WO2020200452A1

WO2020200452A1 - Network communications with feedback

Info

Publication number: WO2020200452A1
Application number: PCT/EP2019/058476
Authority: WO
Inventors: Onurcan ISCAN; Ömer BULAKCI; Wen Xu
Original assignee: Huawei Technologies Duesseldorf Gmbh
Priority date: 2019-04-04
Filing date: 2019-04-04
Publication date: 2020-10-08

Abstract

A transmitting device configured to transmit packets including messages to a plurality of receiving devices over a communication network, the transmitting device being configured to, in response to identifying from feedback messages from the plurality of receiving devices a group of receiving devices that each failed to decode one of a set of previously received messages: encode each of the set of messages and combine the encoded messages into a single retransmission packet; transmit the retransmission packet to the group of receiving devices; and transmit to the group of receiving devices control information including identification information identifying each message encoded within the retransmission packet and encoding information associated with each message within the retransmission packet.

Description

NETWORK COMMUNICATIONS WITH FEEDBACK

FIELD

The present disclosure relates to communications within a communication network from a transmitting device to multiple receiving devices that supports a feedback channel between the receiving devices and the transmitting device.

BACKGROUND

A communication system may support different types of communication schemes over a communication network. One such scheme is when a transmitting device transmits a packet, or stream of packets, over the network to a single receiving device. This type of communication scheme is a one-to-one scheme, and may be referred to a unicast transmission. Another type of scheme is when a transmitting device transmits a packet/stream of packets over the network to all receiving devices in the communication system. This type of scheme is a one-to-all scheme, and may be referred to as a broadcast transmission. In a third type of scheme, a transmitting device transmits a packet/stream of packets over the network to multiple receiving devices of the communication system. This third type of scheme is a one-to-many scheme, and may be referred to as a multicast transmission.

Some communication networks support feedback channels between the receiving devices and the transmitting device. The feedback channels enable the receiving devices to communicate feedback messages to the transmitting device indicating whether a packet transmitted by the transmitting device was successfully decoded or not. The feedback messages may be in the form of acknowledgement (ACK) messages (indicating a packet has been successfully received and decoded) or negative-acknowledgement (NACK) messages (indicating a packet has not been successfully decoded). These feedback messages may be single bit messages. In some implementations, each receiving device may communicate a feedback message to the transmitting device for each packet transmitted to that receiving device by the transmitting device.

An example of a communication system supporting feedback channels is illustrated in figure 1 . Here, the communication system 100 comprises transmitting device 102 and receiving devices 104, 106 and 108. The transmitting device 102 communicates with receiving devices 104-108 using unicast transmissions. An example unicast communication is shown at 1 10, where device 102 transmits a packet to receiving device 104. The receiving device 104 in return transmits a feedback message - shown at 1 12 - to the transmitting device that indicates whether the packet was successfully decoded by device 104 or not. In this example, the device 104 does not successfully decode the packet and so returns a NACK message to the transmitting device. In response to receiving the NACK message, the transmitting retransmits the packet to the device 104 in a separate unicast transmission, shown at 1 14.

This scheme of retransmitting a single packet to a single receiving device in response to receiving a NACK message can work well for unicast communications, where each transmitted packet is in any event directed to only a single receiving device. However, in situations where the transmitting device transmits packets to multiple receiving devices (e.g. via multicast or broadcast transmissions), this retransmission scheme can suffer from the drawback of being inefficient.

SUMMARY

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

According to one aspect of the present disclosure there is provided a transmitting device configured to transmit packets including messages to a plurality of receiving devices over a communication network, the transmitting device being configured to, in response to identifying from feedback messages from the plurality of receiving devices a group of receiving devices that each failed to decode one of a set of previously received messages: encode each of the set of messages and combine the encoded messages into a single retransmission packet; transmit the retransmission packet to the group of receiving devices; and transmit to the group of receiving devices control information including identification information identifying each message encoded within the retransmission packet and encoding information associated with each message within the retransmission packet.

This enables multiple messages to be encoded and combined into a single retransmission packet, which can result in a reduced amount of retransmissions and increased throughput in the communication network. Such a single retransmission packet may be transmitted by multiple access nodes, such as, in case of packet duplication (aka packet data convergence protocol (PDCP) duplication) and multi-connectivity, e.g., to further improve the reliability of the communication.

The transmitting device may be configured to provide to the group of receiving devices configuration information indicating whether the retransmission packet includes a combination of encoded messages. This enables the receiving device to perform an appropriate decoding operation on the received packet. The configuration information can be part of a control information and may be sent to the group of devices or each of the devices as part of radio resource control (RRC) procedures, e.g., RRC connection establishment and/or RRC re configuration. Such RRC configuration may include one or more configuration options, where a configuration option may be activated by a downlink control information (DCI). A configuration option may include different options on how a combination of the packets would take place including the option that there is no combination of encoded messages.

The transmitting device may be configured to encode each of the set of messages to a respective codeword, and to combine the codewords into the single retransmission packet. Combining the messages at the codeword level can enable each message to be encoded with different encoding rates and/or redundancy versions, providing additional flexibility.

The encoding information may include at least one of a redundancy version and an encoding rate. This enables different encoded messages to be generated that represent the same message.

The encoding information may be different for at least two messages of the set of messages. This can facilitate increased encoding flexibility.

The transmitting device may be configured to select a value of the redundancy version for each codeword in the retransmission packet in dependence on the number of previous retransmissions of the respective message. This can facilitate decoding of the codeword at the receiving device.

The control information may further include an indicator indicating whether each of the set of messages encoded in the retransmission packet has been previously transmitted by the transmitting device or not. This can enable the receiving device to manage and update the values of its buffer, e.g. its hybrid automatic repeat request (HARQ) buffer. The transmitting device may be configured to combine the codewords using binary addition. This can enable multiple messages to be encoded in a packet without increasing the size (e.g. the number of bits) of the packet.

The transmitting device may be configured to transmit the control information to the group of receiving devices over a control channel. This enables the control information to be transmitted separately to the retransmission packet.

The identification information identifying each message encoded within the retransmission packet may be a hybrid automatic repeat request (HARQ) process ID (identity). This enables a HARQ buffer to be used for the decoding, avoiding the need for an additional buffer.

The transmitting device may be configured to transmit packets to the plurality of receiving devices as a set of one or more beams using beamforming, and the group of receiving devices are identified as receiving the same beam transmitted from the transmitting device. This enables the messages to be combined and transmitted to receiving devices that receive the same beam, increasing the efficiency of the retransmissions.

There may be provided a receiving device configured to receive: (i) a retransmission packet that includes a combination of encoded messages, and (ii) control information including identification information identifying each message encoded within the retransmission packet and encoding information associated with each message within the retransmission packet; the device being configured to, when the received retransmission packet includes an encoded message corresponding to a message the receiving device previously failed to decode: extract from the retransmission packet the message that receiving device failed to decode based on the control information and the messages in the retransmission packet the receiving device has previously decoded. This enables the receiving device to decode a retransmission packet containing a combination of encoded messages.

The encoding information may include at least one of a redundancy version and an encoding rate. This can increase the flexibility of the encoding.

The encoding information may be different for at least two messages in the retransmission packet. This can increase the flexibility of the encoding. The identification information identifying each message encoded within the retransmission packet may be a hybrid automatic repeat request (HARQ) process ID. This enables a HARQ buffer to be used in the decoding process, avoiding the need for an additional buffer.

There may be provided a method of transmitting packets including messages from a transmitting device to a plurality of receiving devices over a communication network, the method comprising:

identifying, from feedback messages received at the transmitting from the plurality of receiving devices, a group of receiving devices that each failed to decode one of a set of previously received messages;

encoding each of the set of messages and combining the encoded messages into a single retransmission packet;

transmitting the retransmission packet from the transmitting device to the group of receiving devices; and

transmitting from the transmitting device to the group of receiving devices control information including identification information identifying each message encoded within the retransmission packet and encoding information associated with each message within the retransmission packet.

This enables multiple messages to be encoded and combined into a single retransmission packet, which can result in a reduced amount of retransmissions and increased throughput in the communication network.

There may be provided a computer program product comprising instructions which, when executed by a transmitting device configured to transmit packets including messages to a plurality of receiving devices over a communication network, causes the transmitting device to:

identify, from feedback messages received at the transmitting from the plurality of receiving devices, a group of receiving devices that each failed to decode one of a set of previously received messages;

encode each of the set of messages and combining the encoded messages into a single retransmission packet;

transmit the retransmission packet from the transmitting device to the group of receiving devices; and

transmit from the transmitting device to the group of receiving devices control information including identification information identifying each message encoded within the retransmission packet and encoding information associated with each message within the retransmission packet.

There may be provided a communication system that comprises a transmitting device and a plurality of receiving devices according to any of the examples herein.

A further aspect of the invention also relates to a computer program, characterized in program code, which when run by at least one processor causes said at least one processor to execute any method according to embodiments and aspects of the invention. According to still a further aspect, the invention also relates to a computer program product comprising a computer readable medium and said mentioned computer program, wherein said computer program is included in the computer readable medium, and the computer medium comprises of one or more from the group: ROM (Read-Only Memory), PROM (Programmable ROM), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically EPROM) and hard disk drive.

The above features may be combined as appropriate, as would be apparent to a skilled person, and may be combined with any of the aspects of the examples described herein.

BRIEF DESCRIPTION OF FIGURES

Examples will now be described with reference to the accompanying drawings, in which:

Figure 1 shows an example of a communication system supporting unicast transmissions.

Figure 2 shows an example of a communication system supporting multicast transmissions.

Figure 3 shows an example of a retransmission scheme in which messages are retransmitted as unicast transmissions.

Figure 4 shows an example of a retransmission scheme in which multiple messages combined into a packet and retransmitted as multicast transmissions.

Figure 5 shows an example internal structure of a transmitting device.

Figure 6 shows an example internal structure of a receiving device.

Figure 7 shows a flowchart of steps for performing a retransmission scheme. Figure 8 shows another example of a communication system supporting the retransmission scheme described herein.

DETAILED DESCRIPTION

The following description is presented by way of example to enable a person skilled in the art to make and use the invention. The present invention is not limited to the embodiments described herein and various modifications to the disclosed embodiments will be apparent to those skilled in the art. Embodiments are described by way of example only.

Figure 2 shows an example communication system 200 that comprises a transmitting device 202 and a plurality of receiving devices. In this example, the communication system 200 comprises three receiving devices: 204, 206 and 208, though it will be appreciated that in other examples there may be any suitable number of receiving devices. As used herein, the term ‘transmitting device’ refers generally to any type of device that can perform transmit packets, and the term‘receiving device’ refers generally to any type of device that can receive packets. A transmitting device need not therefore be a dedicated transmitter, and likewise a receiving device need not be a dedicated receiver. The transmitting device 202 could be, for example, a base station, eNodeB/eNB (known as the fourth generation/4G mobile system base station), gNB (known as the fifth generation/5G mobile system base station), a distributed unit (DU) of a disaggregated gNB, a road side unit (RSU), or an end device such as a User Equipment (UE) device. The receiving devices may be User Equipment (UE) devices (e.g. vehicle-to- everything (V2X) UEs, mobile terminals etc.), an internet-of-things (loT) device, a machine, a sensor, an actuator etc.

The transmitting device 202 communicates with the receiving devices 204-208 over a communication network (not shown in figure 2). The network may be a wired and/or wireless network. The communications may be in accordance with a communications protocol, or standard, such as the Long Term Evolution (LTE) or 5G standard. The transmitting device 202 transmits packets (e.g. IP packets or Ethernet packets) over the network using multicast or broadcast transmissions. The transmitting device 202 may also be capable of transmitting packets using unicast transmissions.

A packet transmitted by the transmitting device 202 comprises an encoded message. The message may be encoded to a codeword. The codewords may correspond to the transport blocks or code blocks of a communication standard, such as the LTE or 5G standard. A message may be encoded to a codeword using a redundancy version (RV), for example if Hybrid Automatic Repeat request (HARQ) error coding is used. The redundancy version for a message may be changed if the message is retransmitted, enabling different codewords for the same message to be generated.

In the system shown in figure 2, the transmitting device 202 transmits a stream of three messages, denoted as rm , m and m₃, to the receiving devices 204-208. Each message of u , m₂, and m₃ is encoded to a respective codeword ci , c₂ and c₃ and used to form a packet, which is transmitted to the receiving devices 204-208 as a multicast transmission. In other words, the transmitting device 202 performs a first multicast transmission to transmit a packet containing codeword Ci to each receiving device; a second multicast transmission to transmit a packet containing codeword c₂ to each receiving device; and a third multicast transmission to transmit a packet containing codeword c₃ to each receiving device.

The communication network supports feedback channels between each receiving device 204- 208 and the transmitting device 202. The feedback channels enable each receiving device to communicate a feedback message (e.g. an ACK or NACK message) to the transmitting device 202 for each message encoded and transmitted by the transmitting device 202. Thus, each receiving device transmits a feedback message to the transmitting device for each of messages rm , m₂ and m₃ indicating whether that message has been correctly decoded or not. In figure 2, the multicast transmission of the messages rm , m₂, m₃ - encoded as codewords Ci , c_2, c₃ respectively - from the transmitting device 202 to the receiving devices are shown with the solid lines, and the feedback message from each receiving device for each of those messages is shown with a dashed line.

In the scenario depicted in figure 2, the receiving device 204 correctly decodes codewords c₂ and c₃ to obtain messages m₂ and m₃, but does not correctly decode codeword m ; receiving device 206 correctly decodes codewords ci and c₃ to obtain messages rm and m₃, but does not correctly decode codeword c₂; and receiving device 208 correctly decodes codewords Ci and c₂ to obtain messages rm and m₂, but does not correctly decode codeword c₃.

One retransmission scheme that could be adopted by the transmitting device 202 would be to retransmit the missing packets to each receiving device separately as unicast transmissions; i.e. transmit a packet containing encoded message rm to receiving device 204, transmit another packet containing encoded message m₂ to receiving device 206 and transmit a further packet containing encoded message m₃ to receiving device 208. This is illustrated in figure 3. Though such a scheme would enable the missing messages to be retransmitted to the receiving devices, it results in three unicast transmissions being performed, which increases the packet traffic over the network and doesn’t effectively utilise the multicasting capabilities of the network.

Described herein in a deterministic retransmission scheme in which feedback messages from the receiving devices are used to identify a group of receiving devices that each failed to decode one of a set of M messages previously received at those receiving devices. Put another way, a set of M messages are identified such that each receiving device of a group of receiving devices decoded all but one of that set of messages, i.e. each receiving device in the group decoded M-1 of the set of messages. The set of M messages may have been previously transmitted by the transmitting device. The messages failed to be decoded need not be the same for each receiving device, in other words each receiving device in the group may have failed to decode a different message of the set. Thus, for an identified set of M messages, the number of receiving devices in the group is greater than or equal to M. The set of M messages are then each encoded and combined to form a single retransmission packet that is transmitted to the group of receiving devices.

Each receiving device then uses control information indicating how the set of messages are encoded within the retransmission packet, and the remaining M-1 messages of the set its previously decoded, to attempt to decode the missing message from the retransmission packet. The control information is sent by the transmitting device and may be sent separately (i.e. in a separate communication) to the retransmission packet. The retransmission packet can be sent as a multicast communication to the group of receiving devices, reducing contributory traffic over the network from retransmissions.

Referring back to figure 2, the transmitting device 202 receives feedback messages from each of receiving devices 204, 206 and 208. In accordance with the present disclosure, the transmitting device 202 determines from these feedback messages that for the set of transmitted messages rm , m and m₃, receiving device 204 decoded messages m₂ and m₃ but failed to decode rm , receiving device 206 decoded messages rm and m₃ but failed to decode m₂, and receiving device 208 decoded rm and m₂ but failed to decode m₃. Thus, the transmitting device 202 determines that the group of receiving devices 204-208 each failed to decode one of the set of messages rm , m₂ and m₃ previously transmitted in packets by the transmitting device. Figure 4 illustrates an example of the retransmission scheme of the present disclosure for the transmission scenario shown in figure 2. As shown, the transmitting device 202 encodes the set of messages rm , m₂, m₃ to respective codewords Ci , c₂, c₃ and combines the codewords into a single retransmission packet. As will be explained in more detail below, the codewords may be linearly combined, for example using binary addition, to form the retransmission packet. The retransmission packet containing the codewords corresponding to the set of messages is then transmitted to the group of receiving devices 204-208.

The operation of the transmitting device 202 and the receiving devices 204-208 during the retransmission scheme will now be described in more detail.

An example internal structure of the transmitting device 202 is shown in figure 5. The transmitting device comprises a modulator 502, an encoding unit 504, a buffer 506, a feedback unit 508, a control information unit 510 and a transmitter 512.

The transmitter 512 may be an antenna, or an antenna array. If the transmitting device 202 is equipped with an antenna array, it might be capable of transmitting packets in one or more directional beams using beamforming.

In operation, the feedback unit 508 acts to receive feedback messages from the receiving devices. From these feedback messages, the feedback unit 508 identifies a group of receiving devices that each failed to decode one of a set of M messages previously transmitted to those receiving devices. In this example, that group of receiving devices are devices 204-208. The value of‘M’ might not be fixed, but might be variable depending on the status of the transmitted messages that has developed within the communication system. The set of M messages may have the property that each message of that set had failed to be decoded by at least one receiving device of the group. In other words, the feedback unit 508 may identify a group of receiving devices and a set of M messages previously transmitted to that group of devices, such that each receiving device within the group failed to decode only one of the set of M messages, and each message in the set had failed be to be decoded by at least one receiving device of the group. In the present example, the set of M messages is rm , m₂, m₃ because each of the receiving devices 204-208 failed to decode one of those messages.

For communication systems including a greater number of receiving devices, the feedback unit 508 might not always be able to identify a set of messages that can be combined into a retransmission packet to satisfy all the receiving devices that have failed to decode a previous message. When such situations arise, the feedback unit might 508 identify a group of receiving devices that is as a sub-group of the total number of receiving devices in the communication system. In other words, the feedback unit might analyse the feedback messages from the receiving devices of the communication system, and from these feedback messages identify a group of receiving devices that each failed to decode one of a set of previously transmitted messages.

If the transmitting device 202 performs beamforming, the feedback unit 508 might take this into account when identifying the set of messages and the group of receiving devices. For example, the feedback unit 508 might group receiving devices together that receive the same beam transmitted by the transmitting device. The feedback unit 508 might identify receiving devices that receive the same beam, and then identify from those receiving devices a group of receiving devices and a set of messages transmitted in that beam such that each receiving device within the group failed to decode only one of the set of messages, and each message in the set had failed be to be decoded by at least one receiving device of the group.

The encoding unit 504 receives the set of M messages identified by the feedback unit 508 from the buffer 506. The encoding unit 504 then encodes each of the messages in the set using encoding information for each message. The encoding unit 504 might encode each message to a respective codeword using encoding information associated with that message. The codewords could correspond to transport blocks or code blocks of a communication standard, e.g., the LTE or 5G communication standards. Continuing the present example, the encoding unit 504 encodes the set of messages rm , m , m₃ to the respective set of codewords Ci , c₂, c₃. The codewords for the set of messages may be distinct from each other, i.e. each codeword in the set may be unique within that set. This facilitates decoding of the messages at the receiving devices.

The encoding information associated with each message may include a redundancy version. The encoding unit 504 might select the redundancy version to encode each message in dependence on the number of times that message has been previously retransmitted to the receiving devices. It is noted that the use of redundancy versions enables the encoding unit 504 to generate different codewords representing the same message. It also enables incremental redundancy-based HARQ to be implemented at the receiving devices, which will be discussed in greater detail below.

The encoding information associated with each message may alternatively or in addition include an encoding rate. The encoding information may be different for at least two messages of the set of messages. Having separately encoded each message in the set of M messages, the encoding unit 504 combines the encoded messages into a single retransmission packet. Continuing the present example, the encoding unit 504 combines the codewords CrC₃ into a retransmission packet. The encoder may combine the encoded messages linearly. It may combine the encoded messages using binary addition. This is convenient because it enables information about the set of messages to be stored in the same bit length as a single encoded message, which enables the retransmission packet to be of the same size as a packet containing a single encoded message. Combining the codewords CrC₃ using binary addition may be denoted as: C1@C @C₃.

Combining the messages after they have been encoded (e.g., at the codeword level) is also convenient as it enables each message in the set to be encoded with different encoding information (e.g. different redundancy versions and/or encoding rates), which can provide additional flexibility at the transmitting device.

The combined encoded messages are then modulated, or mapped, by the modulator 502 to form the retransmission packet. The retransmission packet, which includes the set of M encoded messages, is then transmitted to the group of receiving devices as a multicast communication (e.g. as shown in figure 4).

The transmitting device 202 also communicates control information to the group of receiving devices to enable those receiving devices to decode, from the retransmission packet, the message in the set they previously failed to decode. In other words, the control information contains sufficient information to enable each receiving device to reverse the combination and encoding operations performed by the transmitting device. The control information may be communicated separately to the retransmission packet, i.e. in a separate communication. The control information may be communicated to the receiving devices over a control channel. That control channel might be, for example a dedicated physical downlink control channel (PDCCH), or a shared channel carrying control information, e.g., physical downlink shared channel (PDCCH). The control information might be in the form of downlink control information (DCI), a radio resource control (RRC) message or an RRC reconfiguration message. For instance, if the control information is part of an RRC information element (IE), it may be sent to the group of devices or to each device as part of RRC procedures, e.g., RRC connection establishment and/or RRC reconfiguration. The control information includes identification information identifying each message encoded within the retransmission packet and the encoding information associated with each message within the retransmission packet. The identification information may take the form of a message ID. If HARQ error correcting coding is implemented, the message ID may be a HARQ process ID. This is convenient because HARQ process IDs might be in use within the communication system and thus identifiers can be attributed to the messages without increasing information overhead. As explained above, the encoding information for each message might include the redundancy version used to encode the message and/or the encoding rate for the message. The control information may further include an indicator for each message within the retransmission packet that indicates whether that message has previously been transmitted by the transmitting device or not. In other words, the indicator for each message indicates whether that message is being transmitted for the first time or not. The indicator may take the form of a flag, e.g. a binary flag, such as the New Data Indicator (NDI).

The control information may be communicated to the receiving devices before or after the retransmission packet. However, since the receiving devices use the control information to decode the messages from the retransmission packets, it might be preferable for the control information to be transmitted to the receiving devices before the retransmission packet, so that decoding of the retransmission packet can begin when that packet is received. Alternatively, the control information can be communicated to the receiving devices on a different frequency band, e.g. using different subcarriers of a modulated symbol that uses multiple sub-carriers (such as an orthogonal frequency-division multiplexing (OFDM) symbol). In the case of multi-connectivity, e.g., UEs connecting to multiple access points (such as multiple DUs and/or a Master Node and Secondary Node), the control information may be provided from a different access point than the access point transmitting the packets containing encoded messages. Such access points may need to coordinate the transmission schemes or configuration over an inter- access node interface, e.g., Xn interface in 5G, or central unit (CU). DU interface, e.g., F1 interface in 5G. In another case, where the UEs may be connected to different access points, e.g., neighbouring gNBs, the access points may need to coordinate the transmission schemes or configuration over an inter-access node interface, e.g., Xn interface in 5G.

An example receiving device is shown in figure 6. For the purposes of illustration, the receiving device shown is device 204, though it will be appreciated that each receiving device may have similar components. The receiving device 204 comprises a control information decoder unit 602, a demodulator unit 604, a buffer 606, a decoding unit 608, a feedback message unit 610 and an antenna 612.

The receiving device 204 receives the retransmission packet and the control information from the transmitting device 202 and operates to extract from the retransmission packet the message that receiving device had previously failed to decode of the set of M messages. The receiving device extracts the missing message from the retransmission packet using the control information and the remaining messages in the set that the receiving device has previously decoded (i.e. the M-1 messages of the set that receiving device has previously decoded). Thus, in this example, receiving device 204 extracts message rm from the retransmission packet.

The control information decoder 602 decodes the control information to obtain the identification information for each message encoded in the retransmission packet (e.g. the HARQ process ID for each encoded message) and the encoding information for each message in the retransmission packet (e.g. the redundancy version and/or encoding rate for each message).

The demodulator unit 604 demodulates, or de-maps, the received retransmission packet to obtain for each message confidence values for each bit of the message. The confidence values may be log-likelihood values, referred to as L-values or Log-Likelihood Ratio (LLR) values. The L-values for each message are then written to the buffer 606, which in this example is a HARQ buffer. The L-values for each message are written to the buffer 606 according to their message ID. The L-values for the message that has previously failed to be decoded are obtained using the L-values for the previously decoded messages of the set.

To do this, the demodulator unit 604 first demodulates or de-maps the received retransmission packet to obtain a vector of L-values for the combination of encoded messages in the packet. Thus, in this example, the demodulator unit 604 would obtain a vector of L values for the combination of codewords ci@c_2@c₃ (this vector being denoted L123).

Because receiving device 204 has previously decoded codewords c₂ and c₃, it can generate the binary vector c_2@c₃ The demodulator unit then changes the signs of the elements in LI₂₃ at every index, where the binary vector c_2@c₃ contains a binary 1 .

The demodulator unit 604 can then use the updated L-values for the codeword Ci (corresponding to missing message mi). The L-values for the codeword Ci (corresponding to message mi that has not yet been decoded) are then written to the HARQ buffer 606 according to the message ID.

It can therefore be appreciated that the values of the buffer 606 corresponding to each message can be updated as further L-values corresponding to that message are extracted from received packets. This incremental updating of values can facilitate decoding of the message. The values of the buffer 606 can also be updated using the indicators in the control information. For example, if an indicator indicates that a message has not previously been retransmitted (i.e. the message has been transmitted for the first time), then the entry in the buffer corresponding to the ID of that message can be reset, or initialised.

The decoding unit 608 attempts to decode the missing message rm using the corresponding L-values for that message stored in the HARQ buffer 606 and the encoding information for that message decoded from the control information. The decoding unit 608 performs the decoding operation to obtain an estimate of the message rm that has previously failed to be successfully decoded.

The feedback message unit 610 sends a feedback message to the transmitting device 202 indicating whether or not the message rm that had previously failed to be successfully decoded has now been successfully decoded or not. The feedback message may be an ACK or NACK message, for example. The receiving device 204 may determine whether the message has been successfully decoded or not by using an error detection mechanism on the estimated message obtained by the decoding unit 608. The error detection mechanism could be, for example, a cyclic redundancy check (CRC).

It will be appreciated that the above structure and operation of receiving device 204 applies analogously to receiving devices 206 and 208, which attempt to decode messages m and m₃ respectively from the retransmission packet.

A summary of the retransmission scheme described above with respect to figures 4 to 6 will now be provided with reference to the flowchart of figure 7.

Steps 702 to 708 of the method may be performed by the transmitting device.

At 702, a group of receiving devices that each failed to decode one of a set of messages previously received at those devices is identified from feedback messages. The feedback messages are sent from the receiving devices of the communication system to the transmitting device. The combination of the set of messages and group of receiving devices may be identified such that each receiving device in the group failed to decode only one of the set of messages, and each message in the set has previously failed to be decoded by at least one of the group of receiving devices. Step 702 may be performed by the feedback unit 508 of transmitting device 202.

At step 704, the identified set of messages are separately encoded, and the encoded messages then combined into a single retransmission packet. Each message may be encoded into a respective codeword. This step may be performed by encoding unit 504.

At step 706, the retransmission packet containing the set of encoded messages is transmitted to the group of receiving devices.

At step 708, control information including identification information identifying each message encoded within the retransmission packet and encoding information associated with each message within the retransmission packet is transmitted to the group of receiving devices. The control information may be transmitted over a control channel. The identification information might include a message ID for each message encoded in the retransmission packet (e.g. a HARQ process ID). The encoding information might include a redundancy version and/or encoding rate for each message encoded in the retransmission packet. The control information may be generated by the control information unit 510.

Steps 710 and 712 are performed by each of the group of receiving devices.

At step 710, the receiving device receives the retransmission packet and the control information.

At step 712, the receiving device extracts from the retransmission packet the message of the set of messages that receiving device had previously failed to decode. The receiving device extracts this message using the control information and the remaining messages encoded in the retransmission packet that the receiving device has previously decoded. Step 712 may be performed using components 602-612 as described above. The receiving device may then communicate a feedback message to the transmitting device indicating whether the message it had previously failed to decode had now been successfully decoded or not. The retransmission scheme described herein enable multiple messages to be encoded and combined into a single packet, which can be sent to multiple receivers through a multicast transmission. This can advantageously reduce the amount of retransmission traffic over the network and consequently increase throughput compared to approaches in which each retransmission is a separate unicast transmission. Furthermore, the retransmission scheme described herein is deterministic, in the sense that a set of messages are combined and sent to a group of receiving devices that are determined from received feedback messages. This differs to approaches in which messages are combined in a random or pseudo-random manner. Though these latter approaches may achieve acceptable levels of performance for relatively large networks, they tend to perform poorly and inefficiently for relatively small networks. The retransmission scheme described herein can be scaled depending on network size (e.g. by identifying sub-groups of receiving devices as described above) and provide an efficient approach to retransmitting packets regardless of network size. The retransmission scheme described herein can also make use of a HARQ buffer to perform the decoding operations. This is convenient because a HARQ buffer may, depending on the communication system, already be implemented, and thus the retransmission scheme can be implemented without the need of an additional buffer.

The above examples are described in the context of a scenario where the feedback messages indicate that some messages have only been decoded by a subset of the receivers in the communication system. It will be appreciated that, in practice, different scenarios may also arise following the transmission of a set of packets. For example, a message may be received by all the receivers to which it was transmitted. In this case, no retransmission of that message is required. Another example may be that a message was failed to be decoded by all the receivers to which it was transmitted. In this case, the message may be retransmitted in a similar manner to how it was originally transmitted. That is, it may be transmitted in a packet containing only that message.

Thus, the transmitting device may transmit different types of packets at different times depending on the network conditions. It can be appreciated that the processing performed by the receiving devices will differ depending on what type of packet is received, for example whether the received packet contains only a single encoded message or a combination of encoded messages. To enable the receiving devices to perform the appropriate decoding process for the packet it receives, the transmitting device may provide to the receiving devices configuration information indicating whether the retransmission packet includes a combination of encoded messages, or only a single encoded message. The reconfiguration information may be sent as part of the control information, as part of the transmitted packet, or as a separate communication. The reconfiguration information could take various forms, but in one implementation may be in the form of a flag (e.g. a binary value) indicating whether the transmitted packet contains a single encoded message or a combination of encoded messages.

The examples described herein reference a communication system that includes a transmitting device and three receiving devices. It will be appreciated that the approaches herein can be applied to communication systems including any suitable number of receiving devices, for example more than three devices, or less than three receiving devices. Figure 8 shows an example where transmitting device TX determines from feedback messages that message rm (encoded to codeword ci) has been successfully decoded by receiving device RX1 but not receiving device RX2, and message m (encoded to codeword c₂) has been successfully decoded by receiving device RX2 but not receiving device RX1 . In response, and in accordance with the techniques described herein, the transmitting device TX encodes messages rm and m₂ to respective codewords and combines the codewords into a single packet that is transmitted to the receiving devices. It is noted that in this example, messages rm and m₂ have been encoded for retransmission using different redundancy versions than those used to encode the messages for their original transmission. Thus, message rm has been encoded to a different codeword for retransmission than the codeword m used for the original transmission of that message, and the message m₂ has been encoded to a different codeword for retransmission than the codeword c₂ used for the original transmission of that message.

The transmitting devices described herein may be configured to perform any of the retransmission methods described herein. The receiving devices described herein may be configured to perform any of the methods of decoding retransmission packets described herein. Generally, any of the methods, techniques or components described above can be implemented in software, hardware, or any combination thereof. The terms“module,” and “unit” may be used to generally represent software, hardware, or any combination thereof. In the case of a software implementation, the module or unit represents program code that performs the specified tasks when executed on a processor. Any of the algorithms and methods described herein could be performed by one or more processors executing code that causes the processor(s) to perform the algorithms/methods. The code may be stored in a computer program product or non-transitory computer readable storage medium such as, for example, random-access memory (RAM), read-only memory (ROM), an optical disc, hard disk memory, and other memory devices. The code could be any suitable executable code, for example computer program code or computer-readable instructions. The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention. The project leading to this application has received funding from the European Union’s H2020 research and innovation programme under grant agreement No 76144.

Claims

1 . A transmitting device configured to transmit packets including messages to a plurality of receiving devices over a communication network, the transmitting device being configured to, in response to identifying from feedback messages from the plurality of receiving devices a group of receiving devices that each failed to decode one of a set of previously received messages:

encode each of the set of messages and combine the encoded messages into a single retransmission packet;

transmit the retransmission packet to the group of receiving devices; and

transmit to the group of receiving devices control information including identification information identifying each message encoded within the retransmission packet and encoding information associated with each message within the retransmission packet.

2. The transmitting device of claim 1 , further configured to provide to the group of receiving devices configuration information indicating whether the retransmission packet includes a combination of encoded messages.

3. The transmitting device of claim 1 or 2, wherein the transmitting device is configured to encode each of the set of messages to a respective codeword, and to combine the codewords into the single retransmission packet.

4. The transmitting device of any preceding claim, wherein the encoding information includes at least one of a redundancy version and an encoding rate.

5. The transmitting device of claim 4, wherein the encoding information is different for at least two messages of the set of messages.

6. The transmitting device of claim 4 or 5 when dependent on claim 3, wherein the transmitting device is configured to select a value of the redundancy version for each codeword in the retransmission packet in dependence on the number of previous retransmissions of the respective message.

7. The transmitting device of any preceding claim, wherein the control information further includes an indicator indicating whether each of the set of messages encoded in the retransmission packet has been previously transmitted by the transmitting device or not.

8. The transmitting device of any preceding claim, wherein the transmitting device is configured to combine the codewords using binary addition.

9. The transmitting device of any preceding claim, wherein the transmitting device is configured to transmit the control information to the group of receiving devices over a control channel.

10. The transmitting device of any preceding claim, wherein the identification information identifying each message encoded within the retransmission packet is a hybrid automatic repeat request (HARQ) process ID.

1 1 . The transmitting device according of any preceding claim, wherein the transmitting device is configured to transmit packets to the plurality of receiving devices as a set of one or more beams using beamforming, and the group of receiving devices are identified as receiving the same beam transmitted from the transmitting device.

12. A receiving device configured to:

receive: (i) a retransmission packet that includes a combination of encoded messages; and (ii) control information including identification information identifying each message encoded within the retransmission packet and encoding information associated with each message within the retransmission packet; the device being configured to, when the received retransmission packet includes an encoded message corresponding to a message the receiving device previously failed to decode:

extract from the retransmission packet the message that receiving device failed to decode based on the control information and the messages in the retransmission packet the receiving device has previously decoded.

13. The receiving device of claim 12, wherein the encoding information includes at least one of a redundancy version and an encoding rate.

14. The receiving device of claim 12 or 13, wherein the encoding information is different for at least two messages in the retransmission packet.

15. The receiving device of any of claims 12 to 14, wherein the identification information identifying each message encoded within the retransmission packet is a hybrid automatic repeat request (HARQ) process ID.

16. A method of transmitting packets including messages from a transmitting device to a plurality of receiving devices over a communication network, the method comprising:

17. A computer program product comprising instructions which, when executed by a transmitting device configured to transmit packets including messages to a plurality of receiving devices over a communication network, causes the transmitting device to: