ETSI TS 138 355 V19.1.0 (2026-04)

5G; NR; Sidelink Positioning Protocol (SLPP); Protocol Specification (3GPP TS 38.355 version 19.1.0 Release 19)

RTS/TSGR-0238355vj10

General Information

• Status: Not Published
• Technical Committee: 3GPP RAN 2 - Radio layer 2 specification and Radio layer 3 RR specification
• Current Stage: 12 - Citation in the OJ (auto-insert)
• Completion Date: 02-Apr-2026

Standards Content (Sample)

TECHNICAL SPECIFICATION
5G;
NR;
Sidelink Positioning Protocol (SLPP);
Protocol Specification
(3GPP TS 38.355 version 19.1.0 Release 19)

3GPP TS 38.355 version 19.1.0 Release 19 1 ETSI TS 138 355 V19.1.0 (2026-04)

Reference
RTS/TSGR-0238355vj10
Keywords
5G
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ETSI
3GPP TS 38.355 version 19.1.0 Release 19 2 ETSI TS 138 355 V19.1.0 (2026-04)
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ETSI
3GPP TS 38.355 version 19.1.0 Release 19 3 ETSI TS 138 355 V19.1.0 (2026-04)
Contents
Intellectual Property Rights . 2
Legal Notice . 2
Modal verbs terminology . 2
Foreword . 6
1 Scope . 7
2 References . 7
3 Definitions of terms, symbols and abbreviations . 8
3.1 Terms . 8
3.2 Abbreviations . 8
4 Functionality of Protocol . 9
4.1 General . 9
4.1.1 SLPP Configuration . 9
4.1.2 SLPP Sessions and Transactions . 9
4.1.3 SLPP Positioning Methods . 9
4.1.4 SLPP Messages . 9
4.2 Common SLPP Session Procedure . 10
4.3 SLPP Transport . 11
4.3.1 Transport Layer Requirements . 11
4.3.2 SLPP Duplicate Detection . 11
4.3.3 SLPP Acknowledgement . 11
4.3.3.1 General . 11
4.3.3.2 Procedure related to Acknowledgement . 11
4.3.4 SLPP Retransmission . 12
4.3.4.1 General . 12
4.3.4.2 Procedure related to Retransmission . 12
5 SLPP Procedures . 13
5.1 Procedures related to capability transfer . 13
5.1.1 General . 13
5.1.2 Capability Transfer procedure . 13
5.1.3 Capability Indication procedure . 14
5.1.4 Transmission of SLPP Request Capabilities . 14
5.1.5 Reception of SLPP Request Capabilities . 14
5.1.6 Transmission of SLPP Provide Capabilities . 15
5.2 Procedures related to Assistance Data Transfer . 15
5.2.1 General . 15
5.2.2 Assistance Data Transfer procedure . 15
5.2.3 Assistance Data Delivery procedure . 16
5.2.4 Transmission of SLPP Request Assistance Data . 16
5.2.5 Reception of SLPP Request Assistance Data. 16
5.2.6 Reception of SLPP Provide Assistance Data . 16
5.3 Procedures related to Location Information Transfer . 17
5.3.1 General . 17
5.3.2 Location Information Transfer procedure . 17
5.3.3 Location Information Delivery procedure . 17
5.3.4 Transmission of Request Location Information . 18
5.3.5 Reception of Request Location Information . 18
5.3.6 Transmission of Provide Location Information . 18
5.4 Error Handling Procedures . 19
5.4.1 General . 19
5.4.2 Procedures related to Error Indication . 19
5.4.3 SLPP Error Detection . 19
5.4.4 Reception of an SLPP Error Message . 20
5.5 Abort Procedure . 20
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5.5.1 General . 20
5.5.2 Procedures related to Abort . 20
5.5.3 Reception of an SLPP Abort Message . 20
6 Protocol data units, formats and parameters (ASN.1) . 21
6.1 General . 21
6.2 SLPP messages . 21
6.2.1 General message structure . 21
– SLPP-PDU-Definitions . 21
– SLPP-Message . 23
– SLPP-MessageBody . 24
6.2.2 Message body information elements definitions . 25
– RequestCapabilities. 25
– ProvideCapabilities. 25
– RequestAssistanceData . 26
– ProvideAssistanceData . 26
– RequestLocationInformation . 27
– ProvideLocationInformation . 28
– Abort . 28
– Error . 29
6.3 SLPP information elements . 29
6.3.1 Common information elements . 29
– ARFCN-ValueNR . 29
– CommonIEsAbort . 30
– CommonIEsError . 30
– GNSS-ID-Bitmap . 30
– LCS-GCS-Translation . 31
– LOS-NLOS-Indicator . 31
– NCGI . 32
– NR-PhysCellID . 32
– PositioningModes . 32
– SL-RTD-Info . 33
– SL-TimeStamp . 34
– SL-TimingQuality . 35
6.3.2 UE capability information elements . 35
– ScheduledLocationTimeSupportPerMode . 35
6.3.3 Void . 36
6.4 Multiplicity and type constraint values . 36
– Multiplicity and type constraint definitions . 36
– End of SLPP-PDU-Definitions . 36
6.5 SLPP PDU Common Contents . 36
– SLPP-PDU-CommonContents . 36
– CommonIEsRequestCapabilities . 37
– CommonIEsProvideCapabilities . 37
– CommonIEsRequestAssistanceData . 37
– CommonIEsProvideAssistanceData . 38
– CommonIEsRequestLocationInformation . 38
– CommonIEsProvideLocationInformation . 43
– End of SLPP-PDU-CommonContents . 50
6.6 SLPP PDU Common SL-PRS Methods Contents . 50
– SLPP-PDU-CommonSL-PRS-MethodsContents . 50
– CommonSL-PRS-MethodsIEsRequestCapabilities . 51
– CommonSL-PRS-MethodsIEsProvideCapabilities . 51
– CommonSL-PRS-MethodsIEsRequestAssistanceData . 56
– CommonSL-PRS-MethodsIEsProvideAssistanceData . 56
– CommonSL-PRS-MethodsIEsRequestLocationInformation . 59
– CommonSL-PRS-MethodsIEsProvideLocationInformation . 60
– End of SLPP-PDU-CommonSL-PRS-MethodsContents . 60
6.7 SLPP PDU SL-AoA Contents . 60
– SLPP-PDU-SL-AoA-Contents . 60
– SL-AoA-RequestCapabilities . 61
– SL-AoA-ProvideCapabilities . 61
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– SL-AoA-RequestAssistanceData. 63
– SL-AoA-ProvideAssistanceData. 64
– SL-AoA-RequestLocationInformation . 65
– SL-AoA-ProvideLocationInformation . 66
– End of SLPP-PDU-SL-AoA-Contents . 68
6.8 SLPP PDU SL-RTT Contents . 68
– SLPP-PDU-SL-RTT-Contents . 68
– SL-RTT-RequestCapabilities . 69
– SL-RTT-ProvideCapabilities . 69
– SL-RTT-RequestAssistanceData. 72
– SL-RTT-ProvideAssistanceData. 72
– SL-RTT-RequestLocationInformation . 72
– SL-RTT-ProvideLocationInformation . 73
– End of SLPP-PDU-SL-RTT-Contents . 75
6.9 SLPP PDU SL-TDOA Contents . 76
– SLPP-PDU-SL-TDOA-Contents . 76
– SL-TDOA-RequestCapabilities . 76
– SL-TDOA-ProvideCapabilities . 77
– SL-TDOA-RequestAssistanceData . 78
– SL-TDOA-ProvideAssistanceData . 79
– SL-TDOA-RequestLocationInformation . 79
– SL-TDOA-ProvideLocationInformation . 80
– End of SLPP-PDU-SL-TDOA-Contents . 82
6.10 SLPP PDU SL-TOA Contents. 83
– SLPP-PDU-SL-TOA-Contents . 83
– SL-TOA-RequestCapabilities . 83
– SL-TOA-ProvideCapabilities . 84
– SL-TOA-RequestAssistanceData . 85
– SL-TOA-ProvideAssistanceData . 86
– SL-TOA-RequestLocationInformation. 86
– SL-TOA-ProvideLocationInformation. 87
– End of SLPP-PDU-SL-TOA-Contents . 89
6.11 Information elements related to Discovery Message . 89
– NR-DiscoveryMessageMetaDataContents . 89
– RSPP-Metadata . 90
– End of NR-DiscoveryMessageMetaDataContents . 90
Annex A (informative): Change history . 91
History . 92

ETSI
3GPP TS 38.355 version 19.1.0 Release 19 6 ETSI TS 138 355 V19.1.0 (2026-04)
Foreword
This Technical Specification has been produced by the 3rd Generation Partnership Project (3GPP).
The contents of the present document are subject to continuing work within the TSG and may change following formal
TSG approval. Should the TSG modify the contents of the present document, it will be re-released by the TSG with an
identifying change of release date and an increase in version number as follows:
Version x.y.z
where:
x the first digit:
1 presented to TSG for information;
2 presented to TSG for approval;
3 or greater indicates TSG approved document under change control.
y the second digit is incremented for all changes of substance, i.e. technical enhancements, corrections,
updates, etc.
z the third digit is incremented when editorial only changes have been incorporated in the document.
ETSI
3GPP TS 38.355 version 19.1.0 Release 19 7 ETSI TS 138 355 V19.1.0 (2026-04)
1 Scope
The present document specifies the Sidelink Positioning Protocol (SLPP) for the interface between UEs and between
UE and LMF.
2 References
The following documents contain provisions which, through reference in this text, constitute provisions of the present
document.
- References are either specific (identified by date of publication, edition number, version number, etc.) or
non-specific.
- For a specific reference, subsequent revisions do not apply.
- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including
a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same
Release as the present document.
[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] 3GPP TS 38.331: "NR; Radio Resource Control (RRC); Protocol specification".
[3] 3GPP TS 38.305: "NG Radio Access Network (NG-RAN); Stage 2 functional specification of
User Equipment (UE) positioning in NG-RAN".
[4] ITU-T Recommendation X.691 (07/2002) "Information technology - ASN.1 encoding rules:
Specification of Packed Encoding Rules (PER)" (Same as the ISO/IEC International Standard
8825-2).
[5] 3GPP TS 23.273: "5G System (5GS) Location Services (LCS); Stage 2".
[6] 3GPP TS 38.211: "3rd Generation Partnership Project; Technical Specification Group Radio
Access Network; NR; Physical channels and modulation".
[7] 3GPP TS 23.032: "Universal Geographical Area Description (GAD)".
[8] 3GPP TR 38.901: "Technical Specification Group Radio Access Network; Study on channel
model for frequencies from 0.5 to 100 GHz".
[9] 3GPP TS 23.287: "Architecture enhancements for 5G System (5GS) to support Vehicle-to-
Everything (V2X) services".
[10] 3GPP TS 38.101-2: "NR; User Equipment (UE) radio transmission and reception; Part 2: Range 2
Standalone".
[11] 3GPP TS 38.101-1: "NR; User Equipment (UE) radio transmission and reception; Part 1: Range 1
Standalone".
[12] 3GPP TS 23.586: "Technical Specification Group Services and System Aspects; Architectural
Enhancements to support Ranging based services and Sidelink Positioning".
[13] 3GPP TS 38.133: "NR; Requirements for support of radio resource management".
[14] 3GPP TS 23.304: "Technical Specification Group Services and System Aspects; Proximity based
Services (ProSe) in the 5G System (5GS)".
[15] 3GPP TS 38.321: "NR; Medium Access Control (MAC); Protocol specification".
[16] 3GPP TS 38.215: "NR; Physical layer measurements".
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3 Definitions of terms, symbols and abbreviations
3.1 Terms
For the purposes of the present document, the terms given in TR 21.905 [1] and the following apply. A term defined in
the present document takes precedence over the definition of the same term, if any, in TR 21.905 [1].
Field: The individual contents of an information element are referred to as fields.
Ranging: Refers to the determination of the distance between two UEs or more UEs and/or the direction of one UE (i.e.
Target UE) from another UE via PC5 interface.
Ranging/Sidelink Positioning: AS functionality enabling ranging-based services and sidelink positioning as specified
in TS 23.586 [12].
SL Anchor UE: A UE, supporting positioning of target UE, e.g. by transmitting and/or receiving reference signals for
positioning, providing positioning-related information, etc. over the Sidelink interface.
SL Server UE: A UE offering position method determination, assistance data distribution and/or location calculation
functionalities for sidelink positioning and ranging based services. It interacts with other UEs over PC5 as necessary in
order to determine a ranging/SL position method, distribute assistance data and calculate the location of the target UE.
A Target UE or SL Anchor UE can act as SL Server UE if any of the functionalities is supported.
SL Target UE: A UE whose distance, direction and/or position is measured with the support from one or multiple SL
Anchor UEs using Sidelink in the Ranging based service and Sidelink positioning.
UE-only Operation: Operation of Ranging/Sidelink Positioning in which the service request handling and result
calculation are performed by UE.
3.2 Abbreviations
For the purposes of the present document, the abbreviations given in TR 21.905 [1] and the following apply. An
abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in
TR 21.905 [1].
DFN Direct Frame Number
GCS Global Coordinate System (as defined in TR 38.901 [8])
LCS LoCation Services
Local Coordinate System (as defined in TR 38.901 [8])
LMF Location Management Function
LOS Line-of-Sight
NLOS Non-Line-of-Sight
RTD Relative Time Difference
SL Sidelink
SL-AoA Sidelink Angle-of-Arrival
SL-MO-LR Sidelink Mobile Originating Location Request
SL-MT-LR Sidelink Mobile Terminating Location Request
SLPP Sidelink Positioning Protocol
SL-PRS Sidelink Positioning Reference Signals
SL-PRS-RSRP Sidelink Positioning Reference Signals based Reference Signal Received Power
SL-PRS-RSRPP Sidelink Positioning Reference Signals based Reference Signal Received Path Power
SL-PRS-RSTD Sidelink Positioning Reference Signals based Reference Signal Time Difference
SL-PRS-RTOA Sidelink Positioning Reference Signals based Relative Time of Arrival
SL-RTT Sidelink Round Trip Time
SL-TDOA Sidelink Time Difference Of Arrival
SL-TOA Sidelink Time Of Arrival
UE User Equipment
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4 Functionality of Protocol
4.1 General
4.1.1 SLPP Configuration
SLPP is used point-to-point between Endpoints, e.g. Location Server (SL Server UE or LMF) and target in order to
obtain absolute position, relative position, or ranging information of target UE using sidelink measurements obtained by
one or more reference sources.

Figure 4.1.1-1: Void
4.1.2 SLPP Sessions and Transactions
An SLPP session is used between UEs or a Location Server and a UE in order to obtain location related measurements
based on NR PC5 radio signals, a location estimate or to transfer assistance data. A single SLPP session is used to
support a single location request (e.g., for a single SL-MT-LR, or SL-MO-LR). Multiple SLPP sessions can be used
between the same endpoints to support multiple location requests (as required by TS 23.273 [5]). For UE-only
Operation, the instigator of an SLPP session which is the Endpoint who receives the LCS request, initiates an SLPP
session by sending an SLPP message containing an assigned session ID (session identifier) to the other endpoint(s). All
constituent messages within a session shall contain the same session ID. For LMF involved Operation, the session ID is
assigned by target UE and contained in the SLPP messages used for communication between UEs. The session ID may
be included in the SLPP message for the communication between a UE and the LMF.
Each SLPP session comprises one or more SLPP transactions, with each SLPP transaction performing a single
operation (capability exchange, assistance data transfer, or location information transfer). The SLPP transactions are
realized as SLPP procedures. The instigator of an SLPP session will always instigate the first SLPP transaction, but
subsequent transactions may be instigated by either end. SLPP transactions within a session may occur serially or in
parallel. SLPP transactions are indicated at the SLPP protocol level with a transaction ID in order to associate messages
with one another (e.g., request and response).
Messages within a transaction are linked by a common transaction identifier.
4.1.3 SLPP Positioning Methods
This version of the specification defines SL-TDOA, SL-TOA, SL-AoA and SL-RTT positioning methods based on NR
PC5 radio signals.
4.1.4 SLPP Messages
Each SLPP transaction involves the exchange of one or more SLPP messages between Endpoint A and Endpoint B. The
general format of an SLPP message consists of a set of common fields followed by a body. The body (which may be
empty) contains information specific to a particular message type. Each message type contains information specific to
one or more positioning methods and/or information common to all positioning methods.
The common fields are as follows:
Field Role
sessionID Identify messages belonging to the same session
transactionID Identify messages belonging to the same transaction
endTransaction Indicate when a transaction (e.g. one with periodic responses) has ended
sequenceNumber
Enable detection of a duplicate SLPP message at a receiver
acknowledgement
Enable an acknowledgement to be requested and/or returned for any SLPP message

The following message types are defined:
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3GPP TS 38.355 version 19.1.0 Release 19 10 ETSI TS 138 355 V19.1.0 (2026-04)
- Request Capabilities;
- Provide Capabilities;
- Request Assistance Data;
- Provide Assistance Data;
- Request Location Information;
- Provide Location Information;
- Abort;
- Error.
4.2 Common SLPP Session Procedure
The purpose of this procedure is to support an SLPP session comprising a sequence of SLPP transactions. The
procedure is described in Figure 4.2-1.
Endpoint A Endpoint B
1. SLPP Message
(Transaction ID=j, Body)
2. Additional SLPP Message
(Transaction ID=j, Body)
3. SLPP Message
(Transaction ID=k, Body)
4. SLPP Message
(Transaction ID=N, Body)
Figure 4.2-1 SLPP Session Procedure
1. Endpoint A, which is the Endpoint who receives the LCS request, initiates an SLPP session by sending an SLPP
message containing an assigned session ID for an initial SLPP transaction j to the other endpoint B.
2. Endpoints A and B may exchange further messages to continue the transaction started in step 1.
3. Either endpoint may instigate further transactions by sending additional SLPP messages.
4. A session is terminated by a final transaction N in which SLPP messages will be exchanged between the two
endpoints.
Within the same session, all constituent messages shall contain the same session ID and within each transaction, all
constituent messages shall contain the same transaction ID. The last message sent in each transaction shall have the
field endTransaction set to TRUE. Transactions that occur in parallel shall use different transaction IDs; transaction IDs
for completed transactions may be reused at any time after the final message of the previous transaction with the same
ID is known to have been received.
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4.3 SLPP Transport
4.3.1 Transport Layer Requirements
SLPP requires reliable, in-sequence delivery of SLPP messages from the underlying transport layers. This clause
describes the transport capabilities that are available within SLPP. A UE implementing SLPP shall support SLPP
reliable transport (including all three of duplicate detection, acknowledgement, and retransmission).
4.3.2 SLPP Duplicate Detection
A sender shall include a sequence number in all SLPP messages sent for a particular location session. The sequence
number shall be distinct for different SLPP messages sent by the same endpoint for the same endpoint in the same
location session (e.g., may start at zero in the first SLPP message and increase monotonically in each succeeding SLPP
message). Sequence numbers used in the messages transmitted from different endpoints or for different endpoints are
independent (e.g., can be the same).
A receiver shall record the most recent received sequence number for each pair of endpoints of each location session. If
a message is received carrying the same sequence number as that last received for the same pair of endpoints and the
associated location session, it shall be discarded. Otherwise (i.e., if the sequence number is different or the sequence
number is same but for different pair of endpoints), the message shall be processed.
Sending and receiving sequence numbers shall be deleted in a server when the associated location session is terminated
and shall be deleted in the UE(s) when there has been no activity for a particular location session for 10 minutes.
4.3.3 SLPP Acknowledgement
4.3.3.1 General
Each SLPP message may carry an acknowledgement request and/or an acknowledgement indicator. An SLPP message
including an acknowledgement request (i.e., that include the field ackRequested set to TRUE) shall also include a
sequence number. Upon reception of an SLPP message which includes the field ackRequested set to TRUE, a receiver
returns an SLPP message with an acknowledgement response (i.e., that includes the field ackIndicator set to the same
sequence number of the message being acknowledged). An acknowledgement response may contain no SLPP message
body (in which case only the sequence number being acknowledged is significant); alternatively, the acknowledgement
may be sent in an SLPP message along with an SLPP message body. An acknowledgement is returned for each received
SLPP message that requested an acknowledgement including any duplicate(s). Once a sender receives an
acknowledgement for an SLPP message, and provided any included sequence number is matching, it is permitted to
send the next SLPP message. No message reordering is needed at the receiver since this stop-and-wait method of
sending ensures that messages normally arrive in the correct order.
When an SLPP message is transported via a NAS SL-MO-LR request, the message does not request an
acknowledgement.
4.3.3.2 Procedure related to Acknowledgement
Figure 4.3.3.2-1 shows the procedure related to acknowledgement.
ETSI
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Figure 4.3.3.2-1: SLPP Acknowledgement procedure
1. Endpoint A sends an SLPP message N to Endpoint B which includes the field ackRequested set to TRUE and a
sequence number.
2. If SLPP message N is received and Endpoint B is able to decode the ackRequested value and sequence number,
...