-4 can communicate with other users (not
shown) via a base station 5 or relay stations 7-1 and 7-2 and a telephone network 8. As shown in
Figure 1, the base station 5 is directly connected to the core network 8 and so mobile telephones
3-1 and 3-2 directly connected with the base station 5 (hereafter referred to as Direct MTs)
communicate in the normal fashion. However, the relay stations 7 are only connected to the core
network 8 via the base station 5. Therefore, communications to or from mobile telephones 3-3
and 3-4 that are connected to a relay station 7 (hereafter referred to as Relay MTs) must be
transmitted over the air interface between them and the relay station 7 and over the air interface
between the relay station 7 and the base station 5. As illustrated in Figure 1 (by use of the label
Fi), in this embodiment, the base station 5 and the relay stations 7 transmit downlink data in the
same frequency band. In order to avoid interference, the relay stations 7 do not receive data
from the base station 5 when they are transmitting data to the Relay MTs 3 that they are serving.
Similarly, in the uplink the relay stations 7 do not transmit data to the base station 5 at the same
time that they receive data from the Relay MTs 3 that they are serving.
As will be described in more detail below, the present embodiment describes a number of
different ways that control data for the relay stations 7 can be signalled from the base station 5 to
the relay stations 7, whilst maintaining the general sub-frame structure agreed for LTE Rel 8
(and therefore backwards compatibility with legacy (Rel' 8) mobile telephones).
LTE sub-frame data structure
Before discussing the specific ways in which control data for the relay stations 7 is
transmitted from the base station 5, a description will be given of the access scheme and a
general frame structure agreed for LTE Rel 8. An Orthogonal Frequency Division Multiple
Access (OFDMA) technique is used for the downlink to allow the Direct MTs (3-1 and 3-2) and
the relay stations 7 to receive data over the air interface with the base station 5 and to allow the
Relay MTs (3-3 and 3-4) to receive data over the air interface with the relay station 7. Different
sub-carriers are allocated by the base station 5 (for a predetermined amount of time) to each
Direct MT 3 and the relay stations 7 depending on the amount of data to be sent to the mobile
telephone 3 or the relay stations 7. These are referred to as physical resource blocks (PRBs) in
the LTE specifications. PRBs thus have a time and frequency dimension. Similarly, different
subcarriers are allocated by the relay station 7 (for a predetermined amount of time) to each
Relay MT, depending on the amount of data to be sent to the Relay MT. To do this, the base
station 5 (and the relay station 7) dynamically allocates PRBs for each device that it is serving
and signals the allocations for each sub-frame (TTI) to each of the scheduled devices in a control
channel.
Figure 2a illustrates a generic frame structure agreed for LTE Rel 8 communications over
the air interface with the base station 5. As shown, one frame 13 is 10 msec long and comprises
10 sub-frames 15 of 1 msec duration (known as a Transmission Time Interval (TTI)). Each subframe
or TTI comprises two slots 17 of 0.5 msec duration. Each slot 17 comprises either six or
seven OFDM symbols 19, depending on whether the normal or extended cyclic prefix (CP) is
employed. The total number of available sub-carriers depends on the overall transmission
bandwidth of the system. The LTE specifications define parameters for system bandwidths from
1.4 MHz to 20 MHz and one PRB is currently defined to comprise 12 consecutive subcarriers for
one slot 17. A PRB over two slots is also defined by the LTE Rel' 8 specifications as being the
smallest element of resource allocation assigned by the base station scheduler. The transmitted
downlink signal comprises NBW subcarriers for a duration of N sym b OFDM symbols. It can be
represented by a resource grid as illustrated in Figure 2b. Each box in the grid represents a
single sub-carrier for one symbol period and is referred to as a resource element. As shown,
each PRB 2 1 is formed from 12 consecutive sub-carriers and (in this case) seven symbols for
each subcarrier; although in practice the same allocations are made in the second slot 17 of each
sub-frame 15 as well.
MBSFN Frame Structurefor Relaying
It has already been proposed to use MBSFN sub-frames 15 to support relaying, as these
are already defined for multicast channels in LTE Rel 8 and thus provide backwards
compatibility. Based on the LTE Rel 8 structure, sub-frames 0, 4, 5, 9 in FDD and 0,1,5,6 in
TDD cannot be used for MBSFN sub-frames, but some or all of the remaining sub-frames 15 can
be signalled as MBSFN sub-frames 15.
Figure 3 illustrates the MBSFN sub-frame structure 15-B of the base station 5 and the
MBSFN sub-frame structure 15-R of the relay station 7 and illustrates the way in which gaps are
provided in the relay station's sub-frame structure 15-R to provide appropriate communication
opportunities for communications with the base station 5. As illustrated in Figure 3, in this
embodiment, the base station 5 and the relay station 7 are arranged so that their MBSFN subframes
are time synchronised. At the start of each base station MBSFN sub-frame 15-B, the base
station 5 transmits a PDCCH 23-B (Physical Downlink Control Channel) over the first three
symbols.
The control data normally sent by the base station 5 in the PDCCH 23 of each sub-frame
5 includes:
1) the Physical Control Format Indicator Channel (PCFICH) which informs
the relay stations 7 of the size of the PDCCH in terms of the number of
resource blocks in the frequency domain;
2) the PHICH which carries the hybrid-ARQ ACK/NAK data; and
3) the PDCCH which contains all the information required by the receiving
device to decode the downlink transmission in the same sub-frame 15
(resource allocation, modulation scheme TB size etc) and data identifying
where and how to transmit in the uplink in the next TTI (frame) 13.
The remaining symbols in the sub-frame 15-B form the PDSCH 25-B (Physical Downlink
Shared CHannel) and are used to carry downlink user data for the Direct MTs 3-1 and 3-2 and for the
relay stations 7 being served by the base station 5. At the start of a "gap" relay station MBSFN subframe
15-R, the relay stations 7 transmit a PDCCH 23-R over the first two symbols before switching
to listen and receive data from the base station 5. Relay MTs 3-2 and 3-4 will receive the relay
PDCCH 23-R data transmitted over the first two symbols and will see that no data is scheduled for
transmission to them in that sub-frame 15 and so will go to sleep until the start of the next sub-frame
15. During this time, the relay stations 7 will receive the downlink data from in the PDSCH 25-B of
the base station MBSFN sub-frame 15-B.
As those skilled in the art will appreciate, with frame synchronisation between the base
station 5 and the relay stations 7, the relay stations 7 cannot receive the PDCCH 23-B
transmitted by the base station 5 - as they are transmitting their own PDCCH control data 23-R
at the same time. Therefore, the control data for each relay station 7 (i.e. R-PDCCH) has to be
included in the PDSCH 25-B portion of the MBSFN sub-frame 15-B transmitted by the base
station 5. With the above frame structure, therefore, the data to be transmitted in the shared data
channel 25-B includes the R-PDCCH and the normal PDSCH for the Direct MTs 3 served by the
base station 5. There are various ways that this data can be multiplexed together within the
PDSCH 25-B and some of these and the issues surrounding them will now be described.
R-PDCCHMultiplexing Issues
Two viable multiplexing solutions for R-PDCCH and R-PDSCH/PDSCH channels are
pure FDM (Frequency Division Multiplex) and Hybrid TDM (Time Division Multiplex)+FDM
schemes. Figure 4 illustrates examples of these two multiplexing schemes. In particular, Figure
4a illustrates the way in which R-PDCCH control data 26-1 and 26-2 for the relay stations 7 are
provided in separate PRBs from the R-PDSCH and the PDSCH for direct MTs. Figure 4b
illustrates the way in which three separate blocks of R-PDCCH data 26-1, 26-2 and 26-3 are
provided on the first three OFDM symbols of some PRBs within the sub-frame, with the
remaining OFDM symbols being available for use by R-PDSCH and PDSCH (although only for
Rel 10 MTs). For clarity, Figures 4a and 4b do not show the switching time required at the end
of the sub-frame. Therefore, where the PRB is carrying data for the relay station, the last OFDM
symbol of the sub-frame will not carry relay data (control or user data).
Pure FDM multiplexing scheme: As illustrated in Figure 4a, the R-PDCCH 26 resides
on only some PRBs within the sub-frame 15-B, starting from the first OFDM symbol of the subframe
15-B that the relay station 7 can receive and ending at the second last OFDM symbol of
the sub-frame 15-B.
The advantages of the FDM multiplexing scheme include:
■ Power sharing between R-PDCCH and PDSCH is possible.
■ It does not require a new definition of how to reuse the resources that are not used for
R-PDCCH within the PRBs that are semi-statically assigned for R-PDCCH.
The disadvantages of the FDM multiplexing scheme include:
■ It has a long decoding delay for the R-PDSCH as the R-PDCCH spans to the end of
the sub-frame 15-B.
TDM+FDM multiplexing scheme: As illustrated in Figure 4b, the R-PDCCH 26 resides
on a few OFDM symbols of some PRBs within the sub-frame 15-B.
The advantages of the TDM+FDM multiplexing scheme include:
■ The decoding delay is much better than the FDM scheme as the R-PDCCH is placed
in the first slot of the sub-frame 15-B.
■ Frequency diversity is better than the FDM scheme because (for a given R-PDCCH
data size) the transmission will be spread over more PRBs.
The disadvantages of the TDM+FDM multiplexing scheme include:
■ Power sharing between R-PDCCH and PDSCH is difficult. That is if power boosting
is applied to the R-PDCCH OFDM symbols, then the power of all PDSCH OFDM
symbols for Rel'8 MTs needs to be reduced as the transmission power should be kept
constant during the sub-frame, particularly for higher order modulations. However,
this can be dealt with by the proper adjustment of the modulation and coding scheme.
■ It requires a new definition of how to reuse the resources that are not used for RPDCCH
within the semi-statically assigned PRBs. More specifically, how Rel' 10
MTs will reuse the remaining portion of the PRBs used for R-PDCCH transmission.
Currently, some of the open issues that have not yet been decided include:
1) In the TDM+FDM situation, what should be the R-PDCCH region size
in the time domain, i.e. how many OFDM symbols should be assigned
for the R-PDCCH 26;
2) For FDM and TDM+FDM where should the R-PDCCH 26 be placed
in the frequency domain, i.e. which PRBs should be assigned for the RPDCCH
26; and
3) How should the R-PDCCH control data for different relay stations 7
being served by the same base station 5 be interleaved with each other.
With regard to the first issue, the inventors think that the FDM multiplexing scheme is
simpler and more flexible than the TDM+FDM scheme as with the FDM scheme there is no
region size in the time domain to be determined. The inventors also consider that there is no
need to exclude the TDM+FDM multiplexing scheme as the last OFDM symbol used for RPDCCH
in the sub-frame 15-B can be flexibly allocated for R-PDCCH transmission. This can
be achieved for example by flexibly allocating the first slot of the sub-frame for R-PDCCH, with
the symbols in the second slot being provided for R-PDSCH. Alternatively, the first three or six
or eight OFDM symbols (as an example) of the sub-frame can be used to carry the R-PDCCH,
with the remaining symbols in the sub-frame being defined for carrying R-PDSCH.
With regard to the second issue, the inventors think that there are three possible options
Distributed placement where the R-PDCCH 26 for a particular relay
station 7 is distributed on two or more well-separated PRBs which may
be shared by more than one relay. This option achieves frequency
diversity gain.
) Localised placement where the R-PDCCH 26 for a particular relay
station 7 is placed on contiguous or very close PRBs which are not
shared by other relay stations 7. This option achieves frequency
selective gain.
C) Both distributed and localised placements of the R-PDCCH
transmission.
The inventors' preference is that both distributed and localised placements of the RPDCCH
transmission are supported (i.e. option C), and the motivation for this preference will be
described below.
As a general point, regardless of whether FDM and/or TDM+FDM multiplexing is
chosen, the inventors prefer that semi-statically assigned PRBs for the R-PDCCH are chosen so
that they are distributed in the frequency domain to achieve frequency diversity gain and
frequency selective gain. Semi-statically assigned PRBs means that the PRBs used for RPDCCH
are defined in advance of the transmission of the sub-frame and known by the base
station 5 and the relay stations 7. Each relay station 7just does not know if it is scheduled in the
sub-frame 15 and, if it is, on which of the PRBs their R-PDCCH data is to be found. Normally
the semi-statically assigned PRBs will not change, but they can be changed if it turns out that
one or more of the assigned PRBs provides poor reception to one or more of the relay stations 7.
Whenever the semi-statically assigned PRBs are changed, then all the relay stations 7 will be
informed of the change by a suitable control message.
With regard to the third issue, the inventors think that there are three possible options for
interleaving the R-PDCCH data for the different relay stations 7 :
a) Full interleaving where all R-PDCCHs for different relay stations 7 are
interleaved together in the same base station sub-frame 15-B. The unit size of
interleaving can be a resource-element group (REG) (similar to Rel'8 PDCCH
interleaving) or a control channel element (CCE).
b) No interleaving where all R-PDCCHs for different relay stations 7 are not
interleaved in the same base station sub-frame 15-B.
c) Mixed case of interleaving and no-interleaving where some R-PDCCHs for
different relay stations 7 are interleaved together and some R-PDCCHs for other
relay stations 7 are not interleaved.
The inventors' preference is to support the mixed case of interleaving and no-interleaving
(i.e. option c), and the motivation for this preference will be described below.
Frequency diversity R-PDCCH transmission
In Frequency diversity (FD) R-PDCCH transmission, the R-PDCCHs for different relay
stations 7 are multiplexed and interleaved and mapped to all or a subset of PRBs that are semistatically
assigned for R-PDCCH transmission. Such a Frequency diversity R-PDCCH scheme
is illustrated in Figure 5a, where A+B+C+D means that this PRB includes interleaved R-PDCCH
control data for relay nodes A, B, C and D. This scheme corresponds to selecting option A) for
R-PDCCH placement in frequency domain and option a) for Interleaving, described above. The
main motivation of this scheme is to achieve robustness against interference and channel
fluctuations. This FD R-PDCCH transmission has the following characteristics:
■ PRBs semi-statically assigned to R-PDCCH transmission are shared by some or all
relays.
■ All interleaved resources (PRBs) for FD R-PDCCH transmission are occupied even if
the number of Relays is small.
■ Precoding / beamforming can't be applied for FD R-PDCCH transmission.
■ Allocated PRBs are well-separated (i.e. frequency distributed) to achieve frequency
diversity gain.
■ Common RS (CRS) can be used to demodulate the FD R-PDCCH.
■ Dynamic selection of PRBs (i.e. the number of PRBs and placement in frequency
domain) for FD R-PDCCH transmission is possible in each sub-frame.
■ This scheme is suitable for both fixed and mobile relays.
Frequency selective R-PDCCH transmission
In Frequency selective (FS) R-PDCCH transmission, the R-PDCCHs for different relay
stations 7 are multiplexed (but not interleaved) and mapped to all or a subset of semi-statically
assigned PRBs for R-PDCCH transmission. Such a Frequency selective R-PDCCH scheme is
illustrated in Figure 5b, where the R-PDCCH control data for the different relay stations (here
stations A, B C and D) are transmitted on different PRBs. This scheme corresponds to selecting
option B) for R-PDCCH placement in the frequency domain and option b) for Interleaving,
described above. With this scheme, the base station 5 transmits the R-PDCCH for each relay
station 7 on the PRBs (within the semi-statically assigned PRBs for R-PDCCH transmission)
with good channel conditions, which the base station 5 determines from feedback received from
the relay stations 7 (e.g. Channel Quality Indicators (CQI), etc.). The motivation of this scheme
is to achieve frequency selective gain. This FS R-PDCCH transmission has the following
characteristics:
■ The PRBs assigned to each relay station 7 are not shared with other relay stations
7.
■ The resources (PRBs) not used for FS R-PDCCH transmission can be reused for
R-PDSCH and Rel'8/Rel' 10 MT's PDSCH transmission particularly if the
number of relay stations is small.
■ CQI feedback is used to select the best PRBs from the semi-statically assigned
PRBs for FS R-PDCCH transmission.
■ Precoding / beamforming can be applied for FS R-PDCCH transmission.
■ Common RS (CRS) or Precoded DM-RS can be used to demodulate the FS RPDCCH.
■ Allocated PRBs can be contiguous or separated.
■ Dynamic selection of PRBs (i.e. number of PRBs and their placement in the
frequency domain) for FS R-PDCCH transmission is possible in each sub-frame.
■ This scheme is mainly suitable for fixed relays and mobile relays with low
mobility (where the channel conditions are not changing quickly over time).
As mentioned above, the inventors believe that the deployment scenarios at the initial
stage of Rel'lO will be mainly based on fixed relay stations 7, so the Frequency selective (FS) RPDCCH
transmission scheme will have some feasibility.
Table 1. Summary of characteristics of FS and FD R-PDCCH transmissions
As discussed above, both FD and FS R-PDCCH transmissions exhibit characteristics that
are important for reliable reception of the R-PDCCH for mobile and fixed relays. Therefore,
from the Layer LI perspective, it is preferable that both FD and FS R-PDCCH transmissions are
supported at an early stage of the Relay specification development. Therefore, the inventors
prefer the option C) for R-PDCCH placement in frequency domain and option c) for Interleaving
described above.
Different options will now be discussed for supporting both FD and FS R-PDCCH
transmissions with the same donor base station 5.
Option 1: Frequency diversity R-PDCCH and Frequency selective R-PDCCH
transmissions are not supported in the same cell of the donor base station 5. For example, in the
low mobility areas or for fixed relays, only Frequency selective R-PDCCH transmission is
supported within the corresponding cell and in the high mobility areas, only Frequency diversity
R-PDCCH transmission is supported in the corresponding cell. This option has a small impact
on the LTE specification. For example, in cell specific mapping, 1 bit can be added in the
system information to define whether the cell is FD R-PDCCH or FS R-PDCCH. However, this
option provides no flexibility for co-existence of Frequency diversity R-PDCCH and Frequency
selective R-PDCCH transmissions in the cell.
Option 2 : Both Frequency diversity R-PDCCH and Frequency selective R-PDCCH
transmissions are supported in the same cell, but not in the same sub-frame 15-B. With this
option, the base station 5 will apply Time Division Multiplexing into different sub-frames for
Frequency diversity and Frequency selective R-PDCCH transmissions. Each relay station 7 will
be informed by higher layers, in a semi-static manner (i.e. semi-static signaling from higher
layers (RRC/MAC layers)), about which of these two types of R-PDCCH transmissions to
monitor. Each relay station 7 will then monitor its R-PDCCH in all the backhaul sub-frames 15-
B regardless of whether the sub-frame 15-B carries the Frequency diversity R-PDCCH
transmission or the Frequency selective R-PDCCH transmission. If the relay station 7 is not
scheduled then the decoding will fail anyway. In this way, the relay station 7 does not need to be
told if the sub-frame uses Frequency diversity R-PDCCH transmission or Frequency selective RPDCCH
transmission.
Option 3: Both Frequency diversity and Frequency selective R-PDCCH transmissions
are supported in the same cell and in the same sub-frame 15-B, as shown on Figure 6. In this
option, the base station 5 will use FDM multiplexing in the same sub-frame 15-B (and,
depending on the number of relay stations 7, TDM multiplexing into different sub-frames) for
Frequency diversity R-PDCCH and Frequency selective R-PDCCH transmissions. Thus, as
shown in Figure 6, the R-PDCCH control data for relay stations A, B and C is transmitted using
Frequency diversity R-PDCCH transmission and the R-PDCCH control data for relay stations D
ad E is transmitted using Frequency selective R-PDCCH transmission; and Frequency Division
Multiplexing is used to separate the two types of transmissions. If the base station 5 is serving
other relay stations 7 in the same cell, then it will use TDM multiplexing between different subframes
15-B to provide the R-PDCCH for all the served relay stations. With this option, each
relay station 7 will be informed from higher layers, in a semi-static manner (i.e. semi-static
signaling from higher layers (RRC/MAC)), about which of these two R-PDCCH transmissions to
monitor. The relay station 7 will then monitor its R-PDCCH in all the backhaul sub-frames 15-B
and if it is not scheduled in the sub-frame 15-B then the decoding will fail anyway.
PRB Determination
In 3GPP standards Specification TR36.814 VI. 5.0, it was agreed that the actual resources
used for R-PDCCH transmission within the semi-statically assigned PRBs may vary dynamically
between sub-frames 15. As a result, it seems necessary that the relay stations 7 will have to
perform a number of blind decodings of the R-PDCCH, in order to find out the actual PRBs
used for R-PDCCH transmission for that relay station 7 within the semi-statically assigned PRBs
in each backhaul sub-frame 15-B. The way in which such blind decoding is performed will be
apparent to those skilled in the art and further details can be found from the 3GPP standards
documentation. In summary, however, the relay station will perform a blind decoding by
collecting the data from the PRBs, demodulating the data, de-rate-matching, convolutional
decoding, computing the CRC and masking with the Relay ID. Only if the PRBs carry data for
the relay station will the blind decoding output a useful result. Otherwise the decoding will fail
and the output will be meaningless.
When carrying out the blind decodings, each relay station 7 will try different
combinations of PRBs in each attempt within the semi-statically assigned PRBs. It is not
desirable that the relay stations 7 try all possible combinations of PRBs as this increases
complexity and decoding delay. In order to reduce the blind decoding search space, the semistatically
assigned PRBs can be divided into groups or subsets and the relay stations 7 attempt
the blind decodings based on the PRBs in the groups/subsets. This will be explained by way of
example in the following:
In case of frequency diversity (FD) R-PDCCH transmission:
In this case it is proposed to use a list of predefined subsets where each subset consists of
a number of the PRBs that have been semi-statically defined as being PRBs used for R-PDCCH.
For example with a 5MHz bandwidth (i.e. 25PRBs) the number of semi-statically allocated
PRBs used for R-PDCCH may be set as the following eight PRBs:
■ PRB indices = {0, 3, 6, 9, 13, 16, 19, 22}
And three subsets are defined as follows:
■ Subset 1, 8PRB indices {0, 3, 6, 9, 13, 16, 19, 22}
■ Subset 2, 4PRB indices = {0, 3, 13, 16}
■ Subset 3, 2PRB indices = {0, 13}
A relay station 7 assigned to receive its R-PDCCH data on a Frequency Diversity
transmission would then perform the blind decoding firstly by trying to decode subset 1 and if
that does not decode, then by trying to decode subset 2 and if that does not decode then by trying
to decode subset 3. If none of the blind decodings work, then the relay station 7 concludes that
the sub-frame 15-B does not have any data for it and takes no further action in respect of the
current sub-frame 15-B. If a decoding does work, then the relay station 7 recovers the RPDCCH
data from the decoded resources and receives any user data in the R-PDSCH on the
resources defined by the decoded R-PDCCH.
In case of frequency selective (FS) R-PDCCH transmission:
In this case it is proposed to define only one large subset upon which each relay station 7
can do the blind decoding satisfactorily. It is preferable that this subset is the same as the first
subset (i.e. the largest subset - Subset 1) defined for the case of FD R-PDCCH transmission. For
example with a 5MHz bandwidth (i.e. 25PRBs) the number of semi-statically allocated PRBs
used for R-PDCCH may be set to the following eight PRBs:
■ PRB indices = {0, 3, 6, 9, 13, 16, 19, 22}
And one subset is defined as follows:
■ 8PRB indices {0, 3, 6, 9, 13, 16, 19, 22}
A relay station 7 assigned to receive its R-PDCCH data on a Frequency Selective
transmission would then perform the blind decoding firstly by trying to decode PRB index 0
separately, then PRB index 3 etc. until the last PRB index 22. It is also possible to aggregate two
PRBs or more in each sub-frame within the subset. If none of the blind decodings work, then the
relay station 7 concludes that the sub-frame 15-B does not have any data for it and so it takes no
further action in respect of the current sub-frame. If a decoding does work, then the relay station
7 recovers the R-PDCCH data from the decoded resources and receives any user data in the RPDSCH
on the resources defined by the decoded R-PDCCH.
As discussed above, each relay station 7 will be signaled in advanced to monitor FD or
FS R-PDCCH transmissions and it will store data that defines the subsets of PRBs upon which
the blind decodings are to be performed.
Figure 7 shows an example of how the R-PDCCH data for different relay stations 7 can
be multiplexed onto different ones of the semi-statically assigned PRBs used for carrying the RPDCCH
on FD or FS R-PDCCH transmissions. Figure 7 also illustrates how the R-PDCCH data
for different relay stations 7 can be transmitted in different sub-frames 15-B.
In particular, in this example there are ten relay stations Rl to R10 that are served by the
base station 5, with relay stations R2, R3, R6, R8, R9 and R10 being semi-statically configured
to receive their R-PDCCH data on FD R-PDCCH transmissions and with relay stations Rl, R4,
R5, R6 and R7 being semi-statically configured to receive their R-PDCCH data on FS RPDCCH
transmissions. PRBs used for FD R-PDCCH transmissions are shown with hatching
and the PRBs used for FS R-PDCCH transmissions are shown with stippling. Thus in the
example illustrated in Figure 7 :
1) during sub-frame n the FD relay stations R2, R3, R6, R8, R9 and R10
(or a subset of them) receive their R-PDCCH control data on the PRBs
in Subset 2 defined above; whilst FS relay station Rl receives its RPDCCH
control data on PRB 6, FS relay station R4 receives its RPDCCH
control data on PRB 9, FS relay station R7 receives its RPDCCH
control data on PRB 19 and FS relay station R5 receives its RPDCCH
control data on PRB 22.
2) during sub-frame n+4 the FD relay stations R2, R3, R6, R8, R9 and
Rl 0 (or a subset of them) receive their R-PDCCH control data on the
PRBs in Subset 2 defined above; whilst FS relay station Rl receives its
R-PDCCH control data on PRBs 6 and 9 and FS relay station R5
receives its R-PDCCH control data on PRBs 19 and 22.
3) during sub-frame n+7 the FD relay stations R2, R3, R6, R8, R9 and
RIO (or a subset of them) receive their R-PDCCH control data on the
PRBs in Subset 3 defined above; whilst FS relay station Rl receives its
R-PDCCH control data on PRB 3, FS relay station R4 receives its RPDCCH
control data on PRBs 6 and 9, FS relay station R5 receives its
R-PDCCH control data on PRB 16 and FS relay station R7 receives its
R-PDCCH control data on PRBs 19 and 22.
4) during sub-frame n+10 the FD relay stations R2, R3, R6, R8, R9 and
RIO are not scheduled by the base station 5 to receive any data; whilst
FS relay station R4 receives its R-PDCCH control data on PRBs 0 and
3, FS relay station Rl receives its R-PDCCH control data on PRBs 6
and 9, and FS relay station R7 receives its R-PDCCH control data on
PRBs 13, 16, 19 and 22.
5) during sub-frame n+13 the FS relay stations Rl, R4, R5, R6 and R7 are
not scheduled by the base station 5 to receive any data; whilst FD relay
stations R2, R3, R6, R8, R9 and RIO (or a subset of them) receive their
R-PDCCH control data on the PRBs in Subset J defined above.
In this way, the base station 5 is able to vary the number of relay stations 7 and which
ones that will receive R-PDCCH and user data in any given sub-frame. This facilitates the
efficient use of the PRBs that have been semi-statically allocated for carrying the R-PDCCH for
the different relay stations 7 served by the base station 5.
As those skilled in the art will appreciate, it is preferable that the number of PRB subsets
that are defined is not too large as the number of blind decodings that the FD relay stations 7
have to perform increases with the number of subsets that are defined.
In the above example, the largest subset (Subset 1) includes all the PRBs that are semistaticaly
allocated for R-PDCCH transmission. However, it is possible that the number of semistatically
allocated PRBs is larger than the number of PRBs in the largest "Subset" described
above. In this case, the PRBs allocated for R-PDCCH transmission can be divided into two or
more smaller and distinct groups. Each relay station 7 would then be semi-statically assigned
from a higher layer to one of these PRE groups. It is also possible some relay stations will be
more powerfull than others and can therefore carry out more complex blind decodings than
others. For example some relays staions may be exected to serve many mobile devices (such as
in a built up urban area, whereas other relay stations in rural or domestic locaions may be
simpler and may only be intended to serve a few mobile devices. In this case, the simpler relay
stations may be assigned to a smaller group of PRBs - so that its search space for the blind
decodings is small and the more complex relay stations may be assigned to a larger group or
groups of PRBs as it is capable of performing more blind decodings.
Conclusion
Among the above three options, Option 1 is the least preferred by the inventors as it can
not support both FD and FS R-PDCCH transmissions in the same cell. Of the remaining two
options, Option 3 is preferred by the inventors due to flexible multiplexing and co-existence of
FD and FS R-PDCCH transmissions in the same backhaul sub-frame 15-B of the cell.
Base station
Figure 8 is a block diagram illustrating the main components in the base station 5 shown
in Figure 1. As shown, the base station 5 includes a transceiver circuit 31 which is operable to
transmit sigrials to, and to receive signals from, the Direct MTs 3 and the relay stations 7 via one
or more antennae 33 (using the above described sub-carriers) and which is operable to transmit
signals to and to receive signals from the core network 8 via a network interface 35. The
operation of the transceiver circuit 3 1 is controlled by a controller 37 in accordance with
software stored in memory 39. The software includes, among other things, an operating system
41, a communications control module 43 having a resource allocation module 45 and a scheduler
module 47. The communications control module is operable to control the generation of the subframes
for carrying the data to the Direct MTs 3 and the relay stations 7 using the resource
allocations module 45 and the scheduler module 47. The resource allocation module 45 is
operable for allocating the resource blocks to be used by the transceiver circuit 31 in its
communications with each of the Direct MTs 3 and with the relay stations 7, depending on the
amount of data to be transmitted to those devices. The scheduler module 47 is operable to
schedule the times for the transmission of the downlink data to the Direct MTs 3 and the relay
stations 7. The communications control module 43 controls the generation of the appropriate RPDCCH
control data 26 for each relay station and the way that it is transmitted in the sub-frame
15-B, in the manner discussed above. The communications control module 43 also generates
and signals the relevant semi-static configuration data for each relay station 7 defining, for
example, whether the relay station 7 is to receive its R-PDCCH control data in an FD or FS RPDCCH
transmission; defining the semi-statically allocated PRBs to be used for R-PDCCH and
any other semi-statically defined parameters (such as the above described subsets).
Relay Station
Figure 9 schematically illustrates the main components of each of the relay stations 7
shown in Figure 1. Each relay station 7 may be a fixed communications node like a base station
5 or may itself be a mobile device. Indeed, some mobile telephones 3 may provide relay
services and therefore act as relay stations. As shown, each relay station 7 includes a transceiver
circuit 51 which is operable to transmit signals to, and to receive signals from, Relay MTs 3 and
the base station 5 via one or more antennae 53 (using the above described sub-carriers). The
operation of the transceiver circuit 51 is controlled by a controller 57 in accordance with
software stored in memory 59. The software includes, among other things, an operating system
6 1 and a communications control module 62 that includes a resource decoding module 63, a
resource allocation module 65 and a scheduler module 67. The communications control module
62 is operable to generate the relay sub-frames 15-R discussed above and to generate the
appropriate gaps in some of those sub-frames to allow the relay station to receive part of the subframes
15-B transmitted by the base station 5. The communications control module 62 is also
operable to control the transceiver circuit 5 1 to transmit those sub-frames and then to switch the
transceiver to a receive mode to receive the base station data (and then to switch the transceiver
back to the transmit mode before the start of the next sub-frame). The resource decoding module
63 is operable to process (in accordance with the semi-statically defined configuration data
received from the base station 5 or the core network 8) the received portion of the base station
sub-frame 15-B to locate and decode its R-PDCCH control data 26 in the manner described
above and, if decoded, to determine if the received base station sub-frame 15-B also includes
"user" data (as opposed to control data) for that relay station 7. If it does, then the resource
blocks in which that user data can be found is determined from the decoded R-PDCCH control
data and the user data is then recovered from the sub-frame 15-B and stored in memory for use
by the relay station 7 or for onward transmission to a Relay MT 3. The resource allocation
module 65 is operable for allocating the resource blocks used by the transceiver circuit 51 in its
communications with each of the Relay MTs 3 and with the base station 5, depending on the
amount of data to be transmitted to those devices. The scheduler module 67 is operable to
schedule the times for the transmission of appropriate sub-frames to relay the appropriate data to
the Relay MTs 3.
In the above description, the base station 5 and the relay stations 7 are described, for ease
of understanding, as having a number of discrete modules (such as the communications control,
resource allocation and scheduler 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.
Modifications and Alternatives
A number of 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 whilst still benefiting from the inventions embodied therein.
In the above embodiments, a mobile telephone based telecommunications system was
described. As those skilled in the art will appreciate, the signalling techniques described in the
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.
In the above embodiments, MBSFN sub-frames were used for relay purposes. As those
skilled in the art will appreciate, this is not essential and as other types of sub-frames may be
used.
In the above embodiments, the relay station received data from the base station and
relayed it to the Relay MTs. As those skilled in the art will appreciate, the relay station may
relay the received data to one or more other relay stations, before the data reaches its destination.
In this case, the first relay station would generate a sub-frame that included relay control data in
the user data part of the sub-frame (i.e. in the PDSCH) - so that the subsequent relay station can
recover the relay control data in a similar manner to that described above.
In the above embodiment, the base station transmitted PDCCH control data for a number
of relay stations within the same sub-frame. As those skilled in the art will appreciate, the
number of relay stations that will receive relay control data within a sub-frame may be varied
and the above embodiments have been described by way of example only.
In the embodiments described above, the mobile telephone, the relay station and the base
station will each include transceiver circuitry. Typically this circuitry will be formed by
dedicated hardware circuits. However, in some embodiments, part of the transceiver circuitry
may be implemented as software run by the corresponding controller.
In the above embodiments, a number of software modules were described. As those
skilled in the art will appreciate, the software modules may be provided in compiled or uncompiled
form and may be supplied to the base station or the relay station as a signal over a
computer network, or on a recording medium. Further, the functionality performed by part or
all of this software may be performed using one or more dedicated hardware circuits. However,
the use of software modules is preferred as it facilitates the updating of the base stations,
gateways, and the mobile telephones in order to update their functionalities.
Various other modifications will be apparent to those skilled in the art and will not be
described in further detail here.
The following is a detailed description of the way in which the present inventions may be
implemented in the currently proposed 3GPP standard. Whilst various features are described as
being essential or necessary, this may only be the case for the proposed 3GPP standard, for
example due to other requirements imposed by the standard. These statements should not,
therefore, be construed as limiting the present invention in any way.
1 Introduction
Prior current RANl#59Bis meeting, an e-mail discussion was re-initiated to discuss the
open issues of the Relay Type 1 backhaul design. One of the open issues is the R-PDCCH
multiplexing comprising Interleaving, R-PDCCH placement in frequency domain and R-PDCCH
region size in time domain.
It is our views that the deployment scenarios at the early stage of Rel'lO will be mainly
based on fixed relay nodes, and for further deployments at the later stages, mobile relay will also
be employed. Therefore, it is important to clarify the necessity of supporting both frequency
diversity R-PDCCH transmission for mobile relays and frequency selective R-PDCCH
transmissions for fixed relays in the backhaul subframe of the cell and their impact on the choice
of the open issues such as interleaving and R-PDCCH placement in frequency domain.
This contribution provides motivation and methods of supporting both frequency
diversity and frequency selective R-PDCCH transmissions in the system (e.g. same donor eNB).
2 R-PDCCH Multiplexing issues
The open issues of R-PDCCH multiplexing comprise R-PDCCH region size in time
domain, R-PDCCH placement in frequency domain and Interleaving.
For R-PDCCH region size in time domain, the discussion points remain as in our
earlier contribution [5] in RANl#58Bis relating FDM and TDM+FDM multiplexing schemes.
In terms of flexibility for resource and power sharing between R-PDCCH and Rel'8 UE's
PDSCH, it seems that FDM scheme is more flexible and simpler.
Therefore, our preference is FDM multiplexing scheme. We also see no reason to
exclude the TDM+FDM multiplexing scheme by flexibly allocating the last OFDM symbol for
R-PDCCH transmission in the cell.
For R-PDCCH placement in frequency domain, we think that there are three possible
options described below.
A) Distributed placement where the R-PDCCH for a particular relay is distributed on
two or more well-separated PRBs which may be shared by more than one relay. This option
achieves frequency diversity gain.
B) Localised placement where the R-PDCCH for a particular relay is placed on
contiguous or very close PRBs which are not shared by other relays. This option achieves
frequency selective gain.
C) Both distributed and localised placements of the R-PDCCH transmission.
Our preference is that both distributed and localised placements of the R-PDCCH
transmission are supported (i.e. option C), and we will discuss the motivation of that in the
coming sections.
We note that on the R-PDCCH region point of view (i.e. semi-statically assigned PRBs),
we prefer that the R-PDCCH region is distributed in frequency domain as a baseline for all
options achieving their frequency diversity gain and frequency selective gain.
For Interleaving, we think that there are three possible options of:
a) Full interleaving where all R-PDCCHs for different relays are interleaved together in
the current backhaul subframe. The unit size of interleaving can be resource-element group
(REG) similar to Rel'8 PDCCH interleaving or control channel element (CCE).
b) No interleaving where all R-PDCCHs for different relays are not interleaved in the
current backhaul subframe.
c) Mixed case of interleaving and no-interleaving where some R-PDCCHs for different
relays are interleaved together and some R-PDCCHs for other relays are not interleaved.
Our preference is to support "mixed case of interleaving and no-interleaving" (i.e.
option c), and we will discuss the motivation of that in the coming sections.
3 Frequency diversity R-PDCCH transmission
In Frequency diversity (FD) R-PDCCH transmission, the R-PDCCHs for different relays
are multiplexed and interleaved and mapped to all or subset of semi-statically assigned PRBs for
R-PDCCH transmission shown on Fig. 10a as A+B+C+D below. It is the case of selecting option
A) for R-PDCCH placement in frequency domain and option a) for Interleaving described in the
previous section 2. The main motivation is to achieve robustness against interference and
channel fluctuations. This FD R-PDCCH transmission has the following characteristics:
■ PRBs semi-statically assigned to R-PDCCH transmission are shared by some or
all relays.
■ All interleaved resources (PRBs) for FD R-PDCCH transmission are occupied
even if the number of Relays is small.
■ Precoding / beamforming can't be applied for FD R-PDCCH transmission.
■ Allocated PRBs are well-separated (i.e. frequency distributed) to achieve
frequency diversity gain.
■ Common RS (CRS) can be used to demodulate the FD R-PDCCH.
■ Dynamic selection of PRBs (i.e. number of PRBs and placement in frequency
domain) for FD R-PDCCH transmission is possible in each subframe.
■ This is suitable for both fixed and mobile relays.
4 Frequency selective R-PDCCH transmission
The Frequency selective (FS) R-PDCCH transmission is the case selecting of option B)
for R-PDCCH placement in frequency domain and option b) for Interleaving described in the
previous section 2. It is based on the feedback from the Relay (CQI, etc.). The motivation is to
achieve frequency selective gain by placing each Relay's R-PDCCH on the PRBs with good
channel conditions within the semi-statically assigned PRBs for R-PDCCH transmission shown
on Fig. 10b as A, B, C, D below. This FS R-PDCCH transmission has the following
characteristics:
■ PRBs assigned to each relay are not shared with other relays.
■ The resources (PRBs) not used for FS R-PDCCH transmission can be reused for
R-PDSCH and Rel'8 UE's PDSCH transmission particularly if the number of
Relays is small.
■ CQI feedback is used to select the best PRBs from the semi-statically assigned
PRBs for FS R-PDCCH transmission.
■ Precoding / beamforming can be applied for FS R-PDCCH transmission.
■ Common RS (CRS) or Precoded DM-RS can be used to demodulate the FS RPDCCH.
■ Allocated PRBs can be contiguous or separated.
■ Dynamic selection of PRBs (i.e. number of PRBs placement in frequency
domain) for FS R-PDCCH transmission is possible in each subframe.
■ This is mainly suitable for fixed relays and mobile relays with low mobility.
As mentioned in section 1, we think that the deployment scenarios at the initial stage of
Rel'lO will be mainly based on fixed relay nodes, so the Frequency selective (FS) R-PDCCH
transmission will have some feasibility.
Table 2. Summary of characteristics for FS and FD R-PDCCH transmissions
5 How to support both FD and FS R-PDCCH transmissions in the system
As discussed in section 3 and 4 above, both FD and FS R-PDCCH transmissions exhibit
characteristics that are important for reliable reception of the R-PDCCH for mobile and fixed
relays. Therefore, from LI perspective, it is preferable both FD and FS R-PDCCH transmissions
to be supported at early stage of the Relay specification development. So we prefer the option C)
for R-PDCCH placement in frequency domain and option c) for Interleaving described in the
previous section 2. Next, we discuss possible options for supporting both FD and FS R-PDCCH
transmissions in the system (e.g. same donor eNB).
Option 1: Frequency diversity R-PDCCH and Frequency selective R-PDCCH
transmissions are not supported in the same cell. For example, in the low mobility areas or for
fixed relays, only Frequency selective R-PDCCH is supported and in the high mobility areas,
only Frequency diversity R-PDCCH transmission is supported in the cell.
■ Small impact for the specification. For example, in cell specific mapping, 1
bit can be added in the system information.
■ No flexibility for co-existence of Frequency diversity R-PDCCH and
Frequency selective R-PDCCH transmissions in the cell.
Option 2: Both Frequency diversity R-PDCCH and Frequency selective R-PDCCH
transmissions are supported in the same cell, but not in the same subframe.
■ eNB will apply TDM multiplexing into different subframes for Frequency
diversity and Frequency selective R-PDCCH transmissions.
Relay will be informed from higher layers in semi-static manner about which
of these two R-PDCCH transmissions to monitor.
■ Relay will monitor its R-PDCCH in all the backhaul subframes regardless
whether the subframe carries the Frequency diversity R-PDCCH and
Frequency selective R-PDCCH and if it is not scheduled the decoding will
fail anyway.
Option 3: Both Frequency diversity and Frequency selective R-PDCCH transmissions
are supported in the same cell and in the same subframe as shown on Fig. 11 below.
■ eNB will use FDM multiplexing in the same subframe and TDM
multiplexing into different subframes for Frequency diversity R-PDCCH and
Frequency selective R-PDCCH transmissions.
■ Same as Option 2, Relay will be informed from higher layers in semi-static
manner about which of these two R-PDCCH transmissions to monitor.
■ Relay will monitor its R-PDCCH in all the backhaul subframes and if it is
not scheduled the decoding will fail anyway.
Among above three options, Option 1 is least preferred as it can not support both FD and
FS R-PDCCH transmissions in the same cell. From the remaining two options, Option 3 is
preferable due to flexible multiplexing and co-existence of FD and FS R-PDCCH transmissions
in the same backhaul subframe of the cell.
6 Conclusion
In this contribution, we have discussed the motivation and methods of supporting both
frequency diversity and frequency selective R-PDCCH transmissions in the system (e.g. same
donor eNB). The following three methods/options were identified:
Option 1: Frequency diversity R-PDCCH and Frequency selective R-PDCCH
transmissions are not supported in the same cell.
Option 2 : Both Frequency diversity R-PDCCH and Frequency selective R-PDCCH
transmissions are supported in the same cell, but not in the same subframe.
■ eNB will apply TDM multiplexing into different subframes for Frequency
diversity and Frequency selective R-PDCCH transmissions.
Option 3 : Both Frequency diversity and Frequency selective R-PDCCH transmissions
are supported in the same subframe and in the same cell.
■ eNB will use FDM multiplexing in the same subframe and TDM
multiplexing into different subframes for Frequency diversity R-PDCCH and
Frequency selective R-PDCCH transmissions.
We propose to support both Frequency diversity R-PDCCH and Frequency selective RPDCCH
transmissions in the same subframe and in the same cell (i.e. Option 3) due to flexible
multiplexing.
7 References
1) TR 36.814 Vl.5.0
2) Rl -092249, "Text proposal on backhaul resource assignment", Nokia, Nokia Siemens
Networks, Ericsson, Motorola, RIM, TI, NEC, Samsung, Huawei, CATT,LGE,
CMCC, Qualcomm, ZTE.
3) Rl -092969, "Type 1 backhaul link", Ericsson, NEC, Samsung, Motorola, Panasonic,
RIM, LGE, Nokia, Nokia Siemens Networks, Qualcomm, Huawei, Alcatel-Lucent,
CATT,Texas Instruments.
4) Rl -092965, "Control Structure for Relay Type 1 nodes", NEC group.
5) Rl-093863, "Issues on Relay type J control design", NEC group.
6) Rl -0945 17, "Control signalling placement design for relay nodes", Panasonic
7) Rl -095088, "Summary of email discussion on Type 1 Relay backhaul design issues",
Panasonic.
This application is based upon and claims the benefit of priority from United Kingdom
patent application No. 1000449.7, filed on January 12, 2010, the disclosure of which is
incorporated herein in its entirety by reference.
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CLAIMS
1. A communications station operable to communicate with a number of communications
devices, including a number of relay stations, using a communication cell, wherein the
communications station is operable to transmit, within the cell, a sequence of sub-frames, and is
operable to use frequency division multiplexing to transmit relay control data for different relay
stations using both frequency selective transmission and frequency diversity transmission in the
same sub-frame of the cell.
2. A communications station according to claim 1, which is operable to transmit
configuration data in advance to each relay station identifying if the relay station is to monitor
frequency selective transmissions or frequency diversity transmissions.
3. A communications station according to claim 2, wherein the configuration data includes
data defining one or more subsets of Physical Resource Blocks that may carry the control data.
4. A communications station according to any of claims 1, 2 or 3, wherein for said frequency
diversity transmission, the communications station is operable to transmit relay control data for
plural relay stations in an interleaved manner on one or more Physical Resource Blocks.
5. A communications station according to any of claims 1 to 4, wherein for said frequency
selective transmission, the communications station is operable to transmit relay control data for
plural relay stations in a non interleaved manner on a respective plurality of Physical Resource
Blocks.
6. A communications station according to any of claims 1 to 5, which is operable to transmit
relay control data for different groups of relay stations in different sub-frames.
7. A communications station comprising:
a communications controller operable to generate a sub-frame comprising an initial part
including control data and a subsequent part including user data for devices served by the
communications station; and
a transceiver operable to transmit the generated sub-frame for receipt by the devices
served by the communications station;
wherein the communications controller is operable to include relay control data for a
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plurality of relay stations served by the communications station within the subsequent part of the
generated sub-frame; wherein the communications controller is operable to use frequency
division multiplexing to transmit relay control data for different relay stations using both a
frequency selective transmission and a frequency diversity transmission in the same sub-frame of
the cell.
8. A relay station operable to communicate with a remote communications device that
communicates using a communication cell, wherein the relay station is operable to receive,
within the cell, a sequence of sub-frames, wherein at least one sub-frame includes relay control
data for different relay stations using a frequency selective transmission and a frequency
diversity transmission; wherein the relay station is operable to receive configuration data
identifying if its relay control data will be transmitted using frequency diversity transmission or
configuration data identifying if its relay control data will be transmitted using frequency
selective transmission and wherein the relay station is operable to use the received configuration
data to recover its relay control data from the at least one sub-frame.
9. A relay station according to claim 8, which is operable to receive said configuration data
in advance of receiving said at least one sub-frame and operable to use the received
configuration data to recover its relay control data from plural sub-frames until the relay station
receives new configuration data.
10. A relay station according to claim 8 or 9, wherein the configuration data identifies a
plurality of Physical Resource Blocks that are used for carrying relay control data and wherein
the relay station is operable to attempt a plurality of blind decodings of the Physical Resource
Blocks identified by the configuration data, in order to find out the actual Physical Resource
Blocks used to carry the control data for the relay station.
11. A relay station according to claim 10, wherein the configuration data includes data
defining a plurality of subsets of Physical Resource Blocks that are used for carrying relay
control data and wherein the relay station is operable to limit the number of blind decodings that
it performs using the data defining the plurality of subsets.
12. A relay station according to any of claims 8 to 11, wherein for said frequency diversity
transmission, the received sub-frame includes relay control data for plural relay stations in an
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interleaved manner on one or more Physical Resource Blocks.
13. Arelay station according to any of claims 8 to 1 , wherein for said frequency selective
transmission, the received sub-frame includes relay control data for plural relay stations in a non
interleaved manner on a respective plurality of Physical Resource Blocks.
14. Arelay station according to any of claims 8 to 13, wherein the received sub-frame uses
separate Physical Resource Blocks to carry the frequency selective transmission and the
frequency diversity transmission.
15. Arelay station according to claim 14, wherein the Physical Resource Blocks used to
carry the frequency selective transmission and the Physical Resource Blocks used to carry the
frequency diversity transmission are interleaved with each other.
16. Arelay station according to any of claims 8 to 15, which is operable to receive a plurality
of sub-frames and is operable to perform blind decodings on predetermined Physical Resource
Blocks of each sub-frame to identify if the sub-frame includes control data for the relay station.
17. A relay station according to claim 16, wherein if the relay station is unable to decode any
of the predetermined Physical Resource Blocks of a frame, then the sub-frame does not include
any data for the relay station; and if the relay station is able to decode one or more of the
Physical Resource Blocks to recover the relay control data, then the relay station uses the relay
control data to identify resources used within the sub-frame that carries other data for the relay
station and is operable to recover this other relay data from the identified resources.
18. Acommunications station operable to communicate with a number of communications
devices, including a number of relay stations, using a communication cell, wherein the
communications device is operable to transmit, within the cell, a sequence of sub-frames, and is
operable to transmit relay control data for different relay stations only using a frequency
selective transmission in some sub-frames of the cell and to transmit relay control data for
different relay stations only using a frequency diversity transmission in other sub-frames of the
cell.
19. Arelay station operable to communicate with a remote communications device that
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communicates using a communication cell, wherein the relay station is operable to receive,
within the cell, a sequence of sub-frames, wherein some sub-frames include relay control data
for different relay stations only using a frequency selective transmission and other sub-frames
include relay control data for different relay stations only using a frequency diversity
transmission; wherein the relay station is operable to receive configuration data identifying if its
relay control data will be transmitted in a sub-frame that uses frequency diversity transmission or
configuration data identifying if its relay control data will be transmitted in a sub-frame that uses
frequency selective transmission and wherein the relay station is operable to use the received
configuration data to recover its relay control data from the corresponding sub-frame.
20. A communications station operable to communicate with a number of communications
devices, including a number of relay stations, using a plurality of communication cells, wherein
the communications device is operable to transmit, in at least one of said cells, relay control data
for different relay stations only using a frequency selective transmission and to transmit, in at
least one other of said communications cells, relay control data for different relay stations only
using a frequency diversity transmission.
21. A communications system comprising a communications device according to any of
claims 1 to 7, 18 or 20 and a relay station of any of claims 8 to 17 or 19 and one or more mobile
devices.
22. A communications method performed by a communications station that communicates
with a number of communications devices, including a number of relay stations, using a
communication cell, wherein the communications method transmits, within the cell, a sequence
of sub-frames, and transmits relay control data for different relay stations using both frequency
selective transmission and frequency diversity transmission in the same sub-frame of the cell.
23. A communications method according to claim 22, comprising transmitting configuration
data in advance to each relay station identifying if the relay station is to monitor frequency
selective transmissions or frequency diversity transmissions.
24. A communications method according to claim 23, wherein the configuration data
includes data defining one or more subsets of Physical Resource Blocks that may carry the
control data.
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25. A communications method according to claim 22, 23 or 24, wherein for said frequency
diversity transmission, the communications method transmits relay control data for plural relay
stations in an interleaved manner on one or more Physical Resource Blocks.
26. A communications method according to any of claims 22 to 25, wherein for said
frequency selective transmission, the communications method transmits relay control data for
plural relay stations in a non interleaved manner on a respective plurality of Physical Resource
Blocks.
27. A communications method according to any of claims 22 to 26, that uses separate
Physical Resource Blocks to carry the frequency selective transmission and the frequency
diversity transmission.
28. A communications method according to claim 27, comprising interleaving the Physical
Resource Blocks used to carry the frequency selective transmission and the Physical Resource
Blocks used to carry the frequency diversity transmission.
29. A communications method according to any of claims 22 to 28, which transmits relay
control data for different groups of relay stations in different sub-frames.
30. A control method performed by a relay station that communicates with a remote
communications device using a communication cell, wherein the method comprises receiving,
within the cell, a sequence of sub-frames, wherein at least one sub-frame includes relay control
data for different relay stations using a frequency selective transmission and a frequency
diversity transmission; receiving configuration data identifying if the relay control data for the
relay station will be transmitted using frequency diversity transmission or frequency selective
transmission and wherein the method uses the received configuration data to recover the relay
control data for the relay station from the at least one sub-frame.
31. A method according to claim 30, that receives said configuration data in advance of
receiving said at least one sub-frame and that use the received configuration data to recover the
relay control data for the relay station from plural sub-frames until the relay station receives new
configuration data.
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32. A method according to claim 30 or 31, wherein the configuration data identifies a
plurality of Physical Resource Blocks that are used for carrying relay control data and wherein
the method attempts a plurality of blind decodings of the Physical Resource Blocks identified by
the configuration data, in order to find out the actual Physical Resource Blocks used to carry the
control data for the relay station.
33. A method according to claim 32, wherein the configuration data includes data defining a
plurality of subsets of Physical Resource Blocks that are used for carrying relay control data and
wherein the method uses the data defining the plurality of subsets to limit the number of blind
decodings that are performed.
34. A method according to any of claims 30 to 33, wherein for said frequency diversity
transmission, the received sub-frame includes relay control data for plural relay stations in an
interleaved manner on one or more Physical Resource Blocks.
35. A method according to any of claims 30 to 34, which receives a plurality of sub-frames
and which performs blind decodings on predetermined Physical Resource Blocks of each subframe
to identify if the sub-frame includes control data for the relay station.
36. A method according to claim 35, wherein if the method is unable to decode any of the
predetermined Physical Resource Blocks of a sub-frame, then the sub-frame does not include
any data for the relay station; and if the method is able to decode one or more of the Physical
Resource Blocks to recover the relay control data, then the method further comprises using the
decoded relay control data to identify resources used within the sub-frame that carries other data
for the relay station and recovering this other relay data from the identified resources.
37. A method according to any of claims 30 to 36, wherein for said frequency selective
transmission, the received sub-frame includes relay control data for plural relay stations in a non
interleaved manner on a respective plurality of Physical Resource Blocks.
38. A method according to any of claims 30 to 37, wherein the received sub-frame uses
separate Physical Resource Blocks to carry the frequency selective transmission and the
frequency diversity transmission.
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39. Amethod according to claim 38, comprising interleaving the Physical Resource Blocks
used to carry the frequency selective transmission and the Physical Resource Blocks used to
carry the frequency diversity transmission.
40. A communications method performed by a communications station that communicates
with a number of communications devices, including a number of relay stations, using a
communication cell, wherein the communications method transmits, within the cell, a sequence
of sub-frames, and transmits relay control data for different relay stations only using a frequency
selective transmission in some sub-frames of the cell and transmits relay control data for
different relay stations only using a frequency diversity transmission in other sub-frames of the
cell.
41. A control method performed by a relay station that communicates with a remote
communications device using a communication cell, wherein the method receives, within the cell,
a sequence of sub-frames, wherein some sub-frames include relay control data for different relay
stations only using a frequency selective transmission and other sub-frames include relay control
data for different relay stations only using a frequency diversity transmission; wherein the
method receives configuration data identifying if the relay control data for the relay station will
be transmitted in a sub-frame that uses frequency diversity transmission or frequency selective
transmission and wherein the method uses the received configuration data to recover the relay
control data for the relay station from the corresponding sub-frame.
42. Acommunications method performed by a communications station that communicates
with a number of relay stations, using a plurality of communication cells, wherein the
communications method transmits, in at least one of said cells, relay control data for different
relay stations only using a frequency selective transmission and transmits, in at least one other of
said communications cells, relay control data for different relay stations only using a frequency
diversity transmission.
43. A computer implementable instructions product comprising computer implementable
instructions for causing a programmable computer device to become configured as the
communications station of any of claims 1 to 7 or 18 or 20 or to become configured as the relay
station of any of claims 8 to 17 or 19 or to perform the method of any of claims 22 to 42.