WO2022027189A1

WO2022027189A1 - Enhancements for sl synchronization

Info

Publication number: WO2022027189A1
Application number: PCT/CN2020/106619
Authority: WO
Inventors: Tao Chen; Zhixun Tang; Min LEI
Original assignee: Mediatek Singapore Pte. Ltd.
Priority date: 2020-08-03
Filing date: 2020-08-03
Publication date: 2022-02-10
Also published as: CN114071409A

Abstract

When performing SL synchronization during SL DRX operation, UE can perform partial search, i.e., some subframes/slots and/or some SL Synchronization Signal Identifies (SLSS ID) detect candidate SLSS instead of full search. Additionally, UE can perform full search within a duration (e.g., 160ms SLSS transmission periodicity) with a (pre-) configured periodicity. UE may perform both partial search and full search periodically with the (pre-) configured searching patterns (i.e., periodicity, duration and/or offset) independently or jointly. The duration for full search and/or partial search can fall into the SL DRX_On duration to save UE power. Alternatively, Rx UE can receive the reference signals and/or data from Tx UE to perform synchronization.

Description

ENHANCEMENTS FOR SL SYNCHRONIZATION

TECHNICAL FIELD

This disclosure relates generally to wireless communications, and, more particularly, to methods and apparatus about enhancements for sidelink (SL) synchronization.

BACKGROUND

In 5G new radio, V2X sidelink (SL) communication can be supported by the unicast, groupcast and broadcast communications. However, there are some issues to be addressed for sidelink synchronization, especially during SL DRX operation, to improve the UE power consumption while keeping synchronization for data transmission/reception performance.

SUMMARY

When performing SL synchronization, especially during SL DRX operation, UE can perform partial search, i.e., some subframes/slots and/or some SL Synchronization Signal Identifies (SLSS ID) , to detect candidate SLSS instead of full search, i.e., on all subframes/slots and all SL Synchronization Signal Identifies (SLSS ID) , to detect candidate SLSS. Additionally, UE can perform full search within a duration (e.g., 160ms SLSS transmission periodicity) with a (pre-) configured periodicity. UE may perform both partial search and full search periodically with the (pre-) configured searching patterns (i.e., periodicity, duration and/or offset) independently or jointly. The duration for full search and/or partial search can fall into the SL DRX_On duration to save UE power. Alternatively, Rx UE can receive the reference signals and/or data from Tx UE to perform synchronization.

Additionally, UE can perform the full search within a duration with a (pre-) configured periodicity, e.g., over 160ms SLSS transmission interval with a (pre-) configured or UE assumed periodicity (e.g., 1s) . In this case, such full search ) can be interpreted as a kind of partial search in terms of the time searching.

Alternatively, UE may perform partial search with the (pre-) configured searching patterns based on the periodicity, the duration and/or the starting time offset. The duration of the partial search can fall into the SL DRX_On duration to save UE power if SL DRX is enabled.

Alternatively, Rx UE can receive the reference signals and/or data from Tx UE to perform synchronization. In this case, Rx UE can skip or reduce all/some occasions for SLSS search and detection. Tx UE may transmit wakeup signals/channels to make Rx UE sleep or wakeup during DRX_On duration. Rx UE can use at least the DMRS of the wakeup signals/channels for synchronization during DRX operation, especially for unicast communication. Such wakeup signals/channels can be transmitted periodically associated with each DRX_ON. Such wakeup signals/channels transmission can be based on the configured grant from Tx UE or BS for resource selection/reservation. The wakeup signals/channels can be based on two stage SCI with the 2nd SCI to carry the information about UE (s) to be wakeup in the coming DRX_ON duration. In this case, there may be no need of the associated data channel, which can be indicated by 1 bit for presence of data channel or a new 2nd SCI format with no associated data channel. For example, a bitmap with each bit representing one UE or a UE ID can be carried in 2nd SCI to indicate which UE is to be wakeup. Alternatively, such wakeup information can be carried in the associated data channel. DMRS in the 1st SCI and/or 2nd SCI/data can be used for SL synchronization at Rx UE.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIG. 1 shows SL sync search with DRX operation.

FIG. 2 shows dual-period SL sync search with DRX operation.

FIG. 3 shows sync search based on wakeup signals/channels with DRX operation.

FIG. 4 shows an exemplary block diagram of a UE (a. k. adevice) according to an embodiment of the disclosure.

DETAILED DESCRIPTION OF PREFERRED IMPLEMENTATIONS

Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to ... " . Also, the term "couple" is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. The making and using of the embodiments of the disclosure are discussed in detail below. It should be appreciated, however, that the embodiments can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative, and do not limit the scope of the disclosure. Some variations of the embodiments are described. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements.

The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. Note that the 3GPP specifications described herein are used to teach the spirit of the invention, and the invention is not limited thereto.

For SL synchronization, especially during SL DRX operation, UE can perform partial search, i.e., only on some subframes/slots and/or detection of some SL Synchronization Signal Identifies (SLSS ID) . Compared to the full search over all subframes/slots for all SSIDs, the partial search can save UE power significantly. However, the partial search may lose some synchronization reference (SyncRef) so that the synchronization performance may be degraded. To avoid such problem, UE can perform full search within a duration (e.g., 160ms SLSS transmission periodicity) with a (pre-) configured periodicity. In this case, UE will perform full search for all SSIDs over some periodic time duration. For example, the SSID is transmitted with 160ms periodicity, the UE can perform full search over 160ms searching window with a (pre-) configured periodicity, e.g., 1s. So the UE can perform full search for all SSIDs over 160ms duration with the time interval or periodicity of 1s. In this case, the full search is only applied for all SSIDs but not on all time subframes/slots so that it may be called as a kind of partial search with full SSIDs detection during the searching window.

UE may perform both partial search and full search (or two types of partial search) periodically with the (pre-) configured searching patterns defined based on the periodicity, the duration and/or the starting timing offset. Such patterns can be (pre-) configured independently or jointly. The duration of the searching patterns can fall into the SL DRX_On duration to save UE power if SL DRX is enabled.

FIG. 1 shows SL sync search with DRX operation for power saving. UE may be (pre-) configured with one searching pattern aligned with DRX pattern so that UE can perform search only within DRX_On duration.

FIG. 2 shows dual-period (P1 search pattern and P2 search pattern) SL sync search with DRX operation. In addition to P1 sync search pattern configuration, UE may be (pre-) configured with another searching pattern (i.e., P2 sync search pattern) for full search of all SSIDs within a duration, e.g., over 160ms duration which can be SSID transmission interval, with a (pre-) configured periodicity, e.g., 1s. In this case, UE may perform dual-period search for detection of the candidate SSLS ID and find the suitable syncRef. In case of overlapping of the two patterns, the superposition of the patterns can be applied for SL syncRef search.

In case UE has synchronized to the GNSS and BS directly as the highest priority, such (pre-) configured searching pattern (s) can be ignored or disabled automatically. Otherwise, UE may apply the (pre-) configured searching pattern (s) for search. Such search pattern can be applied independently with SL DRX operation.

Alternatively, Rx UE can receive the reference signals and/or data from Tx UE to perform synchronization. In this case, Rx UE can skip or reduce all/some occasions for SLSS search and detection. Tx UE may transmit wakeup signals/channels to make Rx UE sleep or wakeup during DRX_On duration. Rx UE can use at least the DMRS of the wakeup signals/channels for synchronization during DRX operation, especially for unicast communication. Such wakeup signals/channels can be transmitted periodically associated with each DRX_ON. Such wakeup signals/channels transmission can be based on the configured grant from Tx UE or BS for resource selection/reservation. The wakeup signals/channels can be based on two stage SCI with the 2nd SCI to carry the information about UE (s) to be wakeup in the coming DRX_ON duration. In this case, there may be no need of the associated data channel, which can be indicated by 1 bit for presence of data channel or a new 2nd SCI format for wakeup message without the associated data channel. For example, a bitmap with each bit representing one UE or a UE ID can be carried in 2nd SCI to indicate which UE is to be wakeup. Alternatively, such wakeup information can be carried in the associated data channel. DMRS in the 1st SCI and/or 2nd SCI/data can be used for SL synchronization at Rx UE.

FIG. 3 shows sync search based on wakeup signals/channels with DRX operation. In this case, sync search during DRX_On may not be needed. Instead, UE can use wakeup signals/channels to perform synchronization to the Tx UE especially in case of unicast communication. Whether to be active is also depending on wakeup signals/channels. So Wakeup signals/channels can be the only signal/channels to be detected for both wakeup and synchronization purposes if there is no traffic during DRX operation. Thus, It can save the UE power significantly.

Additionally, if the Tx UE will change the syncRef, Tx UE can inform the Rx UE such syncRef change by a signaling via wakeup channels, 1 ^st/2 ^nd SCI and/or data channel. The Rx UE can get the new timing information for the consequent communication. Such signaling may indicate the timing offset between the new timing and the current timing. It can be frame/slot/symbol offset. Additionally, such signaling may indicate the time instant to use the new timing. Alternatively, UE may assume the new timing will be applied after X slots or ms. Then Tx UE and Rx UE can still maintain the communication during the SyncRef changes.

Additionally, Rx UE can determine SL radio link failure (RLF) based on the SL radio link monitoring (RLM) measurement over the wakeup signals/channels. For example, UE can measure DMRS of wakeup signals/channels to report the channel quality or Out-of-sync (OoS) /In-Sync (IS) periodically for the higher layer to determine the RLF probably after some layer 3 filtering on the measurement results or reported indications.

Additionally, UE may be (pre-) configured by signaling whether to perform SSID detection based sync search for synchronization and/or wakeup channel DMRS/sequence based synchronization. UE may be (pre-) configured with both of them or one of them.

Additionally, in case of multiple unicast communications from the multiple Tx UEs to one Rx UE, the Rx UE can select the Tx UE’s DMRS with the strongest RSRP as the synchronization reference. Alternatively Rx UE can select the Tx UE’s DMRS associated with the highest priority as the synchronization reference. The priority can be (pre-) configured per unicast communication or indicated in the physical control channels such as 1 ^st and/or 2 ^nd SCI. Alternatively, Rx UE may use both RSRP criteria and priority level jointly to determine which Tx UE’s DMRS can be used for synchronization reference. For example, Rx UE can select the Tx UE’s DRMS firstly according to the priority level. In case of the multiple candidates in the same priority level, the Rx UE can select the Tx UE’s DRMS with the best channel quality (e.g., RSRP/RSRQ) as the synchronization reference. Additionally, Depending on UE capability, UE may maintain multiple synchronization references based on multiple Tx UEs’ DMRS for multiple unicast communications.

Alternatively, If UE is synced to the priority group higher than the certain priority group, UE can perform sync search only within +/-x (e.g., x=1 or 2) symbols (or slots) of the current sync timing (i.e., limited sync search) . Otherwise, UE may need to perform the full sync search over all time. The certain priority group can be defined as the sync reference UEs promoting themselves as the sync references without any synchronization to the other sync references or the synchronization reference UEs synchronized to the GNSS or BS with more than Y (e.g., Y>=2) hops. Such certain priority group may have the lowest priority for sync search and larger timing error due to multiple hops or loss of sync to any other sync reference. In addition, considering the asynchronization cellular network, it is possible to set an indicator or signaling to inform UE whether it is possible to have the limited sync search or full sync search. Such indicator can be set per band/frequency to indicate whether all BSs are synced in the band or the frequency layer. Or such indicator can be set for multiple bands/frequencies to indicate whether all BSs are synced across multiple bands/frequency layers. It may reuse the indicator in the uu interface for sync indication or transmitted in the SIB, RRC, or SL RRC for SL operation. If such indicator is set as “true” or “synced” , the UE can assume that the BSs and the sync reference UEs synced to the different BSs are still synced (w/the limited timing offset) , the UE can perform the limited sync search. Otherwise, the UE may need to perform the full sync search.

FIG. 4 shows an exemplary block diagram of a UE 800 (a. k. adevice) according to an embodiment of the disclosure. The processor 810 can be configured to perform various functions of the UE 800 described above with reference to Figs 1-3. The processor 810 can include signal processing circuitry to process received or to be transmitted data according to communication protocols specified in, for example, LTE and NR standards. Additionally, the processor 810 may execute program instructions, for example, stored in the memory 820, to perform functions related with different communication protocols. The processor 810 can be implemented with suitable hardware, software, or a combination thereof. For example, the processor 810 can be implemented with application specific integrated circuits (ASIC) , field programmable gate arrays (FPGA) , and the like, that includes circuitry. The circuitry can be configured to perform various functions of the processor 810.

In one example, the memory 820 can store program instructions that, when executed by the processor 810, cause the processor 810 to perform various functions as described herein. The memory 820 can include a read only memory (ROM) , a random access memory (RAM) , a flash memory, a solid state memory, a hard disk drive, and the like.

The RF module 830 can be configured to receive a digital signal from the processor 810 and accordingly transmit a signal to a base station in a wireless communication network via an antenna 840. In addition, the RF module 830 can be configured to receive a wireless signal from a base station and accordingly generate a digital signal which is provided to the processor 810. The RF module 830 can include digital to analog/analog to digital converters (DAC/ADC) , frequency down/up converters, filters, and amplifiers for reception and transmission operations. For example, the RF module 830 can include converter circuits, filter circuits, amplification circuits, and the like, for processing signals on different carriers or bandwidth parts.

The UE 800 can optionally include other components, such as input and output devices, additional CPU or signal processing circuitry, and the like. Accordingly, the UE 800 may be capable of performing other additional functions, such as executing application programs, and processing alternative communication protocols.

The processes and functions described herein can be implemented as a computer program which, when executed by one or more processors, can cause the one or more processors to perform the respective processes and functions. The computer program may be stored or distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with, or as part of, other hardware. The computer program may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. For example, the computer program can be obtained and loaded into an apparatus, including obtaining the computer program through physical medium or distributed system, including, for example, from a server connected to the Internet.

The computer program may be accessible from a computer-readable medium providing program instructions for use by or in connection with a computer or any instruction execution system. A computer readable medium may include any apparatus that stores, communicates, propagates, or transports the computer program for use by or in connection with an instruction execution system, apparatus, or device. The computer-readable medium can be magnetic, optical, electronic, electromagnetic, infrared, or semiconductor system (or apparatus or device) or a propagation medium. The computer-readable medium may include a computer-readable non-transitory storage medium such as a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM) , a read-only memory (ROM) , a magnetic disk and an optical disk, and the like. The computer-readable non-transitory storage medium can include all types of computer readable medium, including magnetic storage medium, optical storage medium, flash medium and solid state storage medium.

While aspects of the present disclosure have been described in conjunction with the specific embodiments thereof that are proposed as examples, alternatives, modifications, and variations to the examples may be made. Accordingly, embodiments as set forth herein are intended to be illustrative and not limiting. There are changes that may be made without departing from the scope of the claims set forth below.

Claims

A method, comprising:

receiving a (pre-) configuration for SL synchronization about the reference signals and patterns;

performing SL synchronization; and

receiving or transmitting the data based on the timing obtained from the synchronization.