Patent Publication Number: US-2023156749-A1

Title: Radio (nr) multicast feedback switching

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of U.S. Non-Provisional patent application Ser. No. 17/172,485, filed Feb. 10, 2021, which claims priority to and the benefit of U.S. Provisional Patent Application No. 62/975,436, filed Feb. 12, 2020, which is hereby incorporated by reference in its entirety as if fully set forth below and for all applicable purposes. 
    
    
     TECHNICAL FIELD 
     This application relates to wireless communication systems, and more particularly to acknowledgement/negative-acknowledgement (ACK/NACK) feedback operations for multicast communications. 
     INTRODUCTION 
     Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). A wireless multiple-access communications system may include a number of base stations (BSs), each simultaneously supporting communications for multiple communication devices, which may be otherwise known as user equipment (UE). 
     To meet the growing demands for expanded mobile broadband connectivity, wireless communication technologies are advancing from the long-term evolution (LTE) technology to a next generation new radio (NR) technology, which may be referred to as 5 th  Generation (5G). For example, NR is designed to provide a lower latency, a higher bandwidth or a higher throughput, and a higher reliability than LTE. NR is designed to operate over a wide array of spectrum bands, for example, from low-frequency bands below about 1 gigahertz (GHz) and mid-frequency bands from about 1 GHz to about 6 GHz, to high-frequency bands such as millimeter wave (mmWave) bands. NR is also designed to operate across different spectrum types, from licensed spectrum to unlicensed and shared spectrum. Spectrum sharing enables operators to opportunistically aggregate spectrums to dynamically support high-bandwidth services. Spectrum sharing can extend the benefit of NR technologies to operating entities that may not have access to a licensed spectrum. 
     A wireless communication network may support broadcast, multicast, and/or unicast services. A broadcast service is a service that may be received by all users. A multicast service is a service that may be received by a group of users, for example, based on subscriptions. A unicast service is a service intended for a specific user, for example, voice calls. In general, a network may communicate with a group of uses using unicast, broadcast, multicast or a combination thereof. However, as the group becomes larger (e.g., a greater number of users), it may be more efficient to use multicast services. 
     BRIEF SUMMARY OF SOME EXAMPLES 
     The following summarizes some aspects of the present disclosure to provide a basic understanding of the discussed technology. This summary is not an extensive overview of all contemplated features of the disclosure and is intended neither to identify key or critical elements of all aspects of the disclosure nor to delineate the scope of any or all aspects of the disclosure. Its sole purpose is to present some concepts of one or more aspects of the disclosure in summary form as a prelude to the more detailed description that is presented later. 
     For example, in an aspect of the disclosure, a method of wireless communication, including receiving, by a first user equipment (UE) from a base station (BS), a multicast feedback configuration indicating a first resource configuration for a negative-acknowledgement (NACK) feedback mode; and a second resource configuration for an acknowledgement/negative-acknowledgement (ACK/NACK) feedback mode; receiving, by the first UE from the BS, a first multicast communication; transmitting, by the first UE to the BS, a NACK feedback for the first multicast communication based on the first resource configuration; receiving, by the first UE from the BS, a second multicast communication; and transmitting, by the first UE to the BS, an ACK feedback or a NACK feedback for the second multicast communication based on the second resource configuration. 
     In an additional aspect of the disclosure, a method of wireless communication, including transmitting, by a base station (BS), a multicast feedback configuration indicating a first resource configuration for a negative-acknowledgement (NACK) feedback mode; and a second resource configuration for an acknowledgement/negative-acknowledgement (ACK/NACK) feedback mode; transmitting, by the BS to a group of user equipments (UEs), a first multicast communication; receiving, by the BS from one or more UEs of the group of UEs, a NACK feedback for the first multicast communication based on the first resource configuration; transmitting, by the BS to the group of UEs, a second multicast communication; and receiving, by the BS from a first UE of the one or more UEs, an ACK feedback or a NACK feedback for the second multicast communication based on the second resource configuration. 
     In an additional aspect of the disclosure, a user equipment (UE), including means for receiving, from a base station (BS), a multicast feedback configuration indicating a first resource configuration for a negative-acknowledgement (NACK) feedback mode; and a second resource configuration for an acknowledgement/negative-acknowledgement (ACK/NACK) feedback mode; receiving, from the BS, a first multicast communication; means for transmitting, to the BS, a NACK feedback for the first multicast communication based on the first resource configuration; means for receiving, from the BS, a second multicast communication; and means for transmitting, to the BS, an ACK feedback or a NACK feedback for the second multicast communication based on the second resource configuration. 
     In an additional aspect of the disclosure, a base station (BS), including means for transmitting a multicast feedback configuration indicating a first resource configuration for a negative-acknowledgement (NACK) feedback mode; and a second resource configuration for an acknowledgement/negative-acknowledgement (ACK/NACK) feedback mode; means for transmitting, to a group of user equipments (UEs), a first multicast communication; means for receiving, from one or more UEs of the group of UEs, a NACK feedback for the first multicast communication based on the first resource configuration; means for transmitting, to the group of UEs, a second multicast communication; and means for receiving, from a first UE of the one or more UEs, an ACK feedback or a NACK feedback for the second multicast communication based on the second resource configuration. 
     In an additional aspect of the disclosure, a non-transitory computer-readable medium having program code recorded thereon, the program code including code for causing a user equipment (UE) to receive, from a base station (BS), a multicast feedback configuration indicating a first resource configuration for a negative-acknowledgement (NACK) feedback mode; and a second resource configuration for an acknowledgement/negative-acknowledgement (ACK/NACK) feedback mode; code for causing the UE to receive, from the BS, a first multicast communication; code for causing the UE to transmit, to the BS, a NACK feedback for the first multicast communication based on the first resource configuration; code for causing the UE to receive, from the BS, a second multicast communication; and code for causing the UE to transmit, to the BS, an ACK feedback or a NACK feedback for the second multicast communication based on the second resource configuration. 
     In an additional aspect of the disclosure, a non-transitory computer-readable medium having program code recorded thereon, the program code including code for causing a base station (BS) to transmit a multicast feedback configuration indicating a first resource configuration for a negative-acknowledgement (NACK) feedback mode; and a second resource configuration for an acknowledgement/negative-acknowledgement (ACK/NACK) feedback mode; code for causing the BS to transmit, to a group of user equipments (UEs), a first multicast communication; code for causing the BS to receive, from one or more UEs of the group of UEs, a NACK feedback for the first multicast communication based on the first resource configuration; code for causing the BS to transmit, to the group of UEs, a second multicast communication; and code for causing the BS to receive, from a first UE of the one or more UEs, an ACK feedback or a NACK feedback for the second multicast communication based on the second resource configuration. 
     In an additional aspect of the disclosure, a user equipment (UE), including a transceiver configured to receive, from a base station (BS), a multicast feedback configuration indicating a first resource configuration for a negative-acknowledgement (NACK) feedback mode; and a second resource configuration for an acknowledgement/negative-acknowledgement (ACK/NACK) feedback mode; receive, from the BS, a first multicast communication; transmit, to the BS, a NACK feedback for the first multicast communication based on the first resource configuration; receive, from the BS, a second multicast communication; and transmit, to the BS, an ACK feedback or a NACK feedback for the second multicast communication based on the second resource configuration. 
     In an additional aspect of the disclosure, a base station (BS), including a transceiver configured to transmit a multicast feedback configuration indicating a first resource configuration for a negative-acknowledgement (NACK) feedback mode; and a second resource configuration for an acknowledgement/negative-acknowledgement (ACK/NACK) feedback mode; transmit, to a group of user equipments (UEs), a first multicast communication; receive, from one or more UEs of the group of UEs, a NACK feedback for the first multicast communication based on the first resource configuration; transmit, to the group of UEs, a second multicast communication; and receive, from a first UE of the one or more UEs, an ACK feedback or a NACK feedback for the second multicast communication based on the second resource configuration. 
     Other aspects, features, and embodiments of the present invention will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary aspects of the present invention in conjunction with the accompanying figures. While features of the present invention may be discussed relative to certain aspects and figures below, all aspects of the present invention can include one or more of the advantageous features discussed herein. In other words, while one or more aspects may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various aspects of the invention discussed herein. In similar fashion, while exemplary aspects may be discussed below as device, system, or method aspects it should be understood that such exemplary aspects can be implemented in various devices, systems, and methods. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a wireless communication network according to some aspects of the present disclosure. 
         FIG.  2    illustrates a radio frame structure according to some aspects of the present disclosure. 
         FIG.  3    illustrates a multicast communication scheme with feedback mode switching according to some aspects of the present disclosure. 
         FIG.  4    illustrates a multicast feedback resource configuration scheme according to some aspects of the present disclosure. 
         FIG.  5    illustrates a multicast feedback resource configuration scheme according to some aspects of the present disclosure. 
         FIG.  6    illustrates a multicast feedback switching scenario according to some aspects of the present disclosure. 
         FIG.  7    is a block diagram of a user equipment (UE) according to some aspects of the present disclosure. 
         FIG.  8    is a block diagram of an exemplary base station (BS) according to some aspects of the present disclosure. 
         FIG.  9    is a signaling diagram of a multicast communication method with feedback mode switching according to some aspects of the present disclosure. 
         FIG.  10    is a flow diagram of a wireless communication method according to some aspects of the present disclosure. 
         FIG.  11    is a flow diagram of a wireless communication method according to some aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below, in connection with the appended drawings, is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts. 
     This disclosure relates generally to wireless communications systems, also referred to as wireless communications networks. In various aspects, the techniques and apparatus may be used for wireless communication networks such as code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, single-carrier FDMA (SC-FDMA) networks, LTE networks, Global System for Mobile Communications (GSM) networks, 5 th  Generation (5G) or new radio (NR) networks, as well as other communications networks. As described herein, the terms “networks” and “systems” may be used interchangeably. 
     An OFDMA network may implement a radio technology such as evolved UTRA (E-UTRA), Institute of Electrical and Electronics Engineers (IEEE) 802.11, IEEE 802.16, IEEE 802.20, flash-OFDM and the like. UTRA, E-UTRA, and GSM are part of universal mobile telecommunication system (UMTS). In particular, long term evolution (LTE) is a release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents provided from an organization named “3rd Generation Partnership Project” (3GPP), and cdma2000 is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). These various radio technologies and standards are known or are being developed. For example, the 3rd Generation Partnership Project (3GPP) is a collaboration between groups of telecommunications associations that aims to define a globally applicable third generation (3G) mobile phone specification. 3GPP long term evolution (LTE) is a 3GPP project which was aimed at improving the UMTS mobile phone standard. The 3GPP may define specifications for the next generation of mobile networks, mobile systems, and mobile devices. The present disclosure is concerned with the evolution of wireless technologies from LTE, 4G, 5G, NR, and beyond with shared access to wireless spectrum between networks using a collection of new and different radio access technologies or radio air interfaces. 
     5G networks contemplate diverse deployments, diverse spectrum, and diverse services and devices that may be implemented using an OFDM-based unified, air interface. In order to achieve these goals, further enhancements to LTE and LTE-A are considered in addition to development of the new radio technology for 5G NR networks. The 5G NR will be capable of scaling to provide coverage (1) to a massive Internet of things (IoTs) with a ultra-high density (e.g., ˜1M nodes/km 2 ), ultra-low complexity (e.g., ˜10 s of bits/sec), ultra-low energy (e.g., ˜10+ years of battery life), and deep coverage with the capability to reach challenging locations; (2) including mission-critical control with strong security to safeguard sensitive personal, financial, or classified information, ultra-high reliability (e.g., ˜99.9999% reliability), ultra-low latency (e.g., ˜1 ms), and users with wide ranges of mobility or lack thereof; and (3) with enhanced mobile broadband including extreme high capacity (e.g., ˜10 Tbps/km 2 ), extreme data rates (e.g., multi-Gbps rate, 100+ Mbps user experienced rates), and deep awareness with advanced discovery and optimizations. 
     The 5G NR may be implemented to use optimized OFDM-based waveforms with scalable numerology and transmission time interval (TTI); having a common, flexible framework to efficiently multiplex services and features with a dynamic, low-latency time division duplex (TDD)/frequency division duplex (FDD) design; and with advanced wireless technologies, such as massive multiple input, multiple output (MIMO), robust millimeter wave (mmWave) transmissions, advanced channel coding, and device-centric mobility. Scalability of the numerology in 5G NR, with scaling of subcarrier spacing, may efficiently address operating diverse services across diverse spectrum and diverse deployments. For example, in various outdoor and macro coverage deployments of less than 3 GHz FDD/TDD implementations, subcarrier spacing may occur with 15 kHz, for example over 5, 10, 20 MHz, and the like bandwidth (BW). For other various outdoor and small cell coverage deployments of TDD greater than 3 GHz, subcarrier spacing may occur with 30 kHz over 80/100 MHz BW. For other various indoor wideband implementations, using a TDD over the unlicensed portion of the 5 GHz band, the subcarrier spacing may occur with 60 kHz over a 160 MHz BW. Finally, for various deployments transmitting with mmWave components at a TDD of 28 GHz, subcarrier spacing may occur with 120 kHz over a 500 MHz BW. 
     The scalable numerology of the 5G NR facilitates scalable TTI for diverse latency and quality of service (QoS) requirements. For example, shorter TTI may be used for low latency and high reliability, while longer TTI may be used for higher spectral efficiency. The efficient multiplexing of long and short TTIs to allow transmissions to start on symbol boundaries. 5G NR also contemplates a self-contained integrated subframe design with UL/downlink scheduling information, data, and acknowledgement in the same subframe. The self-contained integrated subframe supports communications in unlicensed or contention-based shared spectrum, adaptive UL/downlink that may be flexibly configured on a per-cell basis to dynamically switch between UL and downlink to meet the current traffic needs. 
     Various other aspects and features of the disclosure are further described below. It should be apparent that the teachings herein may be embodied in a wide variety of forms and that any specific structure, function, or both being disclosed herein is merely representative and not limiting. Based on the teachings herein one of an ordinary level of skill in the art should appreciate that an aspect disclosed herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, such an apparatus may be implemented or such a method may be practiced using other structure, functionality, or structure and functionality in addition to or other than one or more of the aspects set forth herein. For example, a method may be implemented as part of a system, device, apparatus, and/or as instructions stored on a computer readable medium for execution on a processor or computer. Furthermore, an aspect may comprise at least one element of a claim. 
     Hybrid automatic repeat request (HARQ) is a physical layer protocol, which combines the use of forward error correction (FEC) with automatic repeat request (ARQ)-control. For instance, a transmitting node may transmit a data transmission with FEC encoding to a receiving node. When FEC decoding is successful at the receiving node, the receiving node may feedback an acknowledgement (ACK) to the transmitter. When FEC decoding fails at the receiving node, the receiving node may feedback a negative-acknowledgement (NACK) to the transmitting node. Upon receiving a NACK, the transmitting node may perform a retransmission. The transmitting node may retransmit the data transmission until an ACK is received from the receiving node or when the number of retransmissions reaches a certain limit. 
     HARQ techniques are commonly used in unicast services to provide high-reliability communications. While HARQ techniques can also be applied to multicast services to improve communication reliability, currently HARQ is not applied to multicast services due to the complexity of having to receive and manage ACK/NACK feedbacks from a large number of recipients or user equipment devices (UEs). One approach to reducing the amount of feedback signaling and feedback resources is to assign all UEs in a multicast group with the same resource for NACK-only feedbacks. In other words, if a receiving UE fails to receive a multicast transmission, the receiving UE may transmit a NACK feedback in the resource. On the other hand, if a receiving UE successfully receives the multicast transmission, no ACK feedback is transmitted. While the use of a common NACK resource with group NACK feedbacks can reduce feedback resource usage and signaling, the network may not be aware of whether a UE miss-detects a scheduling grant for a multicast transmission or the UE falsely detects a multicast transmission. For instance, a missed detection of a multicast scheduling grant at the UE (e.g., due to a discontinuous transmission (DTX) operation) may cause the network to interpret the lack of a NACK feedback from the UE as a successful reception of the multicast transmission while the UE did not receive the multicast transmission. Similarly, a NACK feedback due to a false detection of a multicast transmission at the UE may cause the network to unnecessarily retransmit a multicast transmission. Further, when all multicast UEs use the common NACK resource for group NACK feedbacks, the network may not be able to estimate UE-specific channel state information (CSI) from the NACK feedbacks. 
     Another approach to multicast feedback is to assign each UE in a multicast group with a UE-specific feedback resource where the UE may transmit an ACK upon a successful reception of a multicast transmission or an NACK upon a failed reception of a multicast transmission. The use of UE-specific feedback resource with the ACK/NACK feedback may allow the network to detect a missed detection of a multicast scheduling grant at a receiving UE, for example, when no feedback is received from the UE. Additionally, the network may utilize the ACK/NACK feedbacks received from the UE-specific resource to estimate UE-specific CSI information, which may be useful for subsequent multicast scheduling and/or beamforming. However, the resource usage and signaling for the UE-specific ACK/NACK approach can be large and can increase as the number of UEs in the group increases. As such, there is a compromise between the common group NACK-only feedback approach and the UE-specific ACK/NACK feedback approach. 
     In an example of NR vehicle-to-everything (V2X), a sidelink source UE (or source UE) may transmit sidelink communications to a group of sidelink receiving UEs (or destination UEs) via groupcasting and may apply HARQ techniques to the groupcasting. For instance, a source UE may transmit sidelink control information (SCI) (e.g., in a physical sidelink control channel (PSCCH)) to indicate a groupcast transmission and to identify corresponding destination sidelink UEs. Additionally, the source UE may indicate in the SCI whether the destination UEs are to feedback a NACK-only feedback using a common resource (e.g., in a physical sidelink feedback channel (PSFCH)) or feedback an ACK or a NACK using UE-specific resources (e.g., in a PSFCH). The source UE may transmit the groupcast transmission (e.g., in a physical sidelink shared channel (PSSCH)) and may determine whether to retransmit the groupcast transmission based on feedbacks received from the destination UEs. Thus, the indication of whether to use a group NACK-only feedback or a UE-specific ACK/NACK feedback in NR V2X groupcasting is per groupcast transmission (e.g., per PSSCH transmission). Further, when a UE-specific ACK/NACK is indicated for a PSSCH transmission, NR V2X restricts UE-specific ACK/NACK feedbacks to be from destination sidelink UEs that are located within a certain distance (e.g., a sidelink UE communication range) from a corresponding sidelink source UE. Destination sidelink UEs that do not meet the distance requirement may not send any feedback. 
     The use of HARQ in sidelink groupcast may be relatively less complex than a network using HARQ for multicast since the number of multicast UEs in a network may be significantly greater than the number of sidelink UEs in groupcasting. Additionally, the UEs in a network multicast group can be distributed over a large geographical area, whereas sidelink UEs in groupcasting may be located relatively close to each other. 
     The present disclosure provides techniques for multicast feedback with flexible switching between a common NACK-only feedback mode and a UE-specific ACK/NACK feedback mode. For instance, a BS may configure each UE in a multicast group with a multicast feedback configuration. The multicast feedback configuration may indicate a first resource configuration for a NACK feedback mode and a second resource configuration for an ACK/NACK feedback mode. The first resource configuration may be a common NACK resource configuration among all UEs in the multicast group (for NACK-only feedbacks). The second resource configuration may be a UE-specific ACK/NACK resource configuration designated to the respective UE (for ACK/NACK feedbacks). In some aspects, the BS may transmit a first multicast communication to the group of UEs. A first UE in the group may transmit a NACK feedback for the first multicast communication using the first resource configuration (upon failing to decode the first multicast communication correctly). The BS may transmit a second multicast communication to the group of UEs. The first UE may transmit an ACK feedback or a NACK feedback for the second multicast communication using the second resource configuration. 
     In some instances, the switching from the use of the first resource configuration for transmitting the NACK feedback for the first multicast communication to the use of the second resource configuration for transmitting the ACK feedback or the NACK feedback for the second multicast communication is in response to a multicast feedback mode switch trigger. The multicast feedback mode switch can be triggered via various mechanisms. For instance, the BS may instruct the first UE to switch between the NACK-only feedback mode and the ACK/NACK feedback mode, for example, based on a certain channel condition and/or a network load. In some instances, the BS may configure the first UE with rules to determine whether to utilize the NACK-only feedback mode or the ACK/NACK feedback mode for a particular multicast feedback. The rules can be based on channel measurements or conditions and/or multicast decoding status. For instance, the rules may include a pathloss threshold, a signal-to-interference-plus-noise ratio (SINR) threshold, a reference signal received power (RSRP) threshold, a channel quality indicator (CQI) threshold, or combinations thereof. 
     In some aspects, the BS may configure the first UE with a periodicity when the first UE may potentially switch from one of the NACK-only feedback mode or an ACK/NACK feedback mode to the other one of the NACK-only feedback mode or the ACK/NACK feedback mode. In some instances, the BS may restrict the first UE to perform the switch at the boundary of the periodicity if the first UE decides to switch the feedback mode. In some other instances, the BS may allow the first UE to switch at any time. In some instances, the first UE may not notify the BS of a feedback mode switch. In some instances, the first UE may notify the BS of a feedback mode switch. In some other instances, the first UE may request for a feedback mode switch from the BS. 
     In some aspects, the first resource configuration may include at least one of a different time configuration, a different frequency configuration, or a different sequence configuration than the second resource configuration. For instance, the NACK-only feedback or the ACK/NACK feedback may be transmitted in the form of a physical uplink control channel (PUCCH) format 0 sequence. The sequence configuration may indicate parameters for generating a base sequence. For instance, the first resource configuration may indicate one or more first sequence parameters for generating a sequence to represent a NACK-only feedback. The second resource configuration may indicate one or more second sequence parameters for generating a sequence to represent a NACK feedback and one or more third sequence parameters for generating a sequence to represent an ACK feedback. The first sequence parameters, the second sequence parameters, and the third sequence parameters can be different. 
     In some aspects, the first resource configuration and the second resource configuration may include the same time configuration and the same frequency configuration and the BS may apply code-division-multiplexing (CDM) to multiplex NACK feedbacks from UEs operating in the NACK-only feedback mode and ACK/NACK feedbacks from UEs operating in the ACK/NACK feedback mode. 
     Aspects of the present disclosure can provide several benefits. For example, the configuration of both common NACK-only feedback resources and UE-specific ACK/NACK feedback resource at each multicast UE can allow for flexible, dynamic switching between a NACK-only feedback mode and an ACK/NACK feedback mode. The configuration of rules for switching between the ACK/NACK feedback mode and the NACK-only feedback mode can provide a good compromise between resource usages and feedback information. For instance, in certain channel conditions, the UE-specific ACK/NACKs may not provide the network with useful channel information for multicast, and thus the NACK-only feedback mode may be used to minimize resource overhead. In other channel conditions, the UE-specific ACK/NACKs may provide the network with useful information for multicasting (e.g., for beamforming to reach certain UEs), and thus the UE-specific ACK/NACK feedback mode can be used as needed. The flexible switching between the ACK/NACK feedback mode and the NACK-only feedback mode allows a network to efficiently support HARQ in multicast with a minimal amount of feedback resources. 
       FIG.  1    illustrates a wireless communication network  100  according to some aspects of the present disclosure. The network  100  may be a 5G network. The network  100  includes a number of base stations (BSs)  105  (individually labeled as  105   a ,  105   b ,  105   c ,  105   d ,  105   e , and  105   f ) and other network entities. A BS  105  may be a station that communicates with UEs  115  (individually labeled as  115   a ,  115   b ,  115   c ,  115   d ,  115   e ,  115   f ,  115   g ,  115   h , and  115   k ) and may also be referred to as an evolved node B (eNB), a next generation eNB (gNB), an access point (e.g., an IEEE 802.11 AP), and the like. Each BS  105  may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to this particular geographic coverage area of a BS  105  and/or a BS subsystem serving the coverage area, depending on the context in which the term is used. 
     A BS  105  may provide communication coverage for a macro cell or a small cell, such as a pico cell or a femto cell, and/or other types of cell. A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A small cell, such as a pico cell, would generally cover a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A small cell, such as a femto cell, would also generally cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs for users in the home, and the like). A BS for a macro cell may be referred to as a macro BS. A BS for a small cell may be referred to as a small cell BS, a pico BS, a femto BS or a home BS. In the example shown in  FIG.  1   , the BSs  105   d  and  105   e  may be regular macro BSs, while the BSs  105   a - 105   c  may be macro BSs enabled with one of three dimension (3D), full dimension (PD), or massive MIMO. The BSs  105   a - 105   c  may take advantage of their higher dimension MIMO capabilities to exploit 3D beamforming in both elevation and azimuth beamforming to increase coverage and capacity. The BS  105   f  may be a small cell BS which may be a home node or portable access point. A BS  105  may support one or multiple (e.g., two, three, four, and the like) cells. 
     The network  100  may support synchronous or asynchronous operation. For synchronous operation, the BSs may have similar frame timing, and transmissions from different BSs may be approximately aligned in time. For asynchronous operation, the BSs may have different frame timing, and transmissions from different BSs may not be aligned in time. 
     The UEs  115  are dispersed throughout the wireless network  100 , and each UE  115  may be stationary or mobile. A UE  115  may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE  115  may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, an IEEE 802.11 terminal station (STA), or the like. In one aspect, a UE  115  may be a device that includes a Universal Integrated Circuit Card (UICC). In another aspect, a UE may be a device that does not include a UICC. In some aspects, the UEs  115  that do not include UICCs may also be referred to as IoT devices or internet of everything (IoE) devices. The UEs  115   a - 115   d  are examples of mobile smart phone-type devices accessing network  100 . A UE  115  may also be a machine specifically configured for connected communication, including machine type communication (MTC), enhanced MTC (eMTC), narrowband IoT (NB-IoT) and the like. The UEs  115   e - 115   h  are examples of various machines configured for communication that access the network  100 . The UEs  115   i - 115   k  are examples of vehicles equipped with wireless communication devices configured for communication that access the network  100 . A UE  115  may be able to communicate with any type of the BSs, whether macro BS, small cell, or the like. In  FIG.  1   , a lightning bolt (e.g., communication links) indicates wireless transmissions between a UE  115  and a serving BS  105 , which is a BS designated to serve the UE  115  on the downlink (DL) and/or uplink (UL), desired transmission between BSs  105 , backhaul transmissions between BSs, or sidelink transmissions between UEs  115 . 
     In operation, the BSs  105   a - 105   c  may serve the UEs  115   a  and  115   b  using 3D beamforming and coordinated spatial techniques, such as coordinated multipoint (CoMP) or multi-connectivity. The macro BS  105   d  may perform backhaul communications with the BSs  105   a - 105   c , as well as small cell, the BS  105   f . The macro BS  105   d  may also transmit multicast services which are subscribed to and received by the UEs  115   c  and  115   d . Such multicast services may include mobile television or stream video, or may include other services for providing community information, such as weather emergencies or alerts, such as Amber alerts or gray alerts. 
     The BSs  105  may also communicate with a core network. The core network may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. At least some of the BSs  105  (e.g., which may be an example of a gNB or an access node controller (ANC)) may interface with the core network through backhaul links (e.g., NG-C, NG-U, etc.) and may perform radio configuration and scheduling for communication with the UEs  115 . In various examples, the BSs  105  may communicate, either directly or indirectly (e.g., through core network), with each other over backhaul links (e.g., X1, X2, etc.), which may be wired or wireless communication links. 
     The network  100  may also support mission critical communications with ultra-reliable and redundant links for mission critical devices, such as the UE  115   e , which may be a drone. Redundant communication links with the UE  115   e  may include links from the macro BSs  105   d  and  105   e , as well as links from the small cell BS  105   f . Other machine type devices, such as the UE  115   f  (e.g., a thermometer), the UE  115   g  (e.g., smart meter), and UE  115   h  (e.g., wearable device) may communicate through the network  100  either directly with BSs, such as the small cell BS  105   f , and the macro BS  105   e , or in multi-step-size configurations by communicating with another user device which relays its information to the network, such as the UE  115   f  communicating temperature measurement information to the smart meter, the UE  115   g , which is then reported to the network through the small cell BS  105   f . The network  100  may also provide additional network efficiency through dynamic, low-latency TDD/FDD communications, such asV2V, V2X, C-V2X communications between a UE  115   i ,  115   j , or  115   k  and other UEs  115 , and/or vehicle-to-infrastructure (V2I) communications between a UE  115   i ,  115   j , or  115   k  and a BS  105 . 
     In some implementations, the network  100  utilizes OFDM-based waveforms for communications. An OFDM-based system may partition the system BW into multiple (K) orthogonal subcarriers, which are also commonly referred to as subcarriers, tones, bins, or the like. Each subcarrier may be modulated with data. In some instances, the subcarrier spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system BW. The system BW may also be partitioned into subbands. In other instances, the subcarrier spacing and/or the duration of TTIs may be scalable. 
     In some aspects, the BSs  105  can assign or schedule transmission resources (e.g., in the form of time-frequency resource blocks (RB)) for downlink (DL) and uplink (UL) transmissions in the network  100 . DL refers to the transmission direction from a BS  105  to a UE  115 , whereas UL refers to the transmission direction from a UE  115  to a BS  105 . The communication can be in the form of radio frames. A radio frame may be divided into a plurality of subframes or slots, for example, about 10. Each slot may be further divided into mini-slots. In a FDD mode, simultaneous UL and DL transmissions may occur in different frequency bands. For example, each subframe includes a UL subframe in a UL frequency band and a DL subframe in a DL frequency band. In a TDD mode, UL and DL transmissions occur at different time periods using the same frequency band. For example, a subset of the subframes (e.g., DL subframes) in a radio frame may be used for DL transmissions and another subset of the subframes (e.g., UL subframes) in the radio frame may be used for UL transmissions. 
     The DL subframes and the UL subframes can be further divided into several regions. For example, each DL or UL subframe may have pre-defined regions for transmissions of reference signals, control information, and data. Reference signals are predetermined signals that facilitate the communications between the BSs  105  and the UEs  115 . For example, a reference signal can have a particular pilot pattern or structure, where pilot tones may span across an operational BW or frequency band, each positioned at a pre-defined time and a pre-defined frequency. For example, a BS  105  may transmit cell specific reference signals (CRSs) and/or channel state information—reference signals (CSI-RSs) to enable a UE  115  to estimate a DL channel. Similarly, a UE  115  may transmit sounding reference signals (SRSs) to enable a BS  105  to estimate a UL channel Control information may include resource assignments and protocol controls. Data may include protocol data and/or operational data. In some aspects, the BSs  105  and the UEs  115  may communicate using self-contained subframes. A self-contained subframe may include a portion for DL communication and a portion for UL communication. A self-contained subframe can be DL-centric or UL-centric. A DL-centric subframe may include a longer duration for DL communication than for UL communication. A UL-centric subframe may include a longer duration for UL communication than for UL communication. 
     In some aspects, the network  100  may be an NR network deployed over a licensed spectrum. The BSs  105  can transmit synchronization signals (e.g., including a primary synchronization signal (PSS) and a secondary synchronization signal (SSS)) in the network  100  to facilitate synchronization. The BSs  105  can broadcast system information associated with the network  100  (e.g., including a master information block (MIB), remaining system information (RMSI), and other system information (OSI)) to facilitate initial network access. In some instances, the BSs  105  may broadcast the PSS, the SSS, and/or the MIB in the form of synchronization signal block (SSBs) over a physical broadcast channel (PBCH) and may broadcast the RMSI and/or the OSI over a physical downlink shared channel (PDSCH). 
     In some aspects, a UE  115  attempting to access the network  100  may perform an initial cell search by detecting a PSS from a BS  105 . The PSS may enable synchronization of period timing and may indicate a physical layer identity value. The UE  115  may then receive a SSS. The SSS may enable radio frame synchronization, and may provide a cell identity value, which may be combined with the physical layer identity value to identify the cell. The PSS and the SSS may be located in a central portion of a carrier or any suitable frequencies within the carrier. 
     After receiving the PSS and SSS, the UE  115  may receive a MIB. The MIB may include system information for initial network access and scheduling information for RMSI and/or OSI. After decoding the MIB, the UE  115  may receive RMSI and/or OSI. The RMSI and/or OSI may include radio resource control (RRC) information related to random access channel (RACH) procedures, paging, control resource set (CORESET) for physical downlink control channel (PDCCH) monitoring, physical UL control channel (PUCCH), physical UL shared channel (PUSCH), power control, and SRS. 
     After obtaining the MIB, the RMSI and/or the OSI, the UE  115  can perform a random access procedure to establish a connection with the BS  105 . In some examples, the random access procedure may be a four-step random access procedure. For example, the UE  115  may transmit a random access preamble and the BS  105  may respond with a random access response. The random access response (RAR) may include a detected random access preamble identifier (ID) corresponding to the random access preamble, timing advance (TA) information, a UL grant, a temporary cell-radio network temporary identifier (C-RNTI), and/or a backoff indicator. Upon receiving the random access response, the UE  115  may transmit a connection request to the BS  105  and the BS  105  may respond with a connection response. The connection response may indicate a contention resolution. In some examples, the random access preamble, the RAR, the connection request, and the connection response can be referred to as message 1 (MSG1), message 2 (MSG2), message 3 (MSG3), and message 4 (MSG4), respectively. In some examples, the random access procedure may be a two-step random access procedure, where the UE  115  may transmit a random access preamble and a connection request in a single transmission and the BS  105  may respond by transmitting a random access response and a connection response in a single transmission. 
     After establishing a connection, the UE  115  and the BS  105  can enter a normal operation stage, where operational data may be exchanged. For example, the BS  105  may schedule the UE  115  for UL and/or DL communications. The BS  105  may transmit UL and/or DL scheduling grants to the UE  115  via a PDCCH. The scheduling grants may be transmitted in the form of DL control information (DCI). The BS  105  may transmit a DL communication signal (e.g., carrying data) to the UE  115  via a PDSCH according to a DL scheduling grant. The UE  115  may transmit a UL communication signal to the BS  105  via a PUSCH and/or PUCCH according to a UL scheduling grant. 
     In some aspects, the BS  105  may communicate with a UE  115  using HARQ techniques to improve communication reliability, for example, to provide a URLLC service. The BS  105  may schedule a UE  115  for a PDSCH communication by transmitting a DL grant in a PDCCH. The BS  105  may transmit a DL data packet to the UE  115  according to the schedule in the PDSCH. The DL data packet may be transmitted in the form of a transport block (TB). If the UE  115  receives the DL data packet successfully, the UE  115  may transmit a HARQ ACK to the BS  105 . Conversely, if the UE  115  fails to receive the DL transmission successfully, the UE  115  may transmit a HARQ NACK to the BS  105 . Upon receiving a HARQ NACK from the UE  115 , the BS  105  may retransmit the DL data packet to the UE  115 . The retransmission may include the same coded version of DL data as the initial transmission. Alternatively, the retransmission may include a different coded version of the DL data than the initial transmission. The UE  115  may apply soft-combining to combine the encoded data received from the initial transmission and the retransmission for decoding. The BS  105  and the UE  115  may also apply HARQ for UL communications using substantially similar mechanisms as the DL HARQ. 
     In some aspects, the network  100  may operate over a system BW or a component carrier (CC) BW. The network  100  may partition the system BW into multiple BWPs (e.g., portions). A BS  105  may dynamically assign a UE  115  to operate over a certain BWP (e.g., a certain portion of the system BW). The assigned BWP may be referred to as the active BWP. The UE  115  may monitor the active BWP for signaling information from the BS  105 . The BS  105  may schedule the UE  115  for UL or DL communications in the active BWP. In some aspects, a BS  105  may assign a pair of BWPs within the CC to a UE  115  for UL and DL communications. For example, the BWP pair may include one BWP for UL communications and one BWP for DL communications. 
     In some aspects, the network  100  may serve a multicast service to a group of UEs  115 . The network  100  may apply HARQ techniques to improve communication reliability for multicast. For instance, a BS  105  may transmit a multicast transmission to a group of UEs  115  belonging to a multicast service group (e.g., via subscriptions). The BS  105  may apply HARQ to the multicast transmission. The BS  105  may configure the UEs  115  to feedback a reception status for the multicast transmission. The BS  105  may determine whether to retransmit a multicast transmission based on feedbacks from the UEs  115 . In some aspects, the BS  105  may configure the group of UEs  115  with a common resource for NACK-only feedbacks and may configure each UE  115  in the group with a UE-specific resource for an ACK feedback or a NACK feedback. The BS  105  may configure each multicast UE  115  to operate in a NACK-only feedback mode and/or a UE-specific ACK/NACK feedback mode at each UE  115 . Additionally, the BS  105  may dynamically switch one or more UEs  115  in the group between the NACK-only feedback mode and the UE-specific ACK/NACK feedback mode, for example, depending on a network load and/or channel conditions. Further, the BS  105  may configure the UEs  115  in the group with rules to switch between the NACK-only feedback mode and the UE-specific ACK/NACK feedback mode. For instance, the rules may include various channel measurement criteria and/or data decoding criteria and corresponding thresholds. In some aspects, the BS  105  may apply CDM to multiplex the common NACK-only feedbacks and the UE-specific ACK/NACK feedbacks from the group of UEs  115  in the same time-frequency resource. Mechanisms for multicast feedbacks and multicast feedback mode switching are described in greater detail herein. 
       FIG.  2    is a timing diagram illustrating a radio frame structure  200  according to some aspects of the present disclosure. The radio frame structure  200  may be employed by BSs such as the BSs  105  and UEs such as the UEs  115  in a network such as the network  100  for communications. In particular, the BS may communicate with the UE using time-frequency resources configured as shown in the radio frame structure  200 . In  FIG.  2   , the x-axes represent time in some arbitrary units and the y-axes represent frequency in some arbitrary units. The transmission frame structure  200  includes a radio frame  201 . The duration of the radio frame  201  may vary depending on the aspects. In an example, the radio frame  201  may have a duration of about ten milliseconds. The radio frame  201  includes M number of slots  202 , where M may be any suitable positive integer. In an example, M may be about 10. 
     Each slot  202  includes a number of subcarriers  204  in frequency and a number of symbols  206  in time. The number of subcarriers  204  and/or the number of symbols  206  in a slot  202  may vary depending on the aspects, for example, based on the channel bandwidth, the subcarrier spacing (SCS), and/or the CP mode. One subcarrier  204  in frequency and one symbol  206  in time forms one resource element (RE)  212  for transmission. A resource block (RB)  210  is formed from a number of consecutive subcarriers  204  in frequency and a number of consecutive symbols  206  in time. 
     In an example, a BS (e.g., BS  105  in  FIG.  1   ) may schedule a UE (e.g., UE  115  in  FIG.  1   ) for UL and/or DL communications at a time-granularity of slots  202  or mini-slots  208 . Each slot  202  may be time-partitioned into K number of mini-slots  208 . Each mini-slot  208  may include one or more symbols  206 . The mini-slots  208  in a slot  202  may have variable lengths. For example, when a slot  202  includes N number of symbols  206 , a mini-slot  208  may have a length between one symbol  206  and (N−1) symbols  206 . In some aspects, a mini-slot  208  may have a length of about two symbols  206 , about four symbols  206 , or about seven symbols  206 . In some examples, the BS may schedule UE at a frequency-granularity of a resource block (RB)  210  (e.g., including about 12 subcarriers  204 ). 
       FIG.  3    illustrates a multicast communication scheme  300  with feedback mode switching according to some aspects of the present disclosure. The scheme  300  may be employed by BSs such as the BSs  105  and UEs such as the UEs  115  in a network such as the network  100 . In  FIG.  3   , the x-axis represents time in some arbitrary units. In particular, a BS (e.g., the BSs  105 ) may configure UEs (e.g., the UEs  115 ) in a multicast group with a common NACK-only feedback mode and/or a UE-specific ACK/NACK feedback mode and may dynamically switch the UEs between the common NACK-only feedback mode and the UE-specific ACK/NACK feedback mode as shown in the scheme  300 . For simplicity of illustration and discussion,  FIG.  3    illustrates a BS  305  serving two UEs  315  (shown as UE  315   a  and UE  315   b ) in a multicast group  302 . However, the multicast group  302  may include any suitable number of UEs  315  (e.g., about 3, 4, 5, 10, 20, 30, 40, 50, 100 or more). In some instances, the BS  305  may correspond to a BS  105  of  FIG.  1    and the UEs  315  may correspond to the UEs  115  of  FIG.  1   . Additionally, the scheme  300  is described using the same slot structure as in the radio frame structure  200 , and may use the same reference numerals as in  FIG.  2    for simplicity&#39;s sake. 
       FIG.  3    shows a frame structure  301  including a plurality of slots  202  in time. The slots  202  are indexed from S0 to S11. For example, the BS  305  may communicate with the UEs  315  in units of slots  202 . The slots  202  may also be referred to as transmission time intervals (TTIs). Each slot  202  or TTI carry a medium access control (MAC) layer transport block. Each slot  202  may include a number of symbols in time and a number of frequency tones in frequency. Each slot  202  may include a DL control portion followed by at least one of a subsequent DL data portion, UL data portion, and/or a UL control portion. In the context of LTE or NR, the DL control portion, the DL data portion, the UL data portion, and the UL control portion may be referred to as a PDCCH, a PDSCH, a PUSCH, and a PUCCH, respectively. 
     In  FIG.  3   , the pattern-filled boxes represent transmissions of DL control information, DL data, UL ACK, and/or a UL NACK in corresponding slots  202 . While an entire slot  202  is pattern-filled, a transmission may occur only in a corresponding portion of the slot  202 . As shown, the BS  305  transmits DL control information  320  in the slot  202  indexed S1 (e.g., in a DL control portion of the slot  202 ). The DL control information  320  may indicate a DL multicast grant (e.g., multicast control information) for the UEs  315   a  and  315   b  in the multicast group  302 . The DL multicast grant may be for a multicast data transmission  322  in the same slot  202  indexed S1. For instance, the multicast grant may be transmitted in the form of a DCI format encoded with a multicast group ID so that UEs  315   a  and the UEs  315   b  in the multicast group  302  may identify that the multicast grant is destined for the multicast group  302 . After transmitting the DL control information  320 , the BS  305  transmits multicast data  322  in the slot  202  indexed S1 (e.g., in a DL data portion of the slot  202 ) according to the multicast grant. In some instances, the multicast data  322  can be transmitted in a different slot  202  than the DL control information  320  carrying the multicast control information. The BS  305  may apply HARQ techniques to the multicast data transmission  322 . 
     Upon detecting the multicast grant in the DL control information  320 , the UE  315   a  and the UE  315   b  may receive the multicast data transmission  322  according to the multicast grant. Upon receiving the multicast data  322 , the UEs  315   a  and the UE  315   b  may determine whether to feedback a reception status to the BS  305  and/or whether to feedback an ACK or a NACK to the BS  305 . For instance, the BS  305  may have configured the UEs  315   a  and  315   b  with multicast feedback resources and a multicast feedback mode prior to transmitting the multicast data  322 . The multicast resources may include a common NACK resource among the UEs  315  in the multicast group  302  and a UE-specific ACK/NACK resource for each of the UEs  315  in the multicast group  302  as will be discussed further below in  FIGS.  4  and  5   . The multicast feedback mode may include a NACK-only feedback mode  304  and a ACK/NACK feedback mode  306 . 
     In the illustrated example of  FIG.  3   , the BS  305  configures the UE  315   a  and  315   b  to begin with the NACK-only feedback mode  304 . In the NACK-only feedback mode  304 , a UE  315  may transmit a NACK feedback if the UE  315  fails to receive a multicast transmission, but may refrain from transmitting an ACK feedback if the UE  315  successfully receives the multicast transmission. As an example, the UE  315   a  fails to receive and decode the multicast data  322 . Thus, the UE  315   a  may transmit a NACK feedback  330  (e.g., a PUCCH signal) for the multicast data  322 , for example, in a UL control portion of the slot  202  indexed S5. On the other hand, the UE  315   b  may have successfully received and decoded the multicast data  322 , and thus may not transmit any feedback to the BS  305  (shown by the empty-filled box for the slot  202  indexed S5). In another scenario, the UE  315   b  may fail to receive the DL control information  320  for the multicast data  322 . For example, the UE  315   b  may temporarily power down the frontend due to a due to discontinuous transmission (DTX) operation, and thus may miss the detection of the PDCCH carrying the DL control information  320  and may not transmit any feedback to the BS  305 . In some instances, a multicast UE  315  may determine how to transmit a feedback for a multicast transmission based on a configuration (e.g., a PUCCH resource configuration) indicated by a corresponding multicast grant. For instance, the configuration may indicate a starting symbol, a number of symbols, a starting physical resource block (PRB), a number of PRBs, a PUCCH format, a cyclic shift, a frequency-hopping parameter, an orthogonal cover code (OCC) length and index, and/or a demodulation reference signal (DMRS) parameter. 
     Upon detecting the NACK feedback  330 , the BS  305  may schedule a retransmission of the multicast data  322 . For instance, the BS  305  may transmit DL control information  324  in the slot  202  indexed S8 indicating a DL multicast grant. The BS  305  may retransmit the multicast data  322  or its redundant version (RV) (shown as multicast data  326 ) in the slot  202  indexed S8. In some instances, the multicast data  326  can be transmitted in a different slot  202  than the DL control information  324  carrying the multicast control information. In some instances, the BS  305  may transmit the same coded version of multicast data in both the multicast data transmission  322  and the multicast data retransmission  326 . In some other instances, the BS  305  may transmit different coded versions of multicast data for the multicast data transmission  322  and the multicast data retransmission  326 . For instance, the multicast data transmission  322  may be transmitted with an RV of 0 and the multicast data retransmission  326  may be transmitted with an RV greater than 0. 
     In the illustrated example of  FIG.  3   , the BS  305  may switch the UEs  315   a  and  315   b  in the multicast group  302  from the NACK-only feedback mode  304  to the ACK/NACK feedback mode  306  (shown by the feedback mode switch  350 ) prior to the multicast data retransmission  326 . The BS  305  may indicate the feedback mode switch  350  via various mechanisms, for example, RRC signaling or DCI signaling. 
     In some aspects, the BS  305  may indicate the feedback mode switch  350  using a certain entry in a PUCCH resource configuration to indicate a NACK-only mode. For instance, the BS  305  may include an entry for the NACK-only mode and an entry for ACK/NACK mode in the PUCCH resource configuration and may switch the UEs  315  between the NACK-only mode and the ACK/NACK mode using DCI. Alternatively, the BS  305  may add a new flag to the PUCCH resource configuration to indicate the NACK-only mode or the ACK/NACK mode. For instance, the BS  305  may set the flag to a value of 1 to indicate the NACK-only or a value of 0 to indicate the ACK/NACK mode. 
     In some aspects, the BS  305  may indicate the feedback mode switch  350  using existing fields in DCI (e.g., the DL control information  320  and/or  324 ), such as a redundancy version (RV) (RV=0 for initial transmission and RV=1, 2, 3 for retransmission assuming a maximum of 4 transmissions for multicast), and/or a new data indicator (NDI) (NDI=1 for an initial transmission). For instance, the ACK/NACK mode may be used for an initial transmission (when RV=0 and/or NDI=1) and the NACK-only mode may be used for a subsequent retransmission (when RV=1, 2, or 3). In some other instances, the BS  305  may configure the UEs  315   a  and/or  315   b  with some preconfigured feedback mode switching rules, for example, the ACK/NACK mode may be used for the first and second transmissions and the NACK-only mode may be used for subsequent retransmissions. 
     Upon receiving the multicast data retransmission  326 , the UEs  315   a  and  315   b  may utilize the ACK/NACK feedback mode  306  to feedback a reception status of the multicast data retransmission  326  to the BS  305 . In the ACK/NACK feedback mode  306 , a UE  315  may transmit a NACK feedback if the UE  315  fails to receive a multicast transmission or an ACK feedback if the UE  315  successfully receives the multicast transmission. As an example, the UE  315   a  fails to receive and decode the multicast data  326 . Thus, the UE  315   a  may transmit a NACK feedback  332  (e.g., a PUCCH signal) for the multicast data  326 , for example, in a UL control portion of the slot  202  indexed S11. On the other hand, the UE  315   b  successfully received and decoded the multicast data  326 , and thus may transmit an ACK feedback  340  (e.g., a PUCCH signal), for example, in a UL control portion of the slot  202  indexed S11. 
     Alternatively, for sake of power saving, if UE  315   b  received the initial transmission (e.g., multicast data  322 ) correctly, the UE  315   b  may skip detecting the retransmission (e.g., multicast data  326 ) and may not report PUCCH ACK/NACK configured for the retransmission. For the UE who may have missed the PDCCH (e.g., the DL control information  320 ) of the initial transmission, but received the PDCCH (e.g., the DL control information  324 ) of the retransmission, the UE can report ACK/NACK based on the detection of PDSCH multicast retransmission. In some aspects, the NACK feedback  330 , the NACK feedback  332 , and/or the ACK feedback  340  may be represented using PUCCH format 0. 
     As discussed above, the BS  305  may configure the UEs  315   a  and  315   b  in the multicast group  302  with various multicast feedback resources. For instance, the BS  305  may configure the UEs  315   a  and  315   b  in the multicast group  302  to use a common resource for NACK-only transmissions when the UEs  315   a  and  315   b  operate in the NACK-only mode  304  and may configure each UE  315   a ,  315   b  in the multicast group  302  with a UE-specific resource for ACK/NACK transmissions when the UEs  315   a  and  315   b  operate in the ACK/NACK feedback mode  306  as shown in  FIG.  4   . Alternatively, the BS  305  may configure the UEs  315   a  and  315   b  in the multicast group  302  with the same time-frequency resource and apply CDM to multiplex group NACK transmissions and UE-specific ACK/NACK transmissions as shown in  FIG.  5   . 
       FIGS.  4  and  5    are discussed in relation to  FIG.  3    to illustrate the configuration and usage of multicast feedback resources. In the context of NR, multicast feedbacks are carried by PUCCH, and thus the multicast feedback resources may also be referred to as PUCCH resources. 
       FIG.  4    illustrates a multicast feedback resource configuration scheme  400  according to some aspects of the present disclosure. The scheme  400  may be employed by BSs such as the BSs  105  and  305  and UEs such as the UEs  115  and  315  in a network such as the networks  100  and  200 . In particular, the BS  305  may configure the UEs  315  in the multicast group  302  to use different resources for NACK-only feedbacks (e.g., the NACK feedbacks  330 ) and ACK/NACK feedbacks (e.g., the NACK feedback  332  and ACK feedback  340 ) as shown in the scheme  400 . In  FIG.  4   , the x-axis represents time in some arbitrary units, and the y-axis represents frequency in some arbitrary units. Additionally, the scheme  400  is described using the same slot structure as in the radio frame structure  200 , and may use the same reference numerals as in  FIG.  2    for simplicity&#39;s sake. 
     In the scheme  400 , the BS  305  may configure all UEs  315  (the UE  315   a  and the UE  315   b ) in the multicast group  302  with a common resource configuration (e.g., a PUCCH resource configuration) for NACK-only feedback operations. For instance, the common resource configuration may indicate a common NACK resource  410  within a slot  202   m . The common resource configuration may indicate a starting symbol index  412  (e.g., the symbols  206 ) within a slot  202   m , a number of symbols  414 , a starting RB index  416  (e.g., the RBs  210 ), and a number of RBs  418  for the common NACK resource  410 . Additionally, the common resource configuration may indicate a common sequence configuration (e.g., a scrambling code and/or a cyclic-shift) for generating a sequence to indicate a NACK feedback. In some instances, the scrambling code may correspond to a group UE ID for the multicast group  302 . The common NACK resource  410  and/or the common sequence configuration are shared by all UEs  315  in the multicast group  302  for transmitting NACK-only feedbacks. 
     The BS  305  may configure each UE  315   a ,  315   b  with a UE-specific resource configuration for ACK/NACK feedback operations. For instance, the BS  305  may configure the UE  315   a  with a UE-specific resource configuration indicating a resource  422  designated to the UE  315   a  for ACK/NACK feedbacks. Similar to the common resource configuration, the UE-specific resource configuration may indicate a starting symbol index, a number of symbols, a starting RB index, and/or a number of RBs for the resource  422 . Additionally, the UE-specific resource configuration may indicate a sequence configuration (e.g., scrambling code and/or a cyclic-shift) for the UE  315   a  to generate a signal sequence or waveform sequence to represent a NACK and/or a signal sequence or waveform sequence to represent an ACK. In some aspects, the signal sequence can be a PUCCH format 0 sequence. 
     Similarly, the BS  305  may configure the UE  315   b  with a UE-specific resource configuration indicating a resource  424  designated to the UE  315   b  for ACK/NACK feedbacks. The UE-specific resource configuration may indicate a starting symbol index, a number of symbols, a starting RB index, and/or a number of RBs for the resource  424 . Additionally, the UE-specific resource configuration may indicate a sequence configuration (e.g., scrambling code and/or a cyclic-shift) for the UE  315   b  to generate a signal sequence or waveform sequence to represent a NACK and/or a signal sequence or waveform sequence to represent an ACK. 
     Referring to the example shown in  FIG.  3   , the UE  315   a  may transmit the NACK feedback  330  (when operating in the NACK-only feedback mode  304 ) in a resource within the slot  202  indexed S5 based on the common resource configuration. For instance, if the common NACK resource  410  occupies 2 symbols beginning at symbol index 2 and occupies 2 RBs beginning at RB index 1 within the slot  202   m , the UE  315   a  may transmit the NACK feedback  330  in a resource within the slot  202  indexed S5, where the resource may occupy 2 symbols beginning at symbol index 2 and 2 RBs beginning at RB index 1 within the slot  202  indexed S5. Similarly, the UE  315   a  may transmit the NACK feedback  332  (when operating in the ACK/NACK feedback mode  306 ) in a resource within the slot  202  indexed S11 based on the configuration for the UE-specific ACK/NACK resource  422  designated to the UE  315   a . For instance, if the UE-specific ACK/NACK resource  422  occupies 2 symbols beginning at symbol index 4 and occupies 2 RBs beginning at RB index 10 within the slot  202   m , the UE  315   a  may transmit the NACK feedback  332  in a resource within the slot  202  indexed S11, where the resource may occupy 2 symbols beginning at symbol index 4 and 2 RBs beginning at RB index 10 within the slot  202  indexed S11. 
     In some aspects, the BS  305  may indicate the common resource configuration for the common NACK resource  410  to the UE  315   a  and/or the UE  315   b  via RRC signaling (e.g., in a SIB) and/or UE-specific signaling. The BS  305  may indicate the configuration for the UE-specific ACK/NACK resource  422  to the UE  315   a  and/or the configuration for the UE-specific ACK/NACK resource  424  to the UE  315   b  via UE-specific signaling. 
     While  FIG.  4    is illustrates a single common resource  410  for the multicast group  302 , a single UE-specific ACK/NACK resource  422  for the UE  315   a , and a single UE-specific ACK/NACK resource  424  for the UE  315   b , the scheme  400  may allocate a PUCCH resource for each code block group (CBG) or each TB, where each PUCCH resource may include a time-frequency resource and associated cyclic-shift and/or sequence generation parameter(s). In other words, the BS  305  may configure a multicast UE  315  with a set of common PUCCH resources for per CBG or per TB NACK-only feedbacks and a set of UE-specific PUCCH resources foe per CBG per TB ACK/NACK feedbacks. 
       FIG.  5    illustrates a multicast feedback resource configuration scheme  500  according to some aspects of the present disclosure. The scheme  500  may be employed by BSs such as the BSs  105  and UEs such as the UEs  115  in a network such as the network  100 . In particular, the BS  305  may configure the UEs  315  in the multicast group  302  with the same time-frequency resource for NACK-only feedbacks (e.g., the NACK feedback  330 ) and for UE-specific ACK/NACK feedbacks (e.g., the NACK feedback  332  and the ACK feedback  340 ) and may apply CDM to multiplex the common group NACK-only feedbacks and UE-specific ACK/NACK feedbacks as shown in the scheme  500 . In  FIG.  5   , the x-axis represents time in some arbitrary units, and the y-axis represents frequency in some arbitrary units. Additionally, the scheme  500  is described using the same slot structure as in the radio frame structure  200 , and may use the same reference numerals as in  FIG.  2    for simplicity&#39;s sake. 
     In the scheme  500 , the BS  305  may configure all UEs  315  (the UE  315   a  and the UE  315   b ) in the multicast group  302  with a multicast feedback resource configuration indicating a resource  510  (or a set of resources) for NACK-only feedbacks when operating in the NACK-only feedback mode  304  or ACK/NACK feedbacks when operating in the ACK/NACK feedback mode  306 . For instance, the multicast feedback resource configuration may indicate a starting symbol index within a slot  202   m , a number of symbols, a starting RB index, a number of RBs for a resource  510 . The BS  305  may apply CDM  530  (e.g., with symbol repetitions in time) to multiplex NACK-only transmissions (e.g., the NACK feedback  330 ) from the UEs  315  operating in the NACK-only feedback mode  304  and UE-specific ACK/NACK transmissions (e.g., the NACK feedback  332  and the ACK feedback  340 ) from the UEs  315  operating in the ACK/NACK feedback mode  306 . The BS  305  may configure all the UEs  315  with a common code for NACK-only feedbacks and may configure each UE  315  with a UE-specific code for ACK/NACK feedbacks. For instance, the BS  305  may configure all the UEs  315  (e.g., the UEs  315   a  and  315   b ) in the multicast group  302  with a common code  520  for NACK-only feedbacks. The BS  305  may configure the UE  315   a  with a code  522  for UE-specific ACK/NACK feedbacks and may configure the UE  315   b  with a code  524  for UE-specific ACK/NACK feedbacks. In some instances, the codes  520 ,  522 , and  524  may be orthogonal cover code (OCC) so that the BS  305  may differentiate the different feedback transmissions from the different UEs  315  in the resource  510 . Alternatively, the UE-specific ACK or the UE-specific NACK may be assigned with the same OCC, but with different cyclic shifts so that the BS  305  may differentiate between an ACK sequence and a NACK sequence. 
     Referring to the example shown in  FIG.  3   , the UE  315   a  may transmit the NACK feedback  330  (when operating in the NACK-only feedback mode  304 ) in a resource within the slot  202  indexed S5 based on the configuration for the resource  510  and the code  520 . For instance, if the resource  510  occupies 4 symbols beginning at symbol index 2 and occupies 2 RBs beginning at RB index 1 within the slot  202   m , the resource where the NACK feedback  330  is transmitted may occupy 4 symbols beginning at symbol index 2 and 2 RBs beginning at RB index 1 within the slot  202  indexed S5. Additionally, the UE  315   a  may apply symbol repetitions (e.g., about 4) and the code  520  across the symbol repetitions. The BS  305  may monitor for a feedback in the slot  202  indexed S5 based on configuration for the resource  510 , and the codes  520 ,  522 , and  524 . The BS  305  may detect the NACK feedback  330  from the UE  315   a , for example, by applying the code  520  to a signal received in the slot  202  indexed S5. 
     Similarly, the UE  315   a  may transmit the NACK feedback  332  in a resource occupying 4 symbols beginning at symbol index 2 and 2 RBs beginning at RB index 1 within the slot  202  indexed S11 and may apply symbol repetitions (e.g., about 4) and the code  522  across the symbol repetitions. The UE  315   a  may transmit the ACK feedback  340  in the same resource as the NACK feedback  332 , but may apply symbol repetitions (e.g., about 4) and the code  524  across the symbol repetitions. The BS  305  may monitor for a feedback in the slot  202  indexed S11 based on configuration for the resource  510 , and the codes  520 ,  522 , and  524 . The BS  305  may detect the NACK feedback  332  from the UE  315   a , for example, by applying the code  522  to a signal received in the slot  202  indexed S11 and may detect the ACK feedback  340  from the UE  315   b , for example, by applying the code  524  to the received signal. 
     In some aspects, the BS  305  may indicate the resource configuration for the resource  510  and/or the common code  520  to the UE  315   a  and/or the UE  315   b  via RRC signaling (e.g., in a SIB) and/or UE-specific signaling. In some aspects, the BS  305  may indicate UE-specific code  522  to the UE  315   a  and/or the UE-specific code  524  to the UE  315   b  via DCI (e.g., the DCI  320  and/or  324  via an ACK/NACK resource indicator (ARI)) as will be discussed further below. Additionally, the BS  305  may indicate a power control configuration (e.g., a PUCCH power control configuration) for the transmission of a NACK-only feedback and/or a ACK/NACK feedback. For instance, the NACK-only feedback and the ACK/NACK feedback may use different, separate power control procedures. For example, a power control for the NACK-only feedback may include a first target received power (at a BS) and a first pathloss compensation coefficient and a power control for the ACK/NACK feedback may include a second target received power (at a BS) and a second pathloss compensation coefficient, where the first target received power is different than the second target received power and the first pathloss compensation coefficient is different than the second pathloss compensation coefficient. By using orthogonal PUCCH resources for a NACK-only feedback and for an ACK/NACK feedback, different target received powers may not impact the reception of each PUCCH feedback. 
     While  FIG.  5    illustrates a single resource  510 , the scheme  500  may allocate a PUCCH resource for each code block group (CBG) or each TB, where each PUCCH resource may include a time-frequency resource and associated cyclic-shift and/or sequence generation parameter(s). In other words, the BS  305  may configure a multicast UE  315  with a set of PUCCH resources for per CBG or per TB NACK-only feedbacks and/or per CBG or per TB UE-specific ACK/NACK feedbacks. 
     In some aspects, the BS  305  may configure the UEs  315  in the multicast group  302  to switch between the NACK-only feedback mode  304  and the ACK/NACK feedback  306  based on certain rules, conditions, or restrictions. In some aspects, the BS  305  may configure the UE  315  to select between the NACK-only feedback mode  304  or the ACK/NACK feedback mode  306  based on a DL multicast decoding status. For instance, the BS  305  may configure the UEs  315  to utilize the NACK-only feedback mode when feeding back a reception status for an initial transmission and utilize the ACK/NACK feedback mode when feeding back a reception status for a retransmission. In some instances, the BS  305  may configure the UEs  315  to utilize the NACK-only feedback mode when the number of failed receptions is below a threshold and utilize the ACK/NACK feedback mode when the number of failed receptions is above a threshold. 
     In some aspects, the BS  305  may configure the UE  315  to select between the NACK-only feedback mode  304  or the ACK/NACK feedback mode  306  based on a channel characteristic or measurement over a channel between the UE  315  and the BS  305 . For instance, the UE  315  may perform measurements in the channel. If the channel measurement satisfies a certain threshold, the UE  315  may utilize the NACK-only feedback mode  304 . If the channel measurement does not satisfy the threshold, the UE  315  may utilize the ACK/NACK feedback mode  306 . In some aspects, the channel measurement may be a pathloss. In some aspects, the channel measurement may be a RSRP. In some aspects, the channel measurement may be a SINR. In some instances, the UE  315  may estimate, determine, or calculate the SINR from a DMRS received from the BS  305 . In some instances, the UE  315  may estimate, determine, or calculate the SINR from a configured CSI-RS for the multicast. In some aspects, the channel measurement may be a CQI. In some aspects, the rules or restrictions may include a pathloss threshold, a SINR threshold, a RSRP threshold, or a CQI threshold, or combinations thereof. 
       FIG.  6    illustrates a multicast feedback scenario  600  according to some aspects of the present disclosure. The scenario  600  may correspond to a multicast feedback scenario in the network  100 . In the scenario  600 , a BS  605  may serve multicast data to UEs  615   a  and UEs  615   b  belonging to a multicast group (e.g., the multicast group  302 ). The BS  605  may be substantially similar to the BSs  105  and/or  305 . The UEs  615  may be substantially similar to the UEs  115  and/or  315 . The UEs  615   a  may be located at a region near the BS  605  (shown by the inner circle  630 ). The UEs  615   b  may be located at region farther away from the BS  605  (shown by the outer circle  620 ). The channel condition between the UEs  615   a  and the BS  605  may be good (e.g., a high SINR). For instance, each of the UEs  615   a  may have a SINR greater than a certain threshold. The channel condition between the UEs  615   b  and the BS  605  may be bad (e.g., a low SINR). For instance, each of the UEs  615   b  may have a SINR below the threshold. 
     In the scenario  600 , the BS  605  may configure the UEs  615   a  (in the inner circle  630 ) with the high SINRs to utilize the UE-specific ACK/NACK feedback mode  306  and may configure the UEs  615   b  (in the outer circle  620 ) with the low SINRs to utilize the NACK-only feedback mode  304 . Since each UE  615   a  may transmit an ACK or a NACK using UE-specific resources and the channel condition is good, the BS  605  may estimate accurate CSI from the ACK/NACK feedbacks and may utilize the estimated CSI for retransmission (e.g., for beamforming to the UEs  615   a  and  615   b ). Since the channel conditions for the UEs  615   b  are poor, the BS  605  may be unable to estimate accurate or useful CSI from signals received from the UEs  615   b . Thus, as long as the BS  605  receives a NACK from the UE  615   b , the BS  605  may retransmit a multicast transmission. 
     In some other aspects, the BS  605  may configure the UEs  615   a  (in the inner circle  630 ) with the high SINRs to utilize the NACK-only feedback mode  304  and may configure the UEs  615   b  (in the outer circle  620 ) with the low SINRs to utilize the UE-specific ACK/NACK feedback mode  306 . Such a configuration may allow the BS  605  to be aware of which of the UEs  615   b  may have failed to receive a multicast transmission from the BS  605 , and thus the BS  605  can retransmit the multicast, for example, with certain beamforming to better serve a retransmission to the UE  615   b  with the failed reception. 
     In some aspects, the BS  605  may define a rule to disable a UE to use the PUCCH resource (e.g., the resource  510 ) that is configured for NACK-only and ACK/NACK switching. For example, the BS  605  may indicate a RSRP threshold (via RRC signaling) and a cell-edge UE (e.g., a UE  615   b  (in the outer circle  620 )) who has a low RSRP (e.g., less than a certain RSRP threshold) may not use the PUCCH resource configured for NACK-only and ACK/NACK switching. An example is that the UE may send a request for a handover due to the low RSRP measured from the serving cell and the BS  605  may configure the cell edge UE to utilize the UE-specific PUCCH resource for ACK/NACK feedback so that the BS  605  may know which data packet the cell-edge UE had failed to receive, and thus may forward the failed data packet to the target cell for the handover. This PUCCH resource may not be multiplexed with the PUCCH resource for flexible switching between different feedback mode. 
       FIG.  7    is a block diagram of an exemplary UE  700  according to some aspects of the present disclosure. The UE  700  may be a UE  115  discussed above in  FIG.  1   , a UE  315  discussed above in  FIG.  3   , or a UE  615  discussed above in  FIG.  6   . As shown, the UE  700  may include a processor  702 , a memory  704 , a multicast feedback module  708 , a transceiver  710  including a modem subsystem  712  and a radio frequency (RF) unit  714 , and one or more antennas  716 . These elements may be coupled with one another. The term “coupled” may refer to directly or indirectly coupled or connected to one or more intervening elements. For instance, these elements may be in direct or indirect communication with each other, for example via one or more buses. 
     The processor  702  may include a central processing unit (CPU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), a controller, a field programmable gate array (FPGA) device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor  702  may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The memory  704  may include a cache memory (e.g., a cache memory of the processor  702 ), random access memory (RAM), magnetoresistive RAM (MRAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), flash memory, solid state memory device, hard disk drives, other forms of volatile and non-volatile memory, or a combination of different types of memory. In an aspect, the memory  704  includes a non-transitory computer-readable medium. The memory  704  may store, or have recorded thereon, instructions  706 . The instructions  706  may include instructions that, when executed by the processor  702 , cause the processor  702  to perform the operations described herein with reference to the UEs  115  in connection with aspects of the present disclosure, for example, aspects of  FIGS.  1 - 6  and  9 - 10   . Instructions  706  may also be referred to as program code. The program code may be for causing a wireless communication device to perform these operations, for example by causing one or more processors (such as processor  702 ) to control or command the wireless communication device to do so. The terms “instructions” and “code” should be interpreted broadly to include any type of computer-readable statement(s). For example, the terms “instructions” and “code” may refer to one or more programs, routines, sub-routines, functions, procedures, etc. “Instructions” and “code” may include a single computer-readable statement or many computer-readable statements. 
     The multicast feedback module  708  may be implemented via hardware, software, or combinations thereof. For example, the multicast feedback module  708  may be implemented as a processor, circuit, and/or instructions  706  stored in the memory  704  and executed by the processor  702 . In some instances, the multicast feedback module  708  can be integrated within the modem subsystem  712 . For example, the multicast feedback module  708  can be implemented by a combination of software components (e.g., executed by a DSP or a general processor) and hardware components (e.g., logic gates and circuitry) within the modem subsystem  712 . 
     The multicast feedback module  708  may be used for various aspects of the present disclosure, for example, aspects of  FIGS.  1 - 6  and  9 - 10   . For instance, the multicast feedback module  708  is configured to configure receive, from a BS (e.g., the BSs  105 ,  305 , and/or  605 ) a multicast feedback configuration for a multicast group that the UE  700  is subscribed to. The multicast feedback configuration may indicate a first resource configuration for a NACK feedback mode and a second resource configuration for an ACK/NACK feedback mode. The first resource configuration may be a common NACK resource configuration among all UEs in a multicast group including the UE  700  (for NACK-only feedbacks). The second resource configuration may be a UE-specific ACK/NACK resource configuration designated to the UE  700  (for ACK/NACK feedbacks). In some aspects, the multicast feedback module  708  is configured to receive a first multicast communication from the BS, transmit a NACK feedback for the first multicast communication to the BS using the first resource configuration (upon failing to decode the first multicast communication), receive a second multicast communication from the BS, and transmit an ACK feedback or a NACK feedback for the second multicast communication to the BS using the second resource configuration. 
     In some aspects, the multicast feedback module  708  is configured to receive, from the BS, an instruction to switch from one of the the NACK-only feedback mode or the ACK/NACK feedback mode to the other one of the NACK-only feedback mode or the ACK/NACK feedback mode. For instance, the multicast feedback module  708  may switch from using the first resource configuration for transmitting the NACK feedback for the first multicast communication to using the second resource configuration for transmitting the ACK feedback or the NACK feedback for the second multicast communication in response to the instruction. 
     In some aspects, the multicast feedback configuration includes rules for switching between the NACK-only feedback mode and the ACK/NACK feedback mode. The rules can be based on channel measurements and/or UE decoding status. For instance, the rules can include a pathloss threshold, a SINR threshold, a RSRP threshold, a CQI threshold, or combinations thereof. In some instances, the multicast feedback module  708  may select the first resource configuration for transmitting the NACK feedback for the first multicast communication based on the rules and/or select the second resource configuration for transmitting the ACK feedback or the NACK feedback for the second multicast communication based on the rules. 
     In some aspects, the multicast feedback configuration includes a periodicity for switching between the NACK-only feedback mode and the ACK/NACK feedback mode. In some instances, the multicast feedback configuration may restrict the UE  700  to switch a feedback mode at the boundary of the periodicity if the UE  700  decides to switch the feedback mode. Thus, the multicast feedback module  708  may switch from one of the ACK/NACK feedback mode or the NACK-only feedback mode to the other one of the ACK/NACK feedback mode or NACK-only feedback mode at boundary of the periodicity. In some other instances, the multicast feedback configuration may allow the first UE to switch at any time. In some instances, the multicast feedback configuration may request the first UE not to notify the BS of a feedback mode switch. In some instances, the multicast feedback configuration may request the UE  700  to notify the BS of a feedback mode switch. Thus, the multicast feedback module  708  may transmit an indication to the BS after a feedback mode switch. In some instances, the multicast feedback module  708  may transmit, to the BS, a request to switch from one of the ACK/NACK feedback mode or the NACK-only feedback mode to the other one of the ACK/NACK feedback mode or NACK-only feedback mode. The request can be in the form of a scheduling request, a RSRP report, and/or a CSI report. 
     In some aspects, the first resource configuration may include at least one of a different time configuration, a different frequency configuration, or a different sequence configuration than the second resource configuration. In some other aspects, the first resource configuration and the second resource configuration may include the same time configuration and the same frequency configuration. The multicast feedback module  708  may receive, from the BS, an OCC a NACK-only transmission or an OCC for a ACK/NACK transmission. Mechanisms for multicast feedback with feedback mode switching are described in greater detail herein. 
     As shown, the transceiver  710  may include the modem subsystem  712  and the RF unit  714 . The transceiver  710  can be configured to communicate bi-directionally with other devices, such as the BSs  105 . The modem subsystem  712  may be configured to modulate and/or encode the data from the memory  704  and/or the multicast feedback module  708  according to a modulation and coding scheme (MCS), e.g., a low-density parity check (LDPC) coding scheme, a turbo coding scheme, a convolutional coding scheme, a polar coding scheme, a digital beamforming scheme, etc. The RF unit  714  may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc.) modulated/encoded data (e.g., multicast ACK/NACK feedbacks, multicast group NACKs, multicast feedback mode switch notification, multicast feedback mode switch request, CSI reports, RSRP reports, scheduling requests) from the modem subsystem  712  (on outbound transmissions) or of transmissions originating from another source such as a UE  115  or a BS  105 . The RF unit  714  may be further configured to perform analog beamforming in conjunction with the digital beamforming. Although shown as integrated together in transceiver  710 , the modem subsystem  712  and the RF unit  714  may be separate devices that are coupled together at the UE  115  to enable the UE  115  to communicate with other devices. 
     The RF unit  714  may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information), to the antennas  716  for transmission to one or more other devices. The antennas  716  may further receive data messages transmitted from other devices. The antennas  716  may provide the received data messages for processing and/or demodulation at the transceiver  710 . The transceiver  710  may provide the demodulated and decoded data (e.g., multicast feedback configuration, multicast feedback resource configurations, multicast communications, multicast feedback mode switching instruction and/or rules) to the multicast feedback module  708  for processing. The antennas  716  may include multiple antennas of similar or different designs in order to sustain multiple transmission links. The RF unit  714  may configure the antennas  716 . 
     In an aspect, the UE  700  can include multiple transceivers  710  implementing different RATs (e.g., NR and LTE). In an aspect, the UE  700  can include a single transceiver  710  implementing multiple RATs (e.g., NR and LTE). In an aspect, the transceiver  710  can include various components, where different combinations of components can implement different RATs. 
       FIG.  8    is a block diagram of an exemplary BS  800  according to some aspects of the present disclosure. The BS  800  may be a BS  105  in the network  100  as discussed above in  FIG.  1   , a BS  305  discussed above in  FIG.  3   , or a BS  605  discussed above in  FIG.  6   . As shown, the BS  800  may include a processor  802 , a memory  804 , a multicast feedback module  808 , a transceiver  810  including a modem subsystem  812  and a RF unit  814 , and one or more antennas  816 . These elements may be coupled with one another. The term “coupled” may refer to directly or indirectly coupled or connected to one or more intervening elements. For instance, these elements may be in direct or indirect communication with each other, for example via one or more buses. 
     The processor  802  may have various features as a specific-type processor. For example, these may include a CPU, a DSP, an ASIC, a controller, a FPGA device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor  802  may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The memory  804  may include a cache memory (e.g., a cache memory of the processor  802 ), RAM, MRAM, ROM, PROM, EPROM, EEPROM, flash memory, a solid state memory device, one or more hard disk drives, memristor-based arrays, other forms of volatile and non-volatile memory, or a combination of different types of memory. In some aspects, the memory  804  may include a non-transitory computer-readable medium. The memory  804  may store instructions  806 . The instructions  806  may include instructions that, when executed by the processor  802 , cause the processor  802  to perform operations described herein, for example, aspects of  FIGS.  1 - 3  and  6 - 15   . Instructions  806  may also be referred to as code, which may be interpreted broadly to include any type of computer-readable statement(s) as discussed above with respect to  FIG.  7   . 
     The multicast feedback module  808  may be implemented via hardware, software, or combinations thereof. For example, the multicast feedback module  808  may be implemented as a processor, circuit, and/or instructions  806  stored in the memory  804  and executed by the processor  802 . In some instances, the multicast feedback module  808  can be integrated within the modem subsystem  812 . For example, the multicast feedback module  808  can be implemented by a combination of software components (e.g., executed by a DSP or a general processor) and hardware components (e.g., logic gates and circuitry) within the modem subsystem  812 . 
     The multicast feedback module  808  may be used for various aspects of the present disclosure, for example, aspects of  FIGS.  1 - 6 ,  9 , and  11   . For instance, the multicast feedback module  808  is configured to configure each UE (e.g., the UEs  115 ,  315 , and/or  615 ) in a multicast group (e.g., the multicast group  302 ) with a multicast feedback configuration. The multicast feedback configuration may indicate a first resource configuration for a NACK feedback mode and a second resource configuration for an ACK/NACK feedback mode. The first resource configuration may be a common NACK resource configuration among all UEs in the multicast group (for NACK-only feedbacks). The second resource configuration may be a UE-specific ACK/NACK resource configuration designated to the respective UE (for ACK/NACK feedbacks). In some aspects, the multicast feedback module  808  is configured to transmit a first multicast communication to the group of UEs, receive a NACK feedback for the first multicast communication from one or more UEs of the group of UEs based on the first resource configuration, transmit a second multicast communication to the group of UEs, and receive an ACK feedback or a NACK feedback for the second multicast communication from a first UE of the one or more UEs based on the second resource configuration. 
     In some aspects, the multicast feedback module  808  is configured to transmit, to the first UE, an instruction to switch from one of the NACK feedback mode or the ACK/NACK feedback mode to the other one of the NACK feedback mode or the ACK/NACK feedback mode. 
     In some aspects, the multicast feedback module  808  is configured to include rules in the multicast feedback configuration for the first UE to select between the NACK feedback mode and the ACK/NACK feedback mode. The rules can be based on channel measurements and/or UE decoding status. In some instances, the rules can include a pathloss threshold, a SINR threshold, a RSRP threshold, a CQI threshold, or combinations thereof. 
     In some aspects, the multicast feedback module  808  is configured to include a switching periodicity in the multicast feedback configuration. In some instances, the multicast feedback configuration may restrict the first UE to switch a feedback mode at the boundary of the periodicity if the first UE decides to switch the feedback mode. In some other instances, the multicast feedback configuration may allow the first UE to switch at any time. In some instances, the multicast feedback configuration may request the first UE to notify the BS  800  of a feedback mode switch. In some instances, the multicast feedback configuration may request the first UE not to notify the BS  800  of a feedback mode switch. In some instances the multicast feedback module  808  is configured to receive a request from the first UE to switch from one of the ACK/NACK feedback mode or the NACK feedback mode to the other one of the ACK/NACK feedback mode or the NACK feedback mode. The request can be in the form of a scheduling request, a RSRP report, and/or a CSI report. 
     In some aspects, the first resource configuration may include at least one of a different time configuration, a different frequency configuration, or a different sequence configuration than the second resource configuration. In some other aspects, the first resource configuration and the second resource configuration may include the same time configuration and the same frequency configuration and the multicast feedback module  808  is configured to apply code-division-multiplexing (CDM) to multiplex NACK feedbacks from UEs operating in the NACK-only feedback mode and ACK/NACK feedbacks from UEs operating in the ACK/NACK feedback mode. Mechanisms for multicast feedback with feedback mode switching are described in greater detail herein. 
     As shown, the transceiver  810  may include the modem subsystem  812  and the RF unit  814 . The transceiver  810  can be configured to communicate bi-directionally with other devices, such as the UEs  115  and/or  700  and/or another core network element. The modem subsystem  812  may be configured to modulate and/or encode data according to a MCS, e.g., a LDPC coding scheme, a turbo coding scheme, a convolutional coding scheme, a polar coding scheme, a digital beamforming scheme, etc. The RF unit  814  may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc.) modulated/encoded data (e.g., multicast feedback configuration, multicast feedback resource configurations, multicast communications, multicast feedback mode switching instruction and/or rules) from the modem subsystem  812  (on outbound transmissions) or of transmissions originating from another source such as a UE  115  and/or UE  700 . The RF unit  814  may be further configured to perform analog beamforming in conjunction with the digital beamforming. Although shown as integrated together in transceiver  810 , the modem subsystem  812  and/or the RF unit  814  may be separate devices that are coupled together at the BS  105  to enable the BS  105  to communicate with other devices. 
     The RF unit  814  may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information), to the antennas  816  for transmission to one or more other devices. This may include, for example, transmission of information to complete attachment to a network and communication with a camped UE  115  or  700  according to some aspects of the present disclosure. The antennas  816  may further receive data messages transmitted from other devices and provide the received data messages for processing and/or demodulation at the transceiver  810 . The transceiver  810  may provide the demodulated and decoded data (e.g., multicast ACK/NACK feedbacks, multicast group NACKs, multicast feedback mode switch notification, multicast feedback mode switch request, CSI reports, RSRP reports, scheduling requests) to the multicast feedback module  808  for processing. The antennas  816  may include multiple antennas of similar or different designs in order to sustain multiple transmission links. 
     In an aspect, the BS  800  can include multiple transceivers  810  implementing different RATs (e.g., NR and LTE). In an aspect, the BS  800  can include a single transceiver  810  implementing multiple RATs (e.g., NR and LTE). In an aspect, the transceiver  810  can include various components, where different combinations of components can implement different RATs. 
       FIG.  9    is a signaling diagram of a multicast communication method  900  with feedback mode switching according to some aspects of the present disclosure. The method  900  may be implemented between a BS (e.g., BSs  105 ,  305 ,  605 , and/or  800 ) and two UEs (e.g., UEs  115 ,  315 ,  615 , and/or  700 ) shown as a UE A and a UE B. The UE A and the UE B may belong to a multicast group (e.g., the multicast group  302 ). The BS may utilize one or more components, such as the processor  802 , the memory  804 , the multicast feedback module  808 , the transceiver  810 , the modem  812 , and the one or more antennas  816 , to implement aspects of the method  900 . Each of the UE A and the UE B may utilize one or more components, such as the processor  702 , the memory  704 , the multicast feedback module  708 , the transceiver  710 , the modem  712 , and the one or more antennas  716 , to implement aspects of the method  900 . The method  900  may employ similar mechanisms as in the schemes  300 ,  400 , and  500  described above with respect to  FIGS.  3 ,  4   , and  5 , respectively. As illustrated, the method  900  includes a number of enumerated steps, but aspects of the method  900  may include additional steps before, after, and in between the enumerated steps. In some aspects, one or more of the enumerated steps may be omitted or performed in a different order. 
     At action  910 , the BS transmits a multicast feedback configuration to the UE A and the UE B. The multicast feedback configuration may indicate a first resource configuration for a NACK-only feedback mode (e.g., the NACK-only feedback mode  304 ). The first resource configuration may be a common NACK resource configuration among UEs in the multicast group including the UE A and the UE B. The multicast feedback configuration may indicate a second resource configuration for an ACK/NACK feedback mode (e.g., the ACK/NACK feedback mode  306 ). The second resource configuration may be a UE-specific ACK/NACK resource configuration designated to the UE A. The multicast feedback configuration may also indicate a third resource configuration for an ACK/NACK feedback mode. The third resource configuration may be a UE-specific ACK/NACK resource configuration designated to the UE B. The BS may configure the UE A and the UE B to begin with the NACK-only feedback mode. 
     In some aspects, the BS may transmit the first resource configuration via RRC signaling (e.g., in a SIB). The BS may transmit the second resource configuration to the UE A and the third resource configuration to the UE B via RRC signaling or UE-specific signaling. In some aspects, the first resource configuration, the second resource configuration, and the third resource configuration may indicate different time and/or frequency resources (e.g., the resources  410 ,  422 , and  424  discussed above in the scheme  400  with reference to  FIG.  4   ) and/or different sequence parameters. In some aspects, the first resource configuration, the second resource configuration, and the third resource configuration may indicate the same time-frequency resource (e.g., the resource  510  discussed above in the scheme  500  with reference to  FIG.  5   ), but different CDM codes (e.g., OCCs). In some aspects, the multicast feedback configuration may indicate various rules and/or thresholds (e.g., pathloss threshold, SINR threshold, RSRP threshold, and/or CQI threshold) for switching between the ACK/NACK feedback mode and the NACK-only feedback mode as discussed above with reference to  FIGS.  5  and  6   . 
     In some aspects, the BS may configure each of the UE A and the UE B in one of three feedback modes. For instance, the first mode may correspond to the NACK-only feedback mode and may include an indication of a common NACK-only resource among the group, the second mode may correspond to the ACK/NACK feedback mode and a UE-specific ACK/NACK resource, and the third mode may be a flexible mode with the ACK/NACK feedback mode and the NACK-only feedback mode and may include a time-frequency resource that can be used for a NACK-only transmission or an ACK/NACK transmission. The third mode may include different OCCs for the different NACK-only transmission and the ACK/NACK transmission. In some aspects, the BS may utilize a RRC configuration message with 2 bits indicate one of the three modes. For instance, a bit value of 00 may indicate the first mode, a bit value of 01 may indicate the second mode, and a bit value of 10 may indicate the third mode. 
     In some aspects, the BS may configure each of the UE A and the UE B with different power control procedures (e.g., PUCCH power control) for the NACK-only transmission and for the ACK/NACK transmission. For example, NACK-only transmission and for the ACK/NACK transmission may be configured with different received target power values and different pathloss compensation coefficients for power control. In the context of NR, the received target power may refer to the P 0,PUCCH  parameter and the pathloss compensation coefficient may refer to the α PUCCH  parameter. 
     At action  915 , the BS transmits a first DL multicast transmission to the UE A and the UE B. The BS may apply HARQ techniques for DL multicast as discussed above. 
     At action  920 , the UE A fails to receive and decode the first DL multicast transmission correctly. 
     At action  925 , in response to the failed reception and the active NACK-only feedback mode, the UE A transmits a NACK feedback (e.g., the NACK feedback  330 ) for the first DL multicast transmission to the BS, for example, in a common NACK resource based on the first resource configuration. In some instances, the UE A may apply a power control procedure (e.g., with a certain received target power and pathloss compensation) as configured by the BS for transmitting a NACK-only feedback. 
     At action  930 , the UE B successfully receives the first DL multicast transmission. Since NACK-only feedback mode is active, the UE B may refrain from transmitting an ACK feedback to the BS. 
     At action  935 , a multicast feedback mode switch is triggered. The switch can be triggered via various mechanisms. In some aspect, the BS may transmit an instruction instructing the UE A and/or the UE B to switch from the NACK-only feedback mode to the ACK/NACK feedback mode, via RRC signaling or medium access control-control element (MAC-CE) signaling (e.g., in a PDSCH). In some instances, the BS may transmit the instruction in a unicast transmission to the UE A (e.g., in a UE-specific RRC reconfiguration) and may the instruction (e.g., in a UE-specific RRC reconfiguration) via a unicast PDSCH transmission to the UE B. In some aspects, the UE A may transmit a unicast PUSCH and/or PUCCH to inform the BS of the switch, for example, via MAC-CE signaling, RSRP feedback reporting, and/or SINR feedback reporting. The signaling overhead with unicast signaling can be large as the number of UEs in a multicast group can be large. 
     In some aspects, to reduce the signaling overhead, the BS may include an indication of a switching periodicity (e.g., about 50 ms, 100 ms, or 200 ms) in the multicast feedback configuration at action  910 . Based on the periodicity, the UE A may report to the BS indicating whether the UE A may transmit a ACK/NACK feedback for a multicast transmission and whether the UE A may operate in the NACK-only feedback mode or the ACK/NACK feedback mode for the feedback. For instance, if the periodicity is 100 ms, the UE A may transmit a report to the BS at every 100 ms. In some instances, the UE A may transmit a report including a feedback mode indication (e.g., a NACK-only feedback mode or a ACK/NACK feedback mode). In some other instances, the UE A may transmit a CSI report and/or a RSRP report and the BS may determine the feedback mode based on the CSI report and/or the RSRP report. As discussed above, the BS may configure the UE A with various thresholds for switching between the ACK/NACK feedback mode and the NACK-only feedback mode. As such, the BS may determine whether the UE A is operating in the ACK/NACK feedback mode to the NACK-only feedback mode based on the RSRP report and/or the CSI report received from the UE A. 
     In some aspects, the BS may further restrict the UE A to switch from one of the ACK/NACK feedback mode or the NACK-only feedback mode to the other one of the ACK/NACK feedback mode or the NACK-only feedback mode at the periodicity (e.g., when the UE A reports CSI/RSRP or feedback mode indication to the BS). For instance, if the periodicity is 100 ms, the UE A may switch the feedback mode at the boundaries of 100 ms. 
     In some aspects, the BS may allow the UE A to switch from one of the ACK/NACK feedback mode or the NACK-only feedback mode to the other one of the ACK/NACK feedback mode or the NACK-only feedback mode within the configured periodicity. In other words, the UE A to switch from one of the ACK/NACK feedback mode or the NACK-only feedback mode to the other one of the ACK/NACK feedback mode or the NACK-only feedback mode at any time. In some aspects, the BS may configure the UE A not to report the switch to the BS when the switch occurs within the periodicity (e.g., to reduce signaling overhead). In other words, the switch may be transparent to the BS, where the BS may monitor for common NACK-only feedbacks from the multicast group and UE-specific ACK/NACKs from the UE A without relying on the indication from the UE A. In some other aspects, the BS may configure the UE A to report the switch to the BS when the switch occurs within the periodicity. For instance, the UE A may transmit a request to switch from one of the ACK/NACK feedback mode or the NACK-only feedback mode to the other one of the ACK/NACK feedback mode or the NACK-only feedback mode. In some instances, the UE A may transmit the switch request in the form of a scheduling request (SR). Similarly, the UE B may perform feedback mode switching using some substantially similar mechanisms as the UE A. As an example, both the UE A and the UE B switch from the NACK-only feedback mode to the ACK/NACK feedback mode in response to the multicast feedback mode switch trigger. 
     At action  940 , the BS transmits a second DL multicast transmission to the UE A and the UE B. For instance, the second DL multicast transmission may be a retransmission of the first DL multicast transmission in response to the NACK feedback received from the UE A. 
     At action  945 , the UE A fails to receive the second DL multicast transmission correctly. 
     At action  950 , in response to the failed reception and the active ACK/NACK feedback mode, the UE A transmits a NACK feedback (e.g., the NACK feedback  332 ) for the second DL multicast transmission to the BS, for example, in a UE-specific resource based on the second resource configuration discussed with reference to action  910 . In some instances, the UE A may apply a power control procedure (e.g., with a certain received target power and pathloss compensation) as configured by the BS for transmitting an ACK/NACK feedback. 
     At action  955 , the UE B successfully receives the second DL multicast transmission. 
     At step  960 , in response to the successful reception and the active ACK/NACK feedback mode, the UE B transmits an ACK feedback (e.g., the ACK feedback  340 ) for the second DL multicast transmission to the BS, for example, in a UE-specific resource based on the third resource configuration discussed with reference to action  910 . In some instances, the UE B may apply a power control procedure (e.g., with a certain received target power and pathloss compensation) as configured by the BS for transmitting an ACK/NACK feedback. 
     While  FIG.  9    illustrates that the UE A and the UE B switch from the NACK-only feedback mode to the ACK/NACK feedback mode at the same time, in general, UEs in a multicast group can switch between the ACK/NACK feedback mode and the NACK-only feedback mode at different times. In other words, some multicast UEs in a group may operate in the NACK-only feedback mode, while other multicast UEs in the group may operate in the ACK/NACK feedback mode at a certain time. 
       FIG.  10    is a flow diagram of a wireless communication method  1000  according to some aspects of the present disclosure. Aspects of the method  1000  can be executed by a computing device (e.g., a processor, processing circuit, and/or other suitable component) of a wireless communication device or other suitable means for performing the steps. For example, a wireless communication device, such as the UEs  115 ,  315 ,  615 , and/or  700 , may utilize one or more components, such as the processor  702 , the memory  704 , the multicast feedback module  708 , the transceiver  710 , the modem  712 , and the one or more antennas  716 , to execute the steps of method  1000 . The method  1000  may employ similar mechanisms as in the schemes  300 ,  400 , and  500  discussed above with reference to  FIGS.  3 ,  4   , and/or  5 , respectively, and/or the method  900  discussed above with reference to  FIG.  9   . As illustrated, the method  1000  includes a number of enumerated steps, but aspects of the method  1000  may include additional steps before, after, and in between the enumerated steps. In some aspects, one or more of the enumerated steps may be omitted or performed in a different order. 
     At block  1010 , a first UE (e.g., the UEs  115 ,  315 ,  615 , and/or  700 ) receives, from a BS (e.g., the BSs  105 ,  305 ,  605 , and/or  800 ), a multicast feedback configuration indicating a first resource configuration for a NACK feedback mode (e.g., the NACK-only feedback mode  304 ) and a second resource configuration for an ACK/NACK feedback mode (e.g., the ACK/NACK feedback mode  306 ). In some aspects, the first UE may utilize one or more components, such as the processor  702 , the memory  704 , the multicast feedback module  708 , the transceiver  710 , the modem  712 , and the one or more antennas  716 , to receive the multicast feedback configuration. 
     In some aspects, the first resource configuration may be a common NACK resource configuration among a group of UEs including the first UE and the second resource configuration may be a UE-specific ACK/NACK resource configuration designated to the first UE. In some aspects, the first resource configuration may include at least one of a different time configuration, a different frequency configuration, or a different sequence configuration than the second resource configuration, for example, as shown in the scheme  400  discussed above with reference to  FIG.  4   . In some aspects, the first UE may receive the first resource configuration for the NACK feedback mode via SIB signaling and may receive the second resource configuration for the ACK/NACK feedback mode via UE-specific signaling (e.g., a RRC configuration). 
     At block  1020 , the first UE receives, from the BS, a first multicast communication. In some aspects, the first UE may utilize one or more components, such as the processor  702 , the memory  704 , the multicast feedback module  708 , the transceiver  710 , the modem  712 , and the one or more antennas  716 , and the one or more antennas  816 , to receive the first multicast communication. 
     At block  1030 , the first UE transmits, to the BS, a NACK feedback (e.g., the NACK feedback  330 ) for the first multicast communication based on the first resource configuration. In some aspects, the first UE may utilize one or more components, such as the processor  702 , the memory  704 , the multicast feedback module  708 , the transceiver  710 , the modem  712 , and the one or more antennas  716 , and the one or more antennas  816 , to transmit the NACK feedback for the first multicast communication. 
     At block  1040 , the first UE receives, from the BS, a second multicast communication. In some aspects, the first UE may utilize one or more components, such as the processor  702 , the memory  704 , the multicast feedback module  708 , the transceiver  710 , the modem  712 , and the one or more antennas  716 , to receive the second multicast communication. 
     At block  1050 , the first UE transmits, to the BS, an ACK feedback or a NACK feedback (e.g., the NACK feedback  332  and the ACK feedback  340 ) for the second multicast communication based on the second resource configuration. In some aspects, the first UE may utilize one or more components, such as the processor  702 , the memory  704 , the multicast feedback module  708 , the transceiver  710 , the modem  712 , and the one or more antennas  716 , to transmit the ACK feedback or the NACK feedback for the second multicast communication. 
     In some aspects, the first UE may also receive, from the BS, an instruction to switch from one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode, for example, via RRC signaling or DCI signaling. The transmitting the NACK feedback for the first multicast communication at block  1030  may be in response to receiving the instruction to switch from the ACK/NACK feedback mode to the NACK feedback mode. The transmitting the ACK feedback or the NACK feedback for the second multicast communication at block  1050  may be in response to receiving the instruction to switch from the NACK feedback mode to the ACK/NACK feedback mode. 
     In some aspects, the first resource configuration and the second resource configuration include a same frequency configuration and a same time configuration, for example, as shown in the scheme  500  discussed above with reference to  FIG.  5   . The multicast feedback configuration may further indicate a rule for selecting between the NACK feedback mode or the ACK/NACK feedback mode. In some aspects, the first UE may further receive, from the BS, a scheduling grant for the first multicast communication, where the scheduling grant may include a first spreading code for the NACK feedback mode and a second spread code for the ACK/NACK feedback mode and the second spreading code may be different from the first spreading code. The first UE may further select the first spreading code based on the rule and utilize the selected first spreading code for the transmitting the NACK feedback for the first multicast communication at block  1020 . In some aspects, the first UE may further receive, from the BS, a scheduling grant for the second multicast communication, where the scheduling grant may include a first spreading code for the NACK feedback mode and a second spread code for the ACK/NACK feedback mode and the second spreading code may be different from the first spreading code. The first UE may select the second spreading code based on rule and utilize the selected second spreading code for the transmitting the ACK feedback or the NACK feedback for the second multicast communication at block  1050 . In some aspects, the rule can be based on a pathloss, a SINR, a CQI, a RSRP, and/or a decoding status. 
     In some aspects, the multicast feedback configuration may indicate a periodicity for switching from the one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode. The transmitting the NACK feedback for the first multicast communication or the transmitting the ACK feedback or the NACK feedback for the second multicast communication may be based on the periodicity. In some aspects, the multicast feedback configuration may restrict the switching from the one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode within the periodicity. 
     In some aspects, the first UE may also transmit, to the BS, a request to switch from one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode. 
     In some aspects, the first UE may receive, from the BS, an indication of at least one of a first target received power or a first pathloss compensation for performing a first power control procedure for transmitting the NACK feedback for the first multicast communication. The first UE may also receive, from the BS, and an indication of at least one of a second target received power different from the first target received power or a second pathloss compensation different from the first pathloss compensation for a second power control procedure for transmitting the ACK feedback or the NACK feedback for the second multicast communication. 
       FIG.  11    is a flow diagram of a wireless communication method  1100  according to some aspects of the present disclosure. Aspects of the method  1100  can be executed by a computing device (e.g., a processor, processing circuit, and/or other suitable component) of a wireless communication device or other suitable means for performing the steps. For example, a wireless communication device, such as the BSs  105 ,  305 ,  605 , and/or  800 , may utilize one or more components, such as the processor  802 , the memory  804 , the multicast feedback module  808 , the transceiver  810 , the modem  812 , and the one or more antennas  816 , to execute the steps of method  1100 . The method  1100  may employ similar mechanisms as in the schemes  300 ,  400 , and  500  discussed above with reference to  FIGS.  3 ,  4   , and/or  5 , respectively, and/or the method  900  discussed above with reference to  FIG.  9   . As illustrated, the method  1100  includes a number of enumerated steps, but aspects of the method  1100  may include additional steps before, after, and in between the enumerated steps. In some aspects, one or more of the enumerated steps may be omitted or performed in a different order. 
     At block  1110 , a BS (e.g., the BSs  105 ,  305 ,  605 , and/or  700 ) transmits a multicast feedback configuration indicating a first resource configuration for a NACK feedback mode (e.g., the NACK-only feedback mode  304 ) and a second resource configuration for an ACK/NACK feedback mode (e.g., the ACK/NACK feedback mode  306 ). In some aspects, the BS may utilize one or more components, such as the processor  802 , the memory  804 , the multicast feedback module  808 , the transceiver  810 , the modem  812 , and the one or more antennas  816 , to transmit the multicast feedback configuration. 
     In some aspects, the first resource configuration may be a common NACK resource configuration among the group of UEs and the second resource configuration may be a UE-specific ACK/NACK resource configuration designated to the first UE. In some aspects, the first resource configuration may include at least one of a different time configuration, a different frequency configuration, or a different sequence configuration than the second resource configuration, for example, as shown in the scheme  400  discussed above with reference to  FIG.  4   . In some aspects, the BS may transmit the first resource configuration for the NACK feedback mode via SIB signaling and may transmit the second resource configuration for the ACK/NACK feedback mode via UE-specific signaling (e.g., a RRC configuration). 
     At block  1120 , the BS transmits, to a group of UEs (e.g., the UEs.  115 ,  315 ,  615 , and/or  700 ), a first multicast communication. In some aspects, the BS may utilize one or more components, such as the processor  802 , the memory  804 , the multicast feedback module  808 , the transceiver  810 , the modem  812 , and the one or more antennas  816 , to transmit the first multicast communication. 
     At block  1130 , the BS receives, from one or more UEs of the group of UEs, a NACK feedback for the first multicast communication based on the first resource configuration. In some aspects, the BS may utilize one or more components, such as the processor  802 , the memory  804 , the multicast feedback module  808 , the transceiver  810 , the modem  812 , and the one or more antennas  816 , to receive the NACK feedback for the first multicast communication based on the first resource configuration. 
     At block  1140 , the BS transmits, to the group of UEs, a second multicast communication. In some aspects, the BS may utilize one or more components, such as the processor  802 , the memory  804 , the multicast feedback module  808 , the transceiver  810 , the modem  812 , and the one or more antennas  816 , to transmit the second multicast communication. 
     At block  1150 , the BS receives, from a first UE of the one or more UEs, an ACK feedback or a NACK feedback for the second multicast communication based on the second resource configuration. In some aspects, the BS may utilize one or more components, such as the processor  802 , the memory  804 , the multicast feedback module  808 , the transceiver  810 , the modem  812 , and the one or more antennas  816 , to receive the NACK feedback or the ACK feedback for the second multicast communication based on the first resource configuration. 
     In some aspects, the BS may also transmit, to the first UE, an instruction to switch from one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode, for example, via RRC signaling or DCI signaling. The receiving the NACK feedback for the first multicast communication at block  1130  may be in response to transmitting the instruction to switch from the ACK/NACK feedback mode to the NACK feedback mode. The receiving the ACK feedback or the NACK feedback for the second multicast communication at block  1150  may be in response to transmitting the instruction to switch from the NACK feedback mode to the ACK/NACK feedback mode. 
     In some aspects, the first resource configuration and the second resource configuration include a same frequency configuration and a same time configuration, for example, as shown in the scheme  500  discussed above with reference to  FIG.  5   . The multicast feedback configuration may further indicate a rule for selecting between the NACK feedback mode or the ACK/NACK feedback mode. In some aspects, the BS may further transmit a scheduling grant for the first multicast communication, where the scheduling grant may include a first spreading code for the NACK feedback mode and a second spreading code for the ACK/NACK feedback mode and the second spreading code may be different from the first spreading code. The BS may further monitor, in a resource indicated by the frequency configuration and the time configuration, for a feedback for the first multicast communication based on the first spreading code and the second spreading code. The BS may receive the NACK feedback for the first multicast communication at the block  1130  further based on the monitoring. In some aspects, the BS may further transmit a scheduling grant for the second multicast communication, where the scheduling grant may include a first spreading code for the NACK feedback mode and a second spreading code for the ACK/NACK feedback mode and the second spreading code may be different from the first spreading code. The BS may further monitor, in a resource indicated by the frequency configuration and the time configuration, for a feedback for the second multicast communication based on the first spreading code and the second spreading code. The BS may receive the ACK feedback or the NACK feedback for the second multicast communication at the block  1150  further based on the monitoring. In some aspects, the rule can be based on a pathloss, a SINR, a CQI, a RSRP, and/or a decoding status. 
     In some aspects, the multicast feedback configuration may indicate a periodicity for switching from the one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode. The receiving the NACK feedback for the first multicast communication or the receiving the ACK feedback or the NACK feedback for the second multicast communication may be based on the periodicity. In some aspects, the multicast feedback configuration may restrict the switching from the one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode within the periodicity. 
     In some aspects, the BS may also transmit an indication of at least one of a first target received power or a first pathloss compensation for a first power control of the transmitting the NACK feedback for the first multicast communication. The BS may also transmit an indication of at least one of a second target received power different from the first target received power or a second pathloss compensation different from the first pathloss compensation for a second power control of the transmitting the ACK feedback or the NACK feedback for the second multicast communication. 
     Further aspects of the present disclosure are provided below. 
     Aspect 1 includes a method of wireless communication, comprising receiving, by a first user equipment (UE) from a base station (BS), a multicast feedback configuration indicating: a first resource configuration for a negative-acknowledgement (NACK) feedback mode; and a second resource configuration for an acknowledgement/negative-acknowledgement (ACK/NACK) feedback mode; receiving, by the first UE from the BS, a first multicast communication; transmitting, by the first UE to the BS, a NACK feedback for the first multicast communication based on the first resource configuration; receiving, by the first UE from the BS, a second multicast communication; and transmitting, by the first UE to the BS, an ACK feedback or a NACK feedback for the second multicast communication based on the second resource configuration. 
     Aspect 2 includes the method of aspect 1, wherein the first resource configuration is a common NACK resource configuration among a group of UEs including the first UE, and wherein the second resource configuration is a UE-specific ACK/NACK resource configuration designated to the first UE. 
     Aspect 3 includes the method of any of aspects 1-2, wherein the first resource configuration includes at least one of a different time configuration, a different frequency configuration, or a different sequence configuration than the second resource configuration. 
     Aspect 4 includes the method of any of aspects 1-3, further comprising receiving, by the first UE from the BS, an instruction to switch from one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode. 
     Aspect 5 includes the method of any of aspects 1-4, wherein the transmitting the NACK feedback for the first multicast communication is in response to receiving the instruction to switch from the ACK/NACK feedback mode to the NACK feedback mode. 
     Aspect 6 includes the method of any of aspects 1-4, wherein the transmitting the ACK feedback or the NACK feedback for the second multicast communication is in response to receiving the instruction to switch from the NACK feedback mode to the ACK/NACK feedback mode. 
     Aspect 7 includes the method of aspect of any of aspects 1-6, wherein the receiving the instruction to switch from the one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode includes receiving, by the first UE from the BS, the instruction via at least one of radio resource configuration control (RRC) signaling or downlink control information (DCI) signaling. 
     Aspect 8 includes the method of any of aspects 1-7, wherein the first resource configuration and the second resource configuration include a same frequency configuration and a same time configuration, and wherein the multicast feedback configuration further indicates a rule for selecting between the NACK feedback mode or the ACK/NACK feedback mode. 
     Aspect 9 incudes the method of any of aspects 1-8, further comprising receiving, by the first UE from the BS, a scheduling grant for the first multicast communication, the scheduling grant including a first spreading code for the NACK feedback mode and a second spread code for the ACK/NACK feedback mode, the second spreading code being different from the first spreading code; and selecting, by the first UE, the first spreading code based on the rule, wherein the transmitting the NACK feedback for the first multicast communication is further based on the selected first spreading code. 
     Aspect 10 includes the method of any of aspects 1-9, further comprising receiving, by the first UE from the BS, a scheduling grant for the second multicast communication, the scheduling grant including a first spreading code for the NACK feedback mode and a second spread code for the ACK/NACK feedback mode, the second spreading code being different from the first spreading code; and selecting, by the first UE, the second spreading code based on rule, wherein the transmitting the ACK feedback or the NACK feedback for the second multicast communication is further based on the selected second spreading code. 
     Aspect 11 includes the method any of aspects 1-8, wherein the rule for switching from the one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode is based on a channel measurement. 
     Aspect 12 includes the method of any of aspects 1-11, wherein the channel measurement includes at least one of a pathloss, a reference signal received power (RSRP), a signal-to-interference-plus-noise ratio (SINR), or a channel quality indicator (CQI). 
     Aspect 13 includes includes the method of any of aspects 1-8, wherein the rule for switching from the one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode is based on a DL decoding status. 
     Aspect 14 includes the method of any of aspects 1-8, wherein the multicast feedback configuration indicates a periodicity for switching from the one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode. 
     Aspect 15 includes the method of any of aspects 1-8 or 14, wherein the transmitting the NACK feedback for the first multicast communication is based on the periodicity; or the transmitting the ACK feedback or the NACK feedback for the second multicast communication is based on the periodicity. 
     Aspect 16 includes the method of any of aspects 1-8 or 14-15, wherein the multicast feedback configuration restricts the switching from the one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode within the periodicity. 
     Aspect 17 includes the method of any of aspects 1-3, further comprising transmitting, by the first UE to the BS, a request to switch from one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode. 
     Aspect 18 includes the method of any of aspects 1-3, wherein the transmitting the NACK feedback for the first multicast communication is based on a first power control procedure, and wherein the transmitting the ACK feedback or the NACK feedback for the second multicast communication is based on a second power control procedure different from the first power control procedure. 
     Aspect 19 includes the method of any of aspects 1-3 or 18, further comprising receiving, by the first UE from the BS, an indication of at least one of a first target received power or a first pathloss compensation for the first power control procedure; and receiving, by the first UE from the BS, an indication of at least one of a second target received power different from the first target received power or a second pathloss compensation different from the first pathloss compensation for the second power control procedure. 
     Aspect 20 includes the method of any of aspects 1-19, wherein the receiving the multicast feedback configuration includes receiving, by the first UE from the BS, the first resource configuration for the NACK feedback mode via system information block (SIB) signaling; and receiving, by the first UE from the BS, the second resource configuration for the ACK/NACK feedback mode via UE-specific signaling. 
     Aspect 21 includes a method of wireless communication, comprising transmitting, by a base station (BS), a multicast feedback configuration indicating a first resource configuration for a negative-acknowledgement (NACK) feedback mode; and a second resource configuration for an acknowledgement/negative-acknowledgement (ACK/NACK) feedback mode; transmitting, by the BS to a group of user equipments (UEs), a first multicast communication; receiving, by the BS from one or more UEs of the group of UEs, a NACK feedback for the first multicast communication based on the first resource configuration; transmitting, by the BS to the group of UEs, a second multicast communication; and receiving, by the BS from a first UE of the one or more UEs, an ACK feedback or a NACK feedback for the second multicast communication based on the second resource configuration. 
     Aspect 22 includes the method of aspect 21, wherein the first resource configuration is a common NACK resource configuration among the group of UEs, and wherein the second resource configuration is a UE-specific ACK/NACK resource configuration designated to the first UE. 
     Aspect 23 includes the method of any of aspects 21-22, wherein the first resource configuration includes at least one of a different time configuration, a different frequency configuration, or a different sequence configuration than the second resource configuration. 
     Aspect 24 includes the method of any of aspects 21-23, further comprising transmitting, by the BS to the first UE, an instruction to switch from one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode. 
     Aspect 25 includes the method of any of aspects 21-24, wherein the receiving the NACK feedback for the first multicast communication is in response to transmitting the instruction to switch from the ACK/NACK feedback mode to the NACK feedback mode. 
     Aspect 26 includes the method of any of aspects 21-24, wherein the receiving the ACK feedback or the NACK feedback for the second multicast communication is in response to transmitting the instruction to switch from the NACK feedback mode to the ACK/NACK feedback mode. 
     Aspect 27 includes the method of any of aspects 21-26, wherein the transmitting the instruction to switch from the one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode includes transmitting, by the BS, the instruction via at least one of radio resource configuration control (RRC) signaling or downlink control information (DCI) signaling. 
     Aspect 28 includes the method of any of aspects 21-27, wherein the first resource configuration and the second resource configuration include a same frequency configuration and a same time configuration, and wherein the multicast feedback configuration further indicates a rule for selecting between the NACK feedback mode or the ACK/NACK feedback mode. 
     Aspect 29 includes the method of any of aspects 21-28, further comprising transmitting, by the BS, a scheduling grant for the first multicast communication, the scheduling grant including a first spreading code for the NACK feedback mode and a second spreading code for the ACK/NACK feedback mode, the second spreading code being different from the first spreading code; and monitoring, by the BS in a resource indicated by the frequency configuration and the time configuration, for a feedback for the first multicast communication based on the first spreading code and the second spreading code, wherein the receiving the NACK feedback for the first multicast communication is further based on the monitoring. 
     Aspect 30 includes the method of any of aspects 21-29, further comprising transmitting, by the BS, a scheduling grant for the second multicast communication, the scheduling grant including a first spreading code for the NACK feedback mode and a second spreading code for the ACK/NACK feedback mode, the second spreading code being different from the first spreading code; and monitoring, by the BS in a resource indicated by the frequency configuration and the time configuration, for a feedback for the second multicast communication based on the first spreading code and the second spreading code, the receiving the ACK feedback or the NACK feedback for the second multicast communication is further based on the monitoring. 
     Aspect 31 includes the method of any of aspects 21-28, wherein the rule for switching from the one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode is based on a channel measurement. 
     Aspect 32 includes the method of any of aspects 21-31, wherein the channel measurement includes at least one of a pathloss, a reference signal received power (RSRP), a signal-to-interference-plus-noise ratio (SINR), or a channel quality indicator (CQI). 
     Aspect 33 includes the method of any of aspects 21-28 wherein the rule for switching from the one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode is based on a DL decoding status. 
     Aspect 34 includes the method of any of aspects 21-28, wherein the multicast feedback configuration indicates a periodicity for switching from the one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode. 
     Aspect 35 includes the method of any of aspects 21-28 or 34, wherein the receiving the NACK feedback for the first multicast communication is based on the periodicity; or the receiving the ACK feedback or the NACK feedback for the second multicast communication is based on the periodicity. 
     Aspect 36 includes the method of any of aspects 21-28 or 34-35, wherein the multicast feedback configuration restricts the switching from the one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode within the periodicity. 
     Aspect 37 includes the method of any of aspects 21-23, further comprising receiving, by the BS from the first UE, a request to switch from one of the NACK feedback mode or the ACK/NACK feedback mode to the other of the NACK feedback mode or the ACK/NACK feedback mode. 
     Aspect 38 includes the method of any of aspects 21-23, further comprising transmitting, by the BS, an indication of at least one of a first target received power or a first pathloss compensation for a first power control of the transmitting the NACK feedback for the first multicast communication; and transmitting, by the BS, an indication of at least one of a second target received power different from the first target received power or a second pathloss compensation different from the first pathloss compensation for a second power control of the transmitting the ACK feedback or the NACK feedback for the second multicast communication. 
     Aspect 39 includes the method of any of aspects 21-28, wherein the transmitting the multicast feedback configuration includes transmitting, by the BS, the first resource configuration for the NACK feedback mode via system information block (SIB) signaling; and transmitting, by the BS to the first UE, the second resource configuration for the ACK/NACK feedback mode via UE-specific signaling. 
     Aspect 40 includes an apparatus comprising a processor coupled to a transceiver, wherein the processor and the transceiver are configured to perform the method of any one of aspects 1-20. The processor and the transceiver may correspond to the processor  702  and the transceiver  710  of  FIG.  7   , respectively. 
     Aspect 41 includes an apparatus comprising a processor coupled to a transceiver, wherein the processor and the transceiver are configured to perform the method of any one of aspects 21-39. The processor and the transceiver may correspond to the processor  802  and the transceiver  810  of  FIG.  8   , respectively. 
     Aspect 42 includes an apparatus comprising means for performing the method of any one of aspects 1-20. The means may include components, such as the processor  702 , the memory  704 , the multicast feedback module  708 , the transceiver  710 , the modem  712 , and the one or more antennas  716  of  FIG.  7   . 
     Aspect 43 includes an apparatus comprising means for performing the method of any one of aspects 21-39. The means may include components, such as the processor  802 , the memory  804 , the multicast feedback module  808 , the transceiver  810 , the modem  812 , and the one or more antennas  816  of  FIG.  8   . 
     Aspect 44 includes a non-transitory computer readable medium including program code, which when executed by one or more processors, causes a wireless communication device to perform the method of any one of aspects 1-20. 
     Aspect 45 includes a non-transitory computer readable medium including program code, which when executed by one or more processors, causes a wireless communication device to perform the method of any one of aspects 21-39. 
     Information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
     The various illustrative blocks and modules described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a DSP, an ASIC, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration). 
     The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Also, as used herein, including in the claims, “or” as used in a list of items (for example, a list of items prefaced by a phrase such as “at least one of” or “one or more of”) indicates an inclusive list such that, for example, a list of [at least one of A, B, or C] means A or B or C or AB or AC or BC or ABC (i.e., A and B and C). 
     As those of some skill in this art will by now appreciate and depending on the particular application at hand, many modifications, substitutions and variations can be made in and to the materials, apparatus, configurations and methods of use of the devices of the present disclosure without departing from the spirit and scope thereof. In light of this, the scope of the present disclosure should not be limited to that of the particular aspects illustrated and described herein, as they are merely by way of some examples thereof, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.