COMMUNICATION SYSTEM
Technical Field
The present invention relates to the communication of data within a mobile (cellular)
communication system and to components of the communication system. The invention has
particular, although not exclusive relevance to the reporting of HARQ feedback information in a
multi-subframe allocation system.
Background Art
OFDMA and single carrier FDMA have been selected as the downlink and uplink
multiple access schemes for the E-UTRA air interface currently being studied in 3GPP (which is
a standard based collaboration looking at the Long Term Evolution (LTE) of mobile
telecommunication systems). In the LTE system, a base station (eNB) which communicates with
a number of user devices (UEs) allocates the total amount of time/frequency resource (depending
on bandwidth) among as many simultaneous users as possible, in order to enable efficient and
fast link adaptation and to attain maximum multi-user diversity gain.
The LTE system provides for both real time (RT) services, such as VoIP, and non-real
time (NRT) services, such as web browsing. The time/frequency resources that allow UEs to use
these services may be allocated dynamically (ie on demand at the time that they are needed) or
semi-persistently depending on the service used. For example, for real time services such as
VoIP, where the amount of resources needed is known in advance, the UEs can be allocated the
resources in advance (semi-persistently allocated), for example at the time of the call setup. For
more "bursty" traffic, such as web browsing traffic, the resources would be allocated
dynamically based on the amount of data to be transmitted between the UE and the eNB at the
time.
For the transmission of downlink dynamically allocated data, a scheduler in the eNB has
the flexibility to dynamically send data on a subframe-by-subframe basis, to pick the preferred
transmission parameters (e.g. resource allocation, Modulation and Coding Scheme (MCS),
Hybrid Acknowledge Repeat Request (HARQ), Power, etc.) to adapt to the changing link
conditions between the eNB and the particular UE and to prioritize among users when
scheduling on the current subframe.
In the LTE system, the physical downlink control channel (PDCCH) carries the
scheduling assignments and other control information. A PDCCH consists of an aggregation of
one or more consecutive control channel elements (CCEs), where a CCE occupies a fraction of
the eNB's available physical radio resources. The total number of CCEs that are available
depends on the system bandwidth of the eNB and the number of OFDM symbols reserved for
PDCCH transmission in a given sub-frame.
In LTE Rel-12, 3GPP are considering introducing a new scheduling approach - multisubframe
scheduling; in which the eNB sends a scheduling assignment that persists for several
subframes (ie. resources are assigned to a UE for multiple subframes with one scheduling
assignment). The eNB may use multi-subframe scheduling for some UEs and traditional singlesubframe
scheduling for other UEs at the same time.
Disclosure of the Invention
Problem(s) to be Solved by the Invention
The inventors have realised, however, that such multi-subframe scheduling can cause
problems in how the UEs should send HARQ ACK/NACK feedback to the eNB. In the current
LTE specification, a UE sends ACK/NACK feedback using a Physical Uplink Control Channel
(PUCCH) resource which is determined by the PDCCH CCE used to send the scheduling
assignment. However if the UE uses the same PUCCH resource in every subframe of the multisubframe
assignment then the eNB must avoid reusing the corresponding PDCCH CCE in those
subframes for single-subframe assignments to other UEs. Otherwise two UEs will try to use the
same PUCCH resource in the same subframe to send ACK/NACK feedback.
Means to Solve the Problem
According to one aspect, the present invention provides a communication node arranged
to communicate with another communication node using communications resources that are
arranged in subframes. The communication node may be a base station and the other
communication node may be a user device, such as a cellular telephone. The communication
node comprises: a scheduler that is arranged to generate and output a control message for the
other communication node which control message allocates communications resources within a
plurality of subframes (typically consecutive subframes) over which the communication node
will transmit at least one codeword in each subframe for the other communication node; a
transceiver that is arranged to transmit the codewords to the other communication node using the
allocated communications resources within the plurality of subframes; and an ACK/NACK
module for receiving, from the other communication node, ACK/NACK feedback for each
codeword indicating acknowledgment of receipt or non-receipt of the codeword, wherein the
ACK/NACK module is arranged to receive, during a subframe, aggregated ACK/NACK
feedback from the other communication node indicating acknowledgment of receipt or nonreceipt
of each of a plurality of codewords transmitted by the communication node in different
subframes, and is arranged to process the aggregated ACK/NACK feedback to control the
scheduler so that any codewords that were not received are scheduled for retransmission to the
other communication node.
In one embodiment, the scheduler is configured to use a plurality of HARQ processes to
control transmission of data to the other communication node, such that a different HARQ
process is used for each subframe within which communications resources are allocated to the
other communication node by said control message. In this case, the scheduler may be arranged
so that an HARQ process that is used to transmit a codeword to the other communication node is
not reused until the ACK/NACK module has received and processed the ACK/NACK feedback
for that codeword. Additionally, the scheduler may be arranged: i) to split available HARQ
processes into two or more groups, the HARQ processes in each group being different; ii) to
generate a first control message that allocates resources within a first plurality of subframes and
a second control message that allocates resources within a second plurality of subframes; iii) to
use HARQ processes from the first group for communications made using the resources
allocated by the first control message; and iv) to use HARQ processes from the second group for
communications made using the resources allocated by the second control message.
In one embodiment, the scheduler is arranged to generate said control message such that
it includes resource assignment data that assigns, to the other communication node, the same
communications resources within each of the plurality of subframes. Preferably also, the
scheduler is arranged to generate said control message such that it includes modulation and
coding scheme, MCS, data that indicates that the same modulation and coding scheme will be
used to modulate and code the codewords that are to be transmitted to the other communication
node using the allocated communications resources within each of the plurality of subframes.
The control message may also include data, for each codeword to be transmitted, that indicates
whether the codeword is a new code word or a retransmission of a previous codeword. The
scheduler may also include within the control message data indicating the number of consecutive
subframes to which the allocation relates.
According to another aspect, the present invention provides a communication node
arranged to communicate with another communication node using communications resources
that are arranged in subframes. In this case, the communication node may be a user device and
the other communication node may be a base station. The communication node comprises: a
communications module that is arranged to receive a control message from the other
communication node, which control message allocates communications resources within a
plurality of subframes over which the other communication node will transmit at least one
codeword in each subframe for the communication node; a transceiver that is arranged to receive
the codewords from the other communication node using the allocated communications
resources within the plurality of subframes; and an ACK/NACK module for generating
ACK/NACK feedback for each codeword indicating acknowledgment of receipt or non-receipt
of the codeword, wherein the ACK/NACK module is arranged to generate aggregated
ACK/NACK feedback and to send the aggregated ACK/NACK feedback to the other
communication node, which aggregated ACK/NACK feedback indicating acknowledgment of
receipt or non-receipt of each of a plurality of codewords received by the communication node in
different subframes.
In one embodiment, the communications module uses a plurality of HA Q processes to
control reception of data received from the other communication node, such that a different
HARQ process is used for each subframe within which communications resources are allocated
to the communication node by said control message. In this case, the communications module
may determine an HARQ process for a codeword using a number of a subframe in which the
codeword is received from the other communication node. The communications module may
also be arranged: i) to receive a first control message that allocates resources within a first
plurality of subframes and a second control message that allocates resources within a second
plurality of subframes; iii) to use HARQ processes from a first group of HARQ processes for
communications made using the resources allocated by the first control message; and iv) to use
HARQ processes from a second group of HARQ processes for communications made using the
resources allocated by the second control message, the HARQ processes in the first group being
different from the HARQ processes in the second group.
The received control message may assign the same communications resources within
each of the plurality of subframes. The control message may also indicate that the same
modulation and coding scheme, MCS, will be used to modulate and code the codewords that are
to be received from the other communication node using the allocated communications resources
within each of the plurality of subframes. The control message may also include data, for each
codeword to be received using the allocated communications resources, that indicates whether
the codeword is a new code word or a retransmission of a previous codeword. The control
message may also include data indicating the number of consecutive subframes to which the
allocation relates.
The present invention also provides a method performed by a communication node that
communicates with another communication node using communications resources that are
arranged in subframes, the method comprising: generating and outputting a control message for
the other communication node that allocates communications resources within a plurality of
subframes over which the communication node will transmit at least one codeword in each
subframe for the other communication node; transmitting the codewords to the other
communication node using the allocated communications resources within the plurality of
subframes; receiving, from the other communication node, ACK/NACK feedback for each
codeword indicating acknowledgment of receipt or non-receipt of the codeword, wherein the
receiving ACK/NACK feedback receives, during a subframe, aggregated ACK/NACK feedback
from the other communication node indicating acknowledgment of receipt or non-receipt of each
of a plurality of codewords transmitted by the communication node in different subframes;
processing the aggregated ACK/NACK feedback and causing any codewords that were not
correctly received to be retransmitted to the other communication node.
The present invention also provides a method performed by a communication node that
communicates with another communication node using communications resources that are
arranged in subframes, the method comprising: receiving a control message from the other
communication node, which control message allocates communications resources within a
plurality of subframes over which the other communication node will transmit at least one
codeword in each subframe for the communication node; receiving the codewords from the other
communication node using the allocated communications resources within the plurality of
subframes; generating ACK/NACK feedback for each codeword indicating acknowledgment of
receipt or non-receipt of the codeword, wherein the generating generates aggregated
ACK/NACK feedback that indicates acknowledgment of receipt or non-receipt of each of a
plurality of codewords received by the communication node in different subframes; and
transmitting the ACK/NACK feedback to the other communication node.
According to another aspect, the invention provides a communication node arranged to
communicate with another communication node using communications resources that are
arranged in subframes, the communication node comprising: a scheduler for allocating
communications resources within a plurality of subframes for use in transmitting data to the
other communication node; a transmitter for transmitting a control message to the other
communication node, the control message indicating the allocated communications resources
within the plurality of subframes over which codewords for the other communication node will
be transmitted by the communication node; wherein the scheduler is arranged to cause the
transmitter to transmit at least one codeword to the other communication node during each of the
allocated subframes, using the allocated communications resources within the subframe; an
ACK/NACK module for receiving, from the other communication node, ACK/NACK feedback
for each codeword indicating acknowledgment of receipt or non-receipt of the codeword;
wherein the scheduler is arranged to cause the transmitter to retransmit a codeword to the other
communication node in the event that the codeword is not received by the other communications
node; wherein the ACK/NACK module is arranged to receive, during a subframe, aggregated
ACK/NACK feedback from the other communication node indicating acknowledgment of
receipt or non-receipt of each of a plurality of the codewords transmitted by the communication
node in different subframes, and is arranged to process the aggregated ACK/NACK feedback
and to control the scheduler so that any codewords that were not received are scheduled to be
retransmitted to the other communication node.
According to another aspect, the invention provides a communication node arranged to
communicate with another communication node using communications resources that are
arranged in subframes, the communication node comprising: means for generating and
outputting a control message for the other communication node that allocates communications
resources within a plurality of subframes over which the communication node will transmit at
least one codeword in each subframe for the other communication node; means for transmitting
the codewords to the other communication node using the allocated communications resources
within the plurality of subframes; and means for receiving, from the other communication node,
ACK/NACK feedback for each codeword indicating acknowledgment of receipt or non-receipt
of the codeword, wherein the means for receiving is arranged to receive, during a subframe,
aggregated ACK/NACK feedback from the other communication node indicating
acknowledgment of receipt or non-receipt of each of a plurality of codewords transmitted by the
communication node in different subframes, and is arranged to process the aggregated
ACK/NACK feedback and to cause any codewords that were not received to be retransmitted to
the other communication node.
According to another aspect, the invention provides a communication node arranged to
communicate with another communication node using communications resources that are
arranged in subframes, the communication node comprising: a scheduler that is arranged to
generate and output a control message for the other communication node that allocates
communications resources within a plurality of subframes over which the communication node
will transmit at least one codeword in each subframe for the other communication node; a
transceiver that is arranged to transmit the codewords to the other communication node using the
allocated communications resources within the plurality of subframes; and an ACK/NACK
module for receiving, from the other communication node, ACK/NACK feedback for each
codeword indicating acknowledgment of receipt or non-receipt of the codeword, wherein the
ACK/NACK module is arranged to receive, during a subframe, aggregated ACK/NACK
feedback from the other communication node indicating acknowledgment of receipt or nonreceipt
of each of a plurality of codewords transmitted by the communication node in different
subframes, and is arranged to process the aggregated ACK/NACK feedback to control the
scheduler so that any codewords that were not received are scheduled to be retransmitted to the
other communication node.
According to another aspect, the invention provides a communication node arranged to
communicate with another communication node using communications resources that are
arranged in subframes, the communication node comprising: means for generating and
outputting a control message for the other communication node that allocates communications
resources within a plurality of subframes over which the communication node will transmit at
least one codeword in each subframe for the other communication node; and means for
transmitting the codewords to the other communication node using the allocated communications
resources within the plurality of subframes; wherein the means for generating the control
message is arranged to include resource assignment data that assigns, to the other
communication node, the same communications resources within each of said plurality of
subframes.
According to another aspect, the invention provides a communication node arranged to
communicate with another communication node using communications resources that are
arranged in subframes, the communication node comprising: means for generating and
outputting a control message for the other communication node that allocates communications
resources within a plurality of subframes over which the communication node will transmit at
least one codeword in each subframe for the other communication node; and means for
transmitting the codewords to the other communication node using the allocated communications
resources within the plurality of subframes; wherein the means for generating the control
message is arranged to include modulation and coding scheme, MCS, data that indicates that the
same modulation and coding scheme will be used to modulate and code the codewords that are
to be transmitted to the other communication node using the allocated communications resources
within each of the plurality of subframes.
According to another aspect, the invention provides a communication node arranged to
communicate with another communication node using communications resources that are
arranged in subframes, the communication node comprising: means for generating and
outputting a control message for the other communication node that allocates communications
resources within a plurality of subframes over which the communication node will transmit at
least one codeword in each subframe for the other communication node; and means for
transmitting the codewords to the other communication node using the allocated communications
resources within the plurality of subframes; wherein the means for generating the control
message is arranged to include data for each codeword to be transmitted using the allocated
communications resources that indicates whether the codeword is a new code word or a
retransmission of a previous codeword.
According to another aspect, the invention provides a communication node arranged to
communicate with another communication node using communications resources that are
arranged in subframes, the communication node comprising: means for generating and
outputting a control message for the other communication node that allocates communications
resources within a plurality of subframes over which the communication node will transmit at
least one codeword in each subframe for the other communication node; and means for
transmitting the codewords to the other communication node using the allocated communications
resources within the plurality of subframes; wherein the means for generating the control
message is arranged to include data indicating the number of consecutive subframes to which the
allocation relates.
According to another aspect, the invention provides a communication node arranged to
communicate with another communication node using communications resources that are
arranged in subframes, the communication node comprising: means for receiveing a control
message from the other communication node that allocates communications resources within a
plurality of subframes over which the other communication node will transmit at least one
codeword in each subframe to the communication node; and means for receiving the codewords
from the other communication node using the allocated communications resources within the
plurality of subframes; wherein the received control message includes resource assignment data
that assigns, to the other communication node, the same communications resources within each
of said plurality of subframes.
According to another aspect, the invention provides a communication node arranged to
communicate with another communication node using communications resources that are
arranged in subframes, the communication node comprising: means for receiveing a control
message from the other communication node that allocates communications resources within a
plurality of subframes over which the other communication node will transmit at least one
codeword in each subframe to the communication node; and means for receiving the codewords
from the other communication node using the allocated communications resources within the
plurality of subframes; wherein the received control message includes modulation and coding
scheme, MCS, data that indicates that the same modulation and coding scheme will be used to
modulate and code the codewords that will be received by the communication node using the
allocated communications resources within each of the plurality of subframes.
According to another aspect, the invention provides a communication node arranged to
communicate with another communication node using communications resources that are
arranged in subframes, the communication node comprising: means for receiveing a control
message from the other communication node that allocates communications resources within a
plurality of subframes over which the other communication node will transmit at least one
codeword in each subframe to the communication node; and means for receiving the codewords
from the other communication node using the allocated communications resources within the
plurality of subframes; wherein the received control message includes data for each codeword to
be received that indicates whether the codeword is a new code word or a retransmission of a
previous codeword.
According to another aspect, the invention provides a communication node arranged to
communicate with another communication node using communications resources that are
arranged in subframes, the communication node comprising: means for receiveing a control
message from the other communication node that allocates communications resources within a
plurality of subframes over which the other communication node will transmit at least one
codeword in each subframe to the communication node; and means for receiving the codewords
from the other communication node using the allocated communications resources within the
plurality of subframes; wherein the means the received control message includes data indicating
the number of consecutive subframes to which the allocation relates.
According to another aspect, the invention provides a communication node arranged to
communicate with another communication node using communications resources that are
arranged in subframes, the communication node comprising: means for receiveing a control
message from the other communication node that allocates communications resources within a
plurality of subframes over which the other communication node will transmit at least one
codeword in each subframe to the communication node; and means for receiving the codewords
from the other communication node using the allocated communications resources within the
plurality of subframes; wherein the communication node is arranged to determine an HARQ
process for a codeword using a number of a subframe in which the codeword is received from
the other communication node.
According to another aspect, the invention provides a computer program product
comprising computer implementable instructions for causing a programmable communications
device to become configured as any of the communication nodes discussed above.
The invention provides, for all methods disclosed, corresponding computer programs or
computer program products for execution on corresponding equipment, the equipment itself
(user equipment, nodes or components thereof) and methods of updating the equipment.
Brief Description of Drawings
These and various other aspects of the invention will become apparent, from the
following detailed description of embodiments which are given by way of example only and
which are described with reference to the accompanying Figures in which:
Figure 1 schematically illustrates a communication system comprising a number of user
mobile (cellular) telephones which communicate with a base station connected to the telephone
network;
Figure 2a illustrates a generic frame structure defined for use in the LTE communication
network;
Figure 2b illustrates the way in which a slot illustrated in Figure 2a is formed of a number
of time-frequency resources;
Figure 3a schematically illustrates one way in which ACK/NACK feedback generated
during a multi-subframe assignment is collated and reported in a single subframe after the
assignment and illustrates one way in which sixteen different HARQ processes are divided into
two groups to allow continuous allocation to a mobile telephone;
Figure 3b schematically illustrates another way in which ACK/NACK feedback
generated during a multi-subframe assignment is collated and reported in a single subframe after
the assignment and illustrates a way in which thirteen different HARQ processes are divided into
two groups to allow continuous allocation to a mobile telephone;
Figure 3c schematically illustrates another way in which ACK/NACK feedback
generated during a multi-subframe assignment is collated and reported in a single subframe after
the assignment and illustrates a way in which sixteen different HARQ processes are divided into
four groups to allow continuous allocation to a mobile telephone;
Figure 4 is a block diagram illustrating the main components of the base station shown in
Figure 1; and
Figure 5 is a block diagram illustrating the main components of one of the mobile
telephones shown in Figure 1.
Mode(s) for Carrying Out the Invention
Embodiments
Figure 1 schematically illustrates a mobile (cellular) telecommunication system 1 in
which users of mobile telephones 3-0, 3-1, and 3-2 can communicate with other users (not
shown) via a base station 5 and a telephone network 7. In this embodiment, the base station 5
uses an orthogonal frequency division multiple access (OFDMA) technique in which the data to
be transmitted to the mobile telephones 3 is modulated onto a plurality of sub-carriers. Different
sub-carriers (resources) are allocated by the base station 5 to each mobile telephone 3 depending
on the amount of data to be sent to the mobile telephone 3.
LTE sub-frame data structure
Before discussing the specific ways in which the base station 5 can schedule resources to
the mobile telephones 3, a brief description will be given of the access scheme and a general
frame structure agreed for LTE communications. An Orthogonal Frequency Division Multiple
Access (OFDMA) technique is used for the downlink to allow the mobile telephone 3 to receive
data over the air interface with the base station 5. Different sub-carriers are allocated by the base
station 5 (for a predetermined amount of time) to the mobile telephone 3 depending on the
amount of data to be sent to the mobile telephone 3. These are referred to as physical resource
blocks (PRBs) in the LTE specifications. PRBs thus have a time and frequency dimension. To
do this, the base station 5 allocates PRBs for each device that it is serving and signals the
allocations (in a scheduling assignment message) to each of the scheduled devices, in a control
channel.
Figure 2a illustrates one generic frame structure agreed for LTE communications over the
air interface with the base station 5. As shown, one frame 13 is 10 msec long and comprises ten
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 (although this could clearly be different). Carrier aggregation techniques can extend
the available bandwidth further, for example up to 100 MHz bandwidths. 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 twelve 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.
Scheduling Assignments
In this embodiment, the base station 5 can allocate (schedule) resources to a particular
mobile telephone 3 in the following three ways:
1) Dynamic resource allocation - on a sub-frame by sub-frame basis;
2) Semi-persistent resource allocation - resources are intermittently allocated in a
defined manner; and
3) Multi-subframe resource allocation - resources in plural consecutive sub-frames
are allocated.
The base station 5 has the flexibility to use these resource allocation (scheduling)
techniques to achieve an efficient transmission over the air interface between the base station 5
and each of the mobile telephones 3 it is serving. Thus for example, for a mobile telephone 3
that is stationary or moving slowly, the base station may determine that it is more efficient to use
scheduling assignments that allocate the resources over multiple consecutive subframes to reduce
the signalling overhead between the base station 5 and that mobile telephone 3 (as the channel
conditions between a stationary or slowly moving mobile telephone 3 and the base station 5 will
remain approximately the same at least during a number of consecutive subframes). It is
currently proposed that a maximum of eight consecutive subframes can be allocated with a
single scheduling assignment, although this may of course change in the future. For other
mobile telephones 3 that are perhaps moving relatively quickly, the base station 5 may determine
that scheduling assignments should be made using the dynamic resource allocation procedure -
to maximise the ability of the base station 5 to compensate for changing channel conditions
between the base station and the mobile telephone 3.
HARQfor Multi-Subframe Signalling
The LTE communication system uses HARQ techniques to request retransmission of user
data when it is not correctly received. Forward Error Correction (FEC) techniques can be used
to increase the ability of the mobile telephone to correct for transmission errors. In response to
receiving a data message (referred to herein as a codeword), the mobile telephone 3 sends the
base station 5, an acknowledgement message (ACK) when the codeword is correctly received or
a non-acknowledgement message (NACK) when the codeword is not correctly received. In the
case of a NACK, the base station 5 resends the codeword, perhaps using a different FEC
encoding. If the retransmitted codeword is also not received without error, then the mobile
telephone 3 can combine the two error containing codewords to try to correct the errors and
successfully receive the correct codeword. In order to avoid significant delays in the data
transmission process, a limit is placed on the number of times that the codeword can be
retransmitted by the base station 5 (typically 4 times). Each retransmission may use a different
FEC technique and a Redundancy Version (RV) value is normally signalled to the mobile
telephone 3 so that it knows how to use the FEC data to correct errors in the codeword and how
it should combine the data with the data from previous transmission attempts.
In order that transmission delays are not introduced due to such retransmissions, the base
station 5 sends the mobile telephone 3 its data over a number of "HARQ processes". These are
effectively parallel streams of data (generated by splitting up original user data to be transmitted
to the mobile telephone 3), so that if a retransmission is required on one HARQ process,
transmissions of new data can still be made on the other HARQ processes. Each HARQ process
is associated with a transmitted codeword until the mobile telephone 3 sends an
acknowledgement that the codeword has been received correctly. The current LTE standards
define a maximum of eight HARQ processes per mobile telephone 3. The mobile telephone 3 is
arranged to combine the codewords from the different HARQ processes back into the original
user data. To do this, the mobile telephone 3 needs to know the HARQ process to which each
received codeword relates. When resources are scheduled to a mobile telephone 3 using
dynamic resource allocation (i.e. allocation based on a subframe by subframe basis), the DCI
control data normally indicates the HARQ process to which the codeword that will be
transmitted in that subframe relates.
As discussed in the introduction, the inventors have realised that multi-subframe
scheduling can cause problems with the currently defined HARQ ACK/NACK feedback process.
In particular, if a mobile telephone 3 that has been allocated resources in multiple consecutive
subframes, uses the same PUCCH resource in the corresponding subframes used to transmit the
ACK/NACK feedback, then the base station 5 must avoid reusing the same PDCCH CCE used
to signal the multi-subframe allocation for single-subframe assignments to other mobile
telephones 3. Otherwise two mobile telephones 3 will try to use the same PUCCH resource in
the same subframe to send their ACK/NACK feedback messages.
In order to reduce this problem, in this embodiment, when a mobile telephone 3 is
assigned resources using a multi-subframe scheduling assignment, it is configured to collate the
HARQ ACK/NACK feedback data generated during the multiple subframes to which the
assignment relates and to send aggregated ACK/NACK feedback to the base station 5
(preferably in one subframe) after the scheduled subframes have been received. Provided the
ACK/NACK feedback bits are aggregated in a predefined way, the base station 5 will know how
to process the aggregated ACK/NACK feedback data to recover the ACK/NACK feedback for
each transmitted codeword (and hence for each HARQ process). For example, the individual
ACK/NACK feedback data may be aggregated in the order of the subframes to which they relate.
Additionally, to avoid introducing long intervals between consecutive multi-subframe
allocations, the inventors propose to use at least two groups of HARQ processes for adjacent
multi-subframe assignments, with the HARQ processes in each group being different. As long
as the aggregated ACK/NACK feedback information can be received and processed by the base
station 5 before the same HARQ processes are scheduled again, the base station 5 can ensure that
codewords are retransmitted when necessary.
According to the current LTE standards, a mobile telephone 3 should transmit
ACK/NACK feedback four subframes after receiving the corresponding codeword in the
Physical Downlink Shared Channel (PDSCH) transmission. In this way the base station can
work out to which codeword the ACK/NACK relates. In addition, at least two subframes are
required at the base station 5 to process the ACK/NACK feedback and schedule the transmission
of a new codeword or the retransmission of the previous codeword data. Therefore, in this case,
there must be at least six subframes between the last PDSCH transmission of a multi-subframe
allocation and the first PDSCH transmission of a new multi-subframe allocation that uses the
same HARQ processes. This implies that (at least for the current reporting requirements for
HARQ) at least twelve HARQ processes are needed - six in each of two groups.
The current proposal for multi-subframe assignments is that resources in up to eight
consecutive subframes may be allocated with a single scheduling assignment message. The
minimum number of HARQ processes needed to accommodate multi-subframe assignments of
eight subframes is sixteen HARQ processes. If three or more groups of HARQ processes are to
be used when multi-subframe assignment of eight subframes is performed, then three or more
multiples of eight HARQ processes are required.
Figure 3a illustrates the use of sixteen HARQ processes when multi-subframe
assignments of eight subframes is performed, ie. each scheduling assignment sent by the base
station 5 contains an allocation for eight successive subframes using eight different HARQ
processes. In subframe 0, the base station 5 sends a scheduling assignment to the mobile
telephone 3 for HARQ processes 0 to 7. During subframes 0 to 7 the mobile telephone 3 collects
ACK/NACK feedback for codewords associated with HARQ processes 0 to 7. In subframe 11
(four subframes after the end of the last transmission of the multi-subframe assignment) the
mobile telephone 3 sends the aggregated ACK/NACK feedback associated with HARQ
processes 0 to 7 to the base station 5. As discussed above, the aggregated ACK/NACK feedback
may order the individual ACK/NACK feedback for HARQ processes such that the ACK/NACK
feedback associated with HARQ process 0 comes before the ACK/NACK feedback associated
with HARQ process 1, which comes before the ACK/NACK feedback associated with HARQ
process 2 etc. In subframes 12 to 1 the base station 5 processes the ACK/NACK feedback and
makes scheduling decisions. In subframe 16, the base station 5 sends a new scheduling
assignment to the mobile telephone 3 for HARQ processes 0 to 7; and the process is repeated.
An identical process operates in parallel for HARQ processes 8 to 15. Although not
illustrated in Figure 3a, for HARQ processes 8 to 15 the base station 5 sends a scheduling
assignment message in subframe 8 and the mobile telephone 3 sends the aggregated
ACK/NACK feedback in subframe 19.
By collecting the ACK/NACK feedback for all eight subframes and transmitting it all in
one subframe the mobile telephone 3 uses PUCCH resources in only one subframe. This makes
it easier to avoid PUCCH resource clashes with other mobile telephones 3 (i.e. the restrictions on
PDCCH CCE reuse are relaxed).
Figure 3b illustrates the use of thirteen HARQ processes when multi-subframe
assignments of six and seven subframes is performed in adjacent assignments, ie. the first
scheduling assignment sent by the base station 5 contains an allocation for six successive
subframes using six different HARQ processes; and the second scheduling assignment sent by
the base station 5 contains an allocation for seven successive subframes using seven different
HARQ processes (that are also different from the HARQ processes used in the first assignment).
In this example, in subframe 0, the base station 5 sends a scheduling assignment to the
mobile telephone 3 for HARQ processes 0 to 5. During subframes 0 to 5 the mobile telephone 3
collects ACK/NACK feedback for received codewords associated with HARQ processes 0 to 5.
In subframe 9 (four subframes after the end of the last transmission of the multi-subframe
assignment) the mobile telephone 3 sends the aggregated ACK/NACK feedback associated with
all of HARQ processes 0 to 5 to the base station 5. In subframes 10 to 12 the base station 5
processes the ACK/NACK feedback and makes scheduling decisions. In subframe 13, the base
station 5 sends a new scheduling assignment to the mobile telephone 3 for HARQ processes 0 to
5; and the process is repeated.
An identical process operates in parallel for HARQ processes 6 to 1 . Although not
illustrated in Figure 3b, for HARQ processes 6 to 12 the base station 5 sends a scheduling
assignment message in subframe 6 and the mobile telephone 3 sends the aggregated
ACK/NACK feedback in subframe 16.
In the examples illustrated in Figures 3a and 3b, the HARQ processes have been divided
into two groups. However, as mentioned above, the HARQ processes may be divided into more
than two groups, depending on the number of HARQ processes available and the number of
consecutive subframes that are allocated in a multi-subframe allocation. For example, Figure 3c
illustrates an example where there are sixteen HARQ processes and each multi-subfame
allocation sent by the base station 5 contains an allocation for four successive subframes using
four different HARQ processes.
In general, if there are R subframes for the basic ACK/NACK reporting delay and P
subframes for processing the ACK/NACK feedback at the base station 5, then for assignments of
N subframes the number of HARQ processes needed is N*ceil( (N+R+P)/N ), eg. assuming R=4
and P=3 then:
N NumberOfHARQProcesses
2 10
3 12
4 12
6 18
8 16
DCIFormat
Another aspect of multi-subframe scheduling is the format of the control data that carries
the multi-subframe scheduling assignment. A new Downlink Control Indicator (DCI) format is
needed for multi-subframe scheduling grants because it needs to signal information about
multiple HARQ processes.
The inventors propose that the modulation and coding scheme (MCS) and resource block
assignment are the same for all HARQ processes within a multi-subframe assignment, so that it
is not necessary to signal this information for each HARQ process.
The inventors also propose that the HARQ process number associated with a codeword is
determined from, for example, the subframe number in which the codeword is transmitted. This
may be determined, for example, according to a fixed mapping (such as an equation) known by
the base station 5 and the mobile telephone 3. In this way, it is not necessary for the base station
5 to signal the HARQ process number in the DCI control data allocating the resources. For
example, the equation may be a simple modulo operation:
NSf mod N
where NSf is the subframe number and N is the number of available HARQ processes. Thus, the
base station 5 and the mobile telephone 3 can determine to which HARQ process each
transmitted codeword relates using the subframe number and the known mapping. The mobile
telephone 3 can then combine the codewords to recover the user data.
The inventors propose that in the case of HARQ retransmission, the redundancy version
(RV) follows a fixed predetermined sequence (as is currently the case in the uplink), so that it is
not necessary to signal the RV for each HARQ process. For example, the first retransmission
always uses RVO, the second retransmission always uses RV1 etc. Therefore, provided the
mobile telephone 3 keeps track of how many retransmissions of the codeword there have been, it
can work out how to try to decode the received data for the current transmission attempt and/or
how to combine it with the data received from previous transmission attempts.
The inventors propose to include a field that defines the number of consecutive
subframes to which the multi-subframe assignment relates. This field is only needed in the case
that the multi-subframe assignment can relate to a variable number of consecutive subframes.
Where each multi-subframe assignment relates to a fixed number of subframes, this field can be
omitted if desired.
The inventors also propose to add a "new data indicator" (NDI) for each HARQ process
to indicate if the transmission is a new transmission or a retransmission. So for a multi-subframe
assignment for eight subframes, the NDI may comprise a bitmap of eight bits, one for each
subframe in the assignment, indicating if the data that is being transmitted in that subframe is
new data or a retransmission. For example a "1" may indicate new data and a "0" may indicate a
retransmission, or vice versa.
The proposed DCI format for multi-subframe scheduling grants therefore includes the
following:
• One resource block assignment and one MCS, which is common to all HARQ
processes. In the case of MIMO (multiple input multiple output - as used when
the base station and the mobile telephone employ multiple antennas in their
communications) one MCS is signalled for each transmitted codeword);
An optional field that defines the number of consecutive subframes to which the
multi-subframe assignment relates;
One NDI bit per transmitted codeword (ie. one bit per HARQ process in the case
of single codeword transmission; two bits per HARQ process in the case of
MIMO with two codewords). The NDI information can be represented as a bit
map or by any other suitable encoded data string.
Base Station
Figure 4 is a block diagram illustrating the main components of the base station 5 used in
this embodiment. As shown, the base station 5 includes a transceiver circuit 1 which is
operable to transmit signals to and to receive signals from the mobile telephones 3 via one or
more antennae 23 (using the above described sub-carriers) and which is operable to transmit
signals to and to receive signals from the telephone network 7 via a network interface 25. The
operation of the transceiver circuit 2 1 is controlled by a controller 27 in accordance with
software stored in memory 29. The software includes, among other things, an operating system
31 an ACK/NACK module 33 and a scheduler 35. The ACK/NACK module 33 is responsible to
receive ACK/NACK feedback (aggregated or otherwise) from the mobile telephones 3 and, in
the case of NACKs, to control the scheduler 35 so that the corresponding data can be
retransmitted to the mobile telephone 3. The scheduler 35 is responsible for allocating the
resources to be used by the transceiver circuit 2 1 in its communications with the mobile
telephones 3. The scheduler 35 decides on whether to allocate the resources (sub-carriers) using
the above mentioned techniques of semi-persistent allocation, dynamic resource allocation and
multi-subframe resource allocation. The scheduler 35 also schedules the data to be transmitted
or retransmitted to each mobile telephone 3 in each subframe. As shown in Figure 4, the
resource allocation module 33 includes control parameter generator module 37 for generating the
required DCI control parameters for each mobile telephone 3 that define the resources (PRBs)
that are allocated to each mobile telephone 3.
Mobile Telephone
Figure 5 schematically illustrates the main components of each of the mobile telephones
3 shown in Figure 1. As shown, the mobile telephones 3 include a transceiver circuit 7 1 which is
operable to transmit signals to and to receive signals from the base station 5 via one or more
antennae 73. As shown, the mobile telephone 3 also includes a controller 75 which controls the
operation of the mobile telephone 3 and which is connected to the transceiver circuit 7 1 and to a
loudspeaker 77, a microphone 79, a display 81, and a keypad 83. The controller 75 operates in
accordance with software instructions stored within memory 85. As shown, these software
instructions include, among other things, an operating system 87 and a communications module
89. In this embodiment, the communications module 89 includes a control parameter interpreter
module 9 1 for interpreting received DCI control parameters that define a resource allocation - so
that the communications module 89 knows on which resources downlink data for the mobile
telephone 3 will be received and on which resources the mobile telephone 3 should transmit its
uplink data. The communications module 89 also includes an ACK/NACK module 93 that
generates ACK/NACK feedback information for received codewords and that controls the timing
of when the ACK/NACK feedback is made. For example, in the case of a conventional dynamic
allocation of resources in a current subframe - the ACK/NACK module 93 would send an
ACK/NACK feedback for the data received in a current sub-frame, four subframes later; or in
the case of a multi-subframe assignment, the ACK/NACK feedback module 93 collates the
ACK/NACK feedbacks from all the sub-frames of the multi-subframe assignment and sends the
aggregated ACK/NACK feedback to the base station 5 in a single subframe (in the manner
discussed above).
In the above description, the base station 5 and the mobile telephones 3 are described for
ease of understanding as having a number of discrete modules (such as the resource allocation
module, control parameter generator module, communications module and control parameter
interpreter module). 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. By way of illustration
only a number of these alternatives and modifications will now be described.
In the above embodiments, a mobile telephone based telecommunication system was
described in which the above described signalling techniques were employed. As those skilled
in the art will appreciate, the signalling of such resource allocation data can be employed in any
communication system that uses a plurality of sub-carriers. In particular, the signalling
techniques described above can be used in wire or wireless based communications either using
electromagnetic signals or acoustic signals to carry the data. In the general case, the base station
would be replaced by a communication node which communicates with a number of different
user devices. User devices may include, for example, personal digital assistants, laptop
computers, web browsers, etc. Similarly, the invention can also be used in systems where the
base station is communicating with other types of communication nodes - such as rely nodes.
In the above embodiment, the aggregated ACK NAC feedback for all subframes of a
multi-subframe allocation was sent in a single sub-frame. Transmitting such aggregated
ACK/NACK feedback in a single frame minimises the constraints placed on the base station 5
with regard to the re-use of CCE resources used to send mobile telephones their scheduling
grants. As those skilled in the art will appreciate, transmission of such aggregated ACK/NACK
feedback in a single subframe is not essential. Provided at least some aggregated ACK/NACK
feedback is transmitted, the requirements on the base station are relaxed to some extent. For
example, if a multi-subframe assignment allocates resources for eight sub-frames, then normally
ACK/NACK feedback would be sent in eight subsequent sub-frames, requiring the base station
to avoid using certain CCE resources in those eight sub-frames. In this case improvements are
still made if the ACK/NACK feedback is transmitted back to the base station in seven subframes
- for example where aggregated ACK/NACK feedback for two subframes is transmitted
together in one subframe. Thus provided aggregated ACK/NACK feedback for multiple subframes
is transmitted in at least one subframe, the invention provides an improvement.
In the above embodiments, a number of software modules were described. As those
skilled will appreciate, the software modules may be provided in compiled or un-compiled form
and may be supplied to the base station or to the mobile telephone as a signal over a computer
network, or on a recording medium such as a DVD ROM. 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 station
5 and the mobile telephones 3 in order to update their functionalities.
The following is a detailed description of comments and observations surrounding multisubframe
assignments and other topics relating implementation in the currently proposed 3GPP
LTE standard. Whilst various features may be described as being essential or necessary, this
may only be the case for the proposed 3GPP LTE 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.
Introduction
In RANl#72bis, the control signalling enhancements in small cells have been discussed
and it is observed that multi-subframe scheduling and/or cross-subframe scheduling could reduce
the control signalling overhead by exploiting the channel that is time-invariant over a number of
consecutive subframes. The observation and next steps are restated below:
Observations:
■ Multi-subframe scheduling and/or cross-subframe scheduling are proposed by
many companies
o Not necessarily limited to small cells, but may be able to exploit relatively
time-invariant channels
Next steps:
■ For RANI #73, focus on study of multi-subframe scheduling and cross-subframe
scheduling
o Identify characteristics of potential schemes, e.g. for multi-subframe
scheduling, how does it differ from SPS, how many subframes, how is
link adaptation and HARQ retransmissions handled?
o Evaluate whether there are useful potential gains (in throughput or other
gains) from overhead reduction (multi-subframe scheduling) or statistical
multiplexing gain (cross-subframe scheduling)
o Consider impact of resulting scheduling restrictions and potential means to
mitigate such impact
o Identify potential specification impact
■ Also consider PDSCH/EPDCCH starting in first OFDM symbol
In this contribution, we discuss the issues relating to multi-subframe scheduling and
cross-subframe scheduling such as overhead reduction, scheduling restrictions, HARQ
retransmissions and specification impact.
1 Multi-subframe and cross-subframe scheduling in small cells
The definition of multi-subframe scheduling and cross-subframe scheduling is as follows
[1-2]:
■ In multi-subframe scheduling, one control channel (i.e. DCI format) can schedule
PDSCH or PUSCH for the current and multiple future subframes with the same
transmission format such as resource allocation, MCS, etc.
■ In cross-subframe scheduling, an allocation (e.g. PDSCH) is intended to a
different subframe than the one where control channel is transmitted which
improves the statistical multiplexing gain of the control channels.
The motivation of multi-subframe scheduling is that it can be applied in small cell
scenarios in which the channel is time-invariant in a number of future subframes (i.e. UE
mobility is low). So, in this case, one control channel can schedule to multiple future subframes,
and hence, there seems a non-trivial control signaling overhead reduction. On the other hand,
the argument against is that the number of UEs in a small cell is generally small, the number of
UEs scheduled in a subframe is also small and the average SI R that the UEs experience is
relatively high, hence, resulting using lower aggregation levels for PDCCH/EPDCCH.
Therefore, the control channel overhead is already at its low level and any further overhead
saving would be small. On the other hand, cross-subframe scheduling does not directly reduce
overhead for control signalling, although it might provide statistical multiplexing gain and some
scheduling flexibility. However, the benefits of cross-subframe scheduling are not clear at this
stage.
Nevertheless, as agreed in RANl#72bis, the current ongoing evaluations would definitely
quantify the overhead saving of the multi-subframe scheduling and cross-subframe scheduling.
However, the signalling overhead saving should not be the only decision making parameter;
other aspects such as scheduling restrictions, link adaptation, HARQ issues, specification impact,
etc. have to be considered as well.
Observation 1: Signaling overhead saving should not be the only decision making
parameter; other aspects such as scheduling restrictions, link adaptation, HARQ issues,
specification impact, etc. have to be considered as well.
1.1 Scheduling restriction
In the current LTE system, two scheduling mechanisms are supported: dynamic packet
scheduling (DPS) and semi-persistent scheduling (SPS). In this case, the characteristics of the
incoming data traffic make the scheduler to choose the type of the scheduling mechanism.
For DL DPS, the scheduler has a flexibility to dynamically send data on subframe-bysubframe
basis (i.e. the unit of scheduling is per subframe), to pick the preferred transmission
parameters (e.g. resource allocation, MCS, HARQ, Power, etc.) for a proper link adaptation and
to prioritize among users when scheduling on the current subframe. However, if multi-subframe
scheduling is applied and the incoming data is bursty, the scheduler may lose the flexibility to
prioritize among users as well as to modify transmission parameters in every subframe. That
means the benefits of link adaptations by both MCS change and allocated PRB resources change
might be compromised. Thus, the control channel overhead reduction may not translate into
overall system capacity improvements significantly. In addition, as the incoming data is bursty
with unknown estimate of time of arrival and size, dis-similar to SPS traffic, the scheduler has to
allocate the resources as needed and free otherwise which creates uncertainty and abrupt
decisions at the scheduler, hence, multi-subframe scheduling would increase the complexity of
the scheduler.
Observation 2: Complexity of eNB scheduler and overall system capacity improvements
have to be considered when deciding the benefits of the multi-subframe and cross-subframe
scheduling.
1.2 HARQ retransmissions
For the DL DPS, asynchronous adaptive HARQ with stop-and-wait procedure is
followed in which if decoding of the packet fails, the packet is retransmitted based on
transmission of downlink control information/parameters. The scheduler has flexibility to
dynamically schedule any retransmissions in time-resource as well as frequency-resource.
However, in case of DL multi-subframe scheduling and cross-subframe scheduling, how
to handle HARQ retransmissions is unclear such as the followings:
■ Multi-subframe period in multi-subframe scheduling
■ Possible distance between the subframe with DL grant and the target subframe in
cross-subframe scheduling
■ ACK/NACK feedback method (e.g. timing, concatenation of ACK/NACKs)
■ Total number of HARQ processes
■ Downlink control information (e.g. HARQ process number, redundancy version,
NDI)
Related with the above discussion points, at least for FDD, one example to handle DL
HARQ retransmissions is to employ synchronous non-adaptive HARQ scheme for downlink
transmission. Similar to the current LTE uplink, the HARQ process number in each sub-frame is
determined from the sub-frame number according to a fixed mapping known by the eNB and the
UE, and the redundancy version (RV) follows a fixed predetermined sequence. This will at least
reduce some signalling overhead in the downlink control information.
Observation 3: To handle DL HARQ retransmissions, synchronous non-adaptive HARQ
scheme may be consideredfor reducing the signaling overhead purpose.
1.3 Potential Specification Impact
Based on the discussion above, there may be some specification impacts such as the
followings:
■ To define how many future subframes the scheduling spans for multi-subframe
scheduling and/or how far future subframe can be scheduled for cross-subframe
scheduling, for example 4, 6 or 8 subframes, and corresponding signaling method.
■ To change the way the HARQ retransmissions is handled in both downlink and
uplink subframes.
■ How to handle the collision between the chosen DL HARQ scheme and MBSFN
subframes, system information and the existing signals.
■ The number of blind decoding should not be increased compared to the maximum
number of blind decodings (BDs) that the UE is capable of in previous LTE
Release. This needs to be taken into account during the design and specifications.
2 Conclusion
In this contribution, we have discussed issues relating to multi-subframe scheduling and
cross-subframe scheduling such as overhead reduction, scheduling restrictions, HARQ
retransmissions and specification impact. We have the following observations:
Observation 1: Signaling overhead saving should not be the only decision making
parameter; other aspects such as scheduling restrictions, link adaptation, HARQ issues,
specification impact, etc. have to be considered as well.
Observation 2: Complexity of eNB scheduler and overall system capacity improvements
have to be considered when deciding the benefits of the multi-subframe and cross-subframe
scheduling.
Observation 3: To handle DL HARQ retransmissions, synchronous non-adaptive HARQ
scheme may be considered for reducing the signaling overhead purpose.
This application is based upon and claims the benefit of priority from United Kingdom
patent application No. 1308424.9, filed on May 10, 2013, the disclosure of which is incorporated
herein in its entirety by reference.

CLAIMS
1. A communication node arranged to communicate with another communication node
using communications resources that are arranged in subframes, the communication node
comprising:
a scheduler that is arranged to generate and output a control message for the other
communication node which control message allocates communications resources within a
plurality of subframes over which the communication node will transmit at least one codeword
in each subframe for the other communication node;
a transceiver that is arranged to transmit the codewords to the other communication node
using the allocated communications resources within the plurality of subframes; and
an ACK/NACK module for receiving, from the other communication node, ACK/NACK
feedback for each codeword indicating acknowledgment of receipt or non-receipt of the
codeword, wherein the ACK/NACK module is arranged to receive, during a subframe,
aggregated ACK/NACK feedback from the other communication node indicating
acknowledgment of receipt or non-receipt of each of a plurality of codewords transmitted by the
communication node in different subframes, and is arranged to process the aggregated
ACK/NACK feedback to control the scheduler so that any codewords that were not received are
scheduled for retransmission to the other communication node.
2. A communication node according to claim 1, wherein the scheduler is configured to use a
plurality of HARQ processes to control transmission of data to the other communication node,
such that a different HARQ process is used for each subframe within which communications
resources are allocated to the other communication node by said control message.
3. A communication node according to claim 2, wherein the scheduler is arranged so that an
HARQ process that is used to transmit a codeword to the other communication node is not
reused until the ACK/NACK module has received and processed the ACK/NACK feedback for
that codeword.
4. A communication node according to claim 2 or 3, wherein the scheduler is arranged: i) to
split available HARQ processes into two or more groups, the HARQ processes in each group
being different; ii) to generate a first control message that allocates resources within a first
plurality of subframes and a second control message that allocates resources within a second
WO 2014/181847 PCT/JP2014/062414
plurality of subframes; iii) to use HARQ processes from the first group for communications
made using the resources allocated by the first control message; and iv) to use HARQ processes
from the second group for communications made using the resources allocated by the second
control message.
5. A communication node according to any of claims 1 to 4, wherein the scheduler is
arranged to generate said control message such that it includes resource assignment data that
assigns, to the other communication node, the same communications resources within said
plurality of subframes.
6. A communication node according to any of claims 1 to 5, wherein the scheduler is
arranged to generate said control message such that it includes modulation and coding scheme,
MCS, data that indicates that the same modulation and coding scheme will be used to modulate
and code the codewords that are to be transmitted to the other communication node using the
allocated communications resources within the plurality of subframes.
7. A communication node according to any of claims 1 to 6, wherein the scheduler is
arranged to include, within the control message for the allocated resources, data for each
codeword to be transmitted using the allocated communications resources that indicates whether
the codeword is a new code word or a retransmission of a previous codeword.
8. A communication node according to any of claims 1 to 7, wherein the scheduler is
arranged to include within said control message data indicating the number of consecutive
subframes to which the allocation relates.
9. A communication node arranged to communicate with another communication node
using communications resources that are arranged in subframes, the communication node
comprising:
a communications module that is arranged to receive a control message from the other
communication node, which control message allocates communications resources within a
plurality of subframes over which the other communication node will transmit at least one
codeword in each subframe for the communication node;
a transceiver that is arranged to receive the codewords from the other communication
node using the allocated communications resources within the plurality of subframes; and
WO 2014/181847 PCT/JP2014/062414
an ACK/NACK module for generating ACK/NACK feedback for each codeword
indicating acknowledgment of receipt or non-receipt of the codeword, wherein the ACK/NACK
module is arranged to generate aggregated ACK/NACK feedback and to send the aggregated
ACK/NACK feedback to the other communication node, which aggregated ACK/NACK
feedback indicating acknowledgment of receipt or non-receipt of each of a plurality of
codewords received by the communication node in different subframes.
10. A communication node according to claim 9, wherein the communications module is
configured to use a plurality of HARQ processes to control reception of data received from the
other communication node, such that a different HARQ process is used for each subframe within
which communications resources are allocated to the communication node by said control
message.
1 . A communication node according to claim 10, wherein the communications module is
arranged to determine an HARQ process for a codeword using a number of a subframe in which
the codeword is received from the other communication node.
12. A communication node according to claim 10 or 1, wherein the communications module
is arranged: i) receive a first control message that allocates resources within a first plurality of
subframes and a second control message that allocates resources within a second plurality of
subframes; iii) to use HARQ processes from a first group of HARQ processes for
communications made using the resources allocated by the first control message; and iv) to use
HARQ processes from a second group of HARQ processes for communications made using the
resources allocated by the second control message, the HARQ processes in the first group being
different from the HARQ processes in the second group.
13. A communication node according to any of claims 9 to 12, wherein the received control
message assigns the same communications resources within said plurality of subframes.
. A communication node according to any of claims 9 to 13, wherein the control message
includes modulation and coding scheme, MCS, data that indicates that the same modulation and
coding scheme will be used to modulate and code the codewords that are to be received from the
other communication node using the allocated communications resources within the plurality of
subframes.
WO 2014/181847 PCT/JP2014/062414
15. A communication node according to any of claims 9 to 14, wherein the control message
includes data, for each codeword to be received using the allocated communications resources,
that indicates whether the codeword is a new code word or a retransmission of a previous
codeword.
16. A communication node according to any of claims 9 to 15, wherein the control message
includes data indicating the number of consecutive subframes to which the allocation relates.
17. A communication node according to any of claims 1 to 8, which is a base station of a
communication system.
18. A communication node according to any of claims 9 to 16, which is a user device, such
as a cellular telephone.
19. A method performed by a communication node that communicates with another
communication node using communications resources that are arranged in subframes, the
method comprising:
generating and outputting a control message for the other communication node that
allocates communications resources within a plurality of subframes over which the
communication node will transmit at least one codeword in each subframe for the other
communication node;
transmitting the codewords to the other communication node using the allocated
communications resources within the plurality of subframes;
receiving, from the other communication node, ACK/NACK feedback for each codeword
indicating acknowledgment of receipt or non-receipt of the codeword, wherein the receiving
ACK/NACK feedback receives, during a subframe, aggregated ACK/NACK feedback from the
other communication node indicating acknowledgment of receipt or non-receipt of each of a
plurality of codewords transmitted by the communication node in different subframes;
processing the aggregated ACK/NACK feedback and causing any codewords that were
not correctly received to be retransmitted to the other communication node.
20. A method performed by a communication node that communicates with another
communication node using communications resources that are arranged in subframes, the
WO 2014/181847 PCT/JP2014/062414
method comprising:
receiving a control message from the other communication node, which control message
allocates communications resources within a plurality of subframes over which the other
communication node will transmit at least one codeword in each subframe for the
communication node;
receiving the codewords from the other communication node using the allocated
communications resources within the plurality of subframes; and
generating ACK/NACK feedback for each codeword indicating acknowledgment of
receipt or non-receipt of the codeword, wherein the generating generates aggregated
ACK/NACK feedback that indicates acknowledgment of receipt or non-receipt of each of a
plurality of codewords received by the communication node in different subframes; and
transmitting the ACK/NACK feedback to the other communication node.
21. A first communication node arranged to communicate with a second communication
node using communications resources that are arranged in subframes, the first communication
node comprising:
a scheduler for allocating communications resources within a plurality of subframes for
use in transmitting data to the second communication node;
a transmitter for transmitting a control message to the second communication node, the
control message indicating the allocated communications resources within the plurality of
subframes over which codewords for the second communication node will be transmitted by the
first communication node;
wherein the scheduler is arranged to cause the transmitter to transmit at least one
codeword to the second communication node during each of the allocated subframes, using the
allocated communications resources within the subframe;
an ACK/NACK module for receiving, from the second communication node,
ACK/NACK feedback for each codeword indicating acknowledgment of receipt or non-receipt
of the codeword;
wherein the scheduler is arranged to cause the transmitter to retransmit a codeword to the
second communication node in the event that the codeword is not received by the second
communications node;
wherein the ACK/NACK module is arranged to receive, during a subframe, aggregated
ACK/NACK feedback from the second communication node indicating acknowledgment of
receipt or non-receipt of each of a plurality of the codewords transmitted by the first
WO 2014/181847 PCT/JP2014/062414
communication node in different subframes, and is arranged to process the aggregated
ACK/NACK feedback and to control the scheduler so that any codewords that were not received
are scheduled to be retransmitted to the second communication node.
22. A communication node arranged to communicate with another communication node
using communications resources that are arranged in subframes, the communication node
comprising:
means for generating and outputting a control message for the other communication node
that allocates communications resources within a plurality of subframes over which the
communication node will transmit at least one codeword in each subframe for the other
communication node;
means for transmitting the codewords to the other communication node using the
allocated communications resources within the plurality of subframes; and
means for receiving, from the other communication node, ACK/NACK feedback for each
codeword indicating acknowledgment of receipt or non-receipt of the codeword, wherein the
means for receiving is arranged to receive, during a subframe, aggregated ACK/NACK feedback
from the other communication node indicating acknowledgment of receipt or non-receipt of each
of a plurality of codewords transmitted by the communication node in different subframes, and is
arranged to process the aggregated ACK/NACK feedback and to cause any codewords that were
not received to be retransmitted to the other communication node.
23. A computer program product comprising computer implementable instructions for
causing a programmable communications device to become configured as the communication
node of any of claims 1 to 18 or 2 1 to 32.