U.S. patent application number 16/964770 was filed with the patent office on 2021-11-25 for ue capability dependent sync priority determination mechanism for v2x communication.
This patent application is currently assigned to MEDIATEK SINGAPORE PTE LTD.. The applicant listed for this patent is MEDIATEK SINGAPORE PTE LTD.. Invention is credited to Tao CHEN, Feifei ZHANG.
Application Number | 20210368465 16/964770 |
Document ID | / |
Family ID | 1000005781221 |
Filed Date | 2021-11-25 |
United States Patent
Application |
20210368465 |
Kind Code |
A1 |
CHEN; Tao ; et al. |
November 25, 2021 |
UE CAPABILITY DEPENDENT SYNC PRIORITY DETERMINATION MECHANISM FOR
V2X COMMUNICATION
Abstract
A method for sidelink data retransmission can include receiving
a first negative acknowledgement (NACK) at a base station (BS) from
a receiver user equipment (Rx UE). The NACK corresponds to an
original transmission of sidelink data over a sidelink from a
transmitter user equipment (Tx UE). The method can further include
selecting one or both of the BS and the Tx UE to perform a first
retransmission of the sidelink data to the Rx UE. A method of
sidelink synchronization can include selecting at a UE a timing
reference with a highest priority among available sidelink
synchronization timing references according to a rule indicating
timing references listed from high priority to low priority: gNB or
eNB; UE directly synchronized to gNB or eNB; UE in directly
synchronized to gNB or eNB; GNSS; UE directly synchronized to GNSS;
UE indirectly synchronized to GNSS; and remaining UEs.
Inventors: |
CHEN; Tao; (Beijing, CN)
; ZHANG; Feifei; (Beijing, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MEDIATEK SINGAPORE PTE LTD. |
Singapore |
|
SG |
|
|
Assignee: |
MEDIATEK SINGAPORE PTE LTD.
Singapore
SG
|
Family ID: |
1000005781221 |
Appl. No.: |
16/964770 |
Filed: |
September 27, 2019 |
PCT Filed: |
September 27, 2019 |
PCT NO: |
PCT/CN2019/108568 |
371 Date: |
July 24, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 76/11 20180201;
H04W 56/0015 20130101; H04W 4/40 20180201; H04L 5/0048
20130101 |
International
Class: |
H04W 56/00 20060101
H04W056/00; H04L 5/00 20060101 H04L005/00; H04W 76/11 20060101
H04W076/11 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 28, 2018 |
CN |
PCT/CN2018/108377 |
Sep 28, 2018 |
CN |
PCT/CN2018/108378 |
Claims
1. A method, comprising: selecting at a user equipment (UE) a
timing reference with a highest priority among available sidelink
synchronization timing references according to a sidelink
synchronization source priority rule that includes different types
of sidelink synchronization timing references each having a
priority; and determining at the UE a transmission timing according
to the selected timing reference, wherein when the different types
of sidelink synchronization timing references are gNB or eNB based
timing references, the different types of sidelink synchronization
timing references include the following types of sidelink
synchronization timing references listed from high priority to low
priority: P0': gNB or eNB, P1': UE directly synchronized to gNB or
eNB, P2': UE in directly synchronized to gNB or eNB, P3': global
navigation satellite system (GNSS), P4': UE directly synchronized
to GNSS, P5': UE indirectly synchronized to GNSS, P6': remaining
UEs.
2. The method of claim 1, wherein when the different types of
sidelink synchronization timing references are GNSS based
references, the different types of sidelink synchronization timing
references include the following types of sidelink synchronization
timing references listed from high priority to low priority: P0:
GNSS, P1: UE directly synchronized to GNSS, P2: UE indirectly
synchronized to GNSS, P3: remaining UEs.
3. The method of claim 1, wherein the selecting includes: receiving
a sidelink synchronization signal (SLSS) carrying information of a
slot index.
4. The method of claim 3, wherein a number of bits representing the
slot index depends on a numerology of the SLSS.
5. The method of claim 3, where the SLSS includes a sidelink
secondary synchronization signal (S-SSS) and a demodulation
reference signal (DMRS), and a sequence of the S-SSS, a sequence of
the DMRS, or the sequences of the S-SSS and the DMRS in
combination, represent the slot index.
6. The method of claim 3, wherein information of the slot index and
a subframe index is combined as one field and carried in the
SLSS.
7. The method of claim 1, wherein the selecting includes: receiving
a SLSS carrying sidelink synchronization source priority
information, wherein the sidelink synchronization source priority
information is carried in signals included in the SLSS other than a
sidelink physical broadcast channel (PBCH).
8. The method of claim 1, wherein the selecting includes: receiving
a SLSS carrying sidelink synchronization source priority
information in a sidelink PBCH, wherein bits of the sidelink
synchronization source priority information are arranged at input
bit positions of a polar encoder when information bits of the
sidelink PBCH are encoded with the polar encoder, such that the
bits of the sidelink synchronization source priority information
can be obtained without fully decoding the sidelink PBCH.
9. The method of claim 1, further comprising: receiving a sidelink
identifier (ID) for identifying sidelink unicast, groupcast, or
broadcast, and performing a sidelink transmission using the
sidelink ID scrambled with a cell ID of a serving cell when the UE
is within or out of coverage of the serving cell.
10. A user equipment (UE), comprising circuitry configured to:
select a timing reference with a highest priority among available
sidelink synchronization timing references according to a sidelink
synchronization source priority rule that includes different types
of sidelink synchronization timing references each having a
priority; and determine a transmission timing according to the
selected timing reference, wherein when the different types of
sidelink synchronization timing references are gNB or eNB based
timing references, the different types of sidelink synchronization
timing references include the following types of sidelink
synchronization timing references listed from high priority to low
priority: P0': gNB or eNB, P1': UE directly synchronized to gNB or
eNB, P2': UE in directly synchronized to gNB or eNB, P3': global
navigation satellite system (GNSS), P4': UE directly synchronized
to GNSS, P5': UE indirectly synchronized to GNSS, P6': remaining
UEs.
11. The UE of claim 10, wherein when the different types of
sidelink synchronization timing references are GNSS based
references, the different types of sidelink synchronization timing
references include the following types of sidelink synchronization
timing references listed from high priority to low priority: P0:
GNSS, P1: UE directly synchronized to GNSS, P2: UE indirectly
synchronized to GNSS, P3: remaining UEs.
12. The UE of claim 10, wherein the circuitry is configured to:
receive a sidelink synchronization signal (SLSS) carrying
information of a slot index.
13. The UE of claim 12, wherein a number of bits representing the
slot index depends on a numerology of the SLSS.
14. The UE of claim 12, where the SLSS includes a sidelink
secondary synchronization signal (S-SSS) and a demodulation
reference signal (DMRS), and a sequence of the S-SSS, a sequence of
the DMRS, or the sequences of the S-SSS and the DMRS in
combination, represent the slot index.
15. The UE of claim 12, wherein information of the slot index and a
subframe index is combined as one field and carried in the
SLSS.
16. The UE of claim 10, wherein the circuitry is configured to:
receive a SLSS carrying sidelink synchronization source priority
information, wherein the sidelink synchronization source priority
information is carried in signals included in the SLSS other than a
sidelink physical broadcast channel (PBCH).
17. The UE of claim 10, wherein the circuitry is configured to:
receive a SLSS carrying sidelink synchronization source priority
information in a sidelink PBCH, wherein bits of the sidelink
synchronization source priority information are arranged at input
bit positions of a polar encoder when information bits of the
sidelink PBCH are encoded with the polar encoder, such that the
bits of the sidelink synchronization source priority information
can be obtained without fully decoding the sidelink PBCH.
18. The UE of claim 10, wherein the circuitry is configured to:
receive a sidelink identifier (ID) for identifying sidelink
unicast, groupcast, or broadcast, and perform a sidelink
transmission using the sidelink ID scrambled with a cell ID of a
serving cell when the UE is within or out of coverage of the
serving cell.
19. A non-transitory computer-readable medium storing a program
that is executable by a processor to perform a method, the method
comprising: selecting at a user equipment (UE) a timing reference
with a highest priority among available sidelink synchronization
timing references according to a sidelink synchronization source
priority rule that includes different types of sidelink
synchronization timing references each having a priority; and
determining at the UE a transmission timing according to the
selected timing reference, wherein when the different types of
sidelink synchronization timing references are gNB or eNB based
timing references, the different types of sidelink synchronization
timing references include the following types of sidelink
synchronization timing references listed from high priority to low
priority: P0': gNB or eNB, P1': UE directly synchronized to gNB or
eNB, P2': UE in directly synchronized to gNB or eNB, P3': GNSS,
P4': UE directly synchronized to GNSS, P5': UE indirectly
synchronized to GNSS, P6': remaining UEs.
20. The non-transitory computer-readable medium of claim 19,
wherein when the different types of sidelink synchronization timing
references are global navigation satellite system (GNSS) based
references, the different types of sidelink synchronization timing
references include the following types of sidelink synchronization
timing references listed from high priority to low priority: P0:
GNSS, P1: UE directly synchronized to GNSS, P2: UE indirectly
synchronized to GNSS, P3: remaining UEs.
Description
INCORPORATION BY REFERENCE
[0001] This present disclosure claims the benefit of International
Application No. PCT/CN2018/108378, "Advanced V2X Communication
Mechanism" filed on Sep. 28, 2018, and No. PCT/CN2018/108377, "UE
Capability Dependent Sync Priority Determination Mechanism for V2X
communication" filed on Sep. 28, 2018, which are incorporated
herein by reference in their entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to wireless communications,
and specifically relates to sidelink communications for vehicular
applications and enhancements to cellular infrastructure.
BACKGROUND
[0003] The background description provided herein is for the
purpose of generally presenting the context of the disclosure. Work
of the presently named inventors, to the extent the work is
described in this background section, as well as aspects of the
description that may not otherwise qualify as prior art at the time
of filing, are neither expressly nor impliedly admitted as prior
art against the present disclosure.
[0004] Cellular based vehicle-to-everything (V2X) (e.g., LTE V2X or
NR V2X) is a radio access technology developed by 3GPP to support
advanced vehicular applications. In V2X, a direct radio link
(referred to as a sidelink) can be established between two
vehicles. The sidelink can operate under the control of a cellular
system (e.g., radio resource allocation) when the vehicles are
within the coverage of the cellular system. Or, the sidelink can
operate independently when no cellular system is present.
SUMMARY
[0005] Aspects of the disclosure provide a method for sidelink data
retransmission. The method can include receiving a first negative
acknowledgement (NACK) at a base station (BS) from a receiver user
equipment (Rx UE). The NACK corresponds to an original transmission
of sidelink data over a sidelink from a transmitter user equipment
(Tx UE). The method can further include selecting one or both of
the BS and the Tx UE to perform a first retransmission of the
sidelink data to the Rx UE.
[0006] In an embodiment, when the BS is selected to perform the
first retransmission of the sidelink data to the Rx UE, the
sidelink data can be transmitted to the Rx UE from the BS. When the
Tx UE is selected to perform the first retransmission of the
sidelink data to the Rx UE, a first sidelink grant can be
transmitted from the BS to the Tx UE for the first retransmission
of the sidelink data to the Rx UE.
[0007] In an example, the selecting one or both of the BS and Tx UE
can be based on whether the BS has received the sidelink data of
the original transmission. In an example, the method can further
include executing power control to the Rx UE such that the BS is
able to receive the NACK from the Rx UE. In an example, the
selecting one or both of the BS and Tx UE is based on channel
conditions of the sidelink between the Tx UE and the Rx UE, and a
Uu link between the Rx UE and the BS, determined at the Rx UE.
[0008] In an embodiment, the method can further include receiving a
second NACK from the Rx UE corresponding to the first
retransmission of the sidelink data to the Rx UE from the Tx UE,
and selecting the BS to perform a second retransmission of the
sidelink data to the Rx UE. In an example, the method can further
include receiving the sidelink data of the original transmission
from the Tx UE at the BS, receiving the sidelink data of the first
retransmission from the Tx UE at the BS, and performing soft
combining of the sidelink data of the original transmission and the
first retransmission at the BS.
[0009] In an embodiment, the method can further include
transmitting from the BS a second sidelink grant included in a
downlink control information (DCI) having a cyclic redundancy check
(CRC) scrambled with a common identifier know to both the Tx UE and
the Rx UE. The second sidelink grant indicates radio resources over
the sidelink for the original transmission of the sidelink data. In
an example, a number of time and frequency resources for
transmitting the second sidelink grant is determined based on a
worse one of channel conditions of a first Uu link between the Tx
UE and the BS and a second Uu link between the Rx UE and the
BS.
[0010] Aspects of the disclosure provide a method for sidelink data
transmission. The method can include receiving a sidelink grant
from a BS at a Rx UE indicating radio resources for transmission of
sidelink data over a sidelink from a Tx UE to the Rx UE, and
detecting at the Rx UE the sidelink data transmitted over the
sidelink at the radio resources indicated by the sidelink grant
received from the BS.
[0011] Aspects of the disclosure provide a BS. The BS can include
circuitry configured to receive a first NACK at the BS from a Rx
UE, the NACK corresponding to an original transmission of sidelink
data over a sidelink from a Tx UE, and select one or both of the BS
and the Tx UE to perform a first retransmission of the sidelink
data to the Rx UE. When the BS is selected to perform the first
retransmission of the sidelink data to the Rx UE, the sidelink data
can be transmitted to the Rx UE from the BS. When the Tx UE is
selected to perform the first retransmission of the sidelink data
to the Rx UE, a first sidelink grant can be transmitted from the BS
to the Tx UE for the first retransmission of the sidelink data to
the Rx UE.
[0012] Aspects of the disclosure provide a method of sidelink
synchronization. The method can include selecting at a UE a timing
reference with a highest priority among available sidelink
synchronization timing references according to a sidelink
synchronization source priority rule that includes different types
of sidelink synchronization timing references each having a
priority, and determining at the UE a transmission timing according
to the selected timing reference. When the different types of
sidelink synchronization timing references are gNB or eNB based
timing references, the different types of sidelink synchronization
timing references include the following types of sidelink
synchronization timing references listed from high priority to low
priority: [0013] P0': gNB or eNB, [0014] P1': UE directly
synchronized to gNB or eNB, [0015] P2': UE in directly synchronized
to gNB or eNB, [0016] P3': global navigation satellite system
(GNSS), [0017] P4': UE directly synchronized to GNSS, [0018] P5':
UE indirectly synchronized to GNSS, [0019] P6': remaining UEs.
[0020] In an example, when the different types of sidelink
synchronization timing references are GNSS-based references, the
different types of sidelink synchronization timing references
include the following types of sidelink synchronization timing
references listed from high priority to low priority: [0021] P0:
GNSS, [0022] P1: UE directly synchronized to GNSS, [0023] P2: UE
indirectly synchronized to GNSS, [0024] P3: remaining UEs.
[0025] In an embodiment, the selecting includes receiving a
sidelink synchronization signal (SLSS) carrying information of a
slot index. In an example, a number of bits representing the slot
index depends on a numerology of the SLSS. In an example, the SLSS
includes a sidelink secondary synchronization signal (S-SSS) and a
demodulation reference signal (DMRS), and a sequence of the S-SSS,
a sequence of the DMRS, or the sequences of the S-SSS and the DMRS
in combination, represent the slot index. In an example,
information of the slot index and a subframe index is combined as
one field and carried in the SLSS.
[0026] In an embodiment, the selecting includes receiving a SLSS
carrying sidelink synchronization source priority information,
wherein the sidelink synchronization source priority information is
carried in signals included in the SLSS other than a sidelink
physical broadcast channel (PBCH).
[0027] In an embodiment, the selecting includes receiving a SLSS
carrying sidelink synchronization source priority information in a
sidelink PBCH. Bits of the sidelink synchronization source priority
information are arranged at input bit positions of a polar encoder
when information bits of the sidelink PBCH are encoded with the
polar encoder, such that the bits of the sidelink synchronization
source priority information can be obtained without fully decoding
the sidelink PBCH.
[0028] In an embodiment, the method for sidelink synchronization
further includes receiving a sidelink identifier (ID) for
identifying sidelink unicast, groupcast, or broadcast, and
performing a sidelink transmission using the sidelink ID scrambled
with a cell ID of a serving cell when the UE is within or out of
coverage of the serving cell.
[0029] Aspects of the disclosure provide a UE for sidelink
synchronization. The UE can include circuitry configure to select a
timing reference with a highest priority among available sidelink
synchronization timing references according to a sidelink
synchronization source priority rule that includes different types
of sidelink synchronization timing references each having a
priority, and determine a transmission timing according to the
selected timing reference. When the different types of sidelink
synchronization timing references are gNB or eNB based timing
references, the different types of sidelink synchronization timing
references include the following types of sidelink synchronization
timing references listed from high priority to low priority: [0030]
P0': gNB or eNB, [0031] P1': UE directly synchronized to gNB or
eNB, [0032] P2': UE in directly synchronized to gNB or eNB, [0033]
P3': GNSS, [0034] P4': UE directly synchronized to GNSS, [0035]
P5': UE indirectly synchronized to GNSS, [0036] P6': remaining
UEs.
[0037] Aspects of the disclosure provide a non-transitory
computer-readable medium storing a program. The program is
executable by a processor to perform the method of sidelink
synchronization.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] Various embodiments of this disclosure that are proposed as
examples will be described in detail with reference to the
following figures, wherein like numerals reference like elements,
and wherein:
[0039] FIG. 1A and FIG. 1B show two data retransmission processes
for retransmitting data previously transmitted in a sidelink
communication;
[0040] FIG. 2 shows a cluster of UEs with a base station present
according to an embodiment of the disclosure;
[0041] FIG. 3 shows another cluster of UEs without presence of a
base station according to an embodiment of the disclosure;
[0042] FIG. 4 shows an example of a gNB/eNB-based synchronization
rule according to an embodiment of the disclosure;
[0043] FIG. 5 shows a GNSS-based synchronization rule according to
an embodiment of the disclosure;
[0044] FIG. 6-FIG. 13 show tables of sidelink synchronization
source priority rules according to some embodiments of the
disclosure;
[0045] FIG. 14 shows a sidelink data transmission process according
to an embodiment of the disclosure;
[0046] FIG. 15 shows another sidelink data transmission process
according to an embodiment of the disclosure;
[0047] FIG. 16 shows a sidelink synchronization process according
to an embodiment of the disclosure; and
[0048] FIG. 17 shows an exemplary apparatus according to
embodiments of the disclosure.
DETAILED DESCRIPTION OF EMBODIMENTS
[0049] FIG. 1A and FIG. 1B show two data retransmission processes
130 and 140 for retransmitting data previously transmitted in a
sidelink communication. One of those two data retransmission
processes 130 and 140 can be adaptively selected for data
retransmission, for example, depending on channel conditions.
[0050] FIG. 1A shows a wireless communication system 100 according
to an embodiment of the disclosure. The system 100 can include a
base station (BS) 101, a first user equipment (UE) 102, and a
second UE 103. The BS 101 can be an implementation of a gNB
specified in the 3rd Generation Partnership Project (3GPP) New
Radio (NR) standards, or can be an implementation of an eNB
specified in 3GPP Long Term Evolution (LTE) standards. Accordingly,
the BS 101 can communicate with the UE 102 or 103 via a radio air
interface 110 (referred to as a Uu interface 110) according to
respective wireless communication protocols. Alternatively, the BS
101 may implement other types of standardized or non-standardized
radio access technologies, and communicate with the UE 102 or 103
according to the respective radio access technologies. The UE 102
or 103 can be a vehicle, a computer, a mobile phone, and the
like.
[0051] The UE 102 and UE 103 can communicate with each other based
on vehicle-to-everything (V2X) technologies specified in 3GPP
standards. A direct radio link 120, referred to as a sidelink (SL),
can be established between the UEs 102 and 103. The UE 102 can use
a same frequency for uplink transmissions over a Uu link 111 and SL
transmissions over the SL 120. Similarly, the UE 103 can use a same
frequency for uplink transmissions over a Uu link 112 and SL
transmissions over the SL 120. In addition, allocation of radio
resources over the SL120 can be controlled by the BS 101.
[0052] In an embodiment, the system 100 implements a hybrid
automatic repeat request (HARQ) scheme for data retransmission. A
first HARQ data retransmission process 130 of this HARQ scheme is
illustrated in FIG. 1A. The process 130 can include steps from S131
to S136. During the process 130, the UE 102 transmits SL data,
while the UE 103 receives the SL data. Accordingly, the UE 102 is
referred to as a transmitter UE (Tx UE) while the UE 103 is
referred to as a receiver UE (Rx UE).
[0053] At S131, a first SL grant is transmitted from the BS 101 to
the Tx UE 102 over the Uu link 111. The first SL grant may indicate
radio resources for the data transmission from the Tx UE 102 to the
Rx UE 103. The first SL grant may further indicate radio resources
for positive or negative acknowledgement (ACK/NACK) feedback from
the Rx UE 103 to the Tx UE 102. Alternatively, the radio resources
for ACK/NACK can be determined based on the radio resources
allocated for the data transmission. For example, by configuration,
the frequency and time domain location of the radio resources for
ACK/NACK feedback can be determined based on that for the data
transmission. In an example, the transmission of the first SL grant
is performed as a response to receive a scheduling request from the
Tx UE 102.
[0054] At S132, the SLdata is transmitted from the Tx UE 102 to the
Rx UE 103 over the SL 120 based on the first SL grant received at
S131. For example, using the radio resource indicated by the first
SL grant, the Tx UE 102 may transmit a physical SL control channel
(PSCCH) followed by a physical SL share channel (PSSCH) over the SL
120. The PSCCH carries information scheduling the PSSCH. The Rx UE
103 can detect the PSSCH based on the scheduling information
carried in the PSCCH.
[0055] The signal for transmitting the SL data can be a broadcast
signal, or a beamformed signal, towards both the Rx UE 103 and the
BS 101 over the channel shared between the uplink of the Uu link
111 and the SL 120. In addition, the allocation of the radio
resource for the SL data transmission is provided by the BS 101,
and thus is known to the BS 101. If the BS 101 executes proper
power control over the Tx UE 102, and a channel condition over the
shared wireless channel is good enough, the BS 101 can detect and
decode the SL data transmitted from the Tx UE 102.
[0056] At S133, the reception of the transmitted SL data is failed
at the Rx UE 103, and a NACK is transmitted from the Rx UE 103 over
the SL 120. Similarly, the signal for the transmission of the NACK
can be detected by both the Tx UE 102 and the BS 101.
Alternatively, the signal for the transmission of the NACK is
detected by at least the BS 101 in other examples. For example, due
to poor channel condition of the SL 120, the Rx UE 102 may not
detect the NACK feedback.
[0057] At S134, a second SL grant for retransmission of the SL data
is transmitted from the BS 101 to the Rx UE 102 over the Uu link
111. For example, in response to receiving the NACK for the SL data
transmission from the Rx UE 103, the BS 101 can determine to
transmit the second SL grant. Similarly, radio resources for
ACK/NACK feedback can be indicated by or derived from the second SL
grand.
[0058] At S135, the SL data is retransmitted from the Tx UE 102 to
the Rx UE 103 based on the second SL grant over the SL 120. In
alternative examples, the first SL grant may specify radio
resources for the retransmission of the SL data. Under such a
configuration, the Tx UE 102 may retransmit the SL data if the Tx
UE 102 receives the NACK feedback over the SL 120. Accordingly,
S134 may be skipped in those examples.
[0059] At S136, when the detection of the SL data is successful at
the Rx UE 103, an ACK for the data retransmission can be fed back
to the Tx UE 102 over the SL 120. Similarly, the signal for the ACK
transmission may also reach the BS 101. The first HARQ data
retransmission process 130 can be completed after S36.
[0060] FIG. 1B shows the same wireless communication system 100 as
in FIG. 1A. The system 100 still implements the HARQ data
retransmission scheme. However, a second HARQ data retransmission
process 140 of the HARQ data retransmission scheme takes place in
the system 100. Different from the first process 130 in FIG. 1A
where the Tx UE 102 performs the SL data retransmission, in the
second process 140, the SL data retransmission is performed by the
BS 101. Specifically, the second process 140 can include steps from
S141 to S145.
[0061] The steps of S141 to S143 can be similarly performed as in
the steps of S131 to S133. However, different from the first
process 130, at S144, the BS 101 may determine to use the BS 101 to
perform the SL data retransmission instead of the Tx UE 102. For
example, instead of sending the second SL grant to trigger the Tx
UE 102 to perform the SL data retransmission over the SL 120, the
BS 101 may transmit the SL data (that is previously received at
S142) via the Uu link 112. For example, the BS 101 may transmit
downlink control information (DCI) on a physical downlink control
channel (PDCCH) that schedules a physical downlink shared channel
(PDSCH) carrying the SL data. The Rx UE 103 may detect the DCI and
subsequently detect and decode the SL data.
[0062] At S145, when the detection is successful, the Rx UE 103 may
transmit an ACK for the SL data retransmission over the Uu link 112
as a response to the SL data retransmission over the Uu interface
110 at S144. For example, the ACK information may be carried on a
physical HARQ indicator channel (PHICH) or a physical uplink shared
channel (PUSCH). Those radio resources of the PHICH or the PUSCH
can be indicated by or derived according to the DCI received at
S144.
[0063] Under such a configuration, the Tx UE 102 may not detect the
ACK transmitted over the Uu interface 110. In an example, the Tx UE
102 may receive anew SL grant from the BS 101 carrying a new data
indicator. In response to receiving the latest SL grant carrying
the new data indicator, the Tx UE 102 may understand the SL data
has been transmitted successfully, and accordingly release the SL
data from a buffer.
[0064] The second HARQ data retransmission process 140 can be
completed after S145.
[0065] According to an aspect of the disclosure, by implementing
the HARQ data retransmission scheme, the BS 101 can adaptively
select the BS 101 or the Tx UE 102, or both, to perform HARQ
retransmission for unicast or groupcast communications over the SL
120. For example, depending on a decision of the BS 101, one of the
processes 130 or 140 can be performed. The decision of selecting
one or both of the BS 101 or the Tx UE 102 to perform the HARQ
retransmission can depend on the flowing considerations.
[0066] In an embodiment, the selection of one or both of the BS 101
and the Tx UE 102 for the SL data retransmission can first be based
on whether the SL data is received (e.g., successfully decoded) at
S132 or S142, and whether the NACK is received (e.g., successfully
decoded) at S133 or S143. For example, due to poor channel
conditions, the BS 101 may not receive the SL data or the NACK.
When the SL data is not received, the BS 101 can select the Tx UE
102 to perform the SL data retransmission. When the SL data is
received but the NACK is not received, the BS 101 may not perform
retransmission operations either from the BS 101 or the Tx UE 102.
Alternatively, the BS 101 may be configured to blindly perform a
retransmission via either the BS 101 or the Tx UE 102, or both,
when the ACK or NACK is not received at a scheduled time.
[0067] In an embodiment, in order to receive the SL data and the
ACK/NACK at the BS 101, the BS 101 can be configured to execute
power control for transmissions by the Tx UE 102 and the Rx UE 103.
For example, the power control to the Tx UE 102 can be based on a
pathloss of the worse one between the Uu link 111 and the SL 120,
and capped by a maximum allowed power level applied to the Uu link
111. For example, the Rx UE 103 can perform measurement
periodically for signals received from the Tx UE 102 over the SL
120, and report measurement results to the BS 101. The BS 101 may
obtain measurement results of signals received from the Tx UE 102.
Based on those measurement results, the BS 101 can have knowledge
of the path loss over the Uu link 111 (uplink direction) and the SL
120 (for transmissions from the Tx UE 102). The BS 101 can
accordingly transmit a DCI indicating a power adjustment to the Tx
UE 102 to control transmission power of the Tx UE 102.
[0068] To avoid interference over the Uu interface 110, the Tx UE
102 may increase the transmission power with a restriction of the
maximum allowed power level for the Uu link 111. In an embodiment,
the maximum allowed power level configured for the Uu link 111 is
signaled from the BS 101 to the Tx UE 102.
[0069] In an embodiment, the BS 101 can be configured to separately
execute power control to the SL 120 and the Uu link 111. For
example, different DCIs with different radio network temporary
identifiers (RNTIs) can be transmitted from the BS 101 to the Tx UE
102. The different RNTIs can be used to differentiate the different
DCIs that carry different power adjustments applicable to
transmissions over the SD link 120 or the Uu link 111. Similarly,
the transmission power over the SL 120 can be capped by the maximum
allowed power level configured for the Uu link 111.
[0070] In an embodiment, the selection of one or both of the BS 101
and the Tx UE 102 for the SL data retransmission can further be
based on channel conditions in the SL 120 and the Uu links 111 or
112. For example, the channel conditions can include channel state
information (CSI) and path loss in the SL 120 and the Uu links 111
or 112. For example, the BS 101 can obtain the channel conditions
of the SL 120 and the Uu link 112 by receiving a report from the Rx
UE 103 that performs a related measurement process. In an example,
when a channel quality of the SL 120 (from the Tx UE 102 to the Rx
UE 102) indicated by the channel conditions is better than a
channel quality of the Uu link 112 (downlink direction), the BS 101
may select the Tx UE 102 for the SL data retransmission. Otherwise,
the BS 101 may select the BS 101 itself for the SL data
retransmission.
[0071] In an example, the BS 101 can compare the channel conditions
of the SL 120 and the Uu link 112 with a threshold, or separate
thresholds. When the channel quality of the SL 120 or the Uu link
112 is above the respective threshold, one or both of the SL 120
and the Uu link 112 can be selected for the SL data
retransmission.
[0072] In an embodiment, the selection of the BS 101 or the Tx UE
102 for the SL data retransmission can be based on a reliability or
QoS requirement associated with each of different types of SL data.
For example, given certain channel conditions of the SD link 120
and the Uu links 111 or 112, the BS 101 may make different
selections depending on the types of the SL data, for example, to
satisfy the reliability or QoS requirements of certain types of DL
data.
[0073] In an embodiment, the selection of the BS 101 or the Tx UE
102 for the SL data retransmission can be performed in the
following way. The BS 101 may first select the Tx UE 102 to perform
the SL data retransmission. When reception of the retransmitted SL
data is failed for a second time (e.g., the BS 101 receives a NACK
from the Rx UE 103 for a second time), the BS 101 may determine to
perform a next SL data retransmission using the BS 101.
[0074] Under such a configuration, the BS 101 may be configured
with a soft combining buffer for storage of SL data received from
the Tx UE 102 in the successive occasions (the original
transmission and the retransmission of the Tx UE 102). Those two
pieces of SL data can be soft combined (e.g., with a chase
combining or incremental redundancy scheme) and decoded, and
subsequently used for the next SL data retransmission from the BS
101.
[0075] In an embodiment, the SL grant (e.g., transmitted at S132,
S134, or S142 in the process 130 or 140) can be received by both
the Tx UE 102 and the Rx UE 103. For example, the Uu links 111 and
112 operate on a same frequency layer (e.g., a same cell). The SL
grant can be carried in a DCI having a cyclic redundancy check
(CRC) scrambled with a common identifier (ID) assigned to both the
Tx UE 102 and the Rx UE 103. For example, the common ID can be an
RNTI or a physical layer ID known to both the Tx UE 102 and the Rx
UE 103. Thus, when the DCI is transmitted in the downlink direction
over the Uu interface 110, both the Tx UE 102 and the Rx UE 103 can
detect the DCI to obtain the DL grant. In this way, both the Tx UE
102 and the Rx UE 103 can know the radio resources granted for
transmission of the SL data over the SL 120. Transmission of the
PSCCH (that schedules the PSSCH) over the SD link 120 as performed
in S132, S135, or S142 can be omitted to save radio resources and
reduce SL data transmission complexity.
[0076] In one example, the BS 101 determines a number of time and
frequency resources for the SL grant based on the worse one between
the Uu link 111 and the Uu link 112, such that both the Tx UE 102
and Rx UE 103 can receive the SL grant. For example, the one of the
Uu links 111 and 112 having a worse channel condition (e.g., CSI,
pathloss) is used to determine a the number of time and frequency
resources for transmitting the SL grant provided by the BS 101 to
both Tx UE 102 and the Rx UE 103.
[0077] In an embodiment, two different methods can be used for the
Rx UE 103 transmitting the ACK/NACK feedback over the SL 120 for
reception the DL data from the Tx UE 102. The first method is to
transmit the ACK/NACK feedback using the radio resources configured
by or derived from the SL grant, for example, in a form of a
physical SL HARQ indicator channel. The second method is to attach
the ACK/NACK feedback to a PSSCH transmitted from the Rx UE 103 to
the Tx UE 102. For example, when the Rx UE 103 has SL data to be
transmitted to the Tx UE 102, a PSSCH can be transmitted over the
SL 120 from the Rx UE 103 to the Tx UE 103. The HARQ feedback
information can be included in the PSSCH.
[0078] In an embodiment, when there is SL data stored in a buffer
waiting to be transmitted to the Tx UE 102, the Rx UE 103 transmits
a PSSCH that carries SL scheduling request related information to
the Tx UE 102. The SL scheduling request related information can
include a SL scheduling request, buffer status information
(indicating SL data in a buffer at the Rx UE 103), and/or traffic
type (e.g., unicast, groupcast, or broadcast). In an embodiment,
instead of carrying the SL scheduling request related information
in a PSSCH, the Rx UE 103 may include the SL scheduling request
related information in a media access control (MAC) control element
(CE) of a transport block carried in a PSSCH.
[0079] In an embodiment, at the Tx UE 102, the Tx UE 102 can
transmit a PSSCH to the Rx UE 103 that includes radio resource
allocation information for SL date transmission and/or reception
between the Tx UE 102 and the Rx UE 103. In an example, the
transmission of the radio resource allocation information can be a
response to and based on SL scheduling related information (e.g., a
scheduling request, buffer status, and/or traffic type) received
from the Rx UE 103.
[0080] For example, the radio resource allocation information may
include a radio resource configuration for the SL data transmission
and/or reception between the Tx UE 102 and Rx UE 103 during a
period. For example, the configuration can specify a sequence of
periodical transmission occasions over the period. Alternatively,
the radio resource allocation information may indicate radio
resources for the transmission and/or reception between the Tx UE
102 and Rx UE 103 in a next time unit (e.g., a slot). Based on the
radio resource allocation information carried in the PSSCH, the Tx
UE 102 and Rx UE 103 can have a mutual understanding of when the
respective transmissions and receptions will take place between the
Tx UE 102 and Rx UE 103. Collisions of SL data transmission of two
opposite directions over the SL 120 can thus be avoided.
[0081] In an example, the above scheme of carrying radio resource
allocation information over a PSSCH can be applied to UEs forming a
cluster. The cluster may include a master UE that transmits radio
resource allocation information over a PSSCH to other member UEs of
the cluster. In an example, the master UE is selected by a BS. In
other examples, the master UE can be determined without a BS.
[0082] In various embodiments, the above described examples of
carrying radio resource allocation information over a PSSCH,
carrying a SL scheduling request over a PSSCH or a MAC CE, or
carrying ACK/NACK information over a PSSCH, can be performed by UEs
within a coverage of a BS or out of a coverage of a BS. For
example, when a UE is out of coverage of a BS, the UE can determine
SL radio resource allocation without control of the BS. When a UE
is within the coverage of a BS, SL radio resource allocation may or
may not be controlled by the BS.
[0083] FIG. 2 shows a cluster 200 of UEs 201-205 according to an
embodiment of the disclosure. Each UE 201-205 synchronizes to a
nearby synchronization source and accordingly determines a
transmission timing or a reception timing for sidelink
communications (e.g., unicast, groupcast, or broadcast) with nearby
UEs within the cluster 200. A synchronization source 210 (e.g., a
gNB, an eNB, or a global navigation satellite system (GNSS)) (or a
synchronization signal (SS) from the synchronization source 210) is
used as a top priority timing reference which is extended to the
UEs 201-205 within the cluster 200.
[0084] For example, the UEs 201-202 are within the coverage of the
synchronization source 210, and accordingly can directly
synchronize to the synchronization source 210. For example, a gNB
or eNB may periodically transmit LTE or NR synchronization signals
(SSs) such as primary synchronization signal (PSS), secondary
synchronization signal (SSS), and physical broadcast channel (PBCH)
signal. GNSS satellites may continuously transmit navigation
signals. Using those signals as timing references, the UEs 201-202
can obtain the reference timing, and accordingly determine the
transmission or reception timing of itself.
[0085] After being synchronized to the synchronization source 210,
the UE 202 can transmit a sidelink synchronization signal (SLSS)
that is synchronized to the synchronization source 210. The SLSS
can include a sidelink primary synchronization signal (S-PSS), a
sidelink secondary synchronization signal (S-SSS), and a sidelink
physical broadcast channel (S-PBCH, or PSBCH) signal, and can be
transmitted periodically. In an example, when the UE 202 starts to
transmit the SLSS can be controlled by a gNB or an eNB which the UE
202 is connected to or camped on. In an example, the UE 202 itself
can make a decision when to transmit the SLSS. For example, the UE
202 can determine to transmit the SLSS when a quality (e.g.,
indicated by reference signal received power (RSRP)) of a signal
from the gNB or the eNB is below a threshold.
[0086] By receiving the SLSS from the UE 202 as a timing reference,
the UEs 203 and 205, which are out of the coverage of the top
priority timing reference 210, can synchronize to the UE 202, and
becomes indirectly synchronized to the top priority synchronization
source 210.
[0087] Similarly, the UE 203 can transmit a SLSS that is
synchronized to the timing reference of the UE 202. By using the
SLSS of the UE 203 as a timing reference, the UE 204 can by
synchronized to the UE 203.
[0088] FIG. 3 shows another cluster 300 of UEs 301-304 according to
an embodiment of the disclosure. Each UE 301-304 synchronizes to a
nearby synchronization source in order to determine a transmission
timing or a reception timing for sidelink communications (e.g.,
unicast, groupcast, or broadcast) with nearby UEs within the
cluster 300. In the cluster 300, none of the UEs 301-304 is within
the coverage of a synchronization source (e.g., the synchronization
source 210 in the FIG. 2 example). For example, when the UE 301 is
powered on or has lost synchronization to other synchronization
sources (e.g., a gNB, an eNB, a GNSS, or a UE), the UE 301 tries to
search for a synchronization source (e.g., a gNB, an eNB, a GNSS,
or a UE) and is not successful. Accordingly, the UE 301 may
autonomously determine a transmission timing, and transmit a SLSS
based on this transmission timing. The UE 302 can use the SLSS from
the UE 301 as a timing reference and determine a transmission
timing of the UE 302. In a similar way, the UEs 303-304 can perform
synchronization based on a SLSS transmitted from the UE 302.
[0089] According to an aspect of the disclosure, in order to
facilitate synchronization operations in sidelink communications, a
synchronization rule can be specified. According to the
synchronization rule, different timing references (or
synchronization sources) can be categorized into different groups
or types. Each type of the timing references is given a priority. A
synchronization configuration indicating the synchronization rule
can be configured to a UE. Based on this synchronization
configuration, the UE can select a timing reference with the
highest priority among available timing references to synchronize
with.
[0090] In an embodiment, the synchronization configuration can be
configured to the UE through radio resource control (RRC) signaling
or broadcasted system information when the UE is in coverage of a
BS. The UE can store the synchronization configuration locally, and
use the synchronization configuration when being in an in-coverage
status (connected to a BS in RRC connected mode or camping on a BS
in RRC idle mode), or in an out-of-coverage status. Alternatively,
the synchronization configuration can be configured to the UE, for
example, by storage in a subscriber identity module (SIM) or in a
non-volatile memory of the UE. For example, when the UE is out of
coverage, and has not received a synchronization configuration from
a BS before, the UE can use the locally stored synchronization
configurations to select a timing reference. After the UE receives
the synchronization configuration from the BS, the UE can use the
received synchronization configuration. In an example, the UE can
use the locally stored synchronization configuration when the UE is
in coverage or out of coverage of a BS.
[0091] FIG. 4 shows an example of a gNB/eNB-based synchronization
rule 400 according to an embodiment of the disclosure. The
gNB/eNB-based synchronization rule 400 includes 7 types of timing
references with priorities from P0' to P6'. The 7 types of timing
references are listed in priority decreasing order.
[0092] In an example, a current UE configured (e.g., by signaling
or by storage at the UE) with the rule 400 can perform a
synchronization procedure in the following way. As the gNB or eNB
is configured to be the top priority timing reference, the current
UE can first search for a SS from a gNB or eNB, for example, after
powered on or losing synchronization. If a SS from a gNB or eNB
with a signal quality above a threshold is found, the current UE
can synchronize to the SS. In an example, when both a gNB and an
eNB are found, the one of the respective SSs with a higher signal
quality (e.g., RSRP) is used as the timing reference.
[0093] Using a gNB or an eNB as a top priority timing reference,
UEs within a coverage of a gNB or eNB can be synchronized to a same
BS (or a same cell). As a result, sidelink transmissions among the
UEs will take place within intended time-frequency resources,
thereby reducing uncontrolled interference to other sidelink and
non-sidelink (cellular uplink) transmissions in a same band.
[0094] When no suitable SS from a gNB or eNB is found, the current
UE can continue to search for a SLSS from a UE directly
synchronized to a gNB or an eNB. For example, in the FIG. 2
example, assuming the synchronization source 210 is a gNB, the UE
205 at the current location can receive SLSSs from both the UE 202
and the UE 203. Based on the received SLSSs, the UE 205 can know
the UE 202 is a UE directly synchronized to the gNB (the
synchronization source 20), while the UE 203 is a UE indirectly
synchronized to the gNB. According to the synchronization rule 400,
the UE 205 can select the UE 202 as a timing reference, as the UE
202 has a priority of P1' while the UE 203 has a priority of P2' as
specified in the rule 400.
[0095] When a timing reference is extended through a chain of UEs,
timing errors can accumulate with respect to the original
synchronization source. For example, the UE 202 (that is a hop 0
timing reference (e.g., direct synchronization)) has a higher
timing accuracy than the UE 203 (that is a hop 1 timing reference
(e.g., indirect synchronization)). Accordingly, the UE 205 can
obtain a transmission or reception timing with a higher accuracy
from the UE 202 than from the UE 203.
[0096] In an embodiment, information of a number of hops of a UE
with respect to a top priority synchronization source can be
carried in a SLSS of the respective UE. The current UE can
accordingly select the one with the fewest hops among available UEs
(e.g., UE indirectly synchronized to a gNB or an eNB) as a sidelink
synchronization source.
[0097] When no UE indirectly synchronized to a gNB or an eNB is
found, according to the synchronization rule 400, the current UE
can search for navigation signals of a GNSS (with a priority of
P3'). If no GNSS is available, the current UE can search for a UE
directly synchronized to a GNSS (a UE with a priority of P4') to
synchronize with. If no UE directly synchronized to a GNSS is
available, the current UE may search for a UE indirectly
synchronized to a GNSS (a UE with a priority of P5'). If no UE
indirectly synchronized to a GNSS is found, the current UE may
determine to use one of other available UEs as a timing reference
(a UE with a priority of P6'). For example, those other available
UEs can belong to a cluster of UEs where no gNB, eNB, or GNSS is
present, such as the UEs 301-304 in the FIG. 3 example.
[0098] When no UEs are available around the current UE, the current
UE can autonomously determine a transmission timing and accordingly
transmit a SLSS. Please note that according to different designs,
the orders can be different from the embodiment shown in FIG.
4.
[0099] In some embodiments, when the synchronization source
priority rule 400 is configured to a UE (e.g., by signaling or by
storage in a SIM), the UE may perform a sidelink synchronization
according to the rule 400, however, with consideration of UE
capability restriction.
[0100] For example, a NR UE is able to receive a SS from a NR BS
(e.g., gNB), but may not be able to receive a SS from an LTE BS
(e.g., eNB). In contrast, an LTE UE is able to receive SS from an
LTE BS but may not be able to receive SS from a NR BS.
[0101] For example, a NR V2X UE has the ability to perform sidelink
communications according to protocols specified by a NR V2X
standard, and accordingly can perform synchronization using a SLSS
compliant with the NR V2X standard. Accordingly, the NR V2X UE can
receive a SLSS from an LTE UE or NR UE that operates according to
the NR V2X standard. However, the NR V2X UE may not use a SLSS from
a UE operating according to the LTE V2X standard.
[0102] Similarly, an LTE V2X has the ability to perform sidelink
communications according to protocols specified by the LTE V2X
standard, and accordingly can perform synchronization using a SLSS
compliant with an LTE V2X standard, but may not perform
synchronization suing a SLSS of the NR V2X standard.
[0103] Because of different UE capabilities, available
synchronization sources for different UEs can be different when a
same set of synchronization sources is present. Accordingly, in an
embodiment, a UE configured with the synchronization source
priority rule 400 can derive a synchronization source priority
configuration or rule according to the rule 400 based on a
capability of the UE. For example, some kinds of synchronization
sources unusable for the UE may not be included in the derived rule
or configuration.
[0104] In an embodiment, instead configure the rule 400 to a UE, a
synchronization source priority configuration or rule can first be
derived based on the rule 400 and a capability of the UE, and
subsequently configured to the UE (e.g., by signaling or by storage
at the UE).
[0105] FIG. 5 shows a GNSS-based synchronization rule 500 according
to an embodiment of the disclosure. In the GNSS-based
synchronization rule 500, timing references are categorized into 4
groups or types each with a priority. The 4 types of timing
references are listed in priority decreasing order from P0 to P3.
Different from the rule 400, the rule 500 includes the GNSS as a
top priority synchronization source. Different network operators
may prefer different network deployment strategies and thus may
choose the GNSS or the gNB and/or eNB as the top priority sidelink
synchronization source. When the GNSS is preferred, the rule 500
can be used.
[0106] FIG. 6-FIG. 13 show tables 600-1300 of sidelink
synchronization source priority rules according to some embodiments
of the disclosure. Those priority rules can be configured to a UE
(e.g., by RRC or system information signaling, or storage in a SIM
module (e.g., a universal integrated circuit card (UICC) module or
a memory), and used as a basis for selecting a timing
reference.
[0107] Each table can include 2 or 3 gNB-based, eNB-based, or
GNSS-based priority rules. For example, depending on network
operator's deployment preference, the gNB-based, eNB-based, or
GNSS-based priority rules can be configured to a UE and used as a
basis for selecting a timing reference.
[0108] In some priority rules (e.g., R1-2a, R1-2b in the table
700), different types of synchronization sources are organized into
different priority groups (e.g., PG1, PG2, and the like). For each
such priority rule, the priority groups are listed from high
priority to low priority (e.g., from PG1 to PG6 in R1-2a).
[0109] In addition, in an example, within a same priority group,
when multiple synchronization sources are available, the one with a
higher signal quality (e.g., measured by sidelink RSRP (S-RSRP))
can be selected.
[0110] Different priority rules can be configured to UEs having
different capabilities. For example, the rules in the tables
600-700 can be used by a NR only and NR V2X only UE. The rules in
the tables 800-900 can be used by a NR/LTE (NR and LTE capable) and
NR V2X only UE. The rules in the tables 1000-1100 can be used by a
NR only and NR V2X/LTE V2X UE. The rules in the tables 1200-1300
can be used by a NR/LTE and NR V2X/LTE V2X UE. The invention is not
limited by these.
[0111] For UEs in an in-coverage status (e.g., within a coverage of
a gNB, or eNB), or an our-of-coverage status (e.g., not within a
coverage of a gNB or eNB), different priority rules can be applied.
Accordingly, the priority rules corresponding to the in-coverage
and our-of-coverage status are separate into different tables in
the examples of the tables 600-1300.
[0112] The tables 600 and 700 include priority rules for NR only
and NR V2X only UEs in in-coverage status and out-of-coverage
status, respectively. The table 600 includes two rules, denoted by
R1-1a and R1-1b, that are gNB-based and GNSS-based, respectively.
The table 700 includes two rules, R1-2a and R1-2b, that are
gNB-based and GNSS-based, respectively.
[0113] In the rule R1-1a, when a UE is within a coverage (InC) of a
cell that operates with a frequency the same as that of a sidelink
of the UE, a PCell or SCell of the UE can be used as the
synchronization source when the UE is in RRC connected mode. Or, a
serving cell that the UE camps on can be used as the
synchronization source when the UE is in RRC idle mode. Or, SSs
from a downlink frequency paired with the respective sidelink
frequency of the UE can be used as the timing reference. When the
UE is out of coverage (OoC) of the cell that operates with a
frequency the same as that of a sidelink of the UE, a PCell the UE
is connected with or a serving cell the UE camps on can be used as
a synchronization source. This PCell or serving cell can operate
with a frequency different from that of the sidelink of the UE.
[0114] In the rule R1-1b, one of a GNSS, a NR UE directly
synchronized to the GNSS, and a gNB can be used as a
synchronization source. The GNSS has a highest priority while the
gNB has a lowest priority.
[0115] In addition, NR_UE.sub.GNSS denotes a NR UE synchronized to
a GNSS. NR_UE.sub.gNB denotes a NR UE synchronized to a gNB.
NR_UE.sub.NR_UE-gNB denotes a NR UE synchronized to a
NR_UE.sub.gNB. NR_UE.sub.NR_UE-GNSS denotes a NE UE synchronized to
a NR_UE.sub.GNSS. Meanings of other notations in the tables
600-1300 can be interpreted similarly.
[0116] The tables 800 and 900 include priority rules for NR/LTE and
NR V2X only UEs in in-coverage status and out-of-coverage status,
respectively. Compared with the tables 600 and 700, LTE related
synchronization sources (e.g., PCell/Serving cell of LTE,
NR-UE.sub.NR_UE-eNB, NR_UE.sub.LTE_UE-GNSS) are added to the
rules.
[0117] The tables 1000 and 1100 include priority rules for NR only
and NR V2X/LTE V2X UEs in in-overage status and out-of-coverage
status, respectively. Compared with the tables 600 and 700, LTE UE
related synchronization sources (e.g., LTE_UE.sub.GNSS,
LTE-UE.sub.eNB, LTE_UE.sub.other) are added to the rules.
[0118] The tables 1200 and 1300 include priority rules for NR/LTE
and NR V2X/LTE V2X UEs in in-overage status and out-of-coverage
status, respectively. Compared with the tables 600 and 700, LTE and
LTE UE related synchronization sources are added to the rules.
[0119] As shown in the tables 700/900/1100/1300, the gNB or eNB
based rules for out-of-coverage usage, R1-2a (in the table 700),
R2-2a and R2-2b (in the table 900), R3-2a and R3-2b (in the table
1100), and R4-2a and R4-2b (in the table 1300), each include 6
priority groups from PG1 to PG6. Similar to the priority types from
P1' to P6' listed in the synchronization source priority rule 400
in FIG. 4, the priority group PG1 includes UEs that are directly
synchronized to a gNB or an eNB. The priority group PG2 includes
UEs that are indirectly synchronized to a gNB or an eNB. The
priority group PG3 includes one or more GNSSs. The priority group
PG4 includes UEs that are directly synchronized to a GNSS. The
priority group PG5 includes UEs that are indirectly synchronized to
a GNSS. The priority group PG6 includes other UEs. Please note that
in the tables 700/900/1100/1300, priority group PG0 are omitted for
brevity. Similar to the priority type P0' listed in the
synchronization source priority rule 400 in FIG. 4, the priority
group PG0 includes one or more eNB/gNB (to be synchronized by the
UE).
[0120] As shown in the tables 700/900/1100/1300, the GNSS based
rules for out-of-coverage usage, R1-2b, R2-2c, R3-2c, and R4-2c,
each include 4 priority groups from PG1 to PG4. Similar to the
priority types from P0 to P3 listed in the synchronization source
priority rule 500 in FIG. 5, the priority group PG1 includes one or
more GNSSs. The priority group PG2 includes UEs directly
synchronized to a GNSS. The priority group PG3 includes UEs
indirectly synchronized to a GNSS.
[0121] In some embodiments, beamforming sweeping is employed in
sidelink transmissions. Accordingly, SLSSs in the form of sidelink
synchronization signal blocks (S-SSBs) can be transmitted over
beams towards different directions during a beam sweeping to cover
a cell. The S-SSBs in the beam sweeping can be organized into an
S-SSB burst. Each S-SSB can include an S-PSS, an S-SSS, a PSBCH,
and a demodulation reference signal multiplexed with the PSBCH
(PSBCH DMRS). The S-SSB burst can be transmitted periodically, for
example, for every 5 ms, 10 ms, 20 ms, and the like.
[0122] In addition, different numerologies may be employed for
frequencies used in sidelink transmissions. In an example, a
default numerology or a set of numerologies for sidelink
transmissions can be preconfigured to a UE (e.g., storage in a SIM
module). Accordingly, the UE can search for a SLSS with the default
numerology or one of the set of configured numerologies. In an
example, one or more numerologies can be signaled from a BS to a
UE. Accordingly, the UE can search for a SLSS with the signaled
numerologies.
[0123] For different numerologies, different subcarrier spacings
(e.g., 15 kHz, 30 kHz, 60 kHz, and the like) can be used, and
accordingly, different number of slots can be included in a
subframe of 1 ms. For example, corresponding to the subcarrier
spacings 15 kHz, 30 kHz, 60 kHz, and 120 kHz, each subframe can
include 1, 2, 4, and 8 slots, respectively. Under such a
configuration, for different numerologies, positions of S-SSBs of
an S-SSB burst over a subframe may be arranged differently for
different numerologies.
[0124] In an embodiment, slot index information of an S-SSB
corresponding to a certain numerology is signaled to a UE from a
BS, or is carried in the S-SSB, such that the UE can determine
which slot (e.g., indicated by a slot index) the respective S-SSB
is positioned in. The S-SSB can also carry information of a system
frame number (SFN) and subframe index associated with the S-SSB.
Based on the information of the slot, subframe, and the SFN, the UE
can determine timings of the respective S-SSB.
[0125] In an embodiment, number of bits used for indicating the
slot index of the S-SSB depends on the numerology of the S-SSB. For
example, for the numerology of 120 kHz, there can be 8 slots in a
subframe, while for the numerology of 30 kHz, there can be 2 slots
in a subframe. Accordingly, a maximum allowed positions for S-SSBs
for the numerology of 120 kHz can be more than that for the
numerology of 30 kHz. Thus, more bits are potentially needed for
representing the slot indices for the numerology of 120 kHz that
for the numerology of 30 kHz. In an example, 1 bit, 2 bits, and 4
bits are used for indicating slot indices for the numerologies of
15 kHz, 30 kHz, and 60 kHz, respectively.
[0126] In an embodiment, the slot index information and the
subframe information of an S-SSB is combined into one field and
indicated by a same set of bits carried in the respective
S-SSB.
[0127] In an embodiment, the slot index information is carried in
an S-SSB using sequences of SSS or PSBCH DMRS. For example,
different sequences can be selected or generated (e.g., initialized
with bits of a slot index) to indicate the slot index
information.
[0128] In an embodiment, uplink frequencies of paired frequencies
or frequency division duplex (FDD) frequencies are used for V2X
communication. To facilitate a UE to perform sidelink
synchronization, downlink frequency information (e.g., an absolute
radio frequency channel number (ARFCN)) and/or band information is
signaled to a UE or preconfigured to a UE (e.g., stored in a SIM).
Based on those information, the UE can search uplink frequencies
corresponding to the known downlink frequencies to perform a
synchronization process while in coverage or out of coverage of a
BS.
[0129] In various embodiments, sidelink synchronization source
priority information for indicating a priority of a SLSS can be
carried in the SLSS (e.g., S-SSB) in various ways. The sidelink
synchronization source priority information can include which type
of top-priority source (e.g., GNSS, gNB, or eNB) is used, coverage
status of the respective UE (e.g., in-coverage or out-of-coverage),
whether no top-priority source is present (e.g., a cluster of UEs
are synchronized to a timing reference determined autonomously be a
UE), numbers of hops with respect to a top-priority source, and the
like.
[0130] In an embodiment, part of the synchronization source
priority information (e.g. in-coverage or out-of-coverage) is
included in a PSBCH of a SLSS. Accordingly, the PBSCH has to be
decoded before a priority of the SLSS can be determined. In an
embodiment, information bits of the synchronization source priority
information can be arranged in special input positions to a polar
encoder when polar code is used for channel coding a master
information block (MIB) in a PSBCH. In this way, transmission
reliability of the respective information bits can be improved, and
decoding of those information bits can be accelerated without fully
decoding the MIB in the PSBCH.
[0131] In an embodiment, instead of a PSBCH, the synchronization
source priority information is carried in an S-PSS, an S-SSS, or a
PSBCH DMRS of an S-SSB, or a combination of two or three of an
S-PSS, an S-SSS, or a PSBCH DMRS of an S-SSB. In this way, the
synchronization source priority information can be determined
earlier without decoding the PSBCH.
[0132] In an embodiment, a sidelink ID for identifying sidelink
unicast, groupcast, or broadcast is determined based on different
in-coverage or out-of-coverage scenarios. For example, the sidelink
ID can be configured to a Tx UE by RRC signaling (e.g., similar to
assigning RNTI) or by storage in the Tx UE. The sidelink ID can be
used to identify a sidelink of unicast, groupcast, or broadcast
when the Tx UE performs sidelink transmissions. Or, in other words,
the sidelink ID can be used to identify communications between the
UE and an individual UE, or a group of UEs. During a sidelink
transmission from the Tx UE, such a sidelink ID can be explicitly
carried in a control channel or implicitly carried via CRC
scrambling (e.g., a CRC scrambled by such an ID). A Rx UE can know
if the transmission is intended for the Tx UE or a group including
the Tx UE by detecting or decoding the ID. In addition, the IDs can
also be used for other functions including scrambling control or
data information over a sidelink, or scrambling control or data
DMRS over a sidelink.
[0133] The sidelink ID can be a L1-ID (physical layer ID) that is
derived from a L2-ID or a higher layer ID, or configured by a
higher layer.
[0134] In an example, when the Tx UE is in an out-of-coverage
status without a serving cell (without presence of a BS) (e.g., the
FIG. 3 example), the sidelink ID is used by itself. In contrast,
when the Tx UE is an in-coverage status or an our-of-coverage
status with a serving cell or BS present (e.g., the FIG. 2
example), the sidelink ID can be scrambled by a cell ID of the
serving cell and the resulting ID can be used in place of the
sidelink ID.
[0135] FIG. 14 shows a sidelink data transmission process 1400
according to an embodiment of the disclosure. The BS 101 and the
UEs 102-103 in FIG. 1A and FIG. 1B are used as examples for
explanation of the process 1400. The process 1400 can be performed
by the BS 101 to dynamically select the BS 101 or the Tx UE 102 to
perform a retransmission of sidelink data transmitted from the Tx
UE 102 to the Rx UE 103. The selection can be based on channel
conditions of the sidelink 120 between the Tx UE 102 and the Rx UE
103, and the Uu link 112 between the BS101 and the Rx UE 103. The
process can start from S1401, and proceed to S1410.
[0136] At S1410, the sidelink data can be received at the BS 101.
The sidelink data can be transmitted from the Tx UE 102 to the Rx
UE 103 over the sidelink 120. As the sidelink 120 operates over the
same frequency as the uplink between the Tx UE 102 and the BS 101,
the BS 101 can detect and decode a signal of the sidelink data when
transmission power of the sidelink data is suitable, and a channel
condition over the uplink is above a threshold.
[0137] At the S1420, a NACK can be received from the Rx UE 103 at
the BS 101. For example, when reception of the sidelink data over
the sidelink 120 is failed, the Rx UE 103 can transmit the NACK
over the sidelink 120. Because the uplink between the Rx UE 103 and
the BS 101 shares a same frequency as the sidelink 120, the BS 101
can receive the NACK when transmission power of the NACK is
suitable and a channel condition over the uplink between the Rx UE
103 and the BS 101 is above a threshold.
[0138] At S1430, the BS 101 can make a decision to select one or
both of the BS 101 and the Tx UE 102 to perform a retransmission of
the sidelink data in response to receiving the NACK. The selection
can be based on channel conditions of the sidelink 120 and the Uu
link 112, for example, as measured by the Rx UE 103. In other
examples, other factors may be considered for the selection.
[0139] At 1440, when the BS is selected, the BS 101 can retransmit
the sidelink data received at S1410 to the Rx UE 103 over the Uu
link 112.
[0140] When the Tx UE is selected, the BS 101 can transmit a
sidelink grant to the Tx UE 102 to allocate radio resources of the
sidelink 120 for a retransmission to be performed by the Tx UE 102.
Subsequently, the Tx UE 102 can retransmit the sidelink data to the
Rx UE 103. The process 1400 can proceed to S1499 and terminates at
S1499.
[0141] FIG. 15 shows a sidelink data transmission process 1500
according to an embodiment of the disclosure. The BS 101 and the
UEs 102-103 in FIG. 1A and FIG. 1B are used as examples for
explanation of the process 1500. The process 1500 can be performed
by the Rx UE 103 for reception of sidelink data without receiving
resource allocation information (e.g., carried in a sidelink DCI in
a PSCCH from the Tx UE 102).
[0142] The process 1500 can start from S1501, and proceeds to
S1510.
[0143] At S1510, a sidelink grant can be received from the BS 101
at the Rx UE 103 over the Uu link 112. The sidelink grant can
indicate radio resources for transmitting the sidelink data over
the sidelink 120 from the Tx UE 102 to the Rx UE 103. For example,
the sidelink grant can be carried in a DCI having a CRC scrambled
with a common ID known to both the Tx UE 102 and the Rx UE 103.
Accordingly, the Tx UE 102 and the Rx UE 103 can detect and decode
a PDCCH carrying the DCI, and obtain the sidelink grant.
[0144] At S1520, the sidelink data can be detected over the
sidelink 120 at the Rx UE 103 according to the sidelink grant. For
example, based on the sidelink grant, the Rx UE 103 can know
time-frequency domain locations of the radio resources used for
transmitting the sidelink data, and a respective MCS. Under such a
configuration, transmission of a PSCCH for scheduling resources for
transmitting the sidelink data can be avoided. The process 1500 can
proceed to S1599 and terminates at S1599.
[0145] FIG. 16 shows a sidelink synchronization process 1600
according to an embodiment of the disclosure. The process 1600 can
be performed by a UE to select a reference timing and subsequently
synchronize to the selected reference timing. The process 1600 can
start from S1601, and proceed to S1610.
[0146] At S1610, a sidelink synchronization source priority rule
can be received at the UE. The received rule can be a gNB/eNB-based
rule (e.g., the FIG. 4 example), or a GNSS-based rule (e.g., the
FIG. 5 example), depending a deployment preference of a network
operator. The rule can be received from a BS, for example, by RRC
signaling or system information broadcasting. Alternatively, the
rule can be received from a SIM or UICC module, or a memory at the
UE. In addition, the rule can be represented by a sidelink
synchronization source priority configuration (or rule) derived
from or compliant with the rule, similar to the examples show in
FIG. 6-FIG. 13, considering capabilities of the UE.
[0147] At S1620, a timing reference with a highest priority among
available sidelink synchronization sources is selected according to
the rule received at the S1610. For example, based on a
configuration received from a BS or preconfigured to the UE (e.g.,
stored in a SIM), the UE can know one or more frequencies over
which SSs (e.g., an SS from a BS, or SLSS) are transmitted.
Accordingly, the UE can tune to those frequencies to detect SSs
which can be used as timing references. Those timing references
(the SSs) can each carry sidelink synchronization priority
information.
[0148] According to priorities of different types of
synchronization sources specified in the rule, the UE may
investigate available SSs near the UE one by one (or more than one
at a time) according to an order, and search for an SS with the
highest priority. Take the rule of FIG. 4 as an example, the UE can
first search for an SS from a gNB or eNB of the priority P0. If no
gNB or eNB is found (e.g., no SS from a gNB or eNB exists, or a
signal quality of an SS received from a BS is below a threshold),
the UE can select a SLSS of a UE directly synchronized to a gNB or
an eNB among available SLSSs when the SLSS is available and has a
quality above a threshold. This process can continue until an
available SLSS with a highest priority is found.
[0149] At S1630, a transmission timing can be determined according
to the selected timing reference.
[0150] For example, the UE can adjust a local timing (e.g., a
clock) to align with the selected timing reference, and transmit a
SLSS according to the local timing. The process 1600 can proceed to
S1699 and terminate at S1699.
[0151] FIG. 17 shows an exemplary apparatus 1700 according to
embodiments of the disclosure. The apparatus 1700 can be configured
to perform various functions in accordance with one or more
embodiments or examples described herein. Thus, the apparatus 1700
can provide means for implementation of mechanisms, techniques,
processes, functions, components, systems described herein. For
example, the apparatus 1700 can be used to implement functions of
the UEs102-103 or the BS 101 in various embodiments and examples
described herein. The apparatus 1700 can include a general purpose
processor or specially designed circuits to implement various
functions, components, or processes described herein in various
embodiments. The apparatus 1700 can include processing circuitry
1710, a memory 1720, and a radio frequency (RF) module 1730.
[0152] In various examples, the processing circuitry 1710 can
include circuitry configured to perform the functions and processes
described herein in combination with software or without software.
In various examples, the processing circuitry 1710 can be a digital
signal processor (DSP), an application specific integrated circuit
(ASIC), programmable logic devices (PLDs), field programmable gate
arrays (FPGAs), digitally enhanced circuits, or comparable device
or a combination thereof.
[0153] In some other examples, the processing circuitry 1710 can be
a central processing unit (CPU) configured to execute program
instructions to perform various functions and processes described
herein. Accordingly, the memory 1720 can be configured to store
program instructions. The processing circuitry 1710, when executing
the program instructions, can perform the functions and processes.
The memory 1720 can further store other programs or data, such as
operating systems, application programs, and the like. The memory
1720 can include non-transitory storage media, such as a read only
memory (ROM), a random access memory (RAM), a flash memory, a solid
state memory, a hard disk drive, an optical disk drive, and the
like.
[0154] In an embodiment, the RF module 1730 receives a processed
data signal from the processing circuitry 1710 and converts the
data signal to beamforming wireless signals that are then
transmitted via antenna arrays 1740, or vice versa. The RF module
1730 can include a digital to analog convertor (DAC), an analog to
digital converter (ADC), a frequency up convertor, a frequency down
converter, filters and amplifiers for reception and transmission
operations. The RF module 1730 can include multi-antenna circuitry
for beamforming operations. For example, the multi-antenna
circuitry can include an uplink spatial filter circuit, and a
downlink spatial filter circuit for shifting analog signal phases
or scaling analog signal amplitudes. The antenna arrays 1740 can
include one or more antenna arrays.
[0155] The apparatus 1700 can optionally include other components,
such as input and output devices, additional or signal processing
circuitry, and the like. Accordingly, the apparatus 1700 may be
capable of performing other additional functions, such as executing
application programs, and processing alternative communication
protocols.
[0156] 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.
[0157] 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. The 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.
[0158] 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.
* * * * *