Patent Publication Number: US-2023163923-A1

Title: Feedback design for network coded transmissions in wireless communication network

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates generally to wireless communications, and more specifically to a sidelink feedback design for network coding systems, to reduce peak-to-average-power ratio (PAPR). 
     BACKGROUND 
     Wireless communications systems are widely deployed to provide various telecommunications services such as telephony, video, data, messaging, and broadcasts. Typical wireless communications systems may employ multiple-access technologies capable of supporting communications with multiple users by sharing available system resources. Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems. 
     These multiple access technologies have been adopted in various telecommunications standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunications standard is fifth generation (5G) new radio (NR). 5G NR is part of a continuous mobile broadband evolution promulgated by Third Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., with Internet of Things (IoT)), and other requirements. 5G NR includes services associated with enhanced mobile broadband (eMBB), massive machine type communications (mMTC), and ultra-reliable low latency communications (URLLC). Some aspects of 5G NR may be based on the fourth generation (4G) long term evolution (LTE) standard. Narrowband (NB)-Internet of things (IoT) and enhanced machine-type communications (eMTC) are a set of enhancements to LTE for machine type communications. There exists a need for further improvements in 5G NR technology. These improvements may also be applicable to other multi-access technologies and the telecommunications standards that employ these technologies. 
     Wireless communications systems may include or provide support for various types of communications systems, such as vehicle related cellular communications systems (e.g., cellular vehicle-to-everything (CV2X) communications systems). Vehicle related communications systems may be used by vehicles to increase safety and to help prevent collisions of vehicles. Information regarding inclement weather, nearby accidents, road conditions, and/or other information may be conveyed to a driver via the vehicle related communications system. In some cases, sidelink user equipment (UEs), such as vehicles, may communicate directly with each other using device-to-device (D2D) communications over a D2D wireless link. These communications can be referred to as sidelink communications. 
     As the demands for sidelink communications increase in general, and CV2X technology specifically penetrates the market and the number of cars supporting CV2X communication grows rapidly, the CV2X network is expected to become increasingly crowded, especially for peak traffic scenarios. As a result, the chance of colliding allocations between UEs may increase. An allocation collision may prevent successful decoding of at least one of the colliding UE transmissions and in some cases may prevent all of the colliding UE transmissions from being decoded. For safety reasons, there is a need to minimize the duration of repetitive collisions between semi-persistently scheduled allocations of colliding user equipment (UEs) or to minimize the number of future collisions in general. 
     SUMMARY 
     In aspects of the present disclosure, a method of wireless communication by a receiving sidelink user equipment (UE) includes receiving a first original message from a first transmitting sidelink UE. The method also includes receiving, from a network coding device, a network coded (NC) packet that is coded across the first original message and a second original message from a second transmitting sidelink UE. The first original message corresponds to a first transport block. The second original message corresponds to a second transport block. The method further includes transmitting a first negative acknowledgment (NACK) in response to the first transport block being unsuccessfully decoded. The method still further includes transmitting a second NACK in response to the second transport block being unsuccessfully decoded. The method also includes transmitting a first acknowledgment (ACK) in response to the first transport block being successfully decoded. 
     In other aspects of the present disclosure, a method of wireless communication by a network coding device includes transmitting, to a receiving device, a network coded (NC) packet that is coded across a first original message originating from a first transmitting sidelink user equipment (UE) and a second original message originating from a second transmitting sidelink UE. The first original message corresponds to a first transport block. The second original message corresponds to a second transport block. The method also includes receiving a first negative acknowledgment (NACK) in response to the first transport block being unsuccessfully decoded. The method further includes receiving a second NACK in response to the second transport block being unsuccessfully decoded. The method still further includes receiving a first acknowledgment (ACK) in response to the first transport block being successfully decoded. 
     Other aspects of the present disclosure are directed to an apparatus for wireless communication by a receiving sidelink user equipment (UE) having a memory and one or more processor(s) coupled to the memory. The processor(s) is configured to receive a first original message from a first transmitting sidelink UE. The processor(s) is also configured to receive, from a network coding device, a network coded (NC) packet that is coded across the first original message and a second original message from a second transmitting sidelink UE. The first original message corresponds to a first transport block. The second original message corresponds to a second transport block. The processor(s) is further configured to transmit a first negative acknowledgment (NACK) in response to the first transport block being unsuccessfully decoded. The processor(s) is still further configured to transmit a second NACK in response to the second transport block being unsuccessfully decoded. The processor(s) is still further configured to transmit a first acknowledgment (ACK) in response to the first transport block being successfully decoded. 
     Aspects generally include a method, apparatus, system, computer program product, non-transitory computer-readable medium, user equipment, base station, wireless communications device, and processing system as substantially described with reference to and as illustrated by the accompanying drawings and specification. 
     The foregoing has outlined rather broadly the features and technical advantages of examples according to the disclosure in order that the detailed description that follows may be better understood. Additional features and advantages will be described. The conception and specific examples disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. Such equivalent constructions do not depart from the scope of the appended claims. Characteristics of the concepts disclosed, both their organization and method of operation, together with associated advantages will be better understood from the following description when considered in connection with the accompanying figures. Each of the figures is provided for the purposes of illustration and description, and not as a definition of the limits of the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects. The same reference numbers in different drawings may identify the same or similar elements. 
         FIG.  1    is a diagram illustrating an example of a wireless communications system and an access network. 
         FIGS.  2 A,  2 B,  2 C, and  2 D  are diagrams illustrating examples of a first fifth generation (5G) new radio (NR) frame, downlink (DL) channels within a 5G NR subframe, a second 5G NR frame, and uplink (UL) channels within a 5G NR subframe, respectively. 
         FIG.  3    is a diagram illustrating an example of a base station and user equipment (UE) in an access network. 
         FIG.  4    is a diagram illustrating an example of a vehicle-to-everything (V2X) system, in accordance with various aspects of the present disclosure. 
         FIG.  5    is a block diagram illustrating an example of a vehicle-to-everything (V2X) system with a road side unit (RSU), according to aspects of the present disclosure. 
         FIG.  6    is a graph illustrating a sidelink (SL) communications scheme, in accordance with various aspects of the present disclosure. 
         FIG.  7    is a block diagram illustrating sidelink groupcasting, in accordance with various aspects of the present disclosure. 
         FIG.  8    is a block diagram illustrating network coding, in accordance with various aspects of the present disclosure. 
         FIG.  9    is block diagram illustrating network coding, in accordance with various aspects of the present disclosure. 
         FIG.  10    is a timing diagram illustrating network coding, in accordance with various aspects of the present disclosure. 
         FIG.  11    is a flow diagram illustrating an example process performed, for example, by a receiving sidelink user equipment (UE), in accordance with various aspects of the present disclosure. 
         FIG.  12    is a flow diagram illustrating an example process performed, for example, by a network coding device, in accordance with various aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Various aspects of the disclosure are described more fully below with reference to the accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings, one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the disclosure disclosed, whether implemented independently of or combined with any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth. In addition, the scope of the disclosure is intended to cover such an apparatus or method, which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects of the disclosure set forth. It should be understood that any aspect of the disclosure disclosed may be embodied by one or more elements of a claim. 
     Several aspects of telecommunications systems will now be presented with reference to various apparatuses and techniques. These apparatuses and techniques will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, and/or the like (collectively referred to as “elements”). These elements may be implemented using hardware, software, or combinations thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. 
     It should be noted that while aspects may be described using terminology commonly associated with 5G and later wireless technologies, aspects of the present disclosure can be applied in other generation-based communications systems, such as and including 3G and/or 4G technologies. 
     In cellular communications networks, wireless devices may generally communicate with each other via one or more network entities such as a base station or scheduling entity. Some networks may support device-to-device (D2D) communications that enable discovery of, and communications with nearby devices using a direct link between devices (e.g., without passing through a base station, relay, or another node). D2D communications can enable mesh networks and device-to-network relay functionality. Some examples of D2D technology include Bluetooth pairing, Wi-Fi Direct, Miracast, and LTE-D. D2D communications may also be referred to as point-to-point (P2P) or sidelink communications. 
     D2D communications may be implemented using licensed or unlicensed bands. Additionally, D2D communications can avoid the overhead involving the routing to and from the base station. Therefore, D2D communications can improve throughput, reduce latency, and/or increase energy efficiency. 
     A type of D2D communications may include vehicle-to-everything (V2X) communications. V2X communications may assist autonomous vehicles in communicating with each other. For example, autonomous vehicles may include multiple sensors (e.g., light detection and ranging (LiDAR), radar, cameras, etc.). In most cases, the autonomous vehicle&#39;s sensors are line of sight sensors. In contrast, V2X communications may allow autonomous vehicles to communicate with each other for non-line of sight situations. 
     Sidelink (SL) communications refers to the communications among user equipment (UE) without tunneling through a base station and/or a core network. Sidelink communications can be communicated over a physical sidelink control channel (PSCCH) and a physical sidelink shared channel (PSSCH). The PSCCH and PSSCH are similar to a physical downlink control channel (PDCCH) and a physical downlink shared channel (PDSCH) in downlink (DL) communications between a base station and a UE. For instance, the PSCCH may carry sidelink control information (SCI) and the PSCCH may carry sidelink data (e.g., user data). Each PSCCH is associated with a corresponding PSSCH, where SCI in a PSCCH may carry reservation and/or scheduling information for sidelink data transmission in the associated PSSCH. Use cases for sidelink communications may include, among others, vehicle-to-everything (V2X), industrial Internet of things (IIoT), and/or NR-lite. 
     Network coding is a technique that may increase system capacity and improve resource utilization by reducing a number of retransmissions in the system while maintaining network performance. Network coding may enable an increase in a number of user equipment (UEs) within the system or may increase traffic per UE. With network codding, after an original transmitter sends an initial transmission, a network device sends any expected retransmissions on behalf of the original device. 
     When a message is not successfully decoded, a retransmission of the original message may occur in an attempt to successfully transmit the message to the receiver. Generally speaking, the transmitter of the original message performs the retransmission. With network coding, a network device may retransmit the original message instead of the original device. The network coding device may be a base station, a road side unit (RSU), or even another UE. Although the present description is primarily with respect to retransmissions, the present disclosure also pertains to network coding of initial transmissions on behalf of the original transmitter. 
     A network device generates and sends a network coded transmission (Tx) (also referred to as a network coded packet), including any missed packets or transport blocks. The network coded packet contains a network coded combination of multiple coded packets, such as transport blocks. After receiving the network coded packet, the receiving UE determines whether to send acknowledgement or negative acknowledgement (ACK/NACK) feedback for these coded transport blocks or the entire network coded packet. The receiving UE also determines the type of feedback to be sent. For example, when a multi-erasure code is used, if a network coded packet contains four transport blocks, sending an ACK/NACK for the network coded packet is not sufficient. Feedback for each of the four transport blocks is desired. However, this may lead to an increase in the amount of feedback, and also a high peak-to-average power ratio if not arranged properly. Thus, the type of feedback, and when to send the feedback, is an important consideration. 
     In the case of multiple receiving UEs, when each receiving UE sends multiple feedback messages for a single network coded packet, the peak-to-average power ratio (PAPR) should be reduced. The PAPR is the relation between the maximum power of a sample in a given orthogonal frequency division multiplexing (OFDM) transmit symbol divided by the average power of that OFDM symbol. Reducing the PAPR of the OFDM signal allows use of a power amplifier device with lower power specifications. The power amplifier is one of the most power consuming units of the device. 
     According to aspects of the present disclosure, a receiving UE sends full ACK/NACK feedback in response to receiving a network coded packet. In these aspects, the UE sends NACK feedback for any transport block in the network coding combination that is not successfully decoded. The UE also sends ACK feedback for any transport block in the network coding combination that has been successfully decoded. A UE may determine an index of a physical sidelink feedback channel (PSFCH) resource for transmitting feedback in response to a transport block within the network coded packet. That is, the UE determines which resources to use for transmitting the feedback. 
     In some aspects of the present disclosure, feedback reporting for network coded packets may be reduced. For example, the UE may send NACK feedback for any of the transport blocks in the network coded packet that are unsuccessfully decoded, only when the UE would have sent NACK feedback to the transport block&#39;s original transmitter. That is, the receiver sends NACKS only when the receiver is an intended recipient of the transport block&#39;s original transmitter. According to these aspects of the present disclosure, the UE sends ACK feedback, only if the receiver is an intended recipient of the transport block&#39;s original transmitter. In other aspects, the UE sends ACK feedback for any transport block that is newly decoded. In still other aspects, the UE sends ACK feedback only if the receiver is an intended recipient of the transport block&#39;s original transmitter and the transport block is newly decoded. In still other aspects, the UE may be instructed to send a single ACK to indicate that the UE successfully decoded all of the transport blocks within the network coded packet. By reducing feedback reporting for network coded packets, the chance of feedback collisions is reduced. 
     According to further aspects of the present disclosure, the peak-to-average power ratio (PAPR) may be reduced during feedback reporting. If the UE is configured to send full ACK/NACK feedback, the multiple feedback ACK/NACKs from the UE for one network coded packet may not be consecutive in the PSFCH resources. This may lead to a high peak-to-average power ratio, which results in high radio frequency (RF) emissions. To reduce the peak-to-average power ratio, these multiple feedback ACK/NACKs may be assigned to consecutive PSFCH resources. 
       FIG.  1    is a diagram illustrating an example of a wireless communications system and an access network  100 . The wireless communications system (also referred to as a wireless wide area network (WWAN)) includes base stations  102 , UEs  104 , an evolved packet core (EPC)  160 , and another core network  190  (e.g., a 5G core (5GC)). The base stations  102  may include macrocells (high power cellular base station) and/or small cells  102 ′ (low power cellular base station). The macrocells include base stations. The small cells  102 ′ include femtocells, picocells, and microcells. 
     The base stations  102  configured for 4G LTE (collectively referred to as evolved universal mobile telecommunications system (UMTS) terrestrial radio access network (E-UTRAN)) may interface with the EPC  160  through backhaul links  132  (e.g., S1 interface). The base stations  102  configured for 5G NR (collectively referred to as next generation RAN (NG-RAN)) may interface with core network  190  through backhaul links  184 . In addition to other functions, the base stations  102  may perform one or more of the following functions: transfer of user data, radio channel ciphering and deciphering, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS), subscriber and equipment trace, RAN information management (RIM), paging, positioning, and delivery of warning messages. The base stations  102  may communicate directly or indirectly (e.g., through the EPC  160  or core network  190 ) with each other over backhaul links  134  (e.g., X2 interface). The backhaul links  134  may be wired or wireless. 
     The base stations  102  may wirelessly communicate with the UEs  104 . Each of the base stations  102  may provide communications coverage for a respective geographic coverage area  110 . There may be overlapping geographic coverage areas  110 . For example, the small cell  102 ′ may have a coverage area  110 ′ that overlaps the coverage area  110  of one or more macro base stations  102 . A network that includes both small cell and macrocells may be known as a heterogeneous network. A heterogeneous network may also include home evolved Node Bs (eNBs) (HeNBs), which may provide service to a restricted group known as a closed subscriber group (CSG). The communications links  120  between the base stations  102  and the UEs  104  may include uplink (UL) (also referred to as reverse link) transmissions from a UE  104  to a base station  102  and/or downlink (DL) (also referred to as forward link) transmissions from a base station  102  to a UE  104 . The communications links  120  may use multiple-input and multiple-output (MIMO) antenna technology, including spatial multiplexing, beamforming, and/or transmit diversity. The communications links may be through one or more carriers. The base stations  102 /UEs  104  may use spectrum up to Y MHz (e.g., 5, 10, 15, 20, 100, 400, etc., MHz) bandwidth per carrier allocated in a carrier aggregation of up to a total of Yx MHz (x component carriers) used for transmission in each direction. The carriers may or may not be adjacent to each other. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or fewer carriers may be allocated for DL than for UL). The component carriers may include a primary component carrier and one or more secondary component carriers. A primary component carrier may be referred to as a primary cell (PCell) and a secondary component carrier may be referred to as a secondary cell (SCell). 
     Certain UEs  104  may communicate with each other using device-to-device (D2D) communications link  158 . The D2D communications link  158  may use the DL/UL WWAN spectrum. The D2D communications link  158  may use one or more sidelink channels, such as a physical sidelink broadcast channel (PSBCH), a physical sidelink discovery channel (PSDCH), a physical sidelink shared channel (PSSCH), and a physical sidelink control channel (PSCCH). D2D communications may be through a variety of wireless D2D communications systems, such as FlashLinQ, WiMedia, Bluetooth, ZigBee, Wi-Fi based on the IEEE 802.11 standard, LTE, or NR. 
     The wireless communications system may further include a Wi-Fi access point (AP)  150  in communication with Wi-Fi stations (STAs)  152  via communications links  154  in a 5 GHz unlicensed frequency spectrum. When communicating in an unlicensed frequency spectrum, the STAs  152 /AP  150  may perform a clear channel assessment (CCA) prior to communicating in order to determine whether the channel is available. 
     The small cell  102 ′ may operate in a licensed and/or an unlicensed frequency spectrum. When operating in an unlicensed frequency spectrum, the small cell  102 ′ may employ NR and use the same 5 GHz unlicensed frequency spectrum as used by the Wi-Fi AP  150 . The small cell  102 ′, employing NR in an unlicensed frequency spectrum, may boost coverage to and/or increase capacity of the access network. 
     A base station  102 , whether a small cell  102 ′ or a large cell (e.g., macro base station), may include an eNB, gNodeB (gNB), or another type of base station. Some base stations, such as gNB  180  may operate in a traditional sub 6 GHz spectrum, in millimeter wave (mmWave) frequencies, and/or near mmWave frequencies in communication with the UE  104 . When the gNB  180  operates in mmWave or near mmWave frequencies, the gNB  180  may be referred to as an mmWave base station. Extremely high frequency (EHF) is part of the radio frequency (RF) in the electromagnetic spectrum. EHF has a range of 30 GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters. Radio waves in the band may be referred to as a millimeter wave. Near mmWave may extend down to a frequency of 3 GHz with a wavelength of 100 millimeters. The super high frequency (SHF) band extends between 3 GHz and 30 GHz, also referred to as centimeter wave. Communications using the mmWave/near mmWave radio frequency band (e.g., 3 GHz-300 GHz) has extremely high path loss and a short range. The mmWave base station  180  may utilize beamforming  182  with the UE  104  to compensate for the extremely high path loss and short range. 
     The base station  180  may transmit a beamformed signal to the UE  104  in one or more transmit directions  182 ′. The UE  104  may receive the beamformed signal from the base station  180  in one or more receive directions  182 ″. The UE  104  may also transmit a beamformed signal to the base station  180  in one or more transmit directions. The base station  180  may receive the beamformed signal from the UE  104  in one or more receive directions. The base station  180 /UE  104  may perform beam training to determine the best receive and transmit directions for each of the base station  180 /UE  104 . The transmit and receive directions for the base station  180  may or may not be the same. The transmit and receive directions for the UE  104  may or may not be the same. 
     The EPC  160  may include a mobility management entity (MME)  162 , other MMEs  164 , a serving gateway  166 , a multimedia broadcast multicast service (MBMS) gateway  168 , a broadcast multicast service center (BM-SC)  170 , and a packet data network (PDN) gateway  172 . The MME  162  may be in communication with a home subscriber server (HSS)  174 . The MME  162  is the control node that processes the signaling between the UEs  104  and the EPC  160 . Generally, the MME  162  provides bearer and connection management. All user Internet protocol (IP) packets are transferred through the serving gateway  166 , which itself is connected to the PDN gateway  172 . The PDN gateway  172  provides UE IP address allocation as well as other functions. The PDN gateway  172  and the BM-SC  170  are connected to the IP services  176 . The IP services  176  may include the Internet, an intranet, an IP multimedia subsystem (IMS), a PS streaming service, and/or other IP services. The BM-SC  170  may provide functions for MBMS user service provisioning and delivery. The BM-SC  170  may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS bearer services within a public land mobile network (PLMN), and may be used to schedule MBMS transmissions. The MBMS gateway  168  may be used to distribute MBMS traffic to the base stations  102  belonging to a multicast broadcast single frequency network (MBSFN) area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting eMBMS related charging information. 
     The core network  190  may include an access and mobility management function (AMF)  192 , other AMFs  193 , a session management function (SMF)  194 , and a user plane function (UPF)  195 . The AMF  192  may be in communication with a unified data management (UDM)  196 . The AMF  192  is the control node that processes the signaling between the UEs  104  and the core network  190 . Generally, the AMF  192  provides quality of service (QoS) flow and session management. All user Internet protocol (IP) packets are transferred through the UPF  195 . The UPF  195  provides UE IP address allocation as well as other functions. The UPF  195  is connected to the IP services  197 . The IP services  197  may include the Internet, an intranet, an IP multimedia subsystem (IMS), a PS streaming service, and/or other IP services. 
     The base station  102  may also be referred to as a gNB, Node B, evolved Node B (eNB), an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), a transmit and receive point (TRP), or some other suitable terminology. The base station  102  provides an access point to the EPC  160  or core network  190  for a UE  104 . Examples of UEs  104  include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a tablet, a smart device, a wearable device, a vehicle, an electric meter, a gas pump, a large or small kitchen appliance, a healthcare device, an implant, a sensor/actuator, a display, or any other similar functioning device. Some of the UEs  104  may be referred to as IoT devices (e.g., a parking meter, gas pump, toaster, vehicles, heart monitor, etc.). The UE  104  may also be referred to as a station, a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology. 
     Referring again to  FIG.  1   , in certain aspects, a receiving device, such as the UE  104 , may receive a network coded packet from one or more other UEs  104  or base stations  102 . The UE  104  that received the network coded packet transmits acknowledgment/negative acknowledgment (ACK/NACK) feedback. The UE  104  may include a network coded feedback module  198  configured to receive a first original message from a first transmitting sidelink UE. The network coded feedback module  198  may also be configured to receive, from a network coding device, a network coded (NC) packet that is coded across the first original message and a second original message from a second transmitting sidelink UE. The first original message corresponds to a first transport block. The second original message corresponds to a second transport block. The network coded feedback module  198  may also be configured to transmit a first negative acknowledgment (NACK) in response to the first transport block being unsuccessfully decoded. The network coded feedback module  198  may be configured to transmit a second NACK in response to the second transport block being unsuccessfully decoded. The network coded feedback module  198  may also be configured to transmit a first acknowledgment (ACK) in response to the first transport block being successfully decoded. 
     A network coding device, such as the UEs  104  or base stations  102  may transmit a network coded packet to one or more other UEs  104 . The network coding device receives acknowledgment/negative acknowledgment (ACK/NACK) feedback. The network coding device may include a network coded feedback module  199  configured to transmit, to a receiving device, a network coded (NC) packet that is coded across a first original message originating from a first transmitting sidelink user equipment (UE) and a second original message originating from a second transmitting sidelink UE. The first original message corresponds to a first transport block. The second original message corresponds to a second transport block. The network coded feedback module  199  may also be configured to receive a first negative acknowledgment (NACK) in response to the first transport block being unsuccessfully decoded. The network coded feedback module  199  may also be configured to receive a second NACK in response to the second transport block being unsuccessfully decoded. The network coded feedback module  199  may be configured to receive a first acknowledgment (ACK) in response to the first transport block being successfully decoded. 
     Although the following description may be focused on 5G NR, it may be applicable to other similar areas, such as LTE, LTE-A, CDMA, GSM, and other wireless technologies. 
       FIG.  2 A  is a diagram  200  illustrating an example of a first subframe within a 5G NR frame structure.  FIG.  2 B  is a diagram  230  illustrating an example of DL channels within a 5G NR subframe.  FIG.  2 C  is a diagram  250  illustrating an example of a second subframe within a 5G NR frame structure.  FIG.  2 D  is a diagram  280  illustrating an example of UL channels within a 5G NR subframe. The 5G NR frame structure may be frequency division duplex (FDD) in which for a particular set of subcarriers (carrier system bandwidth), subframes within the set of subcarriers are dedicated for either DL or UL, or may be time division duplex (TDD) in which for a particular set of subcarriers (carrier system bandwidth), subframes within the set of subcarriers are dedicated for both DL and UL. In the examples provided by  FIGS.  2 A,  2 C , the 5G NR frame structure is assumed to be TDD, with subframe  4  being configured with slot format  28  (with mostly DL), where D is DL, U is UL, and X is flexible for use between DL/UL, and subframe  3  being configured with slot format  34  (with mostly UL). While subframes  3 ,  4  are shown with slot formats  34 ,  28 , respectively, any particular subframe may be configured with any of the various available slot formats  0 - 61 . Slot formats  0 ,  1  are all DL, UL, respectively. Other slot formats  2 - 61  include a mix of DL, UL, and flexible symbols. UEs are configured with the slot format (dynamically through DL control information (DCI), or semi-statically/statically through radio resource control (RRC) signaling) through a received slot format indicator (SFI). Note that the description infra applies also to a 5G NR frame structure that is TDD. 
     Other wireless communications technologies may have a different frame structure and/or different channels. A frame (10 ms) may be divided into 10 equally sized subframes (1 ms). Each subframe may include one or more time slots. Subframes may also include mini-slots, which may include 7, 4, or 2 symbols. Each slot may include 7 or 14 symbols, depending on the slot configuration. For slot configuration  0 , each slot may include 14 symbols, and for slot configuration  1 , each slot may include 7 symbols. The symbols on DL may be cyclic prefix (CP) OFDM (CP-OFDM) symbols. The symbols on UL may be CP-OFDM symbols (for high throughput scenarios) or discrete Fourier transform (DFT) spread OFDM (DFT-S-OFDM) symbols (also referred to as single carrier frequency-division multiple access (SC-FDMA) symbols) (for power limited scenarios; limited to a single stream transmission). The number of slots within a subframe is based on the slot configuration and the numerology. For slot configuration  0 , different numerologies μ 0  to  5  allow for 1, 2, 4, 8, 16, and 32 slots, respectively, per subframe. For slot configuration  1 , different numerologies  0  to  2  allow for 2, 4, and 8 slots, respectively, per subframe. Accordingly, for slot configuration  0  and numerology μ, there are 14 symbols/slot and 2μ slots/subframe. The subcarrier spacing and symbol length/duration are a function of the numerology. The subcarrier spacing may be equal to 2{circumflex over ( )}μ*15 kHz, where μ is the numerology  0  to  5 . As such, the numerology μ=0 has a subcarrier spacing of 15 kHz and the numerology μ=5 has a subcarrier spacing of 480 kHz. The symbol length/duration is inversely related to the subcarrier spacing.  FIGS.  2 A- 2 D  provide an example of slot configuration  0  with 14 symbols per slot and numerology μ=0 with 1 slot per subframe. The subcarrier spacing is 15 kHz and symbol duration is approximately 66.7 μs. 
     A resource grid may represent the frame structure. Each time slot includes a resource block (RB) (also referred to as physical RBs (PRBs)) that extends 12 consecutive subcarriers. The resource grid is divided into multiple resource elements (REs). The number of bits carried by each RE depends on the modulation scheme. 
     As illustrated in  FIG.  2 A , some of the REs carry reference (pilot) signals (RS) for the UE. The RS may include demodulation RS (DMRS) (indicated as Rx for one particular configuration, where 100× is the port number, but other DMRS configurations are possible) and channel state information reference signals (CSI-RS) for channel estimation at the UE. The RS may also include beam measurement RS (BRS), beam refinement RS (BRRS), and phase tracking RS (PT-RS). 
       FIG.  2 B  illustrates an example of various DL channels within a subframe of a frame. The physical downlink control channel (PDCCH) carries DCI within one or more control channel elements (CCEs), each CCE including nine RE groups (REGs), each REG including four consecutive REs in an OFDM symbol. A primary synchronization signal (PSS) may be within symbol  2  of particular subframes of a frame. The PSS is used by a UE  104  to determine subframe/symbol timing and a physical layer identity. A secondary synchronization signal (SSS) may be within symbol  4  of particular subframes of a frame. The SSS is used by a UE to determine a physical layer cell identity group number and radio frame timing. Based on the physical layer identity and the physical layer cell identity group number, the UE can determine a physical cell identifier (PCI). Based on the PCI, the UE can determine the locations of the aforementioned DMRS. The physical broadcast channel (PBCH), which carries a master information block (MIB), may be logically grouped with the PSS and SSS to form a synchronization signal (SS)/PBCH block. The MIB provides a number of RBs in the system bandwidth and a system frame number (SFN). The physical downlink shared channel (PDSCH) carries user data, broadcast system information not transmitted through the PBCH such as system information blocks (SIBs), and paging messages. 
     As illustrated in  FIG.  2 C , some of the REs carry DMRS (indicated as R for one particular configuration, but other DMRS configurations are possible) for channel estimation at the base station. The UE may transmit DMRS for the physical uplink control channel (PUCCH) and DMRS for the physical uplink shared channel (PUSCH). The PUSCH DMRS may be transmitted in the first one or two symbols of the PUSCH. The PUCCH DMRS may be transmitted in different configurations depending on whether short or long PUCCHs are transmitted and depending on the particular PUCCH format used. Although not shown, the UE may transmit sounding reference signals (SRS). The SRS may be used by a base station for channel quality estimation to enable frequency-dependent scheduling on the UL. 
       FIG.  2 D  illustrates an example of various UL channels within a subframe of a frame. The PUCCH may be located as indicated in one configuration. The PUCCH carries uplink control information (UCI), such as scheduling requests, a channel quality indicator (CQI), a precoding matrix indicator (PMI), a rank indicator (RI), and hybrid automatic repeat request (HARQ) acknowledgment/negative acknowledgment (ACK/NACK) feedback. The PUSCH carries data, and may additionally be used to carry a buffer status report (BSR), a power headroom report (PHR), and/or UCI. 
       FIG.  3    is a block diagram of a base station  310  in communication with a UE  350  in an access network. In the DL, IP packets from the EPC  160  may be provided to a controller/processor  375 . The controller/processor  375  implements layer  3  and layer  2  functionality. Layer  3  includes a radio resource control (RRC) layer, and layer  2  includes a service data adaptation protocol (SDAP) layer, a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control (MAC) layer. The controller/processor  375  provides RRC layer functionality associated with broadcasting of system information (e.g., MIB, SIBs), RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release), inter radio access technology (RAT) mobility, and measurement configuration for UE measurement reporting; PDCP layer functionality associated with header compression/decompression, security (ciphering, deciphering, integrity protection, integrity verification), and handover support functions; RLC layer functionality associated with the transfer of upper layer packet data units (PDUs), error correction through automatic repeat request (ARQ), concatenation, segmentation, and reassembly of RLC service data units (SDUs), re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto transport blocks (TBs), demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization. 
     The transmit (TX) processor  316  and the receive (RX) processor  370  implement layer  1  functionality associated with various signal processing functions. Layer  1 , which includes a physical (PHY) layer, may include error detection on the transport channels, forward error correction (FEC) coding/decoding of the transport channels, interleaving, rate matching, mapping onto physical channels, modulation/demodulation of physical channels, and MIMO antenna processing. The TX processor  316  handles mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded and modulated symbols may then be split into parallel streams. Each stream may then be mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an inverse fast Fourier transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator  374  may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE  350 . Each spatial stream may then be provided to a different antenna  320  via a separate transmitter  318 TX. Each transmitter  318 TX may modulate an RF carrier with a respective spatial stream for transmission. 
     At the UE  350 , each receiver  354 RX receives a signal through its respective antenna  352 . Each receiver  354 RX recovers information modulated onto an RF carrier and provides the information to the receive (RX) processor  356 . The TX processor  368  and the RX processor  356  implement layer  1  functionality associated with various signal processing functions. The RX processor  356  may perform spatial processing on the information to recover any spatial streams destined for the UE  350 . If multiple spatial streams are destined for the UE  350 , they may be combined by the RX processor  356  into a single OFDM symbol stream. The RX processor  356  then converts the OFDM symbol stream from the time-domain to the frequency domain using a fast Fourier transform (FFT). The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the base station  310 . These soft decisions may be based on channel estimates computed by the channel estimator  358 . The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the base station  310  on the physical channel. The data and control signals are then provided to the controller/processor  359 , which implements layer  3  and layer  2  functionality. 
     The controller/processor  359  can be associated with a memory  360  that stores program codes and data. The memory  360  may be referred to as a computer-readable medium. In the UL, the controller/processor  359  provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, and control signal processing to recover IP packets from the EPC  160 . The controller/processor  359  is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations. 
     Similar to the functionality described in connection with the DL transmission by the base station  310 , the controller/processor  359  provides RRC layer functionality associated with system information (e.g., MIB, SIBs) acquisition, RRC connections, and measurement reporting; PDCP layer functionality associated with header compression/decompression, and security (ciphering, deciphering, integrity protection, integrity verification); RLC layer functionality associated with the transfer of upper layer PDUs, error correction through ARQ, concatenation, segmentation, and reassembly of RLC SDUs, re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization. 
     Channel estimates derived by a channel estimator  358  from a reference signal or feedback transmitted by the base station  310  may be used by the TX processor  368  to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor  368  may be provided to different antenna  352  via separate transmitters  354 TX. Each transmitter  354 TX may modulate an RF carrier with a respective spatial stream for transmission. 
     The UL transmission is processed at the base station  310  in a manner similar to that described in connection with the receiver function at the UE  350 . Each receiver  318 RX receives a signal through its respective antenna  320 . Each receiver  318 RX recovers information modulated onto an RF carrier and provides the information to a RX processor  370 . 
     The controller/processor  375  can be associated with a memory  376  that stores program codes and data. The memory  376  may be referred to as a computer-readable medium. In the UL, the controller/processor  375  provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover IP packets from the UE  350 . IP packets from the controller/processor  375  may be provided to the EPC  160 . The controller/processor  375  is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations. 
     At least one of the TX processor  368 , the RX processor  356 , and the controller/processor  359  may be configured to perform aspects in connection with the network coded feedback module  198  of  FIG.  1   . Additionally, at least one of the TX processor  316 , the RX processor  370 , and the controller/processor  375  may be configured to perform aspects in connection with network coded feedback module  198  and/or  199  of  FIG.  1   . 
     In some aspects, the base station  102 ,  310  and/or the UE  104 ,  350  may include means for receiving, means for transmitting, means for determining, and/or means for deriving. Such means may include one or more components of the base station  102 ,  310  and/or the UE  104 ,  350  described in connection with  FIGS.  1  and  3   . 
     At least one of the TX processor  368 , the RX processor  356 , and the controller/processor  359  may be configured to perform aspects in connection with the (OPTIONAL) component  198  and/or sharing component  199  of  FIG.  1   . Additionally, at least one of the TX processor  316 , the RX processor  370 , and the controller/processor  375  may be configured to perform aspects in connection with (OPTIONAL) component  198  and/or sharing component  199  of  FIG.  1   . 
       FIG.  4    is a diagram of a device-to-device (D2D) communications system  400 , including V2X communications, in accordance with various aspects of the present disclosure. For example, the D2D communications system  400  may include V2X communications, (e.g., a first UE  450  communicating with a second UE  451 ). In some aspects, the first UE  450  and/or the second UE  451  may be configured to communicate in a licensed radio frequency spectrum and/or a shared radio frequency spectrum. The shared radio frequency spectrum may be unlicensed, and therefore multiple different technologies may use the shared radio frequency spectrum for communications, including new radio (NR), LTE, LTE-Advanced, licensed assisted access (LAA), dedicated short range communications (DSRC), MuLTEFire, 4G, and the like. The foregoing list of technologies is to be regarded as illustrative, and is not meant to be exhaustive. 
     The D2D communications system  400  may use NR radio access technology. Of course, other radio access technologies, such as LTE radio access technology, may be used. In D2D communications (e.g., V2X communications or vehicle-to-vehicle (V2V) communications), the UEs  450 ,  451  may be on networks of different mobile network operators (MNOs). Each of the networks may operate in its own radio frequency spectrum. For example, the air interface to a first UE  450  (e.g., Uu interface) may be on one or more frequency bands different from the air interface of the second UE  451 . The first UE  450  and the second UE  451  may communicate via a sidelink component carrier, for example, via the PC5 interface. In some examples, the MNOs may schedule sidelink communications between or among the UEs  450 ,  451  in licensed radio frequency spectrum and/or a shared radio frequency spectrum (e.g., 5 GHz radio spectrum bands). 
     The shared radio frequency spectrum may be unlicensed, and therefore different technologies may use the shared radio frequency spectrum for communications. In some aspects, a D2D communications (e.g., sidelink communications) between or among UEs  450 ,  451  is not scheduled by MNOs. The D2D communications system  400  may further include a third UE  452 . 
     The third UE  452  may operate on the first network  410  (e.g., of the first MNO) or another network, for example. The third UE  452  may be in D2D communications with the first UE  450  and/or second UE  451 . The first base station  420  (e.g., gNB) may communicate with the third UE  452  via a downlink (DL) carrier  432  and/or an uplink (UL) carrier  442 . The DL communications may be use various DL resources (e.g., the DL subframes ( FIG.  2 A ) and/or the DL channels ( FIG.  2 B )). The UL communications may be performed via the UL carrier  442  using various UL resources (e.g., the UL subframes ( FIG.  2 C ) and the UL channels ( FIG.  2 D )). 
     The first network  410  operates in a first frequency spectrum and includes the first base station  420  (e.g., gNB) communicating at least with the first UE  450 , for example, as described in  FIGS.  1 - 3   . The first base station  420  (e.g., gNB) may communicate with the first UE  450  via a DL carrier  430  and/or an UL carrier  440 . The DL communications may be use various DL resources (e.g., the DL subframes ( FIG.  2 A ) and/or the DL channels ( FIG.  2 B )). The UL communications may be performed via the UL carrier  440  using various UL resources (e.g., the UL subframes ( FIG.  2 C ) and the UL channels ( FIG.  2 D )). 
     In some aspects, the second UE  451  may be on a different network from the first UE  450 . In some aspects, the second UE  451  may be on a second network  411  (e.g., of the second MNO). The second network  411  may operate in a second frequency spectrum (e.g., a second frequency spectrum different from the first frequency spectrum) and may include the second base station  421  (e.g., gNB) communicating with the second UE  451 , for example, as described in  FIGS.  1 - 3   . 
     The second base station  421  may communicate with the second UE  451  via a DL carrier  431  and an UL carrier  441 . The DL communications are performed via the DL carrier  431  using various DL resources (e.g., the DL subframes ( FIG.  2 A ) and/or the DL channels ( FIG.  2 B )). The UL communications are performed via the UL carrier  441  using various UL resources (e.g., the UL subframes ( FIG.  2 C ) and/or the UL channels ( FIG.  2 D )). 
     In conventional systems, the first base station  420  and/or the second base station  421  assign resources to the UEs for device-to-device (D2D) communications (e.g., V2X communications and/or V2V communications). For example, the resources may be a pool of UL resources, both orthogonal (e.g., one or more frequency division multiplexing (FDM) channels) and non-orthogonal (e.g., code division multiplexing (CDM)/resource spread multiple access (RSMA) in each channel). The first base station  420  and/or the second base station  421  may configure the resources via the PDCCH (e.g., faster approach) or RRC (e.g., slower approach). 
     In some systems, each UE  450 ,  451  autonomously selects resources for D2D communications. For example, each UE  450 ,  451  may sense and analyze channel occupation during the sensing window. The UEs  450 ,  451  may use the sensing information to select resources from the sensing window. As discussed, one UE  451  may assist another UE  450  in performing resource selection. The UE  451  providing assistance may be referred to as the receiver UE or partner UE, which may potentially notify the transmitter UE  450 . The transmitter UE  450  may transmit information to the receiving UE  451  via sidelink communications. 
     The D2D communications (e.g., V2X communications and/or V2V communications) may be carried out via one or more sidelink carriers  470 ,  480 . The one or more sidelink carriers  470 ,  480  may include one or more channels, such as a physical sidelink broadcast channel (PSBCH), a physical sidelink discovery channel (PSDCH), a physical sidelink shared channel (PSSCH), and a physical sidelink control channel (PSCCH), for example. 
     In some examples, the sidelink carriers  470 ,  480  may operate using the PC5 interface. The first UE  450  may transmit to one or more (e.g., multiple) devices, including to the second UE  451  via the first sidelink carrier  470 . The second UE  451  may transmit to one or more (e.g., multiple) devices, including to the first UE  450  via the second sidelink carrier  480 . 
     In some aspects, the UL carrier  440  and the first sidelink carrier  470  may be aggregated to increase bandwidth. In some aspects, the first sidelink carrier  470  and/or the second sidelink carrier  480  may share the first frequency spectrum (with the first network  410 ) and/or share the second frequency spectrum (with the second network  411 ). In some aspects, the sidelink carriers  470 ,  480  may operate in an unlicensed/shared radio frequency spectrum. 
     In some aspects, sidelink communications on a sidelink carrier may occur between the first UE  450  and the second UE  451 . In an aspect, the first UE  450  may perform sidelink communications with one or more (e.g., multiple) devices, including the second UE  451  via the first sidelink carrier  470 . For example, the first UE  450  may transmit a broadcast transmission via the first sidelink carrier  470  to the multiple devices (e.g., the second and third UEs  451 ,  452 ). The second UE  451  (e.g., among other UEs) may receive such broadcast transmission. Additionally or alternatively, the first UE  450  may transmit a multicast transmission via the first sidelink carrier  470  to the multiple devices (e.g., the second and third UEs  451 ,  452 ). The second UE  451  and/or the third UE  452  (e.g., among other UEs) may receive such multicast transmission. The multicast transmissions may be connectionless or connection-oriented. A multicast transmission may also be referred to as a groupcast transmission. 
     Furthermore, the first UE  450  may transmit a unicast transmission via the first sidelink carrier  470  to a device, such as the second UE  451 . The second UE  451  (e.g., among other UEs) may receive such unicast transmission. Additionally or alternatively, the second UE  451  may perform sidelink communications with one or more (e.g., multiple) devices, including the first UE  450  via the second sidelink carrier  480 . For example, the second UE  451  may transmit a broadcast transmission via the second sidelink carrier  480  to the multiple devices. The first UE  450  (e.g., among other UEs) may receive such broadcast transmission. 
     In another example, the second UE  451  may transmit a multicast transmission via the second sidelink carrier  480  to the multiple devices (e.g., the first and third UEs  450 ,  452 ). The first UE  450  and/or the third UE  452  (e.g., among other UEs) may receive such multicast transmission. Further, the second UE  451  may transmit a unicast transmission via the second sidelink carrier  480  to a device, such as the first UE  450 . The first UE  450  (e.g., among other UEs) may receive such unicast transmission. The third UE  452  may communicate in a similar manner. 
     In some aspects, for example, such sidelink communications on a sidelink carrier between the first UE  450  and the second UE  451  may occur without having MNOs allocating resources (e.g., one or more portions of a resource block (RB), slot, frequency band, and/or channel associated with a sidelink carrier  470 ,  480 ) for such communications and/or without scheduling such communications. Sidelink communications may include traffic communications (e.g., data communications, control communications, paging communications and/or system information communications). Further, sidelink communications may include sidelink feedback communications associated with traffic communications (e.g., a transmission of feedback information for previously-received traffic communications). Sidelink communications may employ at least one sidelink communications structure having at least one feedback symbol. The feedback symbol of the sidelink communications structure may allot for any sidelink feedback information that may be communicated in the device-to-device (D2D) communications system  400  between devices (e.g., a first UE  450 , a second UE  451 , and/or a third UE  452 ). As discussed, a UE may be a vehicle (e.g., UE  450 ,  451 ), a mobile device (e.g.,  452 ), or another type of device. In some cases, a UE may be a special UE, such as a road side unit (RSU). 
       FIG.  5    illustrates an example of a vehicle-to-everything (V2X) system with a road side unit (RSU), according to aspects of the present disclosure. As shown in  FIG.  5   , V 2 x system  500  includes a transmitter UE  504  transmits data to an RSU  510  and a receiving UE  502  via sidelink transmissions  512 . Additionally, or alternatively, the RSU  510  may transmit data to the transmitter UE  504  via a sidelink transmission  512 . The RSU  510  may forward data received from the transmitter UE  504  to a cellular network (e.g., gNB)  508  via an UL transmission  514 . The gNB  508  may transmit the data received from the RSU  510  to other UEs  506  via a DL transmission  516 . The RSU  510  may be incorporated with traffic infrastructure (e.g., traffic light, light pole, etc.) For example, as shown in  FIG.  5   , the RSU  510  is a traffic signal positioned at a side of a road  520 . Additionally or alternatively, RSUs  510  may be stand-alone units. 
       FIG.  6    is a graph illustrating a sidelink (SL) communications scheme, in accordance with various aspects of the present disclosure. A scheme  600  may be employed by UEs such as the UEs  104  in a network such as the network  100 . In  FIG.  6   , the x-axis represents time and the y-axis represents frequency. The C2VX channels may be for 3GPP Release 16 and beyond. 
     In the scheme  600 , a shared radio frequency band  601  is partitioned into multiple subchannels or frequency subbands  602  (shown as  602   S0 ,  602   S1 ,  602 S 2 ) in frequency and multiple sidelink frames  604  (shown as  604   a,    604   b,    604   c,    604   d ) in time for sidelink communications. The frequency band  601  may be at any suitable frequencies. The frequency band  601  may have any suitable bandwidth (BW) and may be partitioned into any suitable number of frequency subbands  602 . The number of frequency subbands  602  can be dependent on the sidelink communications BW requirement. 
     Each sidelink frame  604  includes a sidelink resource  606  in each frequency subband  602 . A legend  605  indicates the types of sidelink channels within a sidelink resource  606 . In some instances, a frequency gap or guard band may be specified between adjacent frequency subbands  602 , for example, to mitigate adjacent band interference. The sidelink resource  606  may have a substantially similar structure as an NR sidelink resource. For instance, the sidelink resource  606  may include a number of subcarriers or RBs in frequency and a number of symbols in time. In some instances, the sidelink resource  606  may have a duration between about one millisecond (ms) to about 20 ms. Each sidelink resource  606  may include a PSCCH  610  and a PSSCH  620 . The PSCCH  610  and the PSSCH  620  can be multiplexed in time and/or frequency. The PSCCH  610  may be for part one of a control channel (CCH), with the second part arriving as a part of the shared channel allocation. In the example of  FIG.  6   , for each sidelink resource  606 , the PSCCH  610  is located during the beginning symbol(s) of the sidelink resource  606  and occupies a portion of a corresponding frequency subband  602 , and the PSSCH  620  occupies the remaining time-frequency resources in the sidelink resource  606 . In some instances, a sidelink resource  606  may also include a physical sidelink feedback channel (PSFCH), for example, located during the ending symbol(s) of the sidelink resource  606 . In general, a PSCCH  610 , a PSSCH  620 , and/or a PSFCH may be multiplexed within a sidelink resource  606 . 
     The PSCCH  610  may carry SCI  660  and/or sidelink data. The sidelink data can be of various forms and types depending on the sidelink application. For instance, when the sidelink application is a V2X application, the sidelink data may carry V2X data (e.g., vehicle location information, traveling speed and/or direction, vehicle sensing measurements, etc.). Alternatively, when the sidelink application is an IIoT application, the sidelink data may carry IIoT data (e.g., sensor measurements, device measurements, temperature readings, etc.). The PSFCH can be used for carrying feedback information, for example, HARQ ACK/NACK for sidelink data received in an earlier sidelink resource  606 . 
     In an NR sidelink frame structure, the sidelink frames  604  in a resource pool  608  may be contiguous in time. A sidelink UE (e.g., the UEs  104 ) may include, in SCI  660 , a reservation for a sidelink resource  606  in a later sidelink frame  604 . Thus, another sidelink UE (e.g., a UE in the same NR-U sidelink system) may perform SCI sensing in the resource pool  608  to determine whether a sidelink resource  606  is available or occupied. For instance, if the sidelink UE detected SCI indicating a reservation for a sidelink resource  606 , the sidelink UE may refrain from transmitting in the reserved sidelink resource  606 . If the sidelink UE determines that there is no reservation detected for a sidelink resource  606 , the sidelink UE may transmit in the sidelink resource  606 . As such, SCI sensing can assist a UE in identifying a target frequency subband  602  to reserve for sidelink communications and to avoid intra-system collision with another sidelink UE in the NR sidelink system. In some aspects, the UE may be configured with a sensing window for SCI sensing or monitoring to reduce intra-system collision. 
     In some aspects, the sidelink UE may be configured with a frequency hopping pattern. In this regard, the sidelink UE may hop from one frequency subband  602  in one sidelink frame  604  to another frequency subband  602  in another sidelink frame  604 . In the illustrated example of  FIG.  6   , during the sidelink frame  604   a,  the sidelink UE transmits SCI  660  in the sidelink resource  606  located in the frequency subband  602   S2  to reserve a sidelink resource  606  in a next sidelink frame  604   b  located at the frequency subband  602   S1 . Similarly, during the sidelink frame  604   b,  the sidelink UE transmits SCI  662  in the sidelink resource  606  located in the frequency subband  602   S1  to reserve a sidelink resource  606  in a next sidelink frame  604   c  located at the frequency subband  602 S 1 . During the sidelink frame  604   c,  the sidelink UE transmits SCI  664  in the sidelink resource  606  located in the frequency subband  602   S1  to reserve a sidelink resource  606  in a next sidelink frame  604   d  located at the frequency subband  602   S0 . During the sidelink frame  604   d,  the sidelink UE transmits SCI  668  in the sidelink resource  606  located in the frequency subband  602   S0 . The SCI  668  may reserve a sidelink resource  606  in a later sidelink frame  604 . 
     The SCI can also indicate scheduling information and/or a destination identifier (ID) identifying a target receiving sidelink UE for the next sidelink resource  606 . Thus, a sidelink UE may monitor SCI transmitted by other sidelink UEs. Upon detecting SCI in a sidelink resource  606 , the sidelink UE may determine whether the sidelink UE is the target receiver based on the destination ID. If the sidelink UE is the target receiver, the sidelink UE may proceed to receive and decode the sidelink data indicated by the SCI. In some aspects, multiple sidelink UEs may simultaneously communicate sidelink data in a sidelink frame  604  in different frequency subband (e.g., via frequency division multiplexing (FDM)). For instance, in the sidelink frame  604   b,  one pair of sidelink UEs may communicate sidelink data using a sidelink resource  606  in the frequency subband  602 S 2  while another pair of sidelink UEs may communicate sidelink data using a sidelink resource  606  in the frequency subband  602 S 1 . 
     In some aspects, the scheme  600  is used for synchronous sidelink communications. That is, the sidelink UEs may be synchronized in time and are aligned in terms of symbol boundary, sidelink resource boundary (e.g., the starting time of sidelink frames  604 ). The sidelink UEs may perform synchronization in a variety of forms, for example, based on sidelink synchronization signal blocks (SSBs) received from a sidelink UE and/or NR-U SSBs received from a base station (e.g., the base stations  105  and/or  205 ) while in-coverage of the base station. In some aspects, the sidelink UE may be preconfigured with the resource pool  608  in the frequency band  601 , for example, while in coverage of a serving base station. The resource pool  608  may include a plurality of sidelink resources  606 . The base station can configure the sidelink UE with a resource pool configuration indicating resources in the frequency band  601  and/or the subbands  602  and/or timing information associated with the sidelink frames  604 . In some aspects, the scheme  600  includes mode-2 RRA (e.g., supporting autonomous radio resource allocation (RRA) that can be used for out-of-coverage sidelink UEs or partial-coverage sidelink UEs). 
     Network coding is a technique that may lead to increased system capacity and improved resource utilization by reducing a number of retransmissions in the system while maintaining performance. Network coding may enable an increase in a number of user equipment (UEs) within the system or may increase traffic per UE. With network codding, after an original transmitter sends an initial transmission, a network device sends any expected retransmissions on behalf of the original device. Although the present description is primarily with respect to retransmissions, the present disclosure also pertains to network coding of initial transmissions on behalf of the original transmitter. 
       FIG.  7    is a block diagram illustrating sidelink groupcasting, in accordance with various aspects of the present disclosure. In the example network of  FIG.  7   , two transmitting UEs, UE 0  and UE 1 , transmit messages to two receiving UEs, UE 2  and UE 3 . Each of the UEs may correspond to the UEs  104 ,  350 ,  450 ,  451 ,  452 ,  502 ,  504 ,  506  of the earlier described figures. As an example, the first transmitting UE, UE 0 , groupcasts a first transmission Tx a  to the receiving UEs, UE 2  and UE 3 . One of the receiving UEs, UE 2 , successfully receives the first transmission Tx a . The other one of the receiving UEs, UE 3 , does not successfully receive the first transmission Tx a . The second transmitting UE, UE 1 , groupcasts a second transmission Tx b  to the receiving UEs, UE 2  and UE 3 . One of the receiving UEs, UE 3 , successfully receives the second transmission Tx b . The other one of the receiving UEs, UE 2 , does not successfully receive the second transmission Tx b . 
     When a message is not successfully decoded, a retransmission of the original message may occur in an attempt to successfully transmit the message to the receiver. Generally speaking, the transmitter of the original message performs the retransmission. With network coding, a network device may retransmit the original message instead of the original device. The network coding device may be a base station, a road side unit (RSU), or even another UE. 
       FIG.  8    is a block diagram illustrating network coding, in accordance with various aspects of the present disclosure. In the example of  FIG.  8   , a base station  102  retransmits the missed first message Tx a  and missed second message Tx b . to the receiving UEs, UE 2  and UE 3 . The missed messages may be combined by some function, such as concatenation. Because the receiving UEs, UE 2  and UE 3 , successfully decoded one of the messages, the receiving UEs, UE 2  and UE 3 , can use the successfully decoded information to help decode the missed transmissions, which are received from the base station  102 . For example, a first receiving UE, UE 2 , knows the first transmission Tx a  and can use that information to attempt to decode the second transmission Tx b . A second receiving UE, UE 3 , knows the second transmission Tx b  and can use that information to attempt to decode the first transmission Tx a . 
     Erasure coding techniques help the receiver to recover the missing information. For example, if one packet is missing, the packet can be recovered from the other packets that have been successfully decoded. Single parity check codes can correct one erasure. For example, an input of [a, b, c] may be encoded to [a, b, c, a⊕b⊕c] and then transmitted, where ⊕ represents the exclusive OR (XOR) operation. Based on this type of coding, any single erasure can be recovered. If the received vector is [a, ?, c, a⊕b⊕c] where ? represents the missing information (or erased element), the missing information can be recovered by summing the others: a⊕c⊕(a⊕b⊕c)=b. This can be viewed as a linear system, over a Galois field, with three variables and four linearly independent constraints represented in matrix form as follows, where T represents the transpose: 
     
       
         
           
             
               
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     With this technique, any three constraints, which is one erasure, are sufficient to find the three variables. 
     Erasure coding may also be used to recover two or more erasures by extending the single parity example. Reed-Solomon codes, or other maximum distance separable (MDS) codes, are block-based error correcting codes that may be used to correct errors. Any k symbols of an n symbol codeword are sufficient to decode the k information symbols. An example encoding to recover from up to two erasures is seen below, where a is a parameter with a value between zero and one: 
     
       
         
           
             
               
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     With network coding, a network device (which may be referred to as an encoder) takes over retransmission responsibility from the original transmitter. The coding is performed across transmissions from different UEs. 
       FIG.  9    is a block diagram illustrating network coding, in accordance with various aspects of the present disclosure. In  FIG.  9   , a transmitting UE, UE 0 , attempts to transmit a message to a receiving UE, UE 2 . Due to the blocking structure  902 , the message is not successfully received at the receiving UE, UE 2 . With network coding, an RSU  510  transmits the message to the receiving UE, UE 2 , on behalf of the transmitting UE, UE 0 . 
       FIG.  10    is a timing diagram illustrating network coding, in accordance with various aspects of the present disclosure. In the example of  FIG.  10   , a transmitting UE, UE 1 , generates a transport block, TB 1 , and a request for network coding. The request for network coding may be provided as a bit in a header of the transport block, TB 1 . At time t 0 , the transmitting UE, UE 1 , transmits the transport block, TB 1 , along with the request for network coding to a network. Another transmitting UE, UE 0 , generates a transport block, TB 0 , and a request for network coding. At time t 1 , the transmitting UE, UE 0 , transmits the transport block, TB 0 , and the request for network coding to the network. At time t 2 , an RSU  510  acknowledges receipt of the request for network coding to handover responsibility for retransmissions. At times t 3  and t 4 , the transmitting UEs, UE 0  and UE 1 , stop any processing for sending retransmissions, after receiving the acknowledgment (ACK) from the RSU  510 . 
     At time t 5 , the RSU  510  generates and sends a network coded transmission (Tx) (also referred to as a network coded packet), including the transport blocks, TB 0  and TB 1 , to a receiving UE, UE 2 . The network coded packet contains a network coded combination of multiple coded packets, in this case the transport blocks, TB 0  and TB 1 . After receiving the network coded packet, the receiving UE, UE 2 , determines whether to send acknowledgement or negative acknowledgement (ACK/NACK) feedback for these coded transport blocks, TB 0  and TB 1 , or the entire network coded packet. The receiving UE, UE 2 , also determines the type of feedback to be sent. 
     For example, when a multi-erasure code is used, if a network coded packet contains four transport blocks, sending an ACK/NACK for the network coded packet is not sufficient. Feedback for each of the four transport blocks is desired. However, this may lead to an increase in the amount of feedback, and also a high peak-to-average power ratio if not arranged properly. Thus, the type of feedback, and when to send the feedback, is an important consideration. After determining the feedback to send, the receiving UE, UE 2 , transmits the feedback to the RSU  510 , at time t 6 . The RSU  510  may then inform the transmitting UEs, UE 0  and UE 1 , of the delivery status, at time t 7 . 
     In the case of multiple receiving UEs, when each receiving UE sends multiple feedback messages for a single network coded packet, the peak-to-average power ratio (PAPR) should be reduced. The PAPR is the relation between the maximum power of a sample in a given orthogonal frequency division multiplexing (OFDM) transmit symbol divided by the average power of that OFDM symbol. Reducing the PAPR of the OFDM signal allows use of a power amplifier device with lower power specifications. The power amplifier is one of the most power consuming units of the device. 
     According to aspects of the present disclosure, a receiving UE sends full ACK/NACK feedback in response to receiving a network coded packet. In these aspects, the UE sends NACK feedback for any transport block in the network coding combination that is not successfully decoded. The UE also sends ACK feedback for any transport block in the network coding combination that has been successfully decoded. 
     A UE may determine an index of a physical sidelink feedback channel (PSFCH) resource for transmitting feedback in response to a transport block within the network coded packet. That is, the UE determines which resources to use for transmitting the feedback. For example, the UE may use the formula: (P ID +M ID )modR PRB,CS   PSFCH , where R PRB,CS   PSFCH  represents a number of PSFCH resources available for feedback associated with this network coded packet for all intended recipients. The parameter M ID  is the identity (ID) of the UE receiving the network coded packet, for example, indicated by higher layers. The network device may be aware of this ID from when the UE initializes access to the network. There can be multiple alternatives for the packet ID parameter P ID . For example, a physical layer source ID may be provided by sidelink control information (SCI) format 2-A or 2-B for the transport block. In other aspects, the parameter P ID  may be included in a network coded packet header. For example, the P ID  values may be provided for each transport block within a network coded packet. 
     In some aspects of the present disclosure, feedback reporting for network coded packets may be reduced. For example, the UE may send NACK feedback for any of the transport blocks in the network coded packet that are unsuccessfully decoded, only when the UE would have sent NACK feedback to the transport block&#39;s original transmitter. That is, the receiver sends NACKS only when the receiver is an intended recipient of the transport block&#39;s original transmitter, for any unsuccessfully decoded transport blocks in the network coded packet. 
     The UE may determine whether it is an intended recipient based on information such as transmitter location and communication range. In one example, only UEs within fifteen meters of the transmitter UE may be intended recipients. An RSU, however, may have different receivers within fifteen meters of the RSU because the RSU may have a different location than the transmitting UE. Other metrics for determining whether the UE is an intended recipient include a unicast destination/source ID, and/or groupcast source ID. Such information may be included in the network coded packet, for example, the information may be included with the header. In other aspects, the information is not provided within the header. 
     According to some aspects of the present disclosure, the UE sends ACK feedback, only if the receiver is an intended recipient of the transport block&#39;s original transmitter. In other aspects, the UE sends ACK feedback for any transport block that is newly decoded. In still other aspects, the UE sends ACK feedback only if the receiver is an intended recipient of the transport block&#39;s original transmitter and the transport block is newly decoded. In still other aspects, the UE may be instructed to send a single ACK to indicate that the UE successfully decoded all of the transport blocks within the network coded packet. According to aspects of the present disclosure, how and when the receiving UE should provide feedback may be indicated in a message from an encoder. In other aspects, how and when the receiving UE should provide feedback may be preconfigured. 
     By reducing feedback reporting for network coded packets, the chance of feedback collisions is reduced. For example, if the P ID  and M ID  parameters for determining the PSFCH resources have the same values for different UEs, the feedback will collide. Reducing feedback reporting may prevent the collision. 
     According to further aspects of the present disclosure, the peak-to-average power ratio (PAPR) may be reduced during feedback reporting. If the UE is configured to send full ACK/NACK feedback, the multiple feedback ACK/NACKs from the UE for one network coded packet may not be consecutive in the PSFCH resources. This may lead to a high peak-to-average power ratio, which results in high radio frequency (RF) emissions. To reduce the peak-to-average power ratio, these multiple feedback ACK/NACKs may be assigned to consecutive PSFCH resources. In some implementations, the P ID  parameter may be designed to be consecutive. For example, the P ID  parameter may be set to a sequence ID. The sequence ID may indicate the transport block&#39;s sequence in the network coded packet. In other words, for N transport blocks in the network coded packet, the sequence ID belongs to the set [0, N−1]. In some aspects, the sequence ID may be explicitly indicated in the header of the network coded packet. In other aspects, the sequence ID may be inferred from the header of the network coded packet. For example, when four transport blocks are declared in the header, the sequence of the transport blocks in the declaration may be used for the sequence ID. 
     As indicated above,  FIGS.  3 - 10    are provided as examples. Other examples may differ from what is described with respect to  FIGS.  3 - 10   . 
       FIG.  11    is a flow diagram illustrating an example process  1100  performed, for example, by a receiving sidelink user equipment (UE), in accordance with various aspects of the present disclosure. The example process  1100  is an example of a sidelink feedback design for network coding systems, to reduce peak-to-average-power ratio (PAPR). The operations of the process  1100  may be implemented by a UE  104 . 
     At block  1102 , the user equipment (UE) receives a first original message from a first transmitting sidelink UE. For example, the UE (e.g. using the antenna  352 , receiver RX  354 , RX processor  356 , and/or channel estimator  358 ) may receive the first original message. At block  1104 , the user equipment (UE) receives, from a network coding device, a network coded (NC) packet that is coded across the first original message and a second original message from a second transmitting sidelink UE. For example, the UE (e.g. using the antenna  352 , receiver RX  354 , RX processor  356 , and/or channel estimator  358 ) may receive the NC packet. The first original message corresponds to a first transport block. The second original message corresponds to a second transport block. 
     At block  1106 , the user equipment (UE) transmits a first negative acknowledgment (NACK) in response to the first transport block being unsuccessfully decoded. For example, the UE (e.g. using the antenna  352 , transmitter TX  354 , TX processor  368 , channel estimator  358 , controller/processor  359 , and/or memory  360 ) may transmit the first NACK. In some aspects, the UE transmits the first NACK in response to the first sidelink UE being an intended recipient of the first transport block. 
     At block  1108 , the user equipment (UE) transmits a second NACK in response to the second transport block being unsuccessfully decoded. For example, the UE (e.g. using the antenna  352 , transmitter TX  354 , TX processor  368 , channel estimator  358 , controller/processor  359 , and/or memory  360 ) may transmit the second NACK. 
     At block  1110 , the user equipment (UE) transmits a first acknowledgment (ACK) in response to the first transport block being successfully decoded. For example, the UE (e.g. using the antenna  352 , transmitter TX  354 , TX processor  368 , channel estimator  358 , controller/processor  359 , and/or memory  360 ) may transmit the first ACK. In some aspects, the UE transmits the first ACK occurs in response to the first sidelink UE being an intended recipient of the first transport block. In other aspects, the UE transmits the first ACK occurs regardless of whether the first sidelink UE is an intended recipient of the first transport block, such that transmitting the first ACK occurs in response to the first transport block being newly decoded. In still other aspects, the UE transmits the first ACK occurs in response to the first sidelink UE being an intended recipient of the first transport block, and the first transport block being newly decoded. The first ACK may indicate the first transport block and the second transport block have both been successfully decoded. 
       FIG.  12    is a flow diagram illustrating an example process  1200  performed, for example, by a network coding device, in accordance with various aspects of the present disclosure. The example process  1200  is an example of a sidelink feedback design for network coding systems, to reduce peak-to-average-power ratio (PAPR). The operations of the process  1200  may be implemented by a network coding device. 
     At block  1202 , the network coding device transmits, to a receiving device, a network coded (NC) packet that is coded across a first original message originating from a first transmitting sidelink user equipment (UE) and a second original message originating from a second transmitting sidelink UE. For example, the network coding device (e.g. using the antenna  320 , transmitter TX  318 , TX processor  316 , and/or channel estimator  374 ) may transmit the NC packet. The first original message corresponds to a first transport block the second original message corresponds to a second transport block. 
     At block  1204 , the network coding device receives a first negative acknowledgment (NACK) in response to the first transport block being unsuccessfully decoded. For example, the network coding device (e.g. using the antenna  320 , receiver RX  318 , RX processor  370 , and/or channel estimator  374 ) may receive the first NACK. The first NACK may be received in response to the first sidelink UE being an intended recipient of the first transport block. 
       20 . The method of claim  13 , in which receiving the first ACK occurs in response to the first sidelink UE being an intended recipient of the first transport block. 
       21 . The method of claim  13 , in which receiving the first ACK occurs regardless of whether the first sidelink UE is an intended recipient of the first transport block, wherein receiving the first ACK occurs in response to the first transport block being newly decoded. 
       22 . The method of claim  13 , in which receiving the first ACK occurs in response to the first sidelink UE being an intended recipient of the first transport block, and the first transport block being newly decoded. 
       23 . The method of claim  13 , in which the first ACK indicates the first transport block and the second transport block have both been successfully decoded. 
     At block  1206 , the network coding device receives a second NACK in response to the second transport block being unsuccessfully decoded. For example, the network coding device (e.g. using the antenna  320 , receiver RX  318 , RX processor  370 , and/or channel estimator  374 ) may receive the NACK. 
     At block  1208 , the network coding device receives a first acknowledgment (ACK) in response to the first transport block being successfully decoded. For example, the network coding device (e.g. using the antenna  320 , receiver RX  318 , RX processor  370 , and/or channel estimator  374 ) may receive the ACK. 
     Example Aspects 
     Aspect 1: A method of wireless communication by a receiving sidelink user equipment (UE), comprising: receiving a first original message from a first transmitting sidelink UE; receiving, from a network coding device, a network coded (NC) packet that is coded across the first original message and a second original message from a second transmitting sidelink UE, the first original message corresponding to a first transport block, the second original message corresponding to a second transport block; transmitting a first negative acknowledgment (NACK) in response to the first transport block being unsuccessfully decoded; transmitting a second NACK in response to the second transport block being unsuccessfully decoded; and transmitting a first acknowledgment (ACK) in response to the first transport block being successfully decoded. 
     Aspect 2: The method of Aspect 1, further comprising determining an index of a physical sidelink feedback channel (PSFCH) resource for transmitting a feedback message for the first transport block, the index based on a number of PSFCH resources available for the NC packet, an identity (ID) of the receiving sidelink UE, and a packet ID. 
     Aspect 3: The method of Aspect 1 or 2, in which the packet ID comprises a physical layer source ID based on a sidelink control information (SCI) format. 
     Aspect 4: The method of any of the preceding Aspects, in which the packet ID ensures any feedback for the NC packet is transmitted in consecutive resources of the PSFCH. 
     Aspect 5: The method of any of the preceding Aspects, further comprising receiving the packet ID in a header of the NC packet. 
     Aspect 6: The method of any of the preceding Aspects, further comprising deriving the packet ID from a header of the NC packet. 
     Aspect 7: The method of any of the preceding Aspects, in which the packet ID corresponds to a transport block sequence in the NC packet. 
     Aspect 8: The method of any of the preceding Aspects, in which transmitting the first NACK occurs in response to the first sidelink UE being an intended recipient of the first transport block. 
     Aspect 9: The method of any of the preceding Aspects, in which transmitting the first ACK occurs in response to the first sidelink UE being an intended recipient of the first transport block. 
     Aspect 10: The method of any of the preceding Aspects, in which transmitting the first ACK occurs regardless of whether the first sidelink UE is an intended recipient of the first transport block, wherein transmitting the first ACK occurs in response to the first transport block being newly decoded. 
     Aspect 11: The method of any of the preceding Aspects, in which transmitting the first ACK occurs in response to the first sidelink UE being an intended recipient of the first transport block, and the first transport block being newly decoded. 
     Aspect 12: The method of any of the preceding Aspects, in which the first ACK indicates the first transport block and the second transport block have both been successfully decoded. 
     Aspect 13: A method of wireless communication by a network coding device, comprising: transmitting, to a receiving device, a network coded (NC) packet that is coded across a first original message originating from a first transmitting sidelink user equipment (UE) and a second original message originating from a second transmitting sidelink UE, the first original message corresponding to a first transport block the second original message corresponding to a second transport block; receiving a first negative acknowledgment (NACK) in response to the first transport block being unsuccessfully decoded; receiving a second NACK in response to the second transport block being unsuccessfully decoded; and receiving a first acknowledgment (ACK) in response to the first transport block being successfully decoded. 
     Aspect 14: The method of Aspect 13, further comprising determining an index of a physical sidelink feedback channel (PSFCH) resource for receiving a feedback message for the first transport block, the index based on a number of PSFCH resources available for the NC packet, an identity (ID) of the receiving device, and a packet ID. 
     Aspect 15: The method of Aspect 13 or 14, in which the packet ID comprises a physical layer source ID based on a sidelink control information (SCI) format. 
     Aspect 16: The method of any of the Aspects 13-15, in which the packet ID comprises an ID included in a header of the NC packet. 
     Aspect 17: The method of any of the Aspects 13-16, in which the packet ID ensures any feedback for the NC packet is received in consecutive resources of the PSFCH. 
     Aspect 18: The method of any of the Aspects 13-17, in which the packet ID corresponds to a transport block sequence in the NC packet. 
     Aspect 19: The method of any of the Aspects 13-18, in which receiving the first NACK occurs in response to the first sidelink UE being an intended recipient of the first transport block. 
     Aspect 20: The method of any of the Aspects 13-19, in which receiving the first ACK occurs in response to the first sidelink UE being an intended recipient of the first transport block. 
     Aspect 21: The method of any of the Aspects 13-20, in which receiving the first ACK occurs regardless of whether the first sidelink UE is an intended recipient of the first transport block, wherein receiving the first ACK occurs in response to the first transport block being newly decoded. 
     Aspect 22: The method of any of the Aspects 13-21, in which receiving the first ACK occurs in response to the first sidelink UE being an intended recipient of the first transport block, and the first transport block being newly decoded. 
     Aspect 23: The method of any of the Aspects 13-22, in which the first ACK indicates the first transport block and the second transport block have both been successfully decoded. 
     Aspect 24: An apparatus for wireless communication by a receiving sidelink user equipment (UE), comprising: a memory; and at least one processor coupled to the memory, the at least one processor configured: to receive a first original message from a first transmitting sidelink UE; to receive, from a network coding device, a network coded (NC) packet that is coded across the first original message and a second original message from a second transmitting sidelink UE, the first original message corresponding to a first transport block, the second original message corresponding to a second transport block; to transmit a first negative acknowledgment (NACK) in response to the first transport block being unsuccessfully decoded; to transmit a second NACK in response to the second transport block being unsuccessfully decoded; and to transmit a first acknowledgment (ACK) in response to the first transport block being successfully decoded. 
     Aspect 25: The apparatus of Aspect 24, in which the at least one processor is further configured to determine an index of a physical sidelink feedback channel (PSFCH) resource for transmitting a feedback message for the first transport block, the index based on a number of PSFCH resources available for the NC packet, an identity (ID) of the receiving sidelink UE, and a packet ID. 
     Aspect 26: The apparatus of Aspect 25, in which the packet ID comprises a physical layer source ID based on a sidelink control information (SCI) format. 
     Aspect 27: The apparatus of Aspect 25 or 26, in which the packet ID ensures any feedback for the NC packet is transmitted in consecutive resources of the PSFCH. 
     Aspect 28: The apparatus of any of the Aspects 25-27, in which the at least one processor is further configured to receive the packet ID in a header of the NC packet. 
     Aspect 29: The apparatus of any of the Aspects 25-28, in which the at least one processor is further configured to derive the packet ID from a header of the NC packet. 
     Aspect 30: The apparatus of any of the Aspects 25-29, in which the packet ID corresponds to a transport block sequence in the NC packet. 
     The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the aspects to the precise form disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the aspects. 
     As used, the term “component” is intended to be broadly construed as hardware, firmware, and/or a combination of hardware and software. As used, a processor is implemented in hardware, firmware, and/or a combination of hardware and software. 
     Some aspects are described in connection with thresholds. As used, satisfying a threshold may, depending on the context, refer to a value being greater than the threshold, greater than or equal to the threshold, less than the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, and/or the like. 
     It will be apparent that systems and/or methods described may be implemented in different forms of hardware, firmware, and/or a combination of hardware and software. The actual specialized control hardware or software code used to implement these systems and/or methods is not limiting of the aspects. Thus, the operation and behavior of the systems and/or methods were described without reference to specific software code—it being understood that software and hardware can be designed to implement the systems and/or methods based, at least in part, on the description. 
     Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of various aspects. In fact, many of these features may be combined in ways not specifically recited in the claims and/or disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of various aspects includes each dependent claim in combination with every other claim in the claim set. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c). 
     No element, act, or instruction used should be construed as critical or essential unless explicitly described as such. Also, as used, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more.” Furthermore, as used, the terms “set” and “group” are intended to include one or more items (e.g., related items, unrelated items, a combination of related and unrelated items, and/or the like), and may be used interchangeably with “one or more.” Where only one item is intended, the phrase “only one” or similar language is used. Also, as used, the terms “has,” “have,” “having,” and/or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.