FIELD

The present disclosure generally relates to wireless communications, and more particularly, to a method of sidelink unicast service management in access stratum layer and a related device.

BACKGROUND

In the sidelink unicast scenario, both of the paired user equipments (UEs) (e.g., UE #1and UE #2) may be formulated in the upper layers (e.g., by application layers, such as vehicle-to-everything (V2X) layer) through control signaling protocols (e.g., PC5-S protocols, which define direct communication between V2X uses above access stratum) for sidelink unicast service. However, in the conventional V2X service, the UEs are considered as “connection-less” in the access stratum (AS) layer, which means there is no efficient mechanisms to monitor and manage the AS layer link quality in the sidelink unicast scenario (in comparison with radio resource control (RRC) connection of Uu interface (a radio interface between the UE and radio access network (RAN) in access stratum) in new radio (NR)/long term evolution (LTE) protocols).

FIG. 1illustrates sidelink unicast scenario in multiple component carriers on PC5 interface. Both of the paired UEs may be configured with one or more than one component carriers for at least one sidelink unicast service. The paired UEs may obtain configuration for one (or more than one) component carrier through a sidelink pre-configuration. In other examples, the UE may obtain configuration for multiple component carriers through control signaling (e.g., a dedicated RRC signaling or broadcasting system information from serving cell(s) through Uu interface).

In addition, the paired UEs may exchange control signaling (e.g., UEs may exchange UE capability on supporting frequency carriers or sidelink reference signal receiving power (SL-RSRP)/Channel Busy Ratio (CBR) measurements results through PC5 RRC signaling) to determine the configuration for multiple component carriers.

Moreover, the operating component carriers may be additionally determined based on measurements between the paired UEs. For example, the UEs may obtain a list of candidate component carriers for SL-unicast service through a sidelink pre-configuration, broadcasting message/dedicated control signaling from serving RAN, or from the dedicated control signaling transmitted by its paired UE. Thus, both of the UEs may implement measurements on (part of) the candidate component carriers in the candidate list. The paired UEs may further determine operating component carrier(s) based on their measurement results through the control signaling exchange between each other (e.g., through the PC5 RRC signaling in PC5 interface). In other examples, the operating component carriers may be determined by the serving RAN, so both of the UEs may need to provide their measurement results to the serving RAN respectively through dedicated control signaling (e.g., RRC signaling in the Uu interface).

In the sidelink unicast scenario, the paired UEs may be grouped as the SL-unicast group {UE #1, UE #2} under in-coverage, out-of-coverage, or partial-coverage implementation.

In-Coverage Case:

Both of the paired UEs may be under the coverage of a RAN. The SL-unicast group {UE #1, UE #2} may be served by the same cell or be served by different cells in the RAN. In one implementation, both of the serving cells may have direct backhaul connection with each other. In some implementations, both of the serving cells may exchange information through the assistance of a core network (CN) (e.g., through intra-system (within the same evolved packet core (EPC)) or inter-system signaling exchange (e.g., between EPC and 5GC)). Both of the in-coverage UEs may obtain sidelink unicast configurations from the serving cell(s) to construct the PC5 interface with each other. The sidelink unicast configurations may be provided by cell-specific broadcasting system information or by dedicated control signaling (e.g., RRC signaling, such as an RRC(Connection)Setup message, RRC(Connection)Reconfiguration message, RRC(Connection)Resume message or RRC(Connection)Release message, in the Uu interface). In other implementations, both of the in-coverage UEs would exchange control signaling (e.g., through PC5 RRC protocols on PC5 interface) to negotiate the sidelink unicast configuration during or after the SL-unicast group {UE #1, UE #2} is established by the upper layers (e.g., through PC5-S protocols in the upper layers).

Out-of-Coverage Case:

Both of the paired UEs may be out of the coverage from the RAN. In this implementation, one UE may implement sidelink unicast service based on the configurations which are pre-configured (e.g., stored in a Universal Mobile Telecommunication System (UMTS) Subscriber Identity Module (USIM) of the UE or through the last serving cell which the UE has accessed before the UE moved out of the coverage of RAN), which is also called the sidelink pre-configuration in this disclosure

In some implementations, both of the out-of-coverage UEs may exchange control signaling (e.g., through PC5 RRC protocols) to negotiate the sidelink unicast configuration during or after the SL-unicast group is established by the upper layers (e.g., through PC5-S protocols in the upper layers).

Partial-Coverage Case:

One of the paired UEs is out of the coverage from a RAN and another UE is under the coverage of the RAN. In one implementation, the in-coverage UE would implement sidelink unicast service based on the sidelink unicast configuration received from the serving cell. In contrast, to the out-of-coverage UE, the UE may implement sidelink unicast service based on the sidelink pre-configuration.

In other implementations, out-of-coverage UEs may obtain the sidelink unicast configuration, which is configured by the serving cell of the in-coverage UE, through the relaying of in-coverage UE. In this case, the paired UEs may negotiate with each other directly to determine the sidelink unicast configuration. Therefore, both of the UEs implement sidelink unicast service based on negotiated sidelink unicast configuration.

However, there is no specification for sidelink unicast configuration application for sidelink unicast service when a sidelink unicast link problem or sidelink unicast link failure occurs in one (or more than one) component carrier on PC5 interface.

SUMMARY

The present disclosure is directed to a method of sidelink unicast service management in an access stratum layer and a related device.

According to an aspect of the present disclosure, a method of sidelink unicast service management in an access stratum layer for a first user equipment (UE) is disclosed. The method comprises receiving, by the first UE through a PC5 interface, a sidelink unicast configuration associated with a second UE, from the second UE, transmitting, by the first UE through a Radio Resource Control (RRC) signaling of the PC5 interface, a sidelink unicast link problem report, to the second UE in responsive to that the first UE is unable to comply with all or part of the sidelink unicast configuration, and performing, by the first UE, a sidelink unicast fallback procedure with the second UE by continuously using a sidelink unicast configuration setting of the first UE with corresponding configurations in a sidelink unicast pre-configuration used prior to the received sidelink unicast configuration.

According to another aspect of the present disclosure, a method of sidelink unicast service management in an access stratum layer for a second user equipment (UE) is disclosed. The method comprises transmitting, by the second UE through a PC5 interface, a sidelink unicast configuration to a first UE, receiving, by the second UE through a first Radio Resource Control (RRC) signaling of the PC5 interface, a first sidelink unicast link problem report, from the first UE, and performing, by the second UE, a sidelink unicast fallback procedure with the first UE by continuously using a sidelink unicast configuration setting of the second UE with corresponding configurations in a sidelink unicast pre-configuration used prior to the transmitted sidelink unicast configuration.

According to another aspect of the present disclosure, a first user equipment (UE) in a wireless communication system is disclosed. The first UE comprises a processor, for executing computer-executable instructions, and a non-transitory machine-readable medium, coupled to the processor, for storing the computer-executable instructions, wherein the computer-executable instructions instruct the processor to receive, by the first UE through a PC5 interface, a sidelink unicast configuration associated with a second UE, from the second UE, transmit, by the first UE through a Radio Resource Control (RRC) signaling of the PC5 interface, a sidelink unicast link problem report, to the second UE in responsive to that the first UE is unable to comply with all or part of the sidelink unicast configuration, and perform, by the first UE, a sidelink unicast fallback procedure with the second UE by continuously using a sidelink unicast configuration setting of the first UE with corresponding configurations in a sidelink unicast pre-configuration used prior to the received sidelink unicast configuration.

According to another aspect of the present disclosure, a second user equipment (UE) in a wireless communication system is disclosed. The second UE comprises a processor, for executing computer-executable instructions, and a non-transitory machine-readable medium, coupled to the processor, for storing the computer-executable instructions, wherein the computer-executable instructions instruct the processor to transmit, by the second UE through a PC5 interface, a sidelink unicast configuration to a first UE, receive, by the second UE through a first Radio Resource Control (RRC) signaling of the PC5 interface, a first sidelink unicast link problem report, from the first UE, and perform, by the second UE, a sidelink unicast fallback procedure with the first UE by continuously using a sidelink unicast configuration setting of the second UE with corresponding configurations in a sidelink unicast pre-configuration used prior to the transmitted sidelink unicast configuration.

