9 Sidelink
36.2113GPPEvolved Universal Terrestrial Radio Access (E-UTRA)Physical channels and modulationRelease 17TS
9.1 Overview
A sidelink is used for ProSe direct communication and ProSe direct discovery between UEs.
9.1.1 Physical channels
A sidelink physical channel corresponds to a set of resource elements carrying information originating from higher layers and is the interface defined between TS 36.212 [3] and the present document TS 36.211. The following sidelink physical channels are defined:
– Physical Sidelink Shared Channel, PSSCH
– Physical Sidelink Control Channel, PSCCH
– Physical Sidelink Discovery Channel, PSDCH
– Physical Sidelink Broadcast Channel, PSBCH
Generation of the baseband signal representing the different physical sidelink channels is illustrated in Figrue 5.3-1.
9.1.2 Physical signals
A sidelink physical signal is used by the physical layer but does not carry information originating from higher layers. The following sidelink physical signals are defined:
– Demodulation reference signal
– Synchronization signal
9.1.3 Handling of simultaneous sidelink and uplink/downlink transmissions
For a given frequency, on an uplink subframe included in discTxGapConfig [9], a UE shall not transmit an uplink transmission that is not a PRACH transmission and that is partly or completely overlapping in time with a PSDCH transmission or a SLSS transmission for PSDCH by the same UE. Else, for a given carrier frequency and sidelink transmission mode 1 or 2 or sidelink discovery, a UE shall not transmit a sidelink signal or channel overlapping partly or completely in time with an uplink transmission from the same UE.
For a given carrier frequency, no PSDCH, PSCCH, or PSSCH transmission shall occur from a UE in a sidelink subframe configured for synchronization purposes by the higher-layer parameters
– syncOffsetIndicator1 or syncOffsetIndicator2 in [9] if the UE has no serving cell fulfilling the S criterion according to [10, clause 5.2.3.2], or
– syncOffsetIndicator in commSyncConfig or discSyncConfig which includes txParameters in [9] if the UE has a serving cell fulfilling the S criterion according to [10, clause 5.2.3.2]. The UE may assume the same configuration in commSyncConfig and discSyncConfig.
For a given carrier frequency, with the exception of PSSCH transmissions with transmission mode 1 and same sidelink cyclic prefix as PUSCH, no sidelink transmissions shall occur in sidelink subframe 
from a UE if uplink SRS is transmitted from the same UE in uplink subframe 
.
A UE with limited transmission capabilities, on an uplink subframe included in discTxGapConfig [9], shall first prioritize a PSDCH transmission or a SLSS transmission for PSDCH over an uplink transmission that is not a PRACH transmission. Else, a UE with limited transmission capabilities shall at a given time first prioritize uplink transmissions, followed by sidelink transmission mode 1 or 2 or sidelink discovery.
A UE with limited transmission capabilities shall at a given time prioritize sidelink communication transmissions (PSSS, SSSS, PSBCH, PSSCH, PSCCH) over sidelink discovery transmissions (PSDCH).
A UE with limited reception capabilities, on a downlink subframe included in discRxGapConfig [9], shall first prioritize reception of PSDCH or 11reception of SLSS for PSDCH over downlink reception. Else, a UE with limited reception capabilities shall at a given time first prioritize downlink reception over sidelink reception.
A UE with limited reception capabilities shall at a given time first prioritize sidelink communication reception, sidelink discovery reception on carriers configured by the eNodeB, and last sidelink discovery reception on carriers not configured by the eNodeB.
9.2 Slot structure and physical resources
Sidelink transmissions are organized into radio frames with a duration of 
, each consisting of 20 slots of duration 
. A sidelink subframe consists of two consecutive slots, starting with an even-numbered slot.
9.2.1 Resource grid
A transmitted physical channel or signal in a slot is described by a resource grid of 
subcarriers and 
SC-FDMA symbols. The sidelink bandwidth 
if the S criterion according to [10, clause 5.2.3.2] is fulfilled for a serving cell having the same uplink carrier frequency as the sidelink, otherwise a preconfigured value is used [9].
The sidelink cyclic prefix is configured independently for type 1 discovery, type 2B discovery, sidelink transmission mode 1, sidelink transmission mode 2, control signalling, and PSBCH and synchronization signals. Configuration is per resource pool for discovery, sidelink transmission mode 2, and control signalling. The PSBCH and synchronization signals always use the same cyclic prefix.
Only normal cyclic prefix is supported for PSSCH, PSCCH, PSBCH, and synchronization signals for a sidelink configured with transmission mode 3 or 4.
The resource grid is illustrated in Figure 5.2.1-1.
An antenna port is defined such that the channel over which a symbol on the antenna port is conveyed can be inferred from the channel over which another symbol on the same antenna port is conveyed. There is one resource grid per antenna port. The antenna ports used for transmission of a physical channel or signal are shown in Table 9.2.1-1.
Table 9.2.1-1: Antenna ports used for different physical channels and signals
|
Physical channel or signal |
Antenna port number |
|
PSSCH |
1000 |
|
PSCCH |
1000 |
|
PSDCH |
1000 |
|
PSBCH |
1010 |
|
Synchronization signals |
1020 |
9.2.2 Resource elements
Each element in the resource grid is called a resource element and is uniquely defined by the index pair 
in a slot where 
and 
are the indices in the frequency and time domains, respectively. Resource element 
on antenna port 
corresponds to the complex value 
. When there is no risk for confusion, or no particular antenna port is specified, the index 
may be dropped.
Quantities 
corresponding to resource elements not used for transmission of a physical channel or a physical signal in a slot shall be set to zero.
9.2.3 Resource blocks
A physical resource block is defined as 
consecutive SC-FDMA symbols in the time domain and 
consecutive subcarriers in the frequency domain, where 
and 
are given by Table 9.2.3-1. A physical resource block in the sidelink thus consists of 
resource elements, corresponding to one slot in the time domain and 180 kHz in the frequency domain.
Table 9.2.3-1: Resource block parameters
|
Configuration |
|
|
|
Normal cyclic prefix |
12 |
7 |
|
Extended cyclic prefix |
12 |
6 |
The relation between the physical resource block number 
in the frequency domain and resource elements 
in a slot is given by
9.2.4 Resource pool
The subframe pools and resource block pools are defined in [4].
For PSSCH, the number of the current slot in the subframe pool 
, where 
is the number of the current slot within the current sidelink subframe 
with 
equal to the subscript of 
, defined in clauses 14.1.4 and 14.2.3 of [4] for sidelink transmission modes 1 and 2, respectively; and where 
is the number of the current slot within the current sidelink subframe 
with 
equal to the subscript of 
, defined in clauses 14.1.1.5 of [4] for sidelink transmission modes 3 and 4.
9.2.5 Guard period
The last SC-FDMA symbol in a sidelink subframe serves as a guard period and shall not be used for sidelink transmission.
9.3 Physical Sidelink Shared Channel
9.3.1 Scrambling
The block of bits 
, where 
is the number of bits transmitted on the physical sidelink shared channel in one subframe shall be scrambled according to clause 5.3.1.
The scrambling sequence generator shall be initialised with 
at the start of every PSSCH subframe where
– for sidelink transmission modes 1 and 2, 
is destination identity obtained from the sidelink control channel, and
– for sidelink transmission modes 3 and 4, 
with 
and 
given by clause 5.1.1 in [3] equals the decimal representation of CRC on the PSCCH transmitted in the same subframe as the PSSCH.
9.3.2 Modulation
Modulation shall be done according to clause 5.3.2. Table 9.3.2-1 specifies the modulation mappings applicable for the physical sidelink shared channel.
Table 9.3.2-1: PSSCH modulation schemes
|
Physical channel |
Modulation schemes |
|
PSSCH |
QPSK, 16QAM, 64QAM |
9.3.3 Layer mapping
Layer mapping shall be done according to clause 5.3.2A assuming a single antenna port, 
.
9.3.4 Transform precoding
Transform precoding shall be done according to clause 5.3.3 with 
and 
replaced by 
and 
, respectively.
9.3.5 Precoding
Precoding shall be done according to clause 5.3.3A assuming a single antenna port, 
.
9.3.6 Mapping to physical resources
The block of complex-valued symbols 
shall be multiplied with the amplitude scaling factor 
in order to conform to the transmit power 
specified in [4], and mapped in sequence starting with 
to physical resource blocks on antenna port 
and assigned for transmission of PSSCH. The mapping to resource elements 
corresponding to the physical resource blocks assigned for transmission and not used for transmission of reference signals shall be in increasing order of first the index 
, then the index
, starting with the first slot in the subframe. If Transmission Format of SCI format 1 is set to 1, the resource elements in the last SC-FDMA symbol within a subframe shall not considered in the mapping process. Otherwise, the resource elements in the last SC-FDMA symbol within a subframe shall be counted in the mapping process but not transmitted.
If sidelink frequency hopping is disabled the set of physical resource blocks to be used for transmission is given by 
where 
is obtained from [4, clause 14.1.1.2.1].
If sidelink frequency hopping with type 1 hopping is enabled, the set of physical resource blocks to be used for transmission is given by [4].
If sidelink frequency hopping with predefined hopping pattern is enabled, the set of physical resource blocks to be used for transmission is given by the sidelink control information together with a predefined pattern in clause 5.3.4 with the following exceptions:
– only inter-subframe hopping shall be used
– the number of subbands 
is given by higher layers as described in [4, clause 14.1.1.2]
– the quantity 
is given by higher layers as described in [4, clause 14.1.1.2]
– the quantity 
where 
is given by clause 9.2.4
– the quantity 
– the pseudo-random sequence generator is initialized at the start of each slot fulfilling 
with the initialization value 
given by hoppingParameter-r12 in [9]
– the quantity 
shall be replaced by 
, given by [4, clause 14.1.1.2.1]
– for sidelink transmission mode 1
– 
– for sidelink transmission mode 2
– 
where 
is given by [4, clause 14.1.3]
– the quantity 
shall be replaced by 
, given by [4, clause 14.1.1.4]
– the physical resource block to use for transmission 
with 
given by [4, clause 14.1.3]
9.4 Physical Sidelink Control Channel
9.4.1 Scrambling
The block of bits 
, where 
is the number of bits transmitted on the physical sidelink control channel in one subframe shall be scrambled according to clause 5.3.1.
The scrambling sequence generator shall be initialised with 
at the start of every PSCCH subframe.
9.4.2 Modulation
Modulation shall be done according to clause 5.3.2. Table 9.4.2-1 specifies the modulation mappings applicable for the physical sidelink control channel.
Table 9.4.2-1: PSCCH modulation schemes
|
Physical channel |
Modulation schemes |
|
PSCCH |
QPSK |
9.4.3 Layer mapping
Layer mapping shall be done according to clause 5.3.2A assuming a single antenna port, 
.
9.4.4 Transform precoding
Transform precoding shall be done according to clause 5.3.3 with 
and 
replaced by 
and 
, respectively.
9.4.5 Precoding
Precoding shall be done according to clause 5.3.3A assuming a single antenna port, 
.
9.4.6 Mapping to physical resources
The block of complex-valued symbols 
shall be multiplied with the amplitude scaling factor 
in order to conform to the transmit power 
specified in [4], and mapped in sequence starting with 
to physical resource blocks on antenna port 
and assigned for transmission of PSCCH. The mapping to resource elements 
corresponding to the physical resource blocks assigned for transmission and not used for transmission of reference signals shall be in increasing order of first the index 
, then the index
, starting with the first slot in the subframe. Resource elements in the last SC-FDMA symbol within a subframe shall be counted in the mapping process but not transmitted.
9.5 Physical Sidelink Discovery Channel
9.5.1 Scrambling
The block of bits 
, where 
is the number of bits transmitted on the physical sidelink discovery channel in one subframe shall be scrambled according to clause 5.3.1.
The scrambling sequence generator shall be initialised with 
at the start of each PSDCH subframe.
9.5.2 Modulation
Modulation shall be done according to clause 5.3.2. Table 9.5.2-1 specifies the modulation mappings applicable for the physical sidelink discovery channel.
Table 9.5.2-1: Sidelink modulation schemes
|
Physical channel |
Modulation schemes |
|
PSDCH |
QPSK |
9.5.3 Layer mapping
Layer mapping shall be done according to clause 5.3.2A assuming a single antenna port, 
.
9.5.4 Transform precoding
Transform precoding shall be done according to clause 5.3.3 with 
and 
replaced by 
and 
, respectively.
9.5.5 Precoding
Precoding shall be done according to clause 5.3.3A assuming a single antenna port, 
.
9.5.6 Mapping to physical resources
The block of complex-valued symbols 
shall be multiplied with the amplitude scaling factor 
in order to conform to the transmit power 
specified in [4], and mapped in sequence starting with 
to physical resource blocks on antenna port 
and assigned for transmission of PSDCH. The mapping to resource elements 
corresponding to the physical resource blocks assigned for transmission and not used for transmission of reference signals shall be in increasing order of first the index 
, then the index
, starting with the first slot in the subframe. Resource elements in the last SC-FDMA symbol within a subframe shall be counted in the mapping process but not transmitted.
The set of physical resource blocks that shall be used are given by [4, clause 14.3.1].
9.6 Physical Sidelink Broadcast Channel
9.6.1 Scrambling
The block of bits 
, where 
is the number of bits transmitted on the physical sidelink broadcast channel in one subframe, shall be scrambled according to clause 5.3.1. The scrambling sequence generator shall be initialised at the start of every PSBCH subframe with 
.
9.6.2 Modulation
Modulation shall be done according to clause 5.3.2. Table 9.6.2-1 specifies the modulation mappings applicable for the physical sidelink broadcast channel.
Table 9.6.2-1: PSBCH modulation schemes
|
Physical channel |
Modulation schemes |
|
PSBCH |
QPSK |
9.6.3 Layer mapping
Layer mapping shal be done according to clause 5.3.2A assuming a single antenna port, 
.
9.6.4 Transform precoding
Transform precoding shall be done according to clause 5.3.3 with 
and 
replaced by 
and 
, respectively.
9.6.5 Precoding
Precoding shall be done according to clause 5.3.3A assuming a single antenna port, 
.
9.6.6 Mapping to physical resources
The block of complex-valued symbols 
shall be multiplied with the amplitude scaling factor 
in order to conform to the transmit power 
specified in [4], and mapped in sequence starting with 
to physical resource blocks on antenna port 
. The PSBCH shall use the same set of resource blocks as the synchronization signal. The mapping to resource elements 
corresponding to the physical resource blocks used for the PSBCH and not used for transmission of reference signals or synchronization signals shall be in increasing order of first the index 
, then the index 
, starting with the first slot in the subframe. The resource-element index 
given by
Resource elements in the last SC-FDMA symbol within a subframe should be counted in the mapping process but not transmitted.
9.7 Sidelink Synchronization Signals
A physical-layer sidelink synchronization identity is represented by 
, divided into two sets id_net and id_oon consisting of identities 
and 
, respectively.
9.7.1 Primary sidelink synchronization signal
The primary sidelink synchronization signal is transmitted in two adjacent SC-FDMA symbols in the same subframe.
9.7.1.1 Sequence generation
Each of the two sequences 
used for the primary sidelink synchronization signal in the two SC-FDMA symbols is given by clause 6.11.1.1 with root index 
if 
and 
otherwise.
9.7.1.2 Mapping to resource elements
The sequence 
shall be multiplied with the amplitude scaling factor 
and mapped to resource elements on antenna port 1020 in the first slot in the subframe according to
9.7.2 Secondary sidelink synchronization signal
The secondary sidelink synchronization signal is transmitted in two adjacent SC-FDMA symbols in the same subframe.
9.7.2.1 Sequence generation
Each of the two sequences 
used for the secondary sidelink synchronization signal is given by clause 6.11.2.1 assuming
– subframe 0 with 
and 
for transmission modes 1 and 2, and
– subframe 5 for transmission modes 3 and 4.
9.7.2.2 Mapping to resource elements
The sequence 
shall be multiplied with the amplitude scaling factor 
in order to conform to the transmit power specified in clause 14.4 in TS 36.213 [4] and mapped to resource elements on antenna port 1020 in the second slot in the subframe according to
9.8 Demodulation reference signals
Demodulation reference signals associated with PSSCH, PSCCH, PSDCH, and PSBCH transmission shall be transmitted according to PUSCH in clause 5.5.2.1 with the following exceptions:
– The parameters in Tables 9.8-1, 9.8-2, and 9.8-3 shall be used.
– The term PUSCH shall be replaced by PSSCH, PSCCH, PSDCH or PSBCH, depending on the physical channel to which the reference signal is associated.
– Antenna ports are given by Table 9.2-1.
– The set of physical resource blocks used in the mapping process shall be identical to the corresponding PSSCH/PSCCH/PSDCH/PSBCH transmission.
– The index 
in the mapping process in clause 5.5.2.1.2 corresponding to the case where higher-layer parameter ul-DMRS-IFDMA is not set shall be identical to that for the corresponding PSSCH/PSCCH/PSDCH/PSBCH transmission.
– For sidelink transmission modes 3 and 4 on the PSSCH and PSCCH, the mapping shall use 
and 
for the first slot in the subframe and 
and 
for the second slot in the subframe.
– For sidelink transmission modes 3 and 4 on the PSBCH, the mapping shall use 
and 
for the first slot in the subframe and 
for the second slot in the subframe.
– For sidelink transmission modes 1 and 2, the pseudo-random sequence generator in clause 5.5.1.3 shall be initialized at the start of each slot fulfilling 
. For sidelink transmission modes 3 and 4 the pseudo-random sequence generator in clause 5.5.1.3 shall be initialized at the start of each slot fulfilling 
.
– For sidelink transmission modes 3 and 4 on the PSCCH, the cyclic shift 
to be applied for all DM-RS in a subframe shall be chosen according to clause 14.2.1 of [4].
– For sidelink transmission modes 1and 2 and sidelink discovery, the quantity 
in clause 5.5.2.1.1 takes the values 
and for sidelink transmission modes 3and 4, the quantity 
in clause 5.5.2.1.1 takes the values 
for PSSCH and 
for PSBCH.
– For sidelink transmission modes 3 and 4, the quantity 
equals the decimal representation of CRC on the PSCCH transmitted in the same subframe as the PSSCH according to 
with 
and 
given by clause 5.1.1 in [3].
Table 9.8-1: Reference signal parameters for PSSCH.
|
Parameter in clause 5.5.2.1 |
PSSCH |
||
|
Sidelink transmission modes 1 and 2 |
Sidelink transmission |
||
|
Group hopping |
enabled |
enabled |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Sequence hopping |
disabled |
disabled |
|
|
Cyclic shift |
|
|
|
|
Orthogonal sequence |
|
|
|
|
Reference signal length |
|
|
|
|
Number of layers |
|
1 |
1 |
|
Number of antenna ports |
|
1 |
1 |
first DM-RS symbol in a slot
second DM-RS symbol in a slot
Table 9.8-2: Reference signal parameters for PSCCH.
|
Parameter in clause 5.5.2.1 |
PSCCH |
||
|
Sidelink transmission modes 1 and 2 |
Sidelink transmission modes 3 and 4 |
||
|
Group hopping |
disabled |
disabled |
|
|
|
– |
– |
|
|
|
– |
– |
|
|
|
0 |
8 |
|
|
Sequence hopping |
disabled |
disabled |
|
|
Cyclic shift |
|
0 |
{0, 3, 6, 9} |
|
Orthogonal sequence |
|
|
|
|
Reference signal length |
|
|
|
|
Number of layers |
|
1 |
1 |
|
Number of antenna ports |
|
1 |
1 |
Table 9.8-3: Reference signal parameters for PSDCH and PSBCH.
|
Parameter in clause 5.5.2.1 |
PSDCH |
PSBCH |
||
|
Sidelink transmission |
Sidelink transmission |
|||
|
Group hopping |
disabled |
disabled |
disabled |
|
|
|
0 |
|
|
|
|
Sequence hopping |
disabled |
disabled |
disabled |
|
|
Cyclic shift |
|
0 |
|
|
|
(Orthogonal) sequence |
|
|
|
|
|
Reference signal length |
|
|
|
|
|
Number of layers |
|
1 |
1 |
1 |
|
Number of antenna ports |
|
1 |
1 |
1 |
9.9 SC-FDMA baseband signal generation
The time-continuous signal 
for antenna port 
in SC-FDMA symbol 
in a sidelink slot is defined by clause 5.6 with 
replaced by 
.
The cyclic prefix length for each sidelink channel or signal may differ from that configured for uplink transmissions.
9.10 Timing
Transmission of a sidelink radio frame number 
from the UE shall start 
seconds before the start of the corresponding timing reference frame at the UE. The UE is not required to receive sidelink or downlink transmissions earlier than 
after the end of a sidelink transmission.
For PSDCH transmission and sidelink synchronization signal transmission for PSDCH:
if the UE has a serving cell fulfilling the S criterion according to [10, clause 5.2.3.2]
– the timing of reference radio frame 
equals that of downlink radio frame 
of the cell c as given in Clause 14.3.1 of [4] and
– 
is given by clause 8.1,
otherwise
– the timing of reference radio frame 
is implicitly obtained from [4] and
– 
.
For all other sidelink transmissions:
if the UE has a serving cell fulfilling the S criterion according to [10, clause 5.2.3.2]
– the timing of reference radio frame 
equals that of downlink radio frame 
in the cell with the same uplink carrier frequency as the sidelink and
– 
is given by clause 8.1,
otherwise
– the timing of reference radio frame 
is implicitly obtained from [4] and
– 
.
Figure 9.9-1: Sidelink timing relation.
The quantity 
differs between channels and signals according to
