WO2021163836A1

WO2021163836A1 - Methods and apparatus of resource assignment for harq feedback to support multicast transmission

Info

Publication number: WO2021163836A1
Application number: PCT/CN2020/075515
Authority: WO
Inventors: Xuelong Wang
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2020-02-17
Filing date: 2020-02-17
Publication date: 2021-08-26
Also published as: WO2021164682A1

Abstract

Apparatus and methods are provided to support the HARQ feedback for NR multicast PDSCH transmission. In one novel aspect, Base Station assigns a unique index to PUCCH Resource instance for multicast feedback. One combinaiton of slot index, starting index of PUCCH resource instances, and number of PUCCH resource instances is used to describe a set of uplink feedback resource. Base Station can explictly indicate the set of PUCCH resource instances to the UEs. Base Station indicates one unique HARQ feedback Resource index to each UE joining multicast service. UE uses the unique HARQ feedback Resource index, the indicated set of PUCCH resource instance, to determine the PUCCH resource instance for its uplink feedback.

Description

METHODS AND APPARATUS OF RESOURCE ASSIGNMENT FOR HARQ FEEDBACK TO SUPPORT MULTICAST TRANSMISSION

FIELD OF THE DISCLOSURE

Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to enable resource assignment of HARQ feedback for NR multicast based transmission.

DESCRIPTION OF THE RELATED ART

3GPP specified the support for MBMS transmission with group scheduling, which is based on UMTS or EUTRAN technology.

The group scheduling specified by 3GPP has no Uplink feedback support so far. At Rel-13, there is a discussion at 3GPP to support physical layer feedback in the context of SC-PTM transmission. However, eventually it is not specified.

In NR, HARQ-ACK feedback for unicast transmission is supported. Multiple DL HARQ Process per UE is supported and Single DL HARQ Process per UE is supported as well. The UE is required to indicate its capability of minimum HARQ processing time (The minimum HARQ processing time means the minimum time that is required from DL data reception to the corresponding HARQ-ACK transmission timing) . From UE perspective, HARQ ACK/NACK feedback for multiple PDSCH in time can be transmitted in one UL data/control region. Timing between PDSCH reception and corresponding ACK/NACK is specified in DCI (e.g. in DCI 1_0, DCI 1_1) .

In NR, CBG (Code Block Group) -based transmission with single/multi-bit HARQ-ACK feedback is also supported. It only allows CBG based (re) -transmission for the same TB of a HARQ process. A CBG can include all CB of a TB regardless of the TBS (TB Size) , meaning that a TB is made up of only one CBG. In this case, UE reports single HARQ ACK bit for the TB. A CBG is allowed to be made up of only one CB. CBG granularity is configurable by higher layer.

In NR, HARQ-ACK codebook is used. There is CBG-based HARQ-ACK codebook determination. In addition, there are two different types of Codebook determination algorithm called Type 1 and Type 2. Each of these types is again divided into two cases depending on whether the HARQ ACK is reported in PUCCH or PUSCH. Which type of algorithm to use is determined by a couple of RRC parameters.

NR V2X in introduced in Rel-16. NR-V2X supports HARQ based on transmission of ACK/NACK (or DTX) for Sidelink unicast and groupcast services, as well as a NACK-only HARQ scheme particular to groupcast services. In addition, it supports blind re-transmission schemes. Sidelink HARQ feedback is carried on PSFCH from an Rx UE to its Tx UE. When ACK/NACK (or DTX) operation is used, the HARQ procedure is similar to the NR Uu scheme for non-codeblock group feedback, i.e. the ACK/NACK is delivered based on the success or failure of the whole transport block. NACK-only operation is defined for groupcast to allow a potentially lower sidelink resource demand to be created when a larger number of Rx UEs need to send feedback to the same Tx UE. It should be noted that Sidelink groupcast has the similar characteristics as NR Multicast services. The resource assignment for HARQ feedback of NR V2X is supported by implicit resource determination.

In Dec 2019, 3GPP approved a work item (WI) on the support of NR Broadcast and Multicast Services. Within the scope of the WI, the reliable transmission of the NR Multicast services with uplink feedback is the key objective. uplink feedback for NR multicast is to be studied.

In this invention, it is sought to achieve reliable multicast transmission via resource assignment for HARQ feedback.

BRIEF SUMMARY

A method is provided to support the HARQ feedback for NR multicast PDSCH transmission. In one novel aspect, Base Station assigns a unique index to each of the PUCCH Resources or PUCCH Resource instances for the feedback of multicast PDSCH transmission. The numbering of the index for the whole feedback resources during uplink feedback resource period in terms of one or mulitple consecutive subframes or slots is indicated to the UE via RRC message (e.g. in system information) .

One or multiple combinaiton (s) of subframe or slot index, starting index of PUCCH resources or PUCCH resource instances, and number of PUCCH resources or PUCCH resource instances is used to describe a particular set of uplink feedback resource for multicast PDSCH transmission.

Base Station can explictly indicate the set of PUCCH resources or PUCCH resource instances via RRC message e.g. MCCH Configuration to the UEs receiving the multicast PDSCH transmission, which is cooresponding to one MTCH transmission. Alternatively, the said set of PUCCH resources or PUCCH resource instances is indicated to UE via multicast DCI.

Base Station indicates one unique HARQ Feedback Resource Index to each UE joining the reception of each multicast service for a particular multicast Radio Bearer. When the UE joins multiple multicast service (s) , a list of HARQ Feedback index is indicated to the UE. One or a list of HARQ Feedback index is configured to the UE via unicast signalling e.g. RRC Reconfiguration.

UE uses the unique HARQ Feedback Resource index, the indicated resource set of PUCCH resource or PUCCH resource instance, and the configured numbering of the whole feedback resource to determine the actual PUCCH resource or PUCCH resource instance for its uplink feedback resource for a particular multicast PDSCH transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and therefore not to be considered limiting of its scope, for the descriptions may admit to other equally effective aspects.

FIG. 1 (a) is a schematic system diagram illustrating an exemplary Base Station (i.e. BS) , in accordance with certain aspects of the present disclosure.

FIG. 1 (b) is a schematic system diagram illustrating an exemplary UE , in accordance with certain aspects of the present disclosure.

FIG. 2 illustrates an exemplary NR wireless communication system, in accordance with certain aspects of the present disclosure.

FIG. 3 illustrates an exemplary NR multicast PUCCH Resource set, in accordance with certain aspects of the present disclosure.

FIG. 4 illustrates an exemplary intra-slot PUCCH Resource allocation for NR multicast, in accordance with certain aspects of the present disclosure.

FIG. 5 illustrates an exemplary inter-slot PUCCH Resource allocation for NR multicast, in accordance with certain aspects of the present disclosure.

FIG. 6 illustrates an exemplary numbering for PUCCH Resource or PUCCH Resource instance for NR multicast, in accordance with certain aspects of the present disclosure.

FIG. 7 illustrates an exemplary mapping between HARQ feedback index and PUCCH Resource or PUCCH Resource instance for NR multicast, in accordance with certain aspects of the present disclosure.

DETAILED DESCRIPTION

Aspects of the present disclosure provide methods, apparatus, processing systems, and computer readable mediums for NR (new radio access technology, or 5G technology) or other radio access technology. NR may support various wireless communication services, such as enhanced mobile broadband targeting wide bandwidth, millimeter wave targeting high carrier frequency, massive machine type communications targeting non-backward compatible MTC techniques, and/or mission critical targeting ultra-reliable low-latency communications. These services may include latency and reliability requirements. These services may also have different transmission time intervals (TTI) to meet respective quality of service (QoS) requirements. In addition, these services may co-exist in the same subframe.

FIG. 1 (a) is a schematic system diagram illustrating an exemplary Base Station (i.e. BS) , in accordance with certain aspects of the present disclosure. The BS may also be referred to as an access point, an access terminal, a base station, a Node-B, an eNode-B, a gNB, or by other terminology used in the art. As an example, base stations serve a number of mobile stations within a serving area, for example, a cell, or within a cell sector. The Base Station has an antenna, which transmits and receives radio signals. A RF transceiver, coupled with the antenna, receives RF signals from antenna, converts them to baseband signals, and sends them to processor. RF transceiver also converts received baseband signals from processor, converts them to RF signals, and sends out to antenna. Processor processes the received baseband signals and invokes different functions. Memory stores program instructions and data to control the operations of Base Station.

FIG. 1 (b) is a schematic system diagram illustrating an exemplary UE, in accordance with certain aspects of the present disclosure. The UE may also be referred to as a mobile station, a mobile terminal, a mobile phone, smart phone, wearable, an IoT device, a table let, a laptop, or other terminology used in the art. UE has an antenna, which transmits and receives radio signals. A RF transceiver, coupled with the antenna, receives RF signals from antenna, converts them to baseband signal, and sends them to processor. RF transceiver also converts received baseband signals from processor, converts them to RF signals, and sends out to antenna. Processor processes the received baseband signals and invokes different functional modules to perform features in UE. Memory stores program instructions and data to control the operations of mobile station.

FIG. 2 illustrates an exemplary NR wireless communication system, in accordance with certain aspects of the present disclosure. Different protocol split options between Central Unit and Distributed Unit of gNB nodes may be possible. In one embodiment, SDAP and PDCP layer are located in the central unit, while RLC, MAC and PHY layers are located in the distributed unit.

In certain systems, such as NR systems, NR multicast is transmitted in the coverage of a cell. From logical channel perspective, one MCCH (i.e. multicast control channel) and one or more MTCH (s) (i.e. multicast traffic channel) are mapped on DL-SCH. The scheduling for NR multicast is done by the gNB-CU. MCCH provides the list of all NR multicast services with ongoing sessions transmitted on MTCH (s) , including each NR multicast service ID (expressed by NR multicast group ID or NR multicast session ID) , associated G-RNTI, scheduling information, etc. As legacy behavior, the MCCH is transmitted by RRC message every MCCH repetition period and MCCH uses a modification period. MCCH and MTCH use the RLC-UM mode or RLC-AM mode. At physical layer, the MCCH is scheduled by gNB in the common search space of PDCCH with MB-RNTI scrambled. MB-RNTI is MCCH logical channel specific RNTI, with fixed value specified in MAC (e.g., the value can be FFFD) . MTCH is scheduled by gNB in the common search space of PDCCH with G-RNTI scrambled. UE decodes the MTCH data for a multicast session in PDSCH according to the resource indicated by DCI.

Framework of HARQ Feedback

In certain systems, such as NR system, two HARQ feedback options are defined for NR multicast transmission. The first option requires only HARQ NACK feedback. The second option requires both ACK and NACK based HARQ feedback.

In the first option based HARQ feedback, all of the UEs receiving the multicast data shares a single feedback resource in a physical channel (e.g. PUCCH) , and only feedback HARQ NACK over the feedback resource. In first option based HARQ feedback, all the UEs transmit NACK in SFN manner. In the second option based HARQ feedback, the UEs receiving the multicast data utilize separate feedback resource in a physical channel (e.g. PUCCH) for uplink feedback. In this case, a set of orthogonal feedback resource is used by the UEs.

As unicast DCI, multicast DCI can include HARQ related information including both HARQ transmission information and HARQ feedback related information. However, multicast DCI has a different set of HARQ feedback related information. A new field to enable HARQ feedback is added into multicast DCI to indicate the feedback request for the corresponding multicast PDSCH transmission. A new field to indicate the HARQ feedback option is added into multicast DCI to indicate the feedback option for the corresponding multicast PDSCH transmission if the HARQ feedback is enabled for multicast PDSCH transmission. A new field to indicate the HARQ feedback timing in unit of subframe or slot between multicast PDSCH transmission and the corresponding uplink channel (e.g. PUCCH) feedback resource can also be indicated in multicast DCI for multicast PDSCH transmission, if the HARQ feedback is enabled for multicast PDSCH transmission. Unlike unicast HARQ feedback timing, the HARQ feedback timing information within multicast DCI for multicast include a duration occupying one or a plural of consecutive subframe or slot. The reason is that the uplink feedback resource within subframe or slot may not be enough to support the HARQ feedback from all of the UEs that receive the multicast PDSCH transmission.

As unicast DCI, multicast DCI can hold the PUCCH resource indicator indicating the PUCCH resource for uplink feedback. Different from unicast DCI, multicast DCI can include one or a set of specific PUCCH resource or PUCCH resource instance for uplink feedback of multicast PDSCH transmission depending on the HARQ feedback option.

The PUCCH resource indicator within multicast DCI has different mean for the two HARQ feedback options. When the first HARQ feedback option applies, the PUCCH resource indicator indicates a concrete PUCCH resource as unicast DCI (e.g., format 1_0) does, or a concrete PUCCH resource instance (with fixed cyclic shift) . When the second HARQ feedback option applies, the PUCCH resource indicator indicates a set of PUCCH resource (e.g., 8 PUCCH resources) or a set of PUCCH resource instance (e.g., 16 PUCCH resource instance) .

In the description of the present disclosure, the concept of PUCCH resource instance is introduced with the indication of a particular PUCCH resource associated with a specific cyclic shift. For example, for a particular PUCCH resource, if there are three cyclic shifts configured by gNB (as specified in TS38.213) , there are three PUCCH resource instances. When the cyclic shift pairs is not configured for a PUCCH resource, this PUCCH resource is identical to PUCCH resource instance. The methods described within the present disclosure based on PUCCH resource instance is applicable to PUCCH resource. During the description of the present disclosure, the uplink (PUCCH) feedback resource means PUCCH resource, PUCCH resource instance, or their combination.

PUCCH Resource Allocation for HARQ Feedback

In certain systems, such as NR system, specific PUCCH Resource for NR multicast feedback needs to be defined in physical layer and needs to be added into TS38.213 clause 9.2. PUCCH Resource for NR multicast feedback is defined in terms of starting PRB ID, hopping PRB, supported UCI format, etc. FIG. 3 illustrates an exemplary NR multicast PUCCH Resource set, in accordance with certain aspects of the present disclosure.

As depicted in FIG. 3, 16 PUCCH Resources is defined for NR multicast feedback and one PUCCH Resources spans two sysmbols and two PRBs. In practice, the hopping PRB should be also defined. One PUCCH Resource include multiple PUCCH Resource instance, each with a different cyclic shift. In FIG. 3, for the 16 defined PUCCH resource, the number of Cyclic Shift pairs for the PUCCH resource is k ₀, k ₁, …, k ₁₅, and then ∑ (k ₀+ k ₁…+ ₁₅) is the sum of the usable PUCCH resource instance.

As an example, assuming all of the number of Cyclic Shift pairs are 4, and then ∑ (k ₀+ k ₁…+ ₁₅) =64. The sum of the usable PUCCH resource instance puts a limitation on the maximum number of the UEs or users that can concurrently provide HARQ feedback via second HARQ feedback option to one or multiple multicast PDSCH transmission (s) during the same period e.g. within one or multiple slot (s) or subframe (s) . The said period for the limitation is subject to the period for defining the PUCCH resources for NR multicast feedback.

In FIG. 3, taking the same example as above, only 64 UEs or users can provide the second HARQ feedback option to one or multiple multicast PDSCH transmission (s) during the same slot. On top of the above example, assuming there are W concurrent multicast PDSCH transmissions and the number of the UEs for the different multicast PDSCH transmission are g ₀, g ₁, …, and g _W-1, then the required uplink feedback resource is ∑ (g ₀+g ₁…+g _W-1) . The second HARQ feedback option can apply only if ∑ (g ₀+g ₁…+g _W-1) ≤ ∑ (k ₀+ k ₁…+ ₁₅) (in the exmaple it is 64) .

If ∑ (g ₀+g ₁…+g _W-1) > ∑ (k ₀+ k ₁…+ ₁₅) , the second HARQ feedback option can not apply, otherwise some of the UEs has not feedback resource to report HARQ ACK/NACK. there are two alternative way to handle from the perspective of gNB and/or UE. The first way is to disable the second HARQ feedback option, and then no HARQ feedback is supported or the first HARQ feedback option is used instead. The second way is to delay the second option based HARQ feedback to the succeeding slots or subframes.

FIG. 4 illustrates an exemplary intra-slot PUCCH Resource allocation for NR multicast, in accordance with certain aspects of the present disclosure. As depicted in FIG. 4, two sets of PUCCH resource or PUCCH resource instance are allocated at slot n corresponding to two different multicast PDSCH transmission (e.g., occur at slot n-awith a as the slot numbers between multicast PDSCH transmission and feedback resource slot n) . The set of feedback resource allocated for the first multicast PDSCH transmission includes 48 PUCCH resources or PUCCH resource instances (i.e. numbering from 0 to 47) . The set of feedback resource allocated for the first multicast PDSCH transmission includes 8 PUCCH resources or PUCCH resource instances (i.e. numbering from 56 to 63) .

FIG. 5 illustrates an exemplary inter-slot PUCCH Resource allocation for NR multicast, in accordance with certain aspects of the present disclosure. As depicted in FIG. 5, one set of PUCCH resources or PUCCH resource instances is allocated spanning both slot n and slot n+1 corresponding to a single multicast PDSCH transmission (e.g., occur at slot n-awith a as the slot numbers between multicast PDSCH transmission and feedback resource slot n) . The set of feedback resource allocated for the multicast PDSCH transmission includes the whole 64 PUCCH resources or PUCCH resource instances within slot n and 32 PUCCH resources or PUCCH resource instances within slot n+1 (i.e. numbering from 0 to 31) .

FIG. 6 illustrates an exemplary numbering for PUCCH Resource or PUCCH Resource instance for NR multicast, in accordance with certain aspects of the present disclosure. As depicted in FIG. 6, the 16 PUCCH Resources are allocated for slot n, each with specific cyclic shift pairs. In the example, the numbering of PUCCH Resource instance starts from the PUCCH Resource with the smallest index. Within a PUCCH Resource, the PUCCH Resource instance with the first cyclic shift of cyclic shift pairs takes the smallest index of PUCCH Resource instance. The index of PUCCH Resource instance takes sequntial number from the first PUCCH Resource to the last PUCCH Resource (i.e. from 0 to 15) . In summary, all of the PUCCH Resources or PUCCH Resource instances for the feedback of multicast PDSCH transmission has a unique index assigned by the Base Station.

The numbering of the index for the whole feedback resources (i.e. PUCCH Resource or PUCCH Resource instance) during uplink feedback resource period and the configuration (or definition ) of the feedback resource (i.e. PUCCH Resource or PUCCH Resource instance) is indicated to the UE via RRC message (e.g. in system information) . The uplink feedback resource period assigned for multicast PDSCH transmission can be one slot, one subframe, mulitple consecutive slots or mulitple consecutive subframes. In a typical implementation in NR, it is one slot. For exmaple, if one slot supports 64 PUCCH Resources or PUCCH Resource instances, the index is from 0 to 63.

Taking account of the numbering in FIG. 6, the set of PUCCH resource or PUCCH resource instance allocated for multicast PDSCH transmission can be indicated as a combination of slot index, starting index of PUCCH resources or PUCCH resource instances, and number of PUCCH resources or PUCCH resource instances (i.e. the consecutive PUCCH resources or PUCCH resource instances occupied) . For example, for the first multicast PDSCH transmission in FIG. 4, its allocated feedback resource is in slot n, starting index of PUCCH resources or PUCCH resource instances is 0, and number of PUCCH resources or PUCCH resource instances are 48.A simple 3-tuple expression can be used, e.g. (k, 0, 48) , where k indicates the number of subfames or slots between the multicast PDSCH transmission and the PUCCH resources or PUCCH resource instances. Taking the same steps, the allocated feedback resource for the multicast PDSCH transmission in FIG. 5 is { (k, 0, 64) , (k+1, 56, 8) } .

As explained, in order to assign a set of the PUCCH resources or PUCCH resource instances for second option based HARQ feedback corresponding to the multicast PDSCH transmission, one or multiple combinaiton (s) of subframe or slot index, starting index of PUCCH resources or PUCCH resource instances, and number of PUCCH resources or PUCCH resource instances is indicated to UE (s) . Specifically, one or multiple combinaiton (s) of subframe or slot index, starting index of PUCCH resources or PUCCH resource instances, and number of PUCCH resources or PUCCH resource instances is used to describe a particular set of uplink feedback resource.

One resource set is corresponding to one multicast PDSCH transmission. If a UE is receiving mulitple multicast PDSCH transmission, the UE can receive multiple resource sets. In addition, this type of resource inidcation can be used to indicate a particular PUCCH resources or PUCCH resource instances for first option based HARQ feedback.

The Base Station can explictly indicate the said resource set of PUCCH resources or PUCCH resource instances via RRC message e.g. MCCH Configuration to the UEs receiving the multicast PDSCH transmission, which is cooresponding to one MTCH transmission. Alternatively, the said set of PUCCH resources or PUCCH resource instances is indicated to UE via multicast DCI. Regardless of the method for resource indication, one or a plural of 3-tuple is used for the indication depending on how long the HARQ feedback lasts (i.e., within one subframe or slot, or multiple consecutive subframes or slots) .

If the resource set indicated by Base Station only spans one uplink feedback resource period (e.g., one slot) , UE can directly use the starting index of PUCCH resources or PUCCH resource instances, and number of PUCCH resources or PUCCH resource instances to locate the PUCCH resources or PUCCH resource instances. UE further numbers the set of PUCCH resources or PUCCH resource instances from 0 by a Resource Index. For exmaple if there are 8 PUCCH resource instances configured (occupied No. 56-63 among the whole 64 instances) , the UE numbers No. 56 PUCCH resource instance with Resource Index 0, and numbers No. 63 PUCCH resource instance with Resource Index 7. Then the Resource Index is from 0 to 7. The same Resource index numbering is performed by Base Station also and it is stored as a context for multicast PDSCH transmission.

If the resource set indicated by Base Station spans multiple uplink feedback resource periods (e.g., two consecutive slots) , UE can sequencially use the starting index of PUCCH resources or PUCCH resource instances, and number of PUCCH resources or PUCCH resource instances within the uplink feedback resource periods to locate the PUCCH resources or PUCCH resource instances one period by one period. Starting from the first uplink feedback resource period to the last uplink feedback resource period within the set, UE further numbers the set of PUCCH resources or PUCCH resource instances from 0 by a Resource Index. For exmaple, if two consecutive slots are included within the resource set, and if there are 8 PUCCH resource instances configured for the first slot (occupied No. 56-63 among the whole 64 instances) and there are 6 PUCCH resource instances configured for the second slot (occupied No. 0-5 among the whole 64 instances) . The UE firstly numbers No. 56 PUCCH resource instance within the first slot with Resource Index 0, and numbers No. 63 PUCCH resource instance within the first slot with Resource Index 7. The UE secondly numbers No. 0 PUCCH resource instance within the second slot with Resource Index 9, and numbers No. 5 PUCCH resource instance within the second slot with Resource Index 13. Then the Resource Index is from 0 to 13. The same Resource index numbering is performed by Base Station also and it is stored as a context for multicast PDSCH transmission.

As a variation, non consecutive allocation of PUCCH resources or PUCCH resource instances for feedback of multicast PDSCH transmission within a uplink feedback resource period is supported with benefit to avoid the generation of resource hole.

When the abovementioned set of PUCCH resources or PUCCH resource instances is indicated to the UEs, the HARQ feedback timing is implictly included, then no additonal HARQ feedback timing (as known as the K value in legacy NR system) is informed to the UEs. Alternatively, mulitple HARQ feedback timings are indicated to the UEs, each with a separate subset of the resource set for the particular subframe (s) or slot (s) . It can be indicated to the UEs via RRC message, MAC CE or multicast DCI.

When the UEs particpating the multicast service receive the allocated set of PUCCH resources or PUCCH resource instances, the UEs can determine the actual PUCCH resource or PUCCH resource instance for their separate HARQ feedback in explict way or implict way for second option based HARQ feedback.

For the explict way of uplink feedback resource determination, for a special multicast PDSCH transmission, the Base Station allocates one unique Resource Index from the stored context for multicast PDSCH transmission for for each RRC_Connected UE that attempts to join the reception of the multicast service (i.e. receiving the multicast PDSCH transmission) over each MTCH. Then Base Station update the stored context for multicast PDSCH transmission with C-RNTI of the UE associated with new allocated Resource Index for UE uplink feedback for the multicast PDSCH transmission.

The Base Station indicates one unique (HARQ feedback) Resource index to each UE joining the reception of the multicast service for a particular multicast Radio Bearer. When the UE joins multiple multicast service, a list of HARQ feedback Resource index is indicated to the UE. One or a list of HARQ feedback Resource Index is configured to the UE via unicast signalling e.g. RRC Reconfiguration or MAC CE. Alternatively, the HARQ feedback Resource Index information can be indicated to UE via a DCI used for unicast PDSCH transmission.

The UE uses the (HARQ feedback) unique Resource index to locate the actual PUCCH resource or PUCCH resource instance within the configured resource set of PUCCH resources or PUCCH resource instances for a multicast PDSCH transmission.

The Base Station allocates exact same number of PUCCH resources or PUCCH resource instances, as the number of the users joining the reception of the multicast service for a particular multicast Radio Bearer, which mapps to a single MTCH logical channel. Alternatively the Base Station may allocates more PUCCH resources or PUCCH resource instances than the number of the users joining the reception of the multicast service for multicast PDSCH transmission to allow some flexiblity.

In determination of the uplink feedback resource, UE uses the unique HARQ feedback Resource Index, the indicated resource set of PUCCH resource or PUCCH resource instance, and the configured numbering of the whole feedback resource within one uplink feedback resource period to decide the actual PUCCH resource or PUCCH resource instance for its uplink feedback resource for a particular multicast PDSCH transmission. An example of the uplink feedback resource determination is depicted in FIG. 7.

FIG. 7 illustrates an exemplary mapping between HARQ feedback Resource Index and PUCCH Resource or PUCCH Resource instance for NR multicast, in accordance with certain aspects of the present disclosure. As depicted in FIG. 7, the 17 UEs joins the multicast service carried by MTCH-A. Correspondingly 17 PUCCH Resources or PUCCH Resource instances are allocated for uplink feedback of this multicast transmision for second option based HARQ feedback. UE-Ais allocated with HARQ feedback Resource Index 0 within MTCH-A, and then UE-Auses the first PUCCH Resource or PUCCH Resource instance among the resource set for second option based HARQ feedback. Meanwhile, UE-Ajoins the multicast service carried by MTCH-B. UE-A is allocated with HARQ feedback Resource Index 0 within MTCH-B, and then UE-Auses the first PUCCH Resource or PUCCH Resource instance among the resource set for second option based HARQ feedback, which is number 17 in FIG. 7.

As an alternative, for second option based HARQ feedback, ACK based HARQ feedback and NACK based HARQ feedback can be differentiated using different cyclic shift of the same base sequence in the PUCCH resource. This will make the size of the resource set smaller, as one second option based HARQ feedback actually occupies a pair of PUCCH Resource or PUCCH Resource instance. This also means PUCCH Resource with more than two cyclic shifts assoicated can be only applicable to one UE.

As an alternative, for second option based HARQ feedback, implicit mechanism is used to determine the PUCCH resource within a set of PUCCH resource or PUCCH resource instance. For second HARQ feedback option, UE specific ID configured by BS (e.g. C-RNTI or its truncated version) is used determine the PUCCH resource within the configured PUCCH resources. Alternatively both UE C-RNTI plus one identity among G-RNTI, multicast Session ID, multicast Group ID and the index of MTCH (i.e. MTCHindex) in the MTCH info list, or its truncated version is used determine the PUCCH resource. The intention is to enable different UE within a multicast Group to utilize different PUCCH resource or PUCCH Resource instance to tranmist uplink HARQ feedback. For example, there is N PUCCH resource or PUCCH Resource instance specific to HARQ feedback of multicast PDSCH transmission shared by all of the ongoing multicast group at the same period, then Hash based algorthim can be used to acquire one of the PUCCH resource or PUCCH Resource instance by the value of C-RNTI mod N.

The description in this invention can be also applicable to the Uplink feedback procedure for NR broadcast services.

While aspects of the present disclosure have been described in conjunction with the specific embodiments thereof that are proposed as examples, alternatives, modifications, and variations to the examples may be made. Accordingly, embodiments as set forth herein are intended to be illustrative and not limiting. There are changes that may be made without departing from the scope of the claims set forth below.

Claims

A method for wireless communications, comprising:

Performing allocation of Uplink feedback resource for multicast transmission by Base Station.
The method of claim 1, wherein the Base Station assigns a unique Resource Index to each of the PUCCH Resources or PUCCH Resource instances for the feedback of multicast PDSCH transmission.
The method of claim 1, wherein the Base Station indicates the numbering of the Resource Index for the whole feedback resources to the UE via RRC message (e. g. in system information) .
The method of claim 1, wherein Base Station explictly indicates the set of PUCCH resources or PUCCH resource instances via RRC message e.g. MCCH Configuration to the UEs receiving the multicast PDSCH transmission, which is cooresponding to one MTCH transmission.
The method of claim 4, wherein the set of PUCCH resources or PUCCH resource instances is described by one or multiple combinaiton (s) of subframe or slot index, starting index of PUCCH resources or PUCCH resource instances, and number of PUCCH resources or PUCCH resource instances.
The method of claim 1, wherein the Base Station indicates the set of PUCCH resources or PUCCH resource instances to UE via multicast DCI.
The method of claim 1, wherein the Base Station indicates one unique HARQ feedback Resource Index to each UE joining the reception of each multicast service for a particular multicast Radio Bearer via unicast signalling e.g. RRC Reconfiguration.
The method of claim 1, wherein the UE uses the unique HARQ feedback Resource index, the indicated resource set of PUCCH resource or PUCCH resource instance, and the configured numbering of the whole feedback resource to determine the actual PUCCH resource or PUCCH resource instance for its uplink feedback resource for a particular multicast PDSCH transmission.