Patent Description:
Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for cyclic shift selection for physical sidelink control channel transmission.

NR is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better P+S Ref. No.: QUAL/201679PC integrating with other open standards using OFDMA with a cyclic prefix (CP) on the downlink (DL) and on the uplink (UL).

After considering this discussion, and particularly after reading the section entitled "Detailed Description" one will understand how the features of this disclosure provide advantages that include improved cyclic shift selection for physical sidelink control channel (PSCCH) retransmission.

Certain aspects of the subject matter described in this disclosure can be implemented in a method for wireless communication by a first user equipment (UE). The method generally includes monitoring one or more sidelink control information (SCI) transmissions from one or more second UEs. The method generally includes determining, based on the one or more SCI, whether one or more collisions occur between one or more retransmissions of the one or more SCI transmissions by the one or more second UEs and a scheduled SCI transmission by the first UE. The method generally includes selecting a cyclic shift to use for the scheduled SCI transmission by the first UE based at least on the determination.

Certain aspects of the subject matter described in this disclosure can be implemented in an apparatus for wireless communication. The apparatus generally includes at least one processor and a memory coupled to the at least one processor. The memory generally includes code executable by the at least one processor to cause the apparatus to monitor one or more SCI transmissions from one or more UEs. The memory generally includes code executable by the at least one processor to cause the apparatus to determine, based on the one or more SCI, whether one or more collisions occur between one or more retransmissions of the one or more SCI transmissions by the one or more UEs and a scheduled SCI transmission by the apparatus. The memory generally includes code executable by the at least one processor to cause the apparatus to select a cyclic shift to use for the scheduled SCI transmission by the apparatus based at least on the determination.

Certain aspects of the subject matter described in this disclosure can be implemented in an apparatus for wireless communication. The apparatus generally includes means for monitoring one or more SCI transmissions from one or more UEs. The apparatus generally includes means for determining, based on the one or more SCI, whether one or more collisions occur between one or more retransmissions of the one or more SCI transmissions by the one or more UEs and a scheduled SCI transmission by the apparatus. The apparatus generally includes means for selecting a cyclic shift to use for the scheduled SCI transmission by the apparatus based at least on the determination.

Certain aspects of the subject matter described in this disclosure can be implemented in a computer readable medium storing computer executable code thereon for wireless communication by a first UE. The computer readable medium generally includes code for monitoring one or more SCI transmissions from one or more second UEs. The computer readable medium generally includes code for determining, based on the one or more SCI, whether one or more collisions occur between one or more retransmissions of the one or more SCI transmissions by the one or more second UEs and a scheduled SCI transmission by the first UE. The computer readable medium generally includes code for selecting a cyclic shift to use for the scheduled SCI transmission by the first UE based at least on the determination.

Aspects of the present disclosure provide apparatus, methods, processing systems, and computer readable mediums for cyclic shift selection for physical sidelink control channel (PSCCH) retransmissions, such as in cellular vehicle-to-anything (C-V2X) direct communications.

In C-V2X systems, user equipment (UE), such as vehicular UEs, may directly communicate with each other using time-frequency resources autonomously selected by the UE. However, the autonomous selection of resources can cause problems when two UEs select the same resources, thereby causing packet collisions or packet overlaps. For example, in some scenarios, a UE may be "hidden" during channel sensing and an initial resource selection (e.g., an autonomous semi-persistent scheduling (SPS) resource selection), and may be interfering.

Aspects of the present disclosure provide techniques for selecting cyclic shifts for PSCCH retransmissions. In some examples, a UE monitors for sidelink control information (SCI) and corresponding SCI transmissions of other UEs and for any collisions between its transmissions (and retransmissions) and transmissions (and retransmissions) from other UEs. The UE may select a cyclic shift for its own SCI transmission (either an initial SCI transmission or a SCI retransmission) based on whether there is a collision.

The following description provides examples of cyclic shift selection for PSCCH retransmissions in communication systems, and is not limiting of the scope, applicability, or examples set forth in the claims.

The techniques described herein may be used for various wireless networks and radio technologies. While aspects may be described herein using terminology commonly associated with <NUM>, <NUM>, and/or new radio (e.g., <NUM> NR) wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems.

NR access may support various wireless communication services, such as enhanced mobile broadband (eMBB) targeting wide bandwidth (e.g., <NUM> or beyond), millimeter wave (mmW) targeting high carrier frequency (e.g., <NUM> or beyond), massive machine type communications MTC (mMTC) targeting non-backward compatible MTC techniques, and/or mission critical targeting ultra-reliable low-latency communications (URLLC). In addition, these services may coexist in the same subframe. NR supports beamforming and beam direction may be dynamically configured.

As shown in <FIG>, the wireless communication network <NUM> may be in communication with a core network <NUM>. The core network <NUM> may in communication with one or more base station (BSs) <NUM> and/or user equipment (UE) <NUM> in the wireless communication network <NUM> via one or more interfaces.

As shown in <FIG>, the wireless communication network <NUM> may be in communication with a core network <NUM>. The core network <NUM> may in communication with one or more base station (BSs) 110a-z (each also individually referred to herein as BS <NUM> or collectively as BSs <NUM>) and/or user equipment (UE) 120a-y (each also individually referred to herein as UE <NUM> or collectively as UEs <NUM>) in the wireless communication network <NUM> via one or more interfaces.

A network controller <NUM> may couple to a set of BSs <NUM> and provide coordination and control for these BSs <NUM> (e.g., via a backhaul).

The BSs <NUM> communicate with UEs 120a-y (each also individually referred to herein as UE <NUM> or collectively as UEs <NUM>) in the wireless communication network <NUM>.

According to certain aspects, the UEs <NUM> may be configured for cyclic shift selection for physical sidelink control channel (PSCCH) retransmission. As shown in <FIG>, the UE 120a includes a sidelink manager <NUM>. The sidelink manager <NUM> may be configured to monitor one or more sidelink control information (SCI) transmissions from one or more second UEs; determine, based on the one or more SCI, whether one or more collisions occur between one or more retransmissions of the one or more SCI transmissions by the one or more second UEs and a scheduled SCI transmission by the first UE; and select a cyclic shift to use for the scheduled SCI transmission by the first UE based at least on the determination, in accordance with aspects of the present disclosure.

At the BS 110a, a transmit processor <NUM> may receive data from a data source <NUM> and control information from a controller/processor <NUM>. The control information may be for the physical broadcast channel (PBCH), physical control format indicator channel (PCFICH), physical hybrid ARQ indicator channel (PHICH), physical downlink control channel (PDCCH), group common PDCCH (GC PDCCH), etc. The data may be for the physical downlink shared channel (PDSCH), etc. A medium access control (MAC)-control element (MAC-CE) is a MAC layer communication structure that may be used for control command exchange between wireless nodes. The MAC-CE may be carried in a shared channel such as a physical downlink shared channel (PDSCH), a physical uplink shared channel (PUSCH), or a physical sidelink shared channel (PSSCH).

The processor <NUM> may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor <NUM> may also generate reference symbols, such as for the primary synchronization signal (PSS), secondary synchronization signal (SSS), and channel state information reference signal (CSI-RS). A transmit (TX) multiple-input multiple-output (MIMO) processor <NUM> may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) in transceivers 232a-232t. Each modulator in transceivers 232a-232t may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Downlink signals from modulators in transceivers 232a-232t may be transmitted via the antennas 234a-234t, respectively.

At the UE 120a, the antennas 252a-252r may receive the downlink signals from the BS 110a and may provide received signals to the demodulators (DEMODs) in transceivers 254a-254r, respectively. Each demodulator in transceivers 254a-254r may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. A MIMO detector <NUM> may obtain received symbols from all the demodulators in transceivers 254a-254r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor <NUM> may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE 120a to a data sink <NUM>, and provide decoded control information to a controller/processor <NUM>.

On the uplink, at UE 120a, a transmit processor <NUM> may receive and process data (e.g., for the physical uplink shared channel (PUSCH)) from a data source <NUM> and control information (e.g., for the physical uplink control channel (PUCCH) from the controller/processor <NUM>. The symbols from the transmit processor <NUM> may be precoded by a TX MIMO processor <NUM> if applicable, further processed by the modulators (MODs) in transceivers 254a-254r (e.g., for SC-FDM, etc.), and transmitted to the BS 110a. At the BS 110a, the uplink signals from the UE 120a may be received by the antennas <NUM>, processed by the modulators in transceivers 232a-232t, detected by a MIMO detector <NUM> if applicable, and further processed by a receive processor <NUM> to obtain decoded data and control information sent by the UE 120a.

Antennas <NUM>, processors <NUM>, <NUM>, <NUM>, and/or controller/processor <NUM> of the UE 120a and/or antennas <NUM>, processors <NUM>, <NUM>, <NUM> may be used to perform the various techniques and methods described herein. As shown in <FIG>, the controller/processor <NUM> of the UE 120a has a sidelink manager <NUM> that may be configured for cyclic shift selection for PSCCH retransmission, according to aspects described herein. Although shown at the controller/processor, other components of the UE 120a and BS 110a may be used to perform the operations described herein.

Each subframe may include a variable number of slots (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>,. slots) depending on the SCS. Each slot may include a variable number of symbol periods (e.g., <NUM> or <NUM> symbols) depending on the SCS.

In NR, a synchronization signal block (SSB) is transmitted. In certain aspects, SSBs may be transmitted in a burst where each SSB in the burst corresponds to a different beam direction for UE-side beam management (e.g., including beam selection and/or beam refinement). The SSB includes a PSS, a SSS, and a two symbol PBCH. The SSB can be transmitted in a fixed slot location, such as the symbols <NUM>-<NUM> as shown in <FIG>. The PBCH carries some basic system information, such as downlink system bandwidth, timing information within radio frame, SS burst set periodicity, system frame number, etc. The SSBs may be organized into SS bursts to support beam sweeping. The SSB can be transmitted up to sixty-four times, for example, with up to sixty-four different beam directions for mmWave. The multiple transmissions of the SSB are referred to as a SS burst set. SSBs in an SS burst set may be transmitted in the same frequency region, while SSBs in different SS bursts sets can be transmitted at different frequency regions.

In some examples, the communication between the UEs <NUM> and BSs <NUM> is referred to as the access link. The access link may be provided via a Uu interface. Communication between devices may be referred as the sidelink.

In some examples, two or more subordinate entities (e.g., UEs <NUM>) may communicate with each other using sidelink signals. Generally, a sidelink signal may refer to a signal communicated from one subordinate entity (e.g., UE 120a) to another subordinate entity (e.g., another UE <NUM>) without relaying that communication through the scheduling entity (e.g., UE <NUM> or BS <NUM>), even though the scheduling entity may be utilized for scheduling and/or control purposes. One example of sidelink communication is PC5, for example, as used in V2V, LTE, and/or NR.

Various sidelink channels may be used for sidelink communications, including a physical sidelink discovery channel (PSDCH), a physical sidelink control channel (PSCCH), a physical sidelink shared channel (PSSCH), and a physical sidelink feedback channel (PSFCH). The PSDCH may carry discovery expressions that enable proximal devices to discover each other. The PSCCH may carry control signaling such as sidelink resource configurations and other parameters used for data transmissions, and the PSSCH may carry the data transmissions. The PSFCH may carry feedback such as CSI related to a sidelink channel quality.

<FIG> and <FIG> show diagrammatic representations of example vehicle-to-everything (V2X) systems, in accordance with some aspects of the present disclosure. For example, the vehicles shown in <FIG> and <FIG> may communicate via sidelink channels and may relay sidelink transmissions as described herein.

The V2X systems, provided in <FIG> and <FIG> provide two complementary transmission modes. A first transmission mode (also referred to as mode <NUM>), shown by way of example in <FIG>, involves direct communications (for example, also referred to as side link communications) between participants in proximity to one another in a local area. A second transmission mode (also referred to as mode <NUM>), shown by way of example in <FIG>, involves network communications through a network, which may be implemented over a Uu interface (for example, a wireless communication interface between a radio access network (RAN) and a UE).

Referring to <FIG>, a V2X system <NUM> (for example, including vehicle to vehicle (V2V) communications) is illustrated with two vehicles <NUM>, <NUM>. The first transmission mode allows for direct communication between different participants in a given geographic location. As illustrated, a vehicle can have a wireless communication link <NUM> with an individual (vehicle-to-person (V2P)) (for example, via a UE) through a PC5 interface. Communications between the vehicles <NUM> and <NUM> may also occur through a PC5 interface <NUM>. In a like manner, communication may occur from a vehicle <NUM> to other highway components (for example, highway component <NUM>), such as a traffic signal or sign (vehicle-to-infrastructure (V2I)) through a PC5 interface <NUM>. With respect to each communication link illustrated in <FIG>, two-way communication may take place between elements, therefore each element may be a transmitter and a receiver of information. The V2X system <NUM> may be a self-managed system implemented without assistance from a network entity. A self-managed system may enable improved spectral efficiency, reduced cost, and increased reliability as network service interruptions do not occur during handover operations for moving vehicles. The V2X system may be configured to operate in a licensed or unlicensed spectrum, thus any vehicle with an equipped system may access a common frequency and share information. Such harmonized/common spectrum operations allow for safe and reliable operation.

<FIG> shows a V2X system <NUM> for communication between a vehicle <NUM> and a vehicle <NUM> through a network entity <NUM>. These network communications may occur through discrete nodes, such as a BS (e.g., the BS 110a), that sends and receives information to and from (for example, relays information between) vehicles <NUM>, <NUM>. The network communications through vehicle to network (V2N) links <NUM> and <NUM> may be used, for example, for long range communications between vehicles, such as for communicating the presence of a car accident a distance ahead along a road or highway. Other types of communications may be sent by the wireless node to vehicles, such as traffic flow conditions, road hazard warnings, environmental/weather reports, and service station availability, among other examples. Such data can be obtained from cloud-based sharing services.

Roadside units (RSUs) may be utilized. An RSU may be used for V2I communications. In some examples, an RSU may act as a forwarding node to extend coverage for a UE. In some examples, an RSU may be co-located with a BS or may be standalone. RSUs can have different classifications. For example, RSUs can be classified into UE-type RSUs and Micro NodeB-type RSUs. Micro NB-type RSUs have similar functionality as the Macro eNB/gNB. The Micro NB-type RSUs can utilize the Uu interface. UE-type RSUs can be used for meeting tight quality-of-service (QoS) requirements by minimizing collisions and improving reliability. UE-type RSUs may use centralized resource allocation mechanisms to allow for efficient resource utilization. Critical information (e.g., such as traffic conditions, weather conditions, congestion statistics, sensor data, etc.) can be broadcast to UEs in the coverage area. Relays can rebroadcasts critical information received from some UEs. UE-type RSUs may be a reliable synchronization source.

As mentioned above, aspects of the present disclosure relate to sidelink communications, which can include cellular V2X (C-V2X) communications. A C-V2X system may operate in various modes. An example mode, referred to as Mode <NUM>, may be used when the UE is in an in-coverage area. In the Mode <NUM>, the network may control allocation of resources for the sidelink UEs. In another example mode for V2X systems, referred to as Mode <NUM>, the sidelink UEs may autonomously select resources (e.g., resource blocks (RBs)) used for transmissions to communicate with each other. For example, resources may be semi-persistent scheduling (SPS) resources. In some examples, the sidelink UEs can autonomously select resources based on an SPS algorithm. The SPS algorithm may be configured, hardcoded, or preconfigured at the UE. For example, the SPS algorithm may be based on an SPS algorithm defined in the 3GPP technical standards.

In some systems, a UE may select resources to transmit using a sensing mechanism. By sensing available and unavailable resources, the UE can select and transmit on vacant resources, which may reduce or prevent collisions. The sensing may involve power estimation (e.g., resource signal strength indicator (RSSI) measurements). The power estimation may exclude unmeasured subframes (e.g. due to previous transmissions). The resource selection may exclude resources based on expected conflict with other UE's transmissions. Hidden UEs; however, may be unaware of each other and, therefore, unable to exclude each other resources. Thus, transmissions by these UEs may collide on neighboring UEs.

In some cases, a "hidden terminal" scenario may occur due to the dynamically changing environment. For example, when the sidelink UE selects resources for transmissions (e.g., in the Mode <NUM>), some other UEs (e.g., vehicles) may be hidden (e.g., undetected), such as when a channel sensing is performed. Thus, two (or more) UEs may (e.g., autonomously) select the same resources. Hidden terminal scenarios (leading to packet collision) may occur when UEs have overlapping coverage area while assigning RBs for transmission.

<FIG> illustrates a hidden terminal scenario. The UE A and UE C cannot sense each other's presence, for example, because these UEs are outside the coverage range of each other. As shown in <FIG>, the physical distance, d, between UE A and UE C is at least rA + rC, where rA is the radius of UEs A's coverage and rC is the radius of UE C's coverage. UE A does not know about the existence of UE C (the "hidden node"), and similarly, UE C does not know about the existence of UE A. Because UE A and UE C do not know about the other, both UEs may allocate/select the same time-frequency resources (some or all) (e.g., overlapping RBs) for transmission. In this case, UEs in the common area of UE A and UE C (A ∩ C), such as UE B shown in <FIG>) cannot decode the data transmitted from either UE A or UE C using the allocated resources, due to the packet collision.

Collisions and overlaps may be seen in congested scenarios. As used herein, overlap occurs when two or more UEs transmit control channel (e.g., PSCCH) and data channels (e.g., PSSCH) on the same resources and collision occurs when two or more UEs transmit control channels (PSCCH) on the same resources. <FIG> illustrates an example collision scenario and <FIG> illustrates an example overlapping scenario. During a collision, as shown in <FIG>, the PSCCH transmissions from UE1 and UE2 are transmitted on the same resources. During an overlap, as shown in <FIG>, the PSCCH and PSSCH transmissions from UE <NUM> and UE2 are transmitted using the same resources.

For both collisions and overlaps, if the UE1 and UE2 transmit PSCCH and PSSCH transmissions, other UEs may not detect the PSCCH (e.g., with sidelink control SCI). Although transmissions from two UEs are shown in <FIG>, the system may involve sidelink transmissions from any number of UEs.

For PSCCH, bit processing may follow downlink control information (DCI) with no scrambling in cyclic redundancy check (CRC) attachment. Scrambling may be initialized with a constant (e.g., cinit = <NUM>). The PSCCH may use quadrature phase shift keying (QPSK) modulation. Layer mapping and precoding may use a single antenna port. SCI may be transmitted in the PSCCH and include a payload and un-coded bits. The same SCI may include the same transmitted symbols (e.g., coded, modulated, mapped symbols). <FIG> is an example table of parameters for reference signals for PSCCH transmissions (e.g., as defined in TS <NUM> Table <NUM>-<NUM>). The reference signals used for PSSCH may not use group or sequence hopping and uses the same orthogonal code. The reference signals for PSSCH can have cyclic shifts that provide channel separation (e.g., four randomly selected values {<NUM>, <NUM>, <NUM>, <NUM>}).

Information regarding sidelink transmissions can be obtained from the SCI sent in the PSCCH. With SPS transmissions, each SPS transmission indicates a transmission period (e.g., <NUM>/<NUM>/<NUM>/<NUM>. <NUM> subframes). In this case, information regarding transmissions can be determined from the indicated periodicity of the SPS transmissions. In another example, hybrid automatic repeat request (HARQ) transmissions may involve binding mechanisms and controls (e.g., <NUM>/<NUM>/. <NUM> subframe gaps). For example, redundancy versions (e.g., RV<NUM>, RV<NUM>) may be associated (e.g., point to each other). Thus, information regarding one RV may be determined from information about another RV. <FIG> illustrates an example SCI RV pair.

In some systems (e.g., in TS <NUM> Section <NUM>), for sidelink transmission modes <NUM> and <NUM> on the PSCCH, the cyclic shift to be applied is randomly selected from among {<NUM>, <NUM>, <NUM>, <NUM>} in each PSCCH transmission and retransmission (e.g., according to TS <NUM> Section <NUM>. Randomly selecting the cyclic shift may help to handle collisions.

Congestion in transmissions, such as collisions due to the hidden UE scenarios, can be detrimental to C-V2X communications and can lead to competition (e.g. Dedicated Short Range Communication (DSRC)) promotion. Congestion in transmissions may impact packet error rate (PER) and/or information age (IA). To deal with these collisions and overlaps, contention control, muting, and other techniques were developed to ease congestion implications (e.g., increasing inter-transmit time (ITT) on account of reducing the PER and IA).

Due to random nature of cyclic shift selection, a UE may receive colliding PSCCH transmissions with the same cyclic shift. A collision of PSCCH transmissions with the same cyclic shift may to the UE misdetecting (i.e., not detecting) the PSCCH. Thus, in some cases, when the UE autonomously selects resources, the UE will not exclude the resources (e.g., sub-channels) of the non-detected PSCCH transmissions. Accordingly, congestion control effectiveness is decreased. Collisions may also cause measurements assisting link management (e.g. sync-time offset) to be missed. In some cases, because of misdetection of the PSCCH, the UEs may misdetect PSSCH transmissions because the sidelink control information points to the corresponding sidelink data transmission.

Collision of PSCCH transmissions with the same cyclic shift lead to the UE being unable to differentiate PSCCH transmissions. A UE with no prior knowledge may simply decode the strongest PSCCH, and unnecessarily lose PSCCH transmissions (and associated PSSCH) with lesser transmission strength where RV<NUM> passes its cyclic redundancy check (CRC).

Accordingly, what is needed are techniques and apparatus for cyclic shift selection for PSCCH transmissions and retransmissions in sidelink communications.

Aspects of the present disclosure provide cyclic shift selection for physical sidelink control channel (PSCCH) transmissions and retransmissions, such as in cellular vehicle to everything (C-V2X) communications. In certain aspects, a first user equipment (UE) monitors for a sidelink control indicator (SCI) transmissions from a second UE. The SCI transmissions from the second UE may collide one of the first UE's SCI transmission (either an initial transmission or a retransmission). Based on whether there is a collision of transmission, the first UE selects a cyclic shift to use for its transmissions. The selection of the cyclic shift may depend on whether there is a transmission and whether the transmissions are initial transmissions or retransmissions from either the first UE or the second UE.

Aspects of the present disclosure aim to prevent selection of the same cyclic shift on overlapping transmission by multiple UEs. Certain aspects of the present disclosure provide criteria for selecting the cyclic shift for PSCCH retransmissions.

According to certain aspects, the UE may transmit a PSCCH retransmission (e.g., a redundancy version, RV<NUM>) on a resource with no known collisions. When there are no known collisions, the UE may select the same cyclic shift for the PSCCH retransmission as the cyclic shift that was randomly selected for the initial PSCCH transmission (e.g., RV<NUM>). In some examples, the cyclic shift is randomly selected from a set of cyclic shifts, such as the set {<NUM>, <NUM>, <NUM>, <NUM>}. When a cyclic shift is used for the retransmission, CSx, that cyclic shift may be removed the set of non-used cyclic shifts.

In some aspects, the UE may transmit on the same resources that another UE (at least one other UE) uses for a PSCCH retransmission (e.g., a collision determined by the UE based on first detecting an SCI from the other UE). If the UE is sending an initial PSCCH transmission (e.g., RV<NUM>) that collides with the PSCCH retransmission by the other UE, then the UE may randomly select a cyclic shift from a group (e.g., the set) of non-used cyclic shifts to use for its initial PSCCH transmission. The group of non-used cyclic shifts may include the list of available cyclic shifts (e.g., {<NUM>, <NUM>, <NUM>, <NUM>}) excluding the cyclic shift used by the other UEs to send its PSCCH retransmission. For example, if the other UE uses a cyclic shift of <NUM> to send its PSCCH retransmission, then the UE may randomly select a cyclic shift from the remaining set of non-used cyclic shifts {<NUM>, <NUM>, <NUM>} to use for its initial PSCCH transmission.

<FIG> is a call flow illustrating example signaling <NUM> between a UE1 and a UE2, in accordance with certain aspects of the present disclosure. At <NUM>, the UE1 may send to UE2 a RV<NUM> PSCCH transmission, which may provide SCI and information about the physical sidelink shared channel (PSSCH) RV<NUM> transmission. At <NUM>, the UE1 receives from UE2 a RV<NUM> PSCCH transmission. After receiving the PSCCH RV0 from the UE2 at <NUM>, then at <NUM>, the UE1 may update the group of non-used cyclic shifts to exclude the cyclic shift used by UE2 to send UE2's PSCCH transmission (at <NUM>).

At <NUM>, the UE1 may detect a collision based on the SCI received from the UE2 (at <NUM>). For example, the SCI from the UE2 may point to the retransmission of the SCI on the PSCCH at 1012b. The UE1 may detect that the UE1 has a colliding PSCCH transmission or retransmission at 1012a.

According to certain aspects, the UE1 may select, at <NUM>, the cyclic shift for its colliding PSCCH transmission at 1012a based the determination.

In some aspects, if the UE (e.g., UE1 of <FIG>) is sending a PSCCH retransmission (e.g., RV<NUM> at 1012a), that collides with the PSCCH retransmission by another UE (e.g., RV<NUM> at 1012b), then the cyclic shift selected by the UE may depend on whether the cyclic shift used for the corresponding initial PSCCH transmission (e.g., RV0 at <NUM>) by the UE is contained in the group of non-used cyclic shifts.

If the cyclic shift selected that was used for the initial PSCCH transmission (e.g., at <NUM>) is contained in the group of non-used cyclic shifts, the UE may select (e.g., at <NUM>) the same cyclic shift for the PSCCH retransmission (e.g., at 1012a). That is, if the cyclic shift used for the initial transmission by the UE is different than the cyclic shift of any colliding PSCCH retransmission by another UE, then the cyclic shift used for the initial transmission by the UE can be reused for the corresponding retransmission. On the other hand, if the cyclic shift used for the initial PSCCH transmission by the UE is not contained in the group of non-used cyclic shifts, then the UE may randomly select the cyclic shift for the retransmission by the UE from the group of non-used cyclic shifts. That is, if the cyclic shift used for the initial transmission by the UE is the same as the cyclic shift of any colliding PSCCH retransmission by another UE, then the cyclic shift used for the initial transmission by the UE cannot be reused for the corresponding retransmission. In some aspects, if the cyclic shift used for the initial PSCCH transmission by the UE is not contained in the group of non-used cyclic shifts, then the UE may select the same cyclic shift for the retransmission by the UE as used for the initial transmission by the UE, which was randomly selected. In other words, when there is a collision, the UE may either randomly select from the non-used CSs or may select the same CS used for the RV0 transmission.

In some aspects, the cyclic shift selection approach described above may be activated or deactivated. For example, the UE may perform the above cyclic shift selection for the PSCCH retransmissions when observing congestion (i.e. as a congestion control mechanism), such as when congestion reaches a defined threshold.

Aspects of the present disclosure may be detected when transmitting an HARQ pair (RV<NUM> and RV<NUM> pair). In some examples, the UE may transmit RV<NUM> and RV<NUM> continuously, and accordingly, the majority of RV<NUM> and RV<NUM> transmissions may have the same cyclic shift. With a random selection of cyclic shifts, transmissions have about a <NUM>% chance of collision.

Aspects of the present disclosure may be detected when transmitting RV<NUM> on a resource with an overlapped RV<NUM>(s). For example, a first UE supporting same cyclic shift transmission may continuously transmit an HARQ pair (with same cyclic shift), and the second UE continuously transmits RV<NUM> colliding with RV<NUM>. Accordingly, aspects of the present disclosure may not use the same cyclic shift for the initial PSCCH transmission, while with a purely random selection of cyclic shifts, the cyclic shifts will be evenly distributed.

<FIG> is a flow diagram illustrating example operations <NUM> for wireless communication, in accordance with certain aspects of the present disclosure. The operations <NUM> may be performed, for example, by a first UE (e.g., such as a UE 120a in the wireless communication network <NUM>). Operations <NUM> may be implemented as software components that are executed and run on one or more processors (e.g., controller/processor <NUM> of <FIG>). Further, the transmission and reception of signals by the UE in operations <NUM> may be enabled, for example, by one or more antennas (e.g., antennas <NUM> of <FIG>). In certain aspects, the transmission and/or reception of signals by the UE may be implemented via a bus interface of one or more processors (e.g., controller/processor <NUM>) obtaining and/or outputting signals.

The operations <NUM> may begin, at <NUM>, by monitoring one or more SCI transmissions for one or more second UEs. For example, the first UE may monitor one or more PSCCHs for SCI from one or more sidelink UEs.

At <NUM>, the first UE determines, based on the one or more SCI, whether one or more collisions occur between one or more retransmissions of the one or more SCI transmissions by the one or more second UEs and a scheduled SCI transmission by the first UE. Determining whether the one or more collision occurs may involve the first UE determining, based on the SCI transmissions from the one or more second UEs, time and frequency resources for the one or more retransmissions of the one or more SCI transmissions by the one or more second UEs. The first UE may determine that a collision occurs when the same time and frequency resources are used (e.g., scheduled, allocated, or indicated) for the scheduled SCI transmission by the first UE as the time and frequency resources for the one or more retransmissions of the one or more SCI transmissions by the one or more second UEs. The first UE may determine that a collision does not occur when the scheduled SCI transmission by the first UE uses different time and/or frequency resources than the time and frequency resources for the one or more retransmissions by the one or more second UEs.

At <NUM>, the first UE selects a cyclic shift to use for the scheduled SCI transmission by the first UE based on at least on the determination.

According to some aspects, when the first UE determines that a collision does not occur, then selecting the cyclic shift to use for the scheduled SCI transmission by the first UE involves randomly selecting the cyclic shift from a set of a plurality of cyclic shifts for an initial transmission by the first UE, and selecting the cyclic shift randomly selected for the initial transmission for a retransmission by the first UE.

According to some aspects, when the first UE determines that a collision occurs, the first UE determines one or more cyclic shifts used for the one or more retransmissions of the one or more SCI transmission by the one or more second UEs based on one or more cyclic shifts used for the one or more SCI transmissions by the one or more second UEs.

In some aspects, selecting the cyclic shift to use for the scheduled SCI transmission by the first UE comprises randomly selecting a cyclic shift from a set of a plurality of cyclic shifts excluding the determined one or more cyclic shift used for the one or more retransmissions of the SCI by the one or more second UEs that collide with the scheduled SCI transmission by the first UE, when the scheduled transmission is an initial transmission.

In some aspects, selecting the cyclic shift to use for the scheduled SCI transmission by the first UE comprises selecting a same cyclic shift used for an initial transmission by the first UE when the scheduled SCI transmission is a retransmission, and a cyclic shift used for the initial transmission is different from the determined one or more cyclic shifts for the one or more retransmissions of the one or more SCI transmission by the one or more second UEs.

In some aspects, selecting the cyclic shift to use for the scheduled SCI transmission by the first UE comprises randomly selecting the cyclic shift, from a set of plurality of cyclic shifts excluding the determined one or more cyclic shifts used for the one or more retransmission of the one or more SCI transmissions by the one or more second UEs that collide with the scheduled SCI transmission by the first UE, when the scheduled SCI transmission is a retransmission and a cyclic shift used for an initial transmission is the same as at least one of the determined one or more cyclic shifts for the one or more retransmissions of the one or more SCI transmissions by the one or more second UEs.

In some aspects, when the scheduled SCI transmission is a retransmission and a cyclic shift used for an initial transmission is the same as at least one of the determined one or more cyclic shifts for the one or more transmissions of the one or more SCI transmissions by the one or more second UEs, selecting the cyclic shift to use for the scheduled SCI transmission by the first UE comprises selecting a same cyclic shift used for an initial transmission by the first UE or randomly selecting the cyclic shift from a set of a plurality of cyclic shifts excluding the determined one or more cyclic shifts used for the one or more retransmissions of the one or more SCI transmissions by the one or more second UEs that collide with the scheduled SCI transmission by the first UE.

In some aspects, selecting the cyclic shift to use for the scheduled SCI transmission by the first UE comprises determining a technique for selecting the cyclic shift based on whether a detected level of congestion is at or above a congestion threshold level.

In some aspects, a transmission by either the first UE or the second UE is associated with a first redundancy version (RV<NUM>), and a retransmission by the first UE or the second UE corresponding to the first SCI transmission is associated with a second redundancy version (RV<NUM>).

In some aspects, the first UE and the one or more second UEs are configured for C-V2X communications, and the first UE monitors for the one or more SCI transmissions from the one or more second UEs in a physical sidelink control channel (PSCCH) in a subframe. In further aspects, the first UE and the one or more second UEs are configured for a transmission mode <NUM> for the C-V2X communications, and the first UE and the one or more second UEs autonomously select transmission resources.

The communications device <NUM> includes a processing system <NUM> coupled to a transceiver <NUM> (e.g., a transmitter and/or a receiver).

The processing system <NUM> includes a processor <NUM> coupled to a computer-readable medium/memory <NUM> via a bus <NUM>. In certain aspects, the computer-readable medium/memory <NUM> is configured to store instructions (e.g., computer-executable code) that when executed by the processor <NUM>, cause the processor <NUM> to perform the operations illustrated in <FIG>, or other operations for performing the various techniques discussed herein for cyclic shift selection for PSCCH transmissions. In certain aspects, computer-readable medium/memory <NUM> stores code <NUM> for monitoring one or more SCI transmissions from one or more UEs; code <NUM> for determining, based on the one or more SCI, whether one or more retransmissions of the one or more SCI transmissions by the one or more second UEs and a scheduled SCI transmission by the first UE; and code <NUM> for selecting a cyclic shift for the scheduled SCI transmission by the first UE based at least on the determination, in accordance with aspect of the disclosure. In certain aspects, the processor <NUM> has circuitry configured to implement the code stored in the computer-readable medium/memory <NUM>. The processor <NUM> includes circuitry <NUM> for monitoring one or more SCI transmissions from one or more second UEs; circuitry <NUM> for determining, based on the one or more SCI, whether one or more collisions occur between one or more retransmissions of the one or more SCI transmissions by the one or more second UEs and a scheduled SCI transmission by the first UE; and circuitry <NUM> for selecting a cyclic shift to use for the scheduled SCI transmission by the first UE based at least on the determination, in accordance with aspects of the disclosure.

In a first aspect, a method for wireless communication by a first user equipment (UE), includes monitoring one or more sidelink control information (SCI) transmissions from one or more second UEs; determining, based on the one or more SCI, whether one or more collisions occur between one or more retransmissions of the one or more SCI transmissions by the one or more second UEs and a scheduled SCI transmission by the first UE; and selecting a cyclic shift to use for the scheduled SCI transmission by the first UE based at least on the determination.

In a second aspect, in combination with the first aspect, determining whether the one or more collisions occur includes determining, based on the SCI transmission, time and frequency resources for the one or more retransmissions of the one or more SCI transmission by the one or more second UEs; and determining the same time and frequency resources for the scheduled SCI transmission by the first UE.

In a third aspect, in combination with any of the first and second aspects, determining whether the one or more collisions occur includes determining that a collision does not occur; and selecting the cyclic shift to use for the scheduled SCI transmission by the first UE includes randomly selecting the cyclic shift, from a set of a plurality of cyclic shifts, for an initial transmission by the first UE; and selecting the cyclic shift that was randomly selected for the initial transmission for a retransmission by the first UE.

In a fourth aspect, in a combination with any of the first through third aspects, the determining whether the one or more collisions occur includes determining that the one or more collisions occur; and the method further comprises determining one or more cyclic shifts used for the one or more retransmissions of the one or more SCI transmissions by the one or more second UEs based on one or more cyclic shifts used for the one or more SCI transmissions by the one or more second UEs.

In a fifth aspect, in a combination with the fourth aspect, selecting the cyclic shift to use for the scheduled SCI transmission by the first UE includes randomly selecting a cyclic shift, from a set of a plurality of cyclic shifts excluding the determined one or more cyclic shifts used for the one or more retransmissions of the one or more SCI transmissions by the one or more second UEs that collide with the scheduled SCI transmission by the first UE, when the scheduled SCI transmission is an initial transmission.

In a sixth aspect, in a combination with any of the fourth or fifth aspects, selecting the cyclic shift to use for the scheduled SCI transmission by the first UE includes selecting a same cyclic shift used for an initial transmission by the first UE when the scheduled SCI transmission is a retransmission and a cyclic shift used for the initial transmission is different than the determined one or more cyclic shifts for the one or more retransmissions of the one or more SCI transmission by the one or more second UEs.

In a seventh aspect, in combination with any of the fourth through sixth aspects, when the scheduled SCI transmission is a retransmission and a cyclic shift used for an initial transmission is the same as at least one of the determined one or more cyclic shifts for the one or more retransmissions of the one or more SCI transmissions by the one or more second UEs, selecting the cyclic shift to use for the scheduled SCI transmission by the first UE includes selecting a same cyclic shift used for an initial transmission by the first UE, or randomly selecting the cyclic shift, from a set of a plurality of cyclic shifts excluding the determined one or more cyclic shifts used for the one or more retransmissions of the one or more SCI transmissions by the one or more second UEs that collide with the scheduled SCI transmission by the first UE.

In an eighth aspect, in combination with any of the first through seventh aspects, selecting the cyclic shift includes determining a technique for selecting the cyclic shift based on whether a detected level of congestion is at or above a congestion threshold level.

In a ninth aspect, in combination with any of the first through eighth aspects, a transmission is associated with a first redundancy version (RV0), and a retransmission corresponding the first SCI transmission is associated with a second RV (RV2).

In a tenth aspect, in combination with any of the first through ninth aspects, the first UE and the one or more second UEs are configured for cellular vehicle-to-anything (C-V2X) communications; and the first UE monitors for the one or more SCI transmissions from the one or more second UEs in a physical sidelink control channel (PSCCH) in a subframe.

In an eleventh aspect, in combination with any of the tenth aspect, the first UE and the one or more second UEs are configured for a transmission mode <NUM> for the C-V2X communications, and wherein the first UE and the one or more second UEs autonomously select transmission resources.

Claim 1:
A method (<NUM>) for wireless communication by a first user equipment, UE, comprising:
monitoring (<NUM>) one or more sidelink control information, SCI, transmissions from one or more second UEs;
determining (<NUM>), based on the one or more SCI, that a collision occurs between one or more retransmissions of the one or more SCI transmissions by the one or more second UEs and a scheduled SCI transmission by the first UE;
selecting (<NUM>) a cyclic shift to use for the scheduled SCI transmission by the first UE based at least on the determination; and characterized in that the method further comprises
determining one or more cyclic shifts used for the one or more retransmissions of the one or more SCI transmissions by the one or more second UEs based on one or more cyclic shifts used for the one or more SCI transmissions by the one or more second UEs.