WO2021028016A1

WO2021028016A1 - Communication device for enhanced harq feedback

Info

Publication number: WO2021028016A1
Application number: PCT/EP2019/071586
Authority: WO
Inventors: Taimoor ABBAS; Wenquan HU; Gustaf Claeson; Bengt Lindoff
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2019-08-12
Filing date: 2019-08-12
Publication date: 2021-02-18

Abstract

The invention relates to a communication device for enhanced HARQ feedback in wireless communications. Especially, the invention relates to a first communication device (100) receiving data packets from a second communication device (300). The first communication device (100) provides HARQ feedback according to a first HARQ feedback procedure, and upon detecting a first switching criterion fulfillment provide HARQ feedback for data packets received from the second communication device (300) according to a second HARQ feedback procedure. Thereby, robust HARQ feedback and/or improved resource utilization is provided. Furthermore, the invention also relates to corresponding methods and a computer program.

Description

COMMUNICATION DEVICE FOR ENHANCED HARQ FEEDBACK

Technical Field

The disclosure relates to a communication device for enhanced HARQ feedback. Furthermore, the disclosure also relates to a corresponding method and a computer program.

Background

Vehicle-to-anything (V2X) communications, is one of the key enablers for future cooperative intelligent transportation systems (C-ITS). The term V2X jointly represents vehicles communicating with anything on the road or along the road, e.g., V2Vehicle, V2Infrastructure, V2Padestrian and V2Network, and so forth. The key requirements for V2X applications are high reliability of data packet reception with low latency and within a predefined communication range, which is challenging due to the high mobility in vehicular environments.

V2Network communication over the Uu interface operating on a regular commercial licensed third generation (3G) or long term evolution (LTE) spectrum, where transmission and resource allocation is coordinated by the eNB, may not always fulfil the reliability and latency requirements for V2X applications. The reason can either be due to the limitations of the technology or due to the network conditions. Therefore, a new interface named PC5 or sidelink (SL) was introduced in LTE that supports direct communication between the vehicles while operating in the ITS band at 5.9GHz, which is specifically designed to meet the requirements for advanced safety applications. LTE SL supports broadcast mode for self-managed direct V2X communication with or without network assistance. Unicast or groupcast/multicast mode, which are essential modes for some of the advanced V2X applications both in coverage and out-of-coverage scenario, are supported for in-coverage scenario in LTE V2X with network assistance only. This implies that LTE V2X is not suitable for advanced V2X applications that enforce higher categories of requirements to achieve advanced level of automation.

New radio (NR) V2X is aiming to mitigate the challenges faced by LTE V2X. The goal is to support lower latencies, higher reliability and increased data rates in more dynamic conditions. NR V2X will also enable unicast, groupcast or multicast mode over NR SL and a multi band support including ITS band as well as the licensed bands. Resource allocation and configuration for LTE SL or NR SL could either be done by the base station, e.g., eNB or gNB, or it could be done in an ad hoc manner, such as listen-before-talk (LBT), from a pre-configured resource pool.

Groupcast communication is simultaneous data transmission to a group of UEs from a single transmission source. System architecture group 2 (SA2) working group at 3 GPP has agreed to enable two types of group communication for V2X groupcast. Type 1 group is when an application forms the group with a group ID and informs the V2X layer about the group ID. Type 2 group is where the group is dynamically formed and application does not inform the V2X layer about the group ID. Instead V2X layer passes the mapping of an application ID and group ID along with the 5G quality-of-service indicator (5QI) and range parameters to the Access Stratum (AS) layer for group formation. SL communication for groupcast can utilize both licensed and unlicensed frequency resources. In a groupcast communication in mode 2, no matter it is type 1 or type 2 group, there is at least one source or transmitter (TX) UE and multiple destination or receiver (RX) UEs. The data sent over the physical sidelink shared channel (PSSCH) in groupcast communication is intended for each member of the group.

Cellular V2X technologies have several advantages in comparison to other complementary V2X technologies and one of them is hybrid automatic repeat request (HARQ) based retransmission mechanism, which enables relatively higher reliability and longer communication range. HARQ feedback mechanism in LTE SL is rather simpler than that in LTE Uu. LTE SL supports broadcast mode where a simplified retransmission of data packets is sufficient and acknowledgment (ACK) and negative acknowledgment (NACK) feedback is not required. Now in NR V2X SL for unicast as well as groupcast communication when HARQ feedback is enabled then the ACK/NACK feedback will be required.

HARQ feedback (ACK/NACK) is important for HARQ operations. In groupcast, the RX UE feedbacks an ACK if it has successfully decoded the groupcast data in the PSSCH from the TX UE without any transmission errors. The RX UE feedbacks a NACK if it has decoded the groupcast data in the PSSCH from the TX UE but with some transmission errors and finally a MISS means that the RX UE does not give any feedback since the RX UE has failed to detect the control channel and will not receive corresponding data channel. For the SL groupcast mode when HARQ feedback is enabled, there are seven possible outcome to happen at the decoders of all the RX UEs involved in a groupcast: SI) ACK for all RX UEs, S2) NACK for all RX UEs, S3) MISS for all RX UEs, S4) ACK for some and NACK for other RX UEs, S5) ACK for some RX UEs and rest are MISS, S6) NACK for some RX UEs and rest are MISS, S7) a mix of ACKs, NACKs and MISS for all RX UEs. Any solution proposed for SL HARQ feedback for groupcast communication should work for all these situations while fulfilling the reliability requirements.

Summary

An objective of embodiments of the invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions.

The above and further objectives are solved by the subject matter of the independent claims. Further advantageous embodiments of the invention can be found in the dependent claims.

According to a first aspect of the invention, the above mentioned and other objectives are achieved with a first communication device for a wireless communication system, the first communication device being configured to receive data packets from a second communication device; provide hybrid automatic repeat request, HARQ, feedback for data packets received from the second communication device according to a first HARQ feedback procedure; and upon detecting a first switching criterion fulfillment provide HARQ feedback for data packets received from the second communication device according to a second HARQ feedback procedure.

A data packet herein can be transmitted over the radio channel. The data content of the data packet can e.g. be a transport block or a code block. In addition to an initial transmission of a data content, one or more retransmissions of the data content might be needed for correct reception. Each such transmission of data packet(s) may include a different set of information bits, where the information bits can be seen as soft bits and the data content can be seen as hard bits, i.e. bits prior to encoding. The information bits, in the respective data packet, in the one or more transmissions might e.g. be associated to different redundancy versions and/or different modulation and coding schemes. Hence, a data packet can be understood as comprising information bits and is transmitted in the radio channel over an air interface in the wireless communication system. In an example, the data packet in the initial transmission and the data packet in the retransmission belong to the same HARQ process.

An advantage of the first communication device according to the first aspect is that enhanced feedback mechanism for HARQ feedback is provided since the first communication device can switch between different HARQ feedback procedures. For example, different HARQ feedback procedures could aim for different performance improvements, such as reliability, robustness and resource consumption in terms of time-frequency resources and power consumption.

In an implementation form of a first communication device according to the first aspect, detecting the first switching criterion fulfillment is based on at least one of: a first channel quality threshold value, a first HARQ feedback procedure switching timer, a first spatial distance between the first communication device and the second communication device, a group identity of the first communication device, and a first number of sequentially and correctly decoded data packets.

An advantage with this implementation form is that the mentioned criteria are non-limiting examples of relevant criteria for deciding to switch from the first HARQ feedback procedure to the second HARQ feedback procedure or not. By using the first criteria suitable switching conditions can be designed for balancing reliability, robustness and resource consumption in the system. It is noted that one or more of the first criteria can be combined.

In an implementation form of a first communication device according to the first aspect, provide HARQ feedback according to the first HARQ feedback procedure comprises transmit a negative acknowledgment, NACK, to the second communication device for each incorrectly decoded data packet; provide HARQ feedback according to the second HARQ feedback procedure comprises transmit a NACK to the second communication device for each incorrectly decoded data packet. An advantage with this implementation form is that by transmitting NACK for each incorrectly decoded data packet the data packet reception rate is increased by retransmission of the data packets that are decoded incorrectly.

In an implementation form of a first communication device according to the first aspect, provide HARQ feedback according to the first HARQ feedback procedure comprises transmit an acknowledgment, ACK, to the second communication device for every n:th correctly decoded data packet, wherein n is a positive integer; provide HARQ feedback according to the second HARQ feedback procedure comprises transmit an ACK to the second communication device for every k. th correctly decoded data packet, wherein k is a positive integer larger than n.

An advantage with this implementation form is that it is not needed to send ACK feedback for all correctly decoded data packet if the channel conditions are good enough. Hence, by switching to the second HARQ feedback procedure, given that the channel conditions are suitable, results in improved resource efficiency since the transmission rate of ACKs for the second HARQ feedback procedure is lower than that in the first HARQ feedback procedure.

In an implementation form of a first communication device according to the first aspect, provide HARQ feedback according to the first HARQ feedback procedure comprises transmit an ACK to the second communication device for each correctly decoded data packet; and provide HARQ feedback according to the second HARQ feedback procedure comprises skip transmit an ACK to the second communication device for each correctly decoded data packet.

An advantage with this implementation form is that it is not needed to send ACK feedback at all for correctly decoded data packet if the channel conditions are good enough. Hence, by switching to the second HARQ feedback procedure under such channel conditions results in improved resource efficiency since the transmission of ACKs for the second HARQ feedback procedure is skipped. Furthermore, in groupcast communications if the second communication device does not know which first communication device that transmits ACKs, then the transmission of ACKs is of no use in such scenarios. In an implementation form of a first communication device according to the first aspect, provide HARQ feedback according to the first HARQ feedback procedure comprises transmit an ACK to the second communication device for every n:th correctly decoded data packet, wherein n is a positive integer; provide HARQ feedback according to the second HARQ feedback procedure comprises transmit an ACK to the second communication device for every k. th correctly decoded data packet, wherein k is a positive integer smaller than n.

An advantage with this implementation form is that when the channel conditions are bad a more robust feedback mechanism is needed. Since the transmission rate of ACKs for the second HARQ feedback procedure is higher than for the first HARQ feedback procedure in this implementation form a more robust HARQ feedback mechanism is provided.

In an implementation form of a first communication device according to the first aspect, the first communication device further being configured to upon detecting a second switching criterion fulfillment provide HARQ feedback for data packets received from the second communication device according to the first HARQ feedback procedure or to a third HARQ feedback procedure.

An advantage with this implementation form is that that one or more further HARQ feedback procedures can be designed for balancing reliability, robustness and resource consumption in the system.

In an implementation form of a first communication device according to the first aspect, detecting the second switching criterion fulfillment is based one at least one of: a second channel quality threshold value, a second HARQ feedback procedure switching timer, a second spatial distance between the first communication device and the second communication device, a group identity of the first communication device, and a second number of sequentially and correctly decoded data packets. An advantage with this implementation form is that the mentioned criteria are non-limiting examples of relevant criteria for deciding to switch from the second HARQ feedback procedure to the first or third HARQ feedback procedure or not. By using the second criteria suitable switching conditions can be designed for balancing reliability, robustness and resource consumption in the system. It is noted that one or more of the second criteria can be combined.

In an implementation form of a first communication device according to the first aspect, provide HARQ feedback according to the third HARQ feedback procedure comprises transmit a NACK to the second communication device for each incorrectly decoded data packet.

An advantage with this implementation form is that by transmitting NACK for each incorrectly decoded data packet data packet reception rate is increased by retransmission of incorrectly decoded data packets.

In an implementation form of a first communication device according to the first aspect, provide HARQ feedback according to the third HARQ feedback procedure comprises transmit an ACK to the second communication device for every p th correctly decoded data packet, wherein p is a positive integer larger than k.

The variable k here denotes the transmission of ACKs for every k:th correctly decoded data packet in the second HARQ feedback procedure.

An advantage with this implementation form is that it is not needed to send ACK feedback for all correctly decoded data packet if the channel conditions are good. Hence, by switching to the third HARQ feedback procedure under such channel conditions results in improved resource efficiency since the transmission rate of ACKs for the third HARQ feedback procedure is lower than for the second HARQ feedback procedure in this implementation form.

In an implementation form of a first communication device according to the first aspect, provide HARQ feedback according to the third HARQ feedback procedure comprises transmit an ACK to the second communication device for every p th correctly decoded data packet, wherein p is a positive integer smaller than k. The variable k here denotes the transmission of ACKs for every k:th correctly decoded data packet in the second HARQ feedback procedure.

An advantage with this implementation form is that when the channel conditions are bad a more robust feedback mechanism is needed. Since the transmission rate of ACKs for the third HARQ feedback procedure is higher than for the second HARQ feedback procedure in this implementation form a more robust HARQ feedback mechanism is provided.

In an implementation form of a first communication device according to the first aspect, the first communication device further being configured to transmit a control signal to the second communication device upon detecting the first switching criterion fulfillment, wherein the control signal indicates a HARQ feedback procedure switching request.

An advantage with this implementation form is that the second communication device is informed about the switching intention of the first communication device meaning that the second communication device can take proper measures. For example, the second communication device can confirm the switching request or reject the switching request. Upon rejection the first communication device must send a new request, if needed.

In an implementation form of a first communication device according to the first aspect, the first communication device further being configured to upon receiving a confirmation for the HARQ feedback procedure switching request from the second communication device provide HARQ feedback for data packets received from the second communication device according to the second HARQ feedback procedure.

An advantage with this implementation form is that by confirming the switching request it is ensured that the first and second communication devices are configured for the application of the same HARQ feedback procedure meaning improved communication robustness in the system. In an implementation form of a first communication device according to the first aspect, the communication between the first communication device and the second communication device is at least one of groupcast communication and unicast communication.

An advantage with this implementation form is that the present solution can be implemented in both groupcast and unicast communications.

In an implementation form of a first communication device according to the first aspect, wherein the groupcast communication and the unicast communication is sidelink communication or Uu communication.

An advantage with this implementation form is that the present solution can be implemented in the NR standard.

According to a second aspect of the invention, the above mentioned and other objectives are achieved with a method for a first communication device, the method comprises receiving data packets from a second communication device; providing hybrid automatic repeat request, HARQ, feedback for data packets received from the second communication device according to a first HARQ feedback procedure; and upon detecting a first switching criterion fulfillment provide HARQ feedback for data packets received from the second communication device according to a second HARQ feedback procedure.

The method according to the second aspect can be extended into implementation forms corresponding to the implementation forms of the first communication device according to the first aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the first communication device.

The advantages of the methods according to the second aspect are the same as those for the corresponding implementation forms of the first communication device according to the first aspect. 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 of the invention. Further, 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 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.

Further applications and advantages of the embodiments of the invention will be apparent from the following detailed description.

Brief Description of the Drawings

The appended drawings are intended to clarify and explain different embodiments of the invention, in which:

- Fig. 1 shows a first communication device according to an embodiment of the invention;

- Fig. 2 shows a method for a first communication device according to an embodiment of the invention;

- Figs. 3a-b show wireless communication systems according to embodiments of the invention;

- Fig. 4 shows a flow chart of a method according to an embodiment of the invention;

- Fig. 5 illustrates signaling between first and second communication devices according to an embodiment of the invention;

- Fig. 6 shows a flow chart of a method according to an embodiment of the invention; and

- Fig. 7 shows a flow chart of a method according to an embodiment of the invention.

Detailed Description

Two options have been proposed for SL HARQ feedback mechanism for groupcast communication. Option 1 - a receiver (RX) UE only transmits NACK for SL HARQ feedback and all the RX UEs share a PSFCH for transmitting NACK. In 3GPP Rl-1905012 it is motivated that NACK based approach is more appropriated compared to ACK/NACK based approach in terms of lower resource consumption especially when the groupcast is intended for a large group. Moreover, if a transmitter (TX) UE does not know the exact number of UEs that are involved in the groupcast and their respective IDs, then it cannot tell which UE sends ACK so sending ACK is not useful. Only a subset of RX UEs should send HARQ feedback (only NACK in this case) because the RX UEs within certain range from the TX UE are supposed to receive messages more reliably than the others. The range is specified by the application. For the distance based NACK feedback instead of using raw location information of TX and RX UEs, which can be challenging to process in the lower layers, the concept of Zone ID from LTE V2X can be utilized to put UE location information in SL control information (SCI), which can be used to estimate an approximate distance between the TX and RX UEs. Option 2 - RX UE transmits ACK/NACK for SL HARQ feedback and each RX UE uses a separate physical sidelink feedback channel (PSFCH) for HARQ ACK/NACK feedback. In 3GPP Rl-1903944 it is motivated that the ACK/NACK feedback offers higher reliability and fulfils the performance requirements in all the situations in cases SI to S7 described previously as this solution do not experience discontinuous transmission (DTX) problem and the UEs with failed reception can easily be identified. Moreover, this solution causes lower interference for other UEs.

A solution that combines option 1 and option 2 has also been discussed but has not been agreed. It proposes that only a limited number of the RX UEs may use option 2 for feedback, i.e., both ACK/NACK feedback, while all other UEs use option 1 for feedback, i.e., NACK only. The applicability of each option for a given UE can be determined semi-statically. It also states that all the RX UEs could use option 2 only if the group size is small otherwise resource consumption will be very high. In terms of applicability there can be several different ways, e.g., use option 1 mainly for session-less groupcast for type 2 group, and use option 2 for session based groupcast for type 1 group. Another example could be to use option 1 for one subset of UEs while option 2 for another subset of UEs. However, none of these is an optimal choice in the sense of signaling overhead, power consumption and reliability.

The inventors have identified drawbacks associated to the solutions of the conventional technology. Option 1 - drawbacks with the NACK only feedback is that it gives rise to severe in-band emissions (IBE) degrading receptions on neighboring resource blocks. Moreover, option 1 prevents TX UE to distinguish the successful PSSCH decoding from the missed SCI, leading to over-dimensioning PSCCH compared to what is necessary in order to ensure it is received reliably. Since the NACK only option is prone to MISS or DTX issue, i.e., this solution cannot identify the UEs that have missed the control channel and cannot efficiently provide the performance requirements in terms of reliability mainly in situations S3, S5, S6 and S7. Option 2 - sending both ACKs and NACKs consume more resources than sending NACKs only. When each RX UE is using a separate PSFCH to feedback ACK and NACK then the number of UEs in a group is proportional to the resources required for feedback. If the group is very large then the resource consumption can also be very large. Occasionally, the resources can be saved by not transmitting ACKs when it is not needed, i.e., when a RX UE is experiencing good channel condition. For example, consider the situations SI to S7 where some or all RX UEs may be sending both ACK and/or NACK. ACK feedback from RX UE often carries no information because the channel quality remains good for a very long time period for that particular RX UE. In such a situation it does not really matter to feedback ACKs or not. Hence, the ACK feedback from all the RX UEs may not always be needed, and by avoiding unnecessary ACKs the resource consumption can be reduced in the system when it is assumed that all the RX UEs are known to the TX UE and if the TX UE has received a NACK from any of the UEs in a group then it will retransmit to the whole group.

Now consider a combination of option 1 and option 2, which could ideally be more suitable choice where benefits of both options could be combined to achieve the best possible outcome. It suggests to consider the option 1 as a fall back mechanism and to use option 2 for a small set of UEs, i.e., only a limited number of receiver UEs are selected to send ACK/NACK while all other UEs feedback NACK only. It may not be the best approach as majority of UEs that are going to feedback only ACK may suffer from the issues associated to option 1. This implies that combining the two options does not solve the reliability issue. Therefore, there is a need for improved HARQ feedback schemes for overcoming drawbacks of conventional solutions. This is especially the case in groupcast communication scenarios.

Fig. 1 shows a first communication device 100 according to an embodiment of the invention. In the embodiment shown in Fig. 1, the first communication device 100 comprises a processor 102, a transceiver 104 and a memory 106. The processor 102 is coupled to the transceiver 104 and the memory 106 by communication means 108 known in the art. The first communication device 100 may further comprises an antenna or antenna array 110 coupled to the transceiver 104, which means that the first communication device 100 is configured for wireless communications in a wireless communication system. The first communication device 100 may further comprises a wired communication interface 112 for wired communication. That the first communication device 100 is configured to perform certain actions can in this disclosure be understood to mean that the first communication device 100 comprises suitable means, such as e.g. the processor 102, the memory 106 and the transceiver 104, configured to perform said actions. Especially, instructions can be stored in the memory 106 such that the processor 102 executes the instructions according to embodiments of the invention.

According to embodiments of the invention the first communication device 100 is configured to receive data packets from a second communication device 300 (illustrated in Figs. 3a and 3b). The first communication device 100 is further configured to provide HARQ feedback for data packets received from the second communication device 300 according to a first HARQ feedback procedure. The first communication device 100 is further configured to upon detecting a first switching criterion fulfillment provide HARQ feedback for data packets received from the second communication device 300 according to a second HARQ feedback procedure.

Fig. 2 shows a flow chart of a corresponding method 200 which may be executed in a first communication device 100, such as the one shown in Fig. 1. The method 200 comprises receiving 202 data packets from a second communication device 300. The method 200 further comprises providing 204 HARQ feedback for data packets received from the second communication device 300 according to a first HARQ feedback procedure. The method 200 further comprises upon detecting 206 a first switching criterion fulfillment provide HARQ feedback for data packets received from the second communication device 300 according to a second HARQ feedback procedure.

Fig. 3 a shows a wireless communication system 500a according to an embodiment of the invention. The wireless communication system 500a comprises a group of first communication devices 100a, 100b, ..., 100h and one second communication device 300, all configured to operate in the wireless communication system 500a. In the embodiment shown in Fig. 3a, the group of first communication devices 100a, 100b, ..., 100h and the second communication device 300 are all client devices, such as UEs. Although not shown in Fig. 3a, the wireless communication system 500a may further comprise one or more network access nodes, such as gNBs of a radio access network (RAN), with which one or more of the group of first communication devices 100a, 100b, ..., 100h and the second communication device 300 may communicate. The group of first communication devices 100a, 100b, ..., 100h and the second communication device 300 are configured to communicate with each other using groupcast communication, e.g. over SLs (not shown in Fig. 3a). Fig. 3a shows groupcast transmission of one or more data packets (DPs) transmitted from the second communication device 300 to the group of first communication devices 100a, 100b, ..., lOOn. Hence, the second communication device 300 is the source communication device or alternatively denoted TX communication device of this groupcast communication and the group of first communication devices 100a, 100b, ..., 100h are destination communication devices or alternatively denoted RX communication devices.

Fig. 3b shows a wireless communication system 500b according to an embodiment of the invention. The wireless communication system 500b comprises a group of first communication devices 100a, 100b, ..., 100h and a second communication device 300, all configured to operate in the wireless communication system 500b. In the embodiment shown in Fig. 3b, the group of first communication devices 100a, 100b, ..., 100h are client devices, while the second communication device 300 is a network access node. The first communication devices 100a, 100b, ..., lOOn and the second communication device 300 are configured to communicate with each other using unicast communication, e.g. over a Uu interface (not shown in Fig. 3b). Fig. 3b shows unicast communication of one or more data packets transmitted from the second communication device 300 to the first communication device 100a. The second communication device 300 determines whether to retransmit the data packet based on feedback from the first communication device 100a according to suitable HARQ procedure. Although not shown in Fig. 3b, the second communication device 300 may further be configured to communicate with one or more of the group of first communication devices 100a, 100b, ..., 100h using groupcast communication. In this case, the second communication device 300 may transmit the data packet in a groupcast to the one or more of the group of first communication devices 100a, 100b, ..., 100h belonging to the group. The second communication device 300 would then determine whether to retransmit the data packet based on feedback from all the first communication devices 100a, 100b, ..., 100h belonging to the group.

As stated above, Figs. 3a and 3b illustrates two non-limiting embodiments of the invention. However, any combination of first communication devices 100 and second communication devices 300 communicating using groupcast communication and/or unicast communication may be used without deviating from the scope of the invention. More generally, the communication between the first communication device 100 and the second communication device 300 is at least one of groupcast communication and unicast communication. Further, the groupcast communication and the unicast communication is sidelink communication or Uu communication.

However, in the following detailed description, for simplicity, embodiments according to the invention are exemplified assuming groupcast communication with SL for SL mode 2 communication, but the same principles can be applied for SL mode 1 as well as uplink (UL) or downlink (DL) groupcast communication. In SL communication mode, the first communication device 100, i.e. a RX UE 100, is configured to send HARQ feedback to the second communication device 300, i.e. a TX UE 300, in response to decoding outcome of data packets transmitted from the TX UE 300 and received by the RX UE 100; while in the UL groupcast mode, the RX UE 100 sends HARQ feedback to a network access node, such as a gNB.

Fig. 4 shows a flow chart of a method 400 for HARQ feedback according to embodiments of the invention. The method 400 may be executed in the first communication device 100 herein exemplified with a RX UE 100. It is assumed that the RX UE 100 is configured for SL groupcast communication and that HARQ feedback is enabled for SL groupcast.

In step 402, the RX UE 100 is configured for a first HARQ feedback procedure, such that the RX UE 100 transmits ACKs and NACKs according to the configured first HARQ feedback procedure. The RX UE 100 is configured to receive data packets transmitted by a second communication device 300 herein exemplified with a TX UE 300. In embodiments, the RX UE 100 is configured to transmit a NACK for each incorrectly decoded data packet according to the first HARQ feedback procedure. The TX UE 100 may in one alternative transmit an ACK to the TX UE 300 for each correctly decoded data packet. However, the RX UE 100 can instead in another alternative be configured to transmit an ACK to the TX UE 300 for every u:th correctly decoded data packet, wherein n is a positive integer. Hence, an ACK may be transmitted for every second, third, fourth, etc. correctly decoded data packet. In step 404, the RX UE 100 monitors for a first switching criterion fulfillment. In embodiments the first switching criterion fulfillment is based on at least one of the following first criteria:

• A first channel quality threshold value, which e.g. may be given as a channel quality metric, such as received signal received power (RSRP), signal-to-noise and interference ratio (SINR), or any other suitable metric. As long as the channel quality remains above the first threshold value the RX UE 100 will be able to reliably receive data packets and decode them correctly. It means that for every correctly received data packet the outcome of decoding will generally be an ACK, and hence an ACK can be considered as redundant information and need not to be transmitted to the TX UE 300 as long as there is no change in the channel quality to the worse;

• A first HARQ feedback procedure switching timer which can be preconfigured e.g. by a standard or dynamically determined e.g. by the RX UE 100 and/or the TX UE 300. The value (i.e. time duration) of the switching timer can be based on and dependent on such aspects as scenario, group size, application, channel condition, etc. For example, if the channel is congested and there are many slow moving vehicles, or if the channel is changing fast due to a few fast moving vehicles. For different scenarios and group sizes the channel condition varies differently implying that the value of the switching timer may vary substantially in different scenarios;

• A first spatial distance between the RX UE 100 and the TX UE 300. The relevance of mentioned spatial distance is different for different applications, e.g. RX UEs (such as vehicles) close to the TX UE 300 can receive data packets more reliably than those farther away from the TX UE 300 which implies the relevance of the first spatial distance. Further, for RX UEs that are beyond a certain spatial threshold the spatial distance may not be relevant at all. The HARQ feedback from RX UEs close to the TX UE 300, i.e. short spatial distance, may almost always be ACK, but for RX UEs farther away from the TX UE 300, i.e. longer spatial distance, both ACK and NACK can be the decoding outcome. Finally, for RX UEs outside a spatial distance threshold HARQ feedback could be meaningless since the decoding outcome will always be NACK. Hence, generally the shorter the spatial distance between the RX UE 100 and the TX UE 300 the rate of transmitted ACKs can be reduced or even totally skipped in some cases. Hence, one or more first spatial distance threshold values may be used to determine whether this criterion is fulfilled or not; • A group identity of RX UE 100 and hence to which subset of RX UEs the RX UE belongs to because it is possible that only a subgroup of UEs in a group of UEs fulfil switching criteria and therefore allowed to switch HARQ feedback procedure;

• A first number of sequentially received and correctly decoded data packets. This case refers to the situation when ACKs are received consecutively for a predefined number of data packets which means that the properties of the radio channel are good. The RX UE 100 can therefore switch the HARQ feedback procedure to a HARQ feedback procedure comprising reduced rate of transmitted ACKs or even skip transmission of ACKs in some cases.

It is to be noted that one or more of the above first criteria can be combined in determining whether the RX UE 100 should switch HARQ feedback procedure or not. For example, the switching timer can be combined with the first channel quality threshold. Despite being the best choice in terms of reliability, transmitting both ACKs and NACKs is not always the optimal solution in terms of efficiency and resource consumption. Hence, ACK feedback can be terminated for a time period under certain conditions to save resources while not making any compromise on reliability. If a switching timer is used as a criterion, it could be possible that the switching timer has not expired but the channel quality has dropped below a threshold value or if the duration of the switching timer is short but the channel quality remains above the threshold value for a time duration longer than the switching timer so that the value of the switching timer can be updated dynamically.

Upon detecting fulfilment of the first switching criterion, i.e. YES in step 406, the RX UE 100 switches in step 408 from the first HARQ feedback procedure to a second HARQ feedback procedure in which the RX UE 100 is configured to transmit HARQ feedback according to the second HARQ feedback procedure. If the first switching criterion fulfilment is not detected the RX UE 100 continues to monitor for the first switching criterion fulfilment in step 404 whilst providing HARQ feedback according to the first HARQ feedback procedure.

In embodiments, to provide HARQ feedback according to the second HARQ feedback procedure comprises transmit a NACK to the TX UE 300 for each incorrectly decoded data packet. The transmission of ACKs according to the second HARQ feedback procedure can be performed in many different ways. Generally, different HARQ feedback procedures with different NACK/ACK schemes means different advantages and disadvantages which implies that there is a trade-off between different performance measure, e.g. between reliability and capacity. Transmissions of more ACKs gives higher reliability at the cost of lower system capacity and vice versa. Hence, the design of different HARQ feedback procedures in respect of NACK/ACK transmission rate must carefully be decided at the system design level for high performance systems. In the following three exemplary cases/embodiments are described.

In one case the RX UE 100 is configured to transmit an ACK to the TX UE 300 for every k: th correctly decoded data packet, wherein k is a positive integer larger than n. It is remembered that integer n denotes the transmission periodicity for transmission of ACKs in the first HARQ feedback procedure. Hence, according to this embodiment ACKs are transmitted more seldom for correctly decoded data packets in the second HARQ feedback procedure compared to the first HARQ feedback procedure since k is larger than n. For example, if n = 2 and k = 3 an ACK is sent for every second correctly decoded data packet in the first HARQ feedback procedure whilst an ACK is sent for every third correctly decoded data packet in the second HARQ feedback procedure. This case can e.g. be applicable when the channel quality is improving such as due to shorter spatial distance between RX UE 100 and TX UE 300.

In another case, the RX UE 100 is instead configured to transmit an ACK to the TX UE 300 for every k. th correctly decoded data packet, wherein k is a positive integer smaller than n. Hence, this case is opposite to the above described case which means that ACKs are transmitted more seldom for correctly decoded data packets in the first HARQ feedback procedure compared to the second HARQ feedback procedure. For example, if n = 3 and k = 2 an ACK is sent for every third correctly decoded data packet in the first HARQ feedback procedure whilst an ACK is sent for every second correctly decoded data packet in the second HARQ feedback procedure. This case can e.g. be applicable when the channel quality is getting lower such as due to longer spatial distance between RX UE 100 and TX UE 300.

In yet another case, the RX UE 100 is configured to skip to transmit an ACK to the TX UE 300 for each correctly decoded data packet. Hence, in this alternative the RX UE 100 will not transmit any ACKs at all irrespective of the decoding outcome. This case is applicable when the quality of the radio channel is so good that the decoding outcome of received data packets are always or almost always ACKs. In step 410, while the second HARQ feedback procedure is enabled the RX UE 100 monitors for a second switching criterion fulfillment, and upon fulfilment of the second switching criterion, i.e. YES in step 412, the RX UE 100 returns back to the first HARQ feedback procedure in step 414.

If the second switching criterion fulfilment is not detected in step 412 the RX UE 100 continues to monitor for the second switching criterion fulfilment whilst providing HARQ feedback according to the second HARQ feedback procedure.

However, in embodiments the RX UE 100 may when detecting the second switching criterion fulfillment, i.e. YES in step 412, either switch back to the first HARQ feedback procedure or switch to a third or higher level HARQ feedback procedure in step 414. In other words, the RX UE 100 is configured to upon detecting the second switching criterion fulfillment provide HARQ feedback for data packets received from the TX UE according to the first HARQ feedback procedure or to a third or higher HARQ feedback procedure. More than two HARQ feedback procedures are hence defined according to these embodiments, e.g., a first, second and third HARQ feedback procedure.

In embodiments, to provide HARQ feedback according to the third HARQ feedback procedure comprises transmit an ACK to the TX UE for every p th correctly decoded data packet, wherein p is a positive integer larger than k. It is remembered that integer k denotes the transmission periodicity for transmission of ACKs in the second HARQ feedback procedure. Hence, in this embodiment ACKs are transmitted more seldom for correctly decoded data packets in the third HARQ feedback procedure compared to the second HARQ feedback procedure since p is larger than k.

In other words, a first, a second and a third fraction of ACKs can be transmitted corresponding to the first, second and third HARQ feedback procedures. The relationship between fraction of ACKs can be l^st>2^nd>3^rd, and the switching between different HARQ feedback procedures may go from the first to the second to the third HARQ feedback procedure, or vice versa, or depending on fulfilled criteria change between first and third and vice versa may also be possible. By a fraction of ACKs it is e.g. meant if a fraction equal to ½ is enabled then only every second successfully decoded data block will generate an ACK transmission on the PSFCH, and so forth. In another embodiment there can be multi-levels of fractions of ACKs, e.g., 1, 1/2 or ¼, etc. and the RX UE 100 may switch between these fractions by following certain criteria. In Fig. 7 embodiments using fractions of ACKs is elaborated more in detail.

In embodiments, detecting the second switching criterion fulfillment is based one at least one of the following second criteria:

• A second channel quality threshold value, which e.g. may be given as a channel quality metric, such as received signal received power (RSRP), signal-to-noise and interference ratio (SINR), or any other suitable metric. As long as the channel quality remains above the second threshold value the RX UE 100 will be able to reliably receive data packets and decode them correctly. It means that for every correctly received data packet the outcome of decoding will generally be an ACK, and hence an ACK can be considered as redundant information and need not to be transmitted to the TX UE 300 as long as there is no change in the channel quality to the worse;

• A second HARQ feedback procedure switching timer which can be preconfigured e.g. by a standard or dynamically determined e.g. by the RX UE 100 and/or the TX UE 300. The value (i.e. time duration) of the switching timer can be based on and dependent on such aspects as scenario, group size, application, channel condition, etc. For example, if the channel is congested and there are many slow moving vehicles, or if the channel is changing fast due to a few fast moving vehicles. For different scenarios and group sizes the channel condition varies differently implying that the value of the switching timer may vary substantially in different scenarios;

• A second spatial distance between the RX UE 100 and the TX UE 300. The relevance of mentioned spatial distance is different for different applications, e.g. RX UEs (such as vehicles) close to the TX UE 300 can receive data packets more reliably than those farther away from the TX UE 300 which implies the relevance of the second spatial distance. Further, for RX UEs that are beyond a certain spatial threshold the spatial distance may not be relevant at all. The HARQ feedback from RX UEs close to the TX UE 300, i.e. short spatial distance, may almost always be ACK, but for RX UEs farther away from the TX UE 300, i.e. longer spatial distance, both ACK and NACK can be the decoding outcome. Finally, for RX UEs outside a spatial distance threshold HARQ feedback could be meaningless since the decoding outcome will always be NACK.

Hence, generally the shorter the spatial distance between the RX UE 100 and the TX UE 300 the rate of transmitted ACKs can be reduced or even totally skipped in some cases. Hence, one or more second spatial distance threshold values may be used to determine whether this criterion is fulfilled or not;

• A group identity of RX UE 100 and hence to which subset of RX UEs the RX UE belongs to because it is possible that only a subgroup of UEs in a group of UEs fulfil switching criteria and therefore allowed to switch HARQ feedback procedure;

• A second number of sequentially received and correctly decoded data packets. This case refers to the situation when ACKs are received consecutively for a predefined number of data packets which means that the properties of the radio channel is good. The RX UE 100 can therefore switch the HARQ feedback procedure to a HARQ feedback procedure comprising reduced rate of transmitted ACKs or even skip transmission of ACKs in some cases.

It is to be noted that one or more of the above second criteria can be combined as previously explained in respect of the first criteria. Moreover, one or more of the second criteria can be the same or have the same values as one or more of the first criteria.

In further embodiments of the invention as illustrated in Fig. 5, the TX UE 300 transmits a procedure change message once the RX UE 100 requests a change between different HARQ feedback procedures. Hence, the RX UE 100 transmits a control signal 502 to the TX UE 300, in step I, upon detecting the first switching criterion fulfillment. The control signal 502 indicates a HARQ feedback procedure switching request. The RX UE 100 then waits for an confirmation/acknowledgement from the TX UE and upon receiving a confirmation 504 for the HARQ feedback procedure switching request from the TX UE 300, in step II, provides HARQ feedback for data packets received from the TX UE 300 according to the second HARQ feedback procedure. The signaling can be performed using existing protocols and standards. For example, the HARQ feedback procedure switching request can be sent in uplink control information (UCI) in Uu groupcast communications and in sidelink control information (SCI) in sidelink groupcast communications. The confirmation 504 on the other hand can be received in downlink control information (DCI) in Uu communications and in SCI in sidelink communications. In case of sidelink, if there is no SCI, the Demodulation Reference Signal (DMRS) or another alternate signal could be used for control signaling. However, in embodiments the RX UE 100 does not wait for a confirmation from the TX UE 300 but instead switch by itself. In this case the TX UE 300 is at least informed about the RX UE wanting to switch HARQ feedback procedure and can switch to receive feedback according to a predefined HARQ feedback procedure indicated by the information in a certain bit or combination of bits. In an alternative, the RX UE 100 waits a predefined time period and switch HARQ feedback procedure at the expiry of the time period even though no confirmation has been received. The time period can be defined by a switching timer as described previously. In other embodiments, the RX UE 100 does not transmit any request signal for HARQ feedback procedure switch at all.

When a TX UE 300 is configured for groupcast communication and enabled to support HARQ the TX UE 300 should be configured to receive both ACK and NACK feedbacks, whether the feedback is provided in shared, separate or dedicated SL feedback channels. Whenever the RX UE 100 is switching between the different HARQ feedback procedures, the TX UE 300 should be able to differentiate between HARQ feedback such as ACK, NACK and discontinuous transmission (DTX). That is, if the RX UE 100 switches from ACK and NACK feedback mode to NACK only mode, the TX UE 300 should interpret no reception of an ACK as an ACK from that RX UE 100 as long as a switching timer does not expire or certain criteria are not met. For that reason, upon mode switch between the different HARQ feedback procedures a handshake between the TX UE 300 and RX UE 100 is important. For the handshake, i.e. to request and acknowledge a mode switch as illustrated in Fig. 5, specific updates to the PSFCH and SCI can be proposed. For example, a specific format or pattern could be used to feedback ACK and NACK for a specific HARQ feedback procedure mode and a certain bit(s) that could be used in the SCI to accept or reject such mode switch request. This can be achieved in many different ways, and example embodiments are described in detail in the following description with reference to Fig. 6 which shows a further flow chart of a method 600 according to embodiments of the invention.

In step 602, a RX UE 100 is configured for SL groupcast communication and SL HARQ feedback is enabled. The RX UE 100 is further configured for a first HARQ feedback procedure which is to send both ACK/NACK with respect to successful/unsuccessful decoding of data packets. In this respect the RX UE 100 uses a separate PSFCH for each HARQ ACK/NACK feedback transmission since ACK/NACK feedback in comparison to NACK only feedback fulfds the reliability requirements in all the situations.

In step 604, the RX UE 100 monitors for a first switching criterion fulfillment, e.g. channel conditions to be above a certain threshold value. The channel condition can e.g. be a measured signal-to-interference and noise ratio (SINR) or a hypothetical block error rate (BLER).

If the first switching criterion is met, i.e. YES in step 606, the RX UE 100 triggers mode switch request to the TX UE 300 by sending a control signal 502 indicating a HARQ feedback procedure switching request upon detecting the first switching criterion fulfillment. Thereafter, the RX UE 100 waits for a response from the TX UE 300 in step 608.

If the RX UE 100 receives a confirmation 504 for the HARQ feedback procedure switching request from the TX UE 300, i.e. YES in step 610, the RX UE 100 initiates a switching timer and activates the second HARQ feedback procedure, which is to send the NACK only feedback of decoded packet data based on unsuccessful decoding of data packets in step 612.

If the TX UE 300 does not confirm the request, i.e. NO in step 610 (not shown), the RX UE 100 instead falls back to the first HARQ feedback procedure. While the second HARQ feedback procedure is configured in step 612, the RX UE 100 monitors the timer to remain below a pre defined time window and also monitors if any NACK is generated. As soon as either of these conditions are true, the RX UE 100 falls back to first HARQ feedback procedure in step 614. It is noted that when an ACK is received by the TX UE 300 in this case, the TX UE 300 knows that the RX UE 100 has switched back to the first HARQ feedback procedure.

In step 702, a RX UE 100 is configured for SL communication and for which SL HARQ feedback is enabled. The RX UE is configured for a first HARQ feedback procedure and hence is configured to transmit both ACK/NACK with respect to successful/unsuccessful decoding of data packet packets for a first fraction of ACKs for received data packets.

The RX UE monitors for a first switching criterion fulfillment in step 704 and determines if the first switching criterion is fulfilled or not in step 706. If YES in step 706 a switch to a second HARQ feedback procedure is controlled by a handshake procedure between the TX UE 300 and the RX UE 100 in step 708 for mode switch. One handshake option is, if high reliability is required there should always be a handshake, i.e., the RX UE triggers mode switch request and it switches to fraction based procedure upon acknowledgement from the TX UE 300. Another option could be a pre-configured fraction upon fulfilment of the first criteria. Another option could be no handshake is required at all.

If the first switching criterion is determined to be fulfilled in step 706 and handshake has been performed in step 708 the RX UE 10 switches HARQ feedback procedure for using only a second fraction of ACKs for received data packets, e.g. every second correctly decoded data packet is ACK:ed (i.e. is an ACK is sent) in step 710.

In step 712 the RX UE 100 monitors for a second switching criterion fulfillment. If the second switching criterion is determined to be fulfilled, i.e. YES in step 714, then there is optional handshake between TX UE and RX UE in step 716, and the RX UE 100 switches in step 718 to fraction based feedback procedure using a third fraction of ACK for the received packets, e.g. every fourth packet is ACK:ed.

In step 720, the RX UE 100 monitors for a third criteria, for example in case of NACK, or expired timer, to revert back to the initial HARQ feedback procedure, i.e. the first HARQ feedback procedure.

It is envisaged that embodiments of the invention can be implemented in the 3GPP standard. For example, as subsections specified for NR SL HARQ or as updates to the NR Uu, LTE Uu and LTE SL HARQ procedure. Embodiments of the invention could impact the NR specifications 38.213, and 38.321 for SL groupcast HARQ feedback procedure design. For example, in specification 38.213 two sections, section 9.1 that specifies HARQ-ACK codebook determination and section 9.2.3 that specifies UE procedures for reporting HARQ-ACK could be revised.

The first communication device 100 and/or the second communication device 300 herein, may be denoted as a user device, a User Equipment (UE), a mobile station, an internet of things (IoT) device, a sensor device, a wireless terminal and/or a mobile terminal, is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The UEs may further be referred to as mobile telephones, cellular telephones, computer tablets or laptops with wireless capability. The UEs in this context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another receiver or a server. The UE can be a Station (STA), which is any device that contains an IEEE 802.11 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM). The UE may also be configured for communication in 3 GPP related LTE and LTE-Advanced, in WiMAX and its evolution, and in fifth generation wireless technologies, such as New Radio.

However, the first communication device 100 and/or the second communication device 300 herein may also be denoted as a radio network access node, an access network access node, an access point, or a base station, e.g. a Radio Base Station (RBS), which in some networks may be referred to as transmitter, “gNB”, “gNodeB”, “eNB”, “eNodeB”, “NodeB” or “B node”, depending on the technology and terminology used. The radio network access nodes may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. The radio network access node can be a Station (STA), which is any device that contains an IEEE 802.11 -conformant Media Access Control (MAC) and Physical Layer (PHY) interface to the Wireless Medium (WM). The radio network access node may also be a base station corresponding to the fifth generation (5G) wireless systems.

Furthermore, any method according to embodiments of the invention may be implemented in a computer program, having code means, which when run by processing means causes the processing means to execute the steps of the method. The computer program is included in a computer readable medium of a computer program product. The computer readable medium may comprise essentially any memory, such as a ROM (Read-Only Memory), a PROM (Programmable Read-Only Memory), an EPROM (Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM), or a hard disk drive.

Moreover, it is realized by the skilled person that embodiments of the first communication device 100 and the second communication device 300 comprises the necessary communication capabilities in the form of e.g., functions, means, units, elements, etc., for performing the solution. Examples of other such means, units, elements and functions are: processors, memory, buffers, control logic, encoders, decoders, rate matchers, de-rate matchers, mapping units, multipliers, decision units, selecting units, switches, interleavers, de-interleavers, modulators, demodulators, inputs, outputs, antennas, amplifiers, receiver units, transmitter units, DSPs, MSDs, TCM encoder, TCM decoder, power supply units, power feeders, communication interfaces, communication protocols, etc. which are suitably arranged together for performing the solution. Especially, the processor(s) of the first communication device 100 and the second communication device 300 may comprise, e.g., one or more instances of a Central Processing Unit (CPU), a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC), a microprocessor, or other processing logic that may interpret and execute instructions. The expression “processor” may thus represent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones mentioned above. The processing circuitry may further perform data processing functions for inputting, outputting, and processing of data comprising data buffering and device control functions, such as call processing control, user interface control, or the like. Finally, it should be understood that the invention is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.

Claims

1. A first communication device (100) for a wireless communication system (500), the first communication device (100) being configured to receive data packets from a second communication device (300); provide hybrid automatic repeat request, HARQ, feedback for data packets received from the second communication device (300) according to a first HARQ feedback procedure; and upon detecting a first switching criterion fulfillment, provide HARQ feedback for data packets received from the second communication device (300) according to a second HARQ feedback procedure.

2. The first communication device (100) according to claim 1, wherein detecting the first switching criterion fulfillment is based on at least one of: a first channel quality threshold value, a first HARQ feedback procedure switching timer, a first spatial distance between the first communication device (100) and the second communication device (300), a group identity of the first communication device (100), and a first number of sequentially and correctly decoded data packets.

3. The first communication device (100) according to claim 1 or 2, wherein provide HARQ feedback according to the first HARQ feedback procedure comprises transmit a negative acknowledgment, NACK, to the second communication device (300) for each incorrectly decoded data packet; and provide HARQ feedback according to the second HARQ feedback procedure comprises transmit a NACK to the second communication device (300) for each incorrectly decoded data packet.

4. The first communication device (100) according to any one of claims 1 to 3, wherein provide HARQ feedback according to the first HARQ feedback procedure comprises transmit an acknowledgment, ACK, to the second communication device (300) for every n th correctly decoded data packet, wherein n is a positive integer; and provide HARQ feedback according to the second HARQ feedback procedure comprises transmit an ACK to the second communication device (300) for every k: th correctly decoded data packet, wherein k is a positive integer larger than n.

5. The first communication device (100) according any one of claims 1 to 3, wherein provide HARQ feedback according to the first HARQ feedback procedure comprises transmit an ACK to the second communication device (300) for each correctly decoded data packet; and provide HARQ feedback according to the second HARQ feedback procedure comprises skip transmit an ACK to the second communication device (300) for each correctly decoded data packet.

6. The first communication device (100) according to any one of claims 1 to 3, wherein provide HARQ feedback according to the first HARQ feedback procedure comprises transmit an ACK to the second communication device (300) for every n th correctly decoded data packet, wherein n is a positive integer; provide HARQ feedback according to the second HARQ feedback procedure comprises transmit an ACK to the second communication device (300) for every k:th correctly decoded data packet, wherein k is a positive integer smaller than n.

7. The first communication device (100) according to any one of the preceding claims, further configured to upon detecting a second switching criterion fulfillment provide HARQ feedback for data packets received from the second communication device (300) according to the first HARQ feedback procedure or to a third HARQ feedback procedure.

8. The first communication device (100) according to claim 7, wherein detecting the second switching criterion fulfillment is based one at least one of: a second channel quality threshold value, a second HARQ feedback procedure switching timer, a second spatial distance between the first communication device (100) and the second communication device (300), a group identity of the first communication device (100), and a second number of sequentially and correctly decoded data packets.

9. The first communication device (100) according to claim 7 or 8, wherein provide HARQ feedback according to the third HARQ feedback procedure comprises transmit a NACK to the second communication device (300) for each incorrectly decoded data packet.

10. The first communication device (100) according to any one of claims 7 to 9 when dependent on any one of claims 4 to 6, wherein provide HARQ feedback according to the third HARQ feedback procedure comprises transmit an ACK to the second communication device (300) for every p th correctly decoded data packet, wherein p is a positive integer larger than k.

11. The first communication device ( 100) according to any one of claims 7 to 9 when dependent on any one of claims 4 to 6, wherein provide HARQ feedback according to the third HARQ feedback procedure comprises transmit an ACK to the second communication device (300) for every p th correctly decoded data packet, wherein p is a positive integer smaller than k.

12. The first communication device (100) according to any one of the preceding claims, further configured to transmit a control signal (502) to the second communication device (300) upon detecting the first switching criterion fulfillment, wherein the control signal (502) indicates a HARQ feedback procedure switching request.

13. The first communication device (100) according to claim 12, configured to upon receiving a confirmation (504) for the HARQ feedback procedure switching request from the second communication device (300) provide HARQ feedback for data packets received from the second communication device (300) according to the second HARQ feedback procedure.

14. The first communication device (100) according to any of the preceding claims, wherein the communication between the first communication device (100) and the second communication device (300) is at least one of groupcast communication and unicast communication.

15. The first communication device (100) according to claim 14, wherein the groupcast communication and the unicast communication is sidelink communication or Uu communication.

16. A method (200) for a first communication device (100), the method (200) comprising receiving (202) data packets from a second communication device (300); providing (204) HARQ feedback for data packets received from the second communication device (300) according to a first HARQ feedback procedure; and upon detecting (206) a first switching criterion fulfillment, provide HARQ feedback for data packets received from the second communication device (300) according to a second HARQ feedback procedure.

17. A computer program with a program code for performing a method according to claim 16 when the computer program runs on a computer.