Patent Publication Number: US-2022217802-A1

Title: Sidelink interface states for control signaling in v2x

Description:
CLAIM OF PRIORITY 
     The present application claims priority to Provisional Application No. 62/842,353, entitled “PC5 STATES FOR CONTROL SIGNALING IN V2X”, filed May 2, 2019, which is assigned to the assignee hereof and hereby expressly incorporated by reference in its entirety. 
    
    
     FIELD 
     This invention generally relates to wireless communications and more particularly to vehicle-to-everything (V2X) communications between wireless communication devices. 
     BACKGROUND 
     Unicast transmissions are meant for one-to-one communications, meaning there is one sender and one intended receiver. In some cases, wireless communication devices communicate with each other via unicast transmissions. 
     SUMMARY 
     The methods, devices, and systems discussed herein define sidelink interface (e.g. PC5) states for a unicast connection between two wireless communication devices. A Sidelink-CONNECTED state is a sidelink interface state in which a first wireless communication device establishes and maintains a sidelink channel connection with a second wireless communication device. The first and second wireless communication devices can transmit sidelink unicast transmissions to each other over the sidelink channel connection while operating in the Sidelink-CONNECTED state. A non-Sidelink-CONNECTED state is a sidelink interface state other than the Sidelink-CONNECTED state. The first and second wireless communication devices transition from the Sidelink-CONNECTED state to the non-Sidelink-CONNECTED state upon the occurrence of a triggering event such as a Radio Link Failure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an example of a system in which a first wireless communication device transitions between operating in a Sidelink-CONNECTED state, in which the first wireless communication device maintains a sidelink channel connection with another wireless communication device, and a non-Sidelink-CONNECTED state. 
         FIG. 2  is a block diagram of an example of a wireless communication device shown in  FIG. 1 . 
         FIG. 3  is an example of a state diagram of the transitions of a wireless communication device between operating in a Sidelink-CONNECTED state and a non-Sidelink-CONNECTED state. 
         FIG. 4  is an example of a messaging diagram illustrating two wireless communication devices using synchronized Radio Link Failure (RLF) timers to trigger a transition from operating in a Sidelink-CONNECTED state to a non-Sidelink-CONNECTED state. 
         FIG. 5  is a flowchart of an example of a method in which a first wireless communication device transitions between operating in a Sidelink-CONNECTED state, in which the first wireless communication device maintains a sidelink channel connection with another wireless communication device, and a non-Sidelink-CONNECTED state. 
     
    
    
     DETAILED DESCRIPTION 
     The examples discussed below are generally directed to vehicle-to-everything (V2X) communication, which is the passing of information from a vehicle to any entity that may affect the vehicle or that the vehicle may affect. For example, V2X is a vehicular communication system that incorporates other, more specific types of communication, including vehicle-to-vehicle (V2V), V2I (vehicle-to-infrastructure), V2N (vehicle-to-network), V2P (vehicle-to-pedestrian), V2D (vehicle-to-device), and V2G (vehicle-to-grid). There are two types of V2X communication technology depending on the underlying technology being used: wireless local area network (WLAN)-based V2X, and cellular-based V2X (C-V2X). Some examples of V2X protocols include Long-Term Evolution (LTE) (Rel-14) V2X Mode 3 and Mode 4 and 5G New Radio (NR) V2X Mode 1 and Mode 2. In some of the examples described herein, the wireless communication devices are vehicle user equipment devices (VUEs) that exchange data (e.g., in the Extended Sensor use case), which is gathered through local sensors, or live video data among vehicles, Road Side Units (RSUs), devices of pedestrians, and V2X application servers. 
     Sidelink unicast transmissions are supported for V2X over a sidelink (SL) channel such as a PC5 interface, which is an interface used for direct communication between a user equipment device (UE) and another UE. Unicast is meant for one-to-one communications, meaning there is one sender and one intended receiver. 
     To support a unicast connection between a UE and a base station over a Uu link, the control layer defined by Radio Resource Control (RRC) is utilized, which specifies the UE behavior associated with each of the states for RRC (e.g., RRC_IDLE, RRC_INACTIVE, and RRC_CONNECTED). For example, the RRC_CONNECTED state defines the procedures for Radio Resource Management (RRM), which includes handover procedures and failure handling procedures. The RRC_IDLE and RRC_INACTIVE states define the procedures regarding how the UE selects or reselects cells for “camping” prior to connection establishment or reestablishment. 
     For Access Stratum (AS)-level link management in unicast, SL Radio Link Monitoring/Radio Link Failure (RLM/RLF) declaration is supported. For Radio Link Control (RLC) Acknowledged Mode (AM) in SL unicast, RLF declaration is triggered by indication from RLC that the maximum number of retransmissions has been reached. The AS-level link status (e.g., failure) should be informed to upper layers. 
     Unlike the Uu case, there is not a concept of “cells” over the PC5 link. From this perspective, there is also no need for “camping” since there are no cells to “camp” on over the PC5 interface. 
     In unicast transmissions, the transmitting UE is directly linked to the receiving UE via the PC5 interface (e.g., a sidelink channel). Thus, there is no need to search for another UE to communicate with just because the sidelink channel connection is broken. For example, assume User A is talking with User B over a PC5 link. If the sidelink connection between User A and User B is broken, User A will not just randomly search for and start a conversation with another available user. 
     In deciding whether PC5-RRC states are needed, it is helpful to understand the purpose for having states, in general, regardless of whether the states are defined within PC5-S (e.g., upper layer signaling) or PC5-RRC (e.g., AS layer signaling). If we initially consider the case when no state is defined, then under normal conditions the unicast connection may be established and released along with capability exchanges in between. However, under poor radio conditions, the unicast connection may be severely disrupted. If we depend solely on PC5-S signaling, and depending on service types, it may take a long time before the upper layer realizes that some problem may have occurred, and latency for services may be severely impacted. 
     In light of the foregoing, sidelink interface (e.g. PC5) states should be defined for unicast connection. If states can be defined, it would be straightforward to define at least two states, a Sidelink-CONNECTED state and a non-Sidelink-CONNECTED state. Sidelink-CONNECTED is a sidelink interface state in which a first wireless communication device establishes and maintains a sidelink channel connection with a second wireless communication device. The Sidelink-CONNECTED state is a logical connection between a pair of a Source Layer-2 ID and a Destination Layer-2 ID in the AS layer. In particular, Sidelink-CONNECTED state is considered as established only when the sidelink signaling radio bearer (SL-SRB) is established, which means sidelink control signals may be exchanged between the two UEs. A non-Sidelink-CONNECTED state is a sidelink interface state other than the Sidelink-CONNECTED state. 
     In examples in which the sidelink interface is PC5, then the states would be a PC5-CONNECTED state and a non-PC5-CONNECTED state. Thus, in examples in which the sidelink interface is PC5, the PC5-CONNECTED state is the PC5 state whereby connection establishment has been successfully completed and prior to Connection Release under good PC5 radio link. Therefore, the non-PC5-CONNECTED state would be a state other than the PC5-CONNECTED state. In further examples, the non-PC5-CONNECTED state is a PC5-IDLE state. 
     The usefulness of defining the operational states may be better explained by the UE (e.g., wireless communication device) behavior under non-PC5-CONNECTED. While the UE is in non-PC5-CONNECTED, unlike the case for RRC_IDLE for the Uu link, there is no need to define where and how the UE should “camp.” Rather, in some examples, non-PC5-CONNECTED is a state whereby the UE determines, in the upper layer, the best available radio interface to establish/reestablish the unicast connection towards a receiving UE. 
     The reestablishment assumes the ongoing unicast connection was terminated unexpectedly and existing service needs to be restored. In some examples, the procedure for reestablishment is similar to the procedure for establishment, and in these cases, it may be assumed that a UE operating in non-PC5-CONNECTED will discard any SL UE context information exchanged between the UEs while in PC5-CONNECTED. In particular, after transitioning to the non-PC5-CONNECTED state the UE&#39;s sidelink Signaling Radio Bearers (SRBs) and sidelink Data Radio Bearers (DRBs) are released. In further examples, the UEs operating in non-PC5-CONNECTED do not perform RLM/RLF procedures. 
     When a UE transitions to non-PC5-CONNECTED, the UE determines the best available radio interface for establishment/reestablishment of a connection with another UE. In some cases, a unicast connection via PC5, for either LTE or NR, will be the best available radio interface, considering the available channel(s). In other cases, the Uu link, which is the wireless communication link between the UE and a base station, may be the best option. Stated differently, the UE may determine that a communication link via a base station may be a better radio interface to another UE than any available sidelink channels. 
     Although the different examples set forth herein may be described separately, any of the features of any of the examples may be added to, omitted from, or combined with any other example. Similarly, any of the features of any of the examples may be performed in parallel or performed in a different manner/order than that described or shown herein. 
       FIG. 1  is a block diagram of an example of a system in which a first wireless communication device transitions between operating in a Sidelink-CONNECTED state, in which the first wireless communication device establishes and maintains a sidelink channel connection with another wireless communication device, and a non-Sidelink-CONNECTED state. For the example of  FIG. 1 , a group  100  of wireless communication devices is located on roadway  101 . The group  100  includes first wireless communication device, WCD 1 ,  102 , second wireless communication device, WCD 2 ,  104 , third wireless communication device, WCD 3 ,  106 , and fourth wireless communication device, WCD 4 ,  108 . In other examples, the group  100  may have a different number of wireless communication devices than that shown in  FIG. 1 . 
     The group  100  is wirelessly connected to a radio access network (not shown) via one or more base stations (not shown), which provide various wireless services to one or more of the wireless communication devices that are part of the group  100 . For the example shown in  FIG. 1 , the group  100  operates in accordance with at least one revision of the 3rd Generation Partnership Project 5G New Radio (3GPP 5G NR) communication specification. In other examples, the group  100  may operate in accordance with other communication specifications. 
     In the example of  FIG. 1 , wireless communication devices  102 ,  104 ,  106 ,  108  are each integrated into a vehicle as an onboard unit (OBU). In other examples, wireless communication devices  102 ,  104 ,  106 ,  108  may simply be user equipment (UE) devices that are located within a vehicle. Some examples of user equipment devices include: a mobile phone, a transceiver modem, a personal digital assistant (PDA), or a tablet, for example. Any of the foregoing devices may also be referenced herein as vehicle UEs (VUEs). Each wireless communication device  102 ,  104 ,  106 ,  108  that is connected to group  100  is considered to be a member of group  100 . 
     As shown in  FIG. 2 , wireless communication device  102  comprises controller  216 , transmitter  218 , and receiver  214 , as well as other electronics, hardware, and code. Although  FIG. 2  specifically depicts the circuitry and configuration of wireless communication device  102 , the same wireless communication device circuitry and configuration is utilized for wireless communication devices  104 ,  106 ,  108  in group  100 . In other examples, any of the wireless communication devices may have circuitry and/or a configuration that differs from that of wireless communication device  102  shown in  FIG. 2 . 
     Wireless communication device  102  is any fixed, mobile, or portable equipment that performs the functions described herein. The various functions and operations of the blocks described with reference to wireless communication device  102  may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device, and the functions described as performed in any single device may be implemented over several devices. 
     Controller  216  includes any combination of hardware, software, and/or firmware for executing the functions described herein as well as facilitating the overall functionality of a wireless communication device. An example of a suitable controller  216  includes code running on a microprocessor or processor arrangement connected to memory. Transmitter  218  includes electronics configured to transmit wireless signals. In some situations, the transmitter  218  may include multiple transmitters. Receiver  214  includes electronics configured to receive wireless signals. In some situations, receiver  214  may include multiple receivers. Receiver  214  and transmitter  218  receive and transmit signals, respectively, through antenna  212 . Antenna  212  may include separate transmit and receive antennas. In some circumstances, antenna  212  may include multiple transmit and receive antennas. 
     Transmitter  218  and receiver  214  in the example of  FIG. 2  perform radio frequency (RF) processing including modulation and demodulation. Receiver  214 , therefore, may include components such as low noise amplifiers (LNAs) and filters. Transmitter  218  may include filters and amplifiers. Other components may include isolators, matching circuits, and other RF components. These components in combination or cooperation with other components perform the wireless communication device functions. The required components may depend on the particular functionality required by the wireless communication device. 
     Transmitter  218  includes a modulator (not shown), and receiver  214  includes a demodulator (not shown). The modulator can apply any one of a plurality of modulation orders to modulate the signals to be transmitted over sidelink channel connection  110 . In the example of  FIG. 1 , the signals transmitted over sidelink channel connection  110  are unicast transmissions. The demodulator demodulates signals received over sidelink channel connection  110 , in accordance with one of a plurality of modulation orders. 
       FIG. 3  is an example of a state diagram showing the transitions of a wireless communication device between operating in a Sidelink-CONNECTED state and a non-Sidelink-CONNECTED state. In the examples described herein, it is generally understood that the Sidelink-CONNECTED state and the non-Sidelink-CONNECTED states are applicable if the UE intends to establish unicast connection with another UE. However, in alternative examples, the Sidelink-CONNECTED state and the non-Sidelink-CONNECTED state, or variations thereof, may be used in conjunction with other types of connections. 
     In  FIG. 3 , Wireless Communication Device Initialization (WCD Initialization) state  302  represents the state in which wireless communication device  102  is powered on. When wireless communication device  102  starts the application  304  that will enable wireless communication device  102  to establish a sidelink channel (e.g., PC5) connection with another wireless communication device, controller  216  of wireless communication device  102  operates wireless communication device  102  in the non-Sidelink-CONNECTED state  306 . In the non-Sidelink-CONNECTED state  306 , wireless communication device  102  determines, via controller  216 , the best available radio interface for the connection with target wireless communication device  104 . 
     In some examples, the best available radio interface is based, at least partially, on which radio interface has the highest Reference Signal Receive Power (RSRP) level. In further examples, the best available radio interface is selected from the following: a Uu interface, and a PC5 interface that complies with at least one of the following specifications: 3rd Generation Partnership Project (3GPP) Long-Term Evolution (LTE), and 3GPP 5G New Radio (NR). In the example shown in  FIG. 3 , wireless communication device  102  informs its upper layer of the determined best available radio interface. In other examples, any suitable radio interface (e.g., that meets a minimum quality threshold) may be utilized, even if it is not the best. In alternative examples, the upper layer is not informed of the selected radio interface. 
     When wireless communication device  102  transmits, via its transmitter  218  and antenna  212 , an establishment request  308  that is accepted by wireless communication device  104 , controller  216  of wireless communication device  102  operates wireless communication device  102  in the Sidelink-CONNECTED state  310 . In the Sidelink-CONNECTED state  310 , wireless communication device  102  maintains sidelink channel connection  110  with wireless communication device  104 . While in the Sidelink-CONNECTED state  310 , wireless communication device  102  transmits, via its transmitter  218  and antenna  212 , sidelink unicast transmissions over the sidelink channel connection  110  to wireless communication device  104 . Likewise, while in the Sidelink-CONNECTED state  310 , wireless communication device  102  receives, via its antenna  212  and receiver  214 , sidelink unicast transmissions over the sidelink channel connection  110  from wireless communication device  104 . 
     Controller  216  of wireless communication device  102  is further configured to transition wireless communication device  102  from the Sidelink-CONNECTED state  310  to the non-Sidelink-CONNECTED state  306  upon the occurrence of a triggering event  312 . In some examples, wireless communication device  102  performs RLM/RLF procedures with regards to the ongoing status/quality of sidelink channel connection  110  while operating in the Sidelink-CONNECTED state  310 . In the example of  FIG. 3 , the triggering event  312 , which triggers transition of wireless communication device  102  from the Sidelink-CONNECTED state  310  to the non-Sidelink-CONNECTED state  306 , is at least one of the following: a decrease in a quality level of the sidelink channel connection  110  between wireless communication device  102  and wireless communication device  104 , as measured during a Radio Link Monitoring (RLM) procedure; and a determination that a Radio Link Failure (RLF) of the sidelink channel connection  110  between wireless communication device  102  and wireless communication device  104  has occurred. In some examples, at least one of the RLM procedure and the RLF determination are based on one or more received Physical Sidelink Control Channel (PSCCH) transmissions. Alternatively, the triggering event  312  could be a normal release of the sidelink channel connection  110  between wireless communication device  102  and wireless communication device  104 . A normal release would involve the upper layer&#39;s instruction to the AS layer to release the connection. In other examples, the triggering event  312  may include expiry of an RLF timer, as described below in connection with  FIG. 4 , or an RLF determination based on reaching the maximum number of RLC retransmissions for the case of RLC AM configuration. In further examples, any other suitable triggering event may be used. 
     If wireless communication device  102  transitions from the Sidelink-CONNECTED state  310  to the non-Sidelink-CONNECTED state  306  because the sidelink channel connection  110  between wireless communication device  102  and wireless communication device  104  was terminated unexpectedly and needs to be reestablished, controller  216  of wireless communication device  102  discards any SL UE context information exchanged between wireless communication device  102  and wireless communication device  104  while operating in the Sidelink-CONNECTED state  310 , in the example shown in  FIG. 3 . In alternative examples, wireless communication device  102  maintains the SL UE context information and utilizes it to facilitate reestablishment of the sidelink channel connection  110  with wireless communication device  104 . 
     Wireless communication device  102  also determines the best available radio interface, as described above, for the reestablishment of the sidelink channel connection  110  with wireless communication device  104  and informs the upper layer of the determined best available radio interface. In other examples, any suitable radio interface may be selected, and the upper layer may not be informed of the selected radio interface. 
     If wireless communication device  102  no longer wishes to utilize a sidelink channel (e.g., PC5) connection with another wireless communication device, wireless communication device  102  terminates the application  314  that enables wireless communication device  102  to operate in the Sidelink-CONNECTED state  310 . 
     The operational states described herein are defined within the PC5-S signaling protocol stack or the PC5-Radio Resource Control (PC5-RRC) Access Stratum (AS) layer. Considering the changes in radio condition, even if the state is defined within PC5-S, some assistance from the AS layer is needed for the upper layer to know the condition of the radio link. Regardless if the states are defined within PC5-S or PC5-RRC, the upper layer should know the UE&#39;s current state. In some examples, it would be straightforward to define the state as part of PC5-RRC since RLM/RLF is typically defined in the AS layer. Although no reference signal is dedicated just for SL RLM, a SL reference signal (RS) introduced for other purpose(s) is reused for SL RLM/RLF, in some examples. 
     In other examples, wireless communication device  102  is allowed to periodically transmit Physical Sidelink Control Channel (PSCCH)-only signals towards wireless communication device  104 , which uses the received PSCCH-only signals for RLM/RLF. As a response to receiving a PSCCH-only signal from wireless communication device  102 , wireless communication device  104  transmits a PSCCH-only transmission to wireless communication device  102  within a specified time period. In some examples, wireless communication device  102  uses the PSCCH-only transmission received from wireless communication device  104  for RLM/RLF. 
     Both wireless communication device  102  and wireless communication device  104  should be able to determine when RLF should be declared. More specifically, wireless communication device  102  should know whether wireless communication device  104  has experienced RLF and vice versa. In some examples, wireless communication devices  102  can determine when to declare RLF based, at least partially, on a lack of Hybrid Automatic Repeat Request (HARQ) feedback (e.g., HARQ discontinuous transmission (DTX)) or Channel State Information Reference Signal (CSI-RS) feedback received from wireless communication device  104 . In particular, in some situations the wireless communication device  104  cannot even decode the Sidelink Control Information (SCI), which is contained within the PSCCH, sent from wireless communication device  102 . 
       FIG. 4  illustrates an alternative example for determining when to declare RLF and when wireless communication device  102  and wireless communication device  104  should transition to the non-Sidelink-CONNECTED state  306 . More specifically,  FIG. 4  is an example of a messaging diagram illustrating two wireless communication devices using synchronized Radio Link Failure (RLF) timers to trigger a transition from operating in a Sidelink-CONNECTED state to a non-Sidelink-CONNECTED state. Initially, wireless communication device  102  and wireless communication device  104  are both operating in a Sidelink-CONNECTED state  310  and are transmitting unicast transmissions  402  with each other via the sidelink channel connection  110 . 
     In the example shown in  FIG. 4 , wireless communication device  104  starts, via its controller  216 , an RLF timer upon receipt of a data or control message (e.g., PC5 data or control message)  404  sent from wireless communication device  102  via sidelink channel connection  110 . Similarly, wireless communication device  102  starts, via its controller  216 , an RLF timer upon transmission of the data or control message (e.g., PC5 data or control message)  404  to wireless communication device  104 . Since both wireless communication device  102  and wireless communication device  104  start their respective RLF timers at approximately the same time, the RLF timers are considered to be synchronized. 
     If another unicast message, including ARQ and HARQ feedbacks, is sent between wireless communication device  102  and wireless communication device  104 , the RLF timers are restarted. Upon expiry of the synchronized RLF timers, both wireless communication device  102  and wireless communication device  104  transition to the non-Sidelink-CONNECTED state  306 . In some cases, the AS layer will inform the upper layer of the RLF, then the upper layer will instruct the AS layer to transition to the non-Sidelink-CONNECTED state  306 . 
     Thus, upon expiry of either or both RLF timers, RLF is declared. One example of this would be if wireless communication device  102  transmitted a message to wireless communication device  104  and started the RLF timer for wireless communication device  102 . In the event that wireless communication device  104  does not receive the message and does not respond by sending either a feedback message or another data/control message to wireless communication device  102 , wireless communication device  102  will declare an RLF upon expiry of the RLF timer of wireless communication device  102 . 
       FIG. 5  is a flowchart of an example of a method in which a first wireless communication device transitions between operating in a Sidelink-CONNECTED state, in which the first wireless communication device establishes and maintains a sidelink channel connection with another wireless communication device, and a non-Sidelink-CONNECTED state. The method  500  begins at step  502  with operating a first wireless communication device  102  in a Sidelink-CONNECTED state  310 , which is a sidelink interface state in which the first wireless communication device  102  maintains a sidelink channel connection  110  with a second wireless communication device  104 . At step  504 , the first wireless communication device  102  is operated in a non-Sidelink-CONNECTED state  306 . At step  506 , the first wireless communication device  102  transitions between the Sidelink-CONNECTED state  310  and the non-Sidelink-CONNECTED state  306  upon the occurrence of a triggering event  312 . At step  508 , first wireless communication device  102  selects, while in the non-Sidelink-CONNECTED state  306 , a best available radio interface to connect to the second wireless communication device  104 . At step  510 , first wireless communication device  102  transmits a sidelink unicast transmission over the sidelink channel connection  110  while operating in the Sidelink-CONNECTED state  310 . In other examples, one or more of the steps of method  500  may be omitted, combined, performed in parallel, or performed in a different order than that described herein or shown in  FIG. 5 . In still further examples, additional steps may be added to method  500  that are not explicitly described in connection with the example shown in  FIG. 5 . 
     Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. The above description is illustrative and not restrictive. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.