4 Main concepts and requirements
38.3053GPPNG Radio Access Network (NG-RAN)Release 17Stage 2 functional specification of User Equipment (UE) positioning in NG-RANTS
4.1 Assumptions and Generalities
The stage 1 description of LCS at the service level is provided in TS 22.071 [3]; the stage 2 LCS functional description, including the LCS system architecture and message flows, is provided in TS 23.501 [2], TS 23.502 [26] and TS 23.273 [35].
Positioning functionality provides a means to determine the geographic position and/or velocity of the UE based on measuring radio signals. The position information may be requested by and reported to a client (e.g., an application) associated with the UE, or by a client within or attached to the core network. The position information shall be reported in standard formats, such as those for cell-based or geographical co-ordinates, together with the estimated errors (uncertainty) of the position and velocity of the UE and, if available, the positioning method (or the list of the methods) used to obtain the position estimate.
Restrictions on the geographic shape encoded within the ‘position information’ parameter may exist for certain LCS client types. The 5GS, including NG-RAN, shall comply with any shape restrictions defined in 5GS and, in a particular country, with any shape restrictions defined for a specific LCS client type in relevant national standards. For example, in the US, national standard J-STD-036-C-2 restricts the geographic shape for an emergency services LCS client to minimally either an "ellipsoid point" or an "ellipsoid point with uncertainty circle" as defined in TS 23.032 [4].
It shall be possible for the majority of the UEs within a network to use the LCS feature without compromising the radio transmission or signalling capabilities of the NG-RAN.
The uncertainty of the position measurement shall be network-implementation-dependent, at the choice of the network operator. The uncertainty may vary between networks as well as from one area within a network to another. The uncertainty may be hundreds of metres in some areas and only a few metres in others. In the event that a particular position measurement is provided through a UE-assisted process, the uncertainty may also depend on the capabilities of the UE. In some jurisdictions, there is a regulatory requirement for location service accuracy that is part of an emergency service. Further details of the accuracy requirements can be found in TS 22.071 [3].
The uncertainty of the position information is dependent on the method used, the position of the UE within the coverage area and the activity of the UE. Several design options of the NG-RAN system (e.g., size of cell, adaptive antenna technique, pathloss estimation, timing accuracy, ng-eNB and gNB surveys) shall allow the network operator to choose a suitable and cost-effective UE positioning method for their market.
There are many different possible uses for the positioning information. The positioning functions may be used internally by the 5GS, by value-added network services, by the UE itself or through the network, and by "third party" services. The feature may also be used by an emergency service (which may be mandated or "value-added"), but the location service is not exclusively for emergencies.
Design of the NG-RAN positioning capability as documented in this specification includes position methods, protocols and procedures that are either adapted from capabilities already supported for E-UTRAN, UTRAN and GERAN, or created separately from first principles. In contrast to GERAN and UTRAN but similarly to E-UTRAN, the NG-RAN positioning capabilities are intended to be forward compatible to other access types and other position methods, in an effort to reduce the amount of additional positioning support needed in the future. This goal also extends to user plane location solutions such as OMA SUPL ([15], [16]), for which NG-RAN positioning capabilities are intended to be compatible where appropriate.
As a basis for the operation of UE Positioning in NG-RAN, the following assumptions apply:
– both TDD and FDD will be supported;
– the provision of the UE Positioning function in NG-RAN and 5GC is optional through support of the specified method(s) in the ng-eNB, gNB and the LMF;
– UE Positioning is applicable to any target UE, whether or not the UE supports LCS, but with restrictions on the use of certain positioning methods depending on UE capability (e.g. as defined within the LPP protocol);
– the positioning information may be used for internal system operations to improve system performance;
– the UE Positioning architecture and functions shall include the option to accommodate several techniques of measurement and processing to ensure evolution to follow changing service requirements and to take advantage of advancing technology.
4.2 Role of UE Positioning Methods
The NG-RAN may utilise one or more positioning methods in order to determine the position of an UE.
Positioning the UE involves two main steps:
– signal measurements; and
– position estimate and optional velocity computation based on the measurements.
The signal measurements may be made by the UE or by the serving ng-eNB or gNB. The basic signals measured for terrestrial position methods are typically the LTE or NR radio transmissions; however, other methods may make use of other transmissions such as general radio navigation signals including those from Global Navigation Satellites Systems (GNSSs).
The positioning function should not be limited to a single method or measurement. That is, it should be capable of utilising other standard methods and measurements, as such methods and measurements are available and appropriate, to meet the required service needs of the location service client. This additional information could consist of readily available E-UTRAN or NG-RAN measurements.
The position estimate computation may be made by the UE or by the LMF.
4.3 Standard UE Positioning Methods
4.3.1 Introduction
The standard positioning methods supported for NG-RAN access are:
– network-assisted GNSS methods;
– observed time difference of arrival (OTDOA) positioning based on LTE signals;
– enhanced cell ID methods based on LTE signals;
– WLAN positioning;
– Bluetooth positioning;
– terrestrial beacon system (TBS) positioning;
– sensor based methods:
– barometric Pressure Sensor;
– motion sensor.
– NR enhanced cell ID methods (NR E-CID) based on NR signals;
– Multi-Round Trip Time Positioning (Multi-RTT based on NR signals);
– Downlink Angle-of-Departure (DL-AoD) based on NR signals;
– Downlink Time Difference of Arrival (DL-TDOA) based on NR signals;
– Uplink Time Difference of Arrival (UL-TDOA) based on NR signals;
– Uplink Angle-of-Arrival (UL-AoA), including A-AoA and Z-AoA based on NR signals.
Hybrid positioning using multiple methods from the list of positioning methods above is also supported.
Standalone mode (e.g. autonomous, without network assistance) using one or more methods from the list of positioning methods above is also supported.
These positioning methods may be supported in UE-based, UE-assisted/LMF-based, and NG-RAN node assisted versions. Table 4.3.1-1 indicates which of these versions are supported in this version of the specification for the standardised positioning methods.
Table 4.3.1-1: Supported versions of UE positioning methods
|
Method |
UE-based |
UE-assisted, LMF-based |
NG-RAN node assisted |
SUPL Note 8 |
|
A-GNSS |
Yes |
Yes |
No |
Yes |
|
OTDOA Note1, Note 2 |
No |
Yes |
No |
Yes |
|
E-CID Note 4, Note 7 |
No |
Yes |
Yes |
Yes for E-UTRA |
|
Sensor |
Yes |
Yes |
No |
No |
|
WLAN |
Yes |
Yes |
No |
Yes |
|
Bluetooth |
No |
Yes |
No |
No |
|
TBS Note 5 |
Yes |
Yes |
No |
Yes (MBS) |
|
DL-TDOA |
Yes |
Yes |
No |
Yes |
|
DL-AoD |
Yes |
Yes |
No |
Yes |
|
Multi-RTT |
No |
Yes |
Yes |
Yes |
|
NR E-CID |
No |
Yes |
Yes |
Yes (DL NR E-CID) |
|
UL-TDOA |
No |
No |
Yes |
Yes |
|
UL-AoA |
No |
No |
Yes |
Yes |
|
NOTE 1: This includes TBS positioning based on PRS signals. NOTE 2: In this version of the specification only OTDOA based on LTE signals is supported. NOTE 3: Void NOTE 4: This includes Cell-ID for NR method when UE is served by gNB. NOTE 5: In this version of the specification only for TBS positioning based on MBS signals. NOTE 6: Void NOTE 7: Enhanced Cell ID based on LTE signals. NOTE 8: This shows whether the positioning method is supported by SUPL ULP [16]. |
||||
Sensor, WLAN, Bluetooth, and TBS positioning methods based on MBS signals are also supported in standalone mode, as described in the corresponding clauses.
4.3.2 Network-assisted GNSS methods
These methods make use of UEs that are equipped with radio receivers capable of receiving GNSS signals. In 3GPP specifications the term GNSS encompasses both global and regional/augmentation navigation satellite systems.
Examples of global navigation satellite systems include GPS, Modernized GPS, Galileo, GLONASS, and BeiDou Navigation Satellite System (BDS). Regional navigation satellite systems include Quasi Zenith Satellite System (QZSS), and NAVigation with Indian Constellation (NavIC), while the many augmentation systems, listed in 8.1.1, are classified under the generic term of Space Based Augmentation Systems (SBAS) and provide regional augmentation services.
In this concept, different GNSSs (e.g. GPS, Galileo, etc.) can be used separately or in combination to determine the location of a UE.
The operation of the network-assisted GNSS methods is described in clause 8.1.
4.3.3 OTDOA positioning
The OTDOA positioning method makes use of the measured timing of downlink signals received from multiple TPs, comprising eNBs, ng-eNBs and PRS-only TPs, at the UE. The UE measures the timing of the received signals using assistance data received from the positioning server, and the resulting measurements are used to locate the UE in relation to the neighbouring TPs.
The operation of the OTDOA method is described in clause 8.2.
4.3.4 Enhanced Cell ID methods
In the Cell ID (CID) positioning method, the position of an UE is estimated with the knowledge of its serving ng-eNB, gNB and cell. The information about the serving ng-eNB, gNB and cell may be obtained by paging, registration, or other methods.
Enhanced Cell ID (E‑CID) based on LTE signals positioning refers to techniques which use additional UE measurements and/or NG-RAN radio resource and other measurements to improve the UE location estimate. In the case of a serving ng-eNB, uplink E-CID may be supported based on NR, GERAN, UTRA or WLAN signals.
Although E-CID based on LTE signals positioning may utilise some of the same measurements as the measurement control system in the RRC protocol, the UE generally is not expected to make additional measurements for the sole purpose of positioning; i.e., the positioning procedures do not supply a measurement configuration or measurement control message, and the UE reports the measurements that it has available rather than being required to take additional measurement actions.
In cases with a requirement for close time coupling between UE and ng-eNB measurements (e.g., TADV type 1 and UE E-UTRA Rx-Tx time difference), the ng-eNB configures the appropriate RRC measurements and is responsible for maintaining the required coupling between the measurements.
The operation of the Enhanced Cell ID based on LTE signals method is described in clause 8.3.
4.3.5 Barometric pressure sensor positioning
The barometric pressure sensor method makes use of barometric sensors to determine the vertical component of the position of the UE. The UE measures barometric pressure, optionally aided by assistance data, to calculate the vertical component of its location or to send measurements to the positioning server for position calculation.
This method should be combined with other positioning methods to determine the 3D position of the UE.
The operation of the Barometric pressure sensor positioning method is described in clause 8.4.
4.3.6 WLAN positioning
The WLAN positioning method makes use of the WLAN measurements (AP identifiers and optionally other measurements) and databases to determine the location of the UE. The UE measures received signals from WLAN [21] access points, optionally aided by assistance data, to send measurements to the positioning server for position calculation. Using the measurement results and a references database, the location of the UE is calculated.
Alternatively, the UE makes use of WLAN measurements and optionally WLAN AP assistance data provided by the positioning server, to determine its location.
The operation of the WLAN positioning method is described in clause 8.5.
4.3.7 Bluetooth positioning
The Bluetooth positioning method makes use of Bluetooth measurements (beacon identifiers and optionally other measurements) to determine the location of the UE. The UE measures received signals from Bluetooth [22] beacons. Using the measurement results and a references database, the location of the UE is calculated. The Bluetooth methods may be combined with other positioning methods (e.g. WLAN) to improve positioning accuracy of the UE.
The operation of the Bluetooth positioning method is described in clause 8.6.
4.3.8 TBS positioning
A Terrestrial Beacon System (TBS) consists of a network of ground-based transmitters, broadcasting signals only for positioning purposes. The current type of TBS positioning signals are the MBS (Metropolitan Beacon System) signals [23] and Positioning Reference Signals (PRS) (TS 36.211 [24]). The UE measures received TBS signals, optionally aided by assistance data, to calculate its location or to send measurements to the positioning server for position calculation.
The operation of the TBS positioning method based on MBS signals is described in clause 8.7.
TBS positioning based on PRS signals is part of OTDOA positioning and described in clause 8.2.
4.3.9 Motion sensor positioning
The motion sensor method makes use of different sensors such as accelerometers, gyros, magnetometers, to calculate the displacement of UE. The UE estimates a relative displacement based upon a reference position and/or reference time. UE sends a report comprising the determined relative displacement which can be used to determine the absolute position.
This method should be used with other positioning methods for hybrid positioning.
The operation of the sensor positioning method is described in clause 8.8.
4.3.10 NR Enhanced Cell ID methods
NR Enhanced Cell ID (NR E‑CID) positioning refers to techniques which use additional UE measurements and/or gNB measurements to improve the UE location estimate.
Although NR E-CID positioning may utilise some of the same measurements as the measurement control system in the RRC protocol, the UE generally is not expected to make additional measurements for the sole purpose of positioning; i.e., the positioning procedures do not supply a measurement configuration or measurement control message, and the UE reports the measurements that it has available rather than being required to take additional measurement actions.
The operation of the NR Enhanced Cell ID method is described in clause 8.9.
4.3.11 Multi-RTT positioning
The Multi-RTT positioning method makes use of the UE Rx-Tx time difference measurements (and optionally DL-PRS-RSRP and/or DL-PRS-RSRPP) of downlink signals received from multiple TRPs, measured by the UE and the measured gNB Rx-Tx time difference measurements (and optionally UL-SRS-RSRP and/or UL-SRS-RSRPP) at multiple TRPs of uplink signals transmitted from UE.
The UE measures the UE Rx-Tx time difference measurements (and optionally DL-PRS-RSRP and/or DL-PRS-RSRPP of the received signals) using assistance data received from the positioning server, and the TRPs measure the gNB Rx-Tx time difference measurements (and optionally UL-SRS-RSRP and/or UL-SRS-RSRPP of the received signals) using assistance data received from the positioning server. The measurements are used to determine the RTT at the positioning server which are used to estimate the location of the UE.
The operation of the Multi-RTT positioning method is described in clause 8.10.
4.3.12 DL-AoD positioning
The DL-AoD positioning method makes use of the measured DL-PRS-RSRP (and optionally DL-PRS-RSRPP) of downlink signals received from multiple TPs, at the UE. The UE measures the DL-PRS-RSRP (and optionally DL-PRS-RSRPP) of the received signals using assistance data received from the positioning server, and the resulting measurements are used along with other configuration information to locate the UE in relation to the neighbouring TPs.
The operation of the DL-AoD positioning method is described in clause 8.11.
4.3.13 DL-TDOA positioning
The DL-TDOA positioning method makes use of the DL RSTD (and optionally DL-PRS-RSRP and/or DL-PRS-RSRPP) of downlink signals received from multiple TPs, at the UE. The UE measures the DL RSTD (and optionally DL-PRS-RSRP and/or DL-PRS-RSRPP) of the received signals using assistance data received from the positioning server, and the resulting measurements are used along with other configuration information to locate the UE in relation to the neighbouring TPs.
The operation of the DL-TDOA positioning method is described in clause 8.12.
4.3.14 UL-TDOA positioning
The UL-TDOA positioning method makes use of the UL-RTOA (and optionally UL-SRS-RSRP and/or UL-SRS-RSRPP) at multiple RPs of uplink signals transmitted from UE. The RPs measure the UL-RTOA (and optionally UL-SRS-RSRP and/or UL-SRS-RSRPP) of the received signals using assistance data received from the positioning server, and the resulting measurements are used along with other configuration information to estimate the location of the UE.
The operation of the UL-TDOA positioning method is described in clause 8.13.
4.3.15 UL-AoA
The UL-AoA positioning method makes use of the measured azimuth angle of arrival (A-AoA) and zenith angle of arrival (Z-AoA) at multiple RPs of uplink signals transmitted from the UE. The RPs measure A-AoA and Z-AoA (and optionally UL-SRS-RSRPP) of the received signals using assistance data received from the positioning server, and the resulting measurements are used along with other configuration information to estimate the location of the UE.
The operation of the UL-AoA positioning method is described in clause 8.14.