5 UTRAN UE Positioning Architecture

25.3053GPPRelease 17Stage 2 functional specification of User Equipment (UE) positioning in UTRANTS

Figure 5.1 shows the general arrangement of the UE positioning feature in UTRAN. Communication among the UTRAN UE Positioning entities makes use of the messaging and signalling capabilities of the UTRAN interfaces (Iub, Iur, Iupc).

The SRNC, receives authenticated requests for UE positioning information from the CN across the Iu interface. RNCs manage the UTRAN resources (including Node Bs, LMUs, the SAS) the UE and calculation functions, to estimate the position of the UE and return the result to the CN. SRNC may also make use of the UE Positioning function for internal purpose e.g. position based handover.

Figure 5.1: General arrangement of UE Positioning in UTRAN

5.1 UE Positioning Operations

The schematic functional description of LCS operations in UMTS is defined in [13].

Upon request from the Core Network or for internal operations, a UTRAN UE Positioning function should:

– request measurements, typically from the UE and one or more Node B;

– send the measurement results to the appropriate calculating function within UTRAN;

– receive the result from the calculating function within UTRAN;

– perform any needed co-ordinate transformations;

– send the results to the LCS entities in the CN or to application entities within UTRAN (this function applies to the RNC only).

In the event that the client is internal to UTRAN the request may be made directly to the UTRAN UE Positioning entities as the internal clients are considered to be "pre-authorised".

As part of its operation, the UTRAN UE Positioning calculating function may require additional information. This may be obtained by the function directly by communication with a database, or it may be through a request to UTRAN UE Positioning entities that will mediate the request and return of information from the appropriate database (or databases if more than one is needed to fulfil the requests).

There may possibly also be available independent information that is able to supply the positioning information directly, or may be able to supply auxiliary information to the calculation function. The UTRAN UE Positioning co-ordination function, as part of its activity to supervise the positioning process, may query the UE or other elements of the UTRAN to determine their capabilities and use this information to select the mode of operation.

This general operation is outlined in the following (generic) sequence diagram figure 5.2. This figure is not intended to show the complete UE Positioning operation for UTRAN, but to simply to outline the basis for operation.

Figure 5.2: General sequence for UE Positioning operation

5.1.1 Co-ordination, Measurement and Calculation Functions

The UTRAN functions for UE Positioning provide the co‑ordination, measurement and calculation functions needed to provide a position and optional velocity estimate. The functions interface with the requesting application and select the appropriate positioning method and speed of response. The functions co‑ordinate the operations of the radio and measurement equipment to transmit the needed signals and to make the needed measurements. The measurements may be made by the Node Bs, or by the LMU. The LMU may be associated with the Node B, independently located or remote (i.e. communicating over the Uu interface).

The functions may also access databases or other sources of information appropriate for the positioning method. The functions also provide the calculation functions appropriate for the positioning method to estimate the UE position and the accuracy of the report. The functions may also make co-ordinates translations to the geographic co-ordinates system requested by the application. The functions also may record information on the usage of the UE Positioning that may be used for administrative purposes (e.g. forwarded to a billing function in the CN). If needed by the positioning method, the functions will ensure the broadcast of information and gather and update information concerning UTRAN operating parameters (e.g. timing of Node B transmissions) needed for UE Positioning operations.

These entities are mainly concerned with the positioning method, controlling the radio equipment and performing the calculations to determine the position and thus may be associated with the RNC in the UTRAN. These functions may receive location requests from either the CN or from applications internal to the UTRAN.

The UTRAN UE Positioning entities may also request the subscription and authorisation functions in the CN to authenticate an application or a UE subscription or to verify the subscriber privacy parameters.

The RNC functions communicate with the CN across the Iu interface, with other RNC entities across the Iur interface and with the Node B and LMU across the Iub interface, with the SAS across the Iupc interface, and with the UE and the remote LMU across the Uu interface.

5.2 Functional Description of UTRAN UE Positioning related elements

5.2.1 Radio Network Controller (RNC)

5.2.1.1 Serving RNC

The SRNC is a network element of UTRAN and contains functionality required to support LCS in one PLMN. The SRNC can work either in the RNC centric mode or in a SAS centric mode where the SAS has control over the positioning procedures.

5.2.1.1.1 RNC Centric Mode

In RNC centric mode the SRNC provides the following functionality:

– request of information from other RNC:
The SRNC may request information regarding UE Positioning from other RNCs;

– flow control of positioning requests:
If several simultaneous positioning requests are present within one SRNC, the SRNC co-ordinates the positioning requests taking into account priority of the requests (e.g. for Emergency Clients);

– positioning method selection:
The positioning method selection is based on the location request, QoS, capabilities of UE Positioning elements and UE positioning capabilities;

– position calculation:
The SRNC may calculate the position of a UE and may also support conversion of the position estimate between different geographic reference systems. In case RNC estimates the UE position, it is also responsible to estimate the accuracy of the position estimate. This accuracy estimate should include, for example, the effect of geometric dilution of precision (GDOP), the capabilities of the signal measuring hardware, the effects of multipath propagation and the effects of timing and synchronisation unknowns. The accuracy should be returned as a measure of distance in the same units as the position estimate. The accuracy zone may be reported as the axis and orientation of an ellipse surrounding the position estimate. If available, the positioning method (or the list of the methods) used to obtain the position estimate may also be returned to the CN with the position information. If the CN has requested an accuracy for the position estimate, the Location response shall include an indication whether the position estimate satisfies the requested accuracy or not.

– provide UE Positioning assistance data:
The SRNC may provide assistance data in the support of the various positioning methods;

– Overall UE Positioning coordination and control:
If both an SAS and an SRNC with SMLC internal functionality are available, the SRNC is responsible for the overall coordination and control of UE Positioning. For example, although the SAS has a position calculation function, the SRNC may also have a position calculation function. The SRNC is responsible for managing the co-ordination and control of these multiple resources.

The SRNC, of course, also provides CRNC functionality regarding UE Positioning for its associated Node Bs and LMUs.

5.2.1.1.2 SAS Centric Mode

In SAS centric mode the SRNC provides the following functionality:

– Forwarding of location requests to the SAS:

The SRNC forwards incoming location requests to the SAS and provides further information like UE capabilities and UE Cell ID to guide the positioning method selection in the SAS

– Forwarding of UE positioning assistance data and measurement instructions

Upon request from the SAS, the SRNC forwards assistance data and/or measurement instructions from the SAS to the UE in support of the various positioning methods.

– Delivery of positioning information

Upon request from the SAS the SRNC gathers location related information from the NodeBs and the UE and sends this information back to the SAS.

– Forwarding of positioning estimates

The SRNC forwards the positioning result received from the SAS to the requesting CN entity.

5.2.1.2 Other RNC

5.2.1.2.1 Controlling RNC

The CRNC provides the following functionality:

– resources management:
When allocating resources the CRNC determines which UTRAN elements are involved and what to measure. The RNC is also responsible for managing the effect of UE Positioning operations on the overall performance of the radio network by:

– controlling the variation of the UL and DL signal power level due to UE Positioning;

– calculating the DL and UL power/interference due to UE Positioning;

– to admit/reject the new positioning requests;

– co-operating with Admission Control, and entities of the RRM (such as power control) to provide the system stability in terms of radio resources;

– controlling the IPDL mechanism for OTDOA measurements. This may include the overall control of the periodical measurement fulfilment. Co-ordination among RNCs (e.g. to assure non-overlapping idle periods) will be communicated through the Iur interface.

– broadcast of system information:
The CRNC broadcasts information in support of the selected positioning method. This broadcast information may be specially coded (i.e. encrypted) to ensure its availability only to subscribers of the service. For the case where there exists an SAS, the broadcast data is generated within the CRNC and/or, depending on the positioning method, may also be generated in the SAS which then forwards it to the CRNC over the Iupc interface for eventual broadcast over the Uu interface.

The information to be broadcast could include, for example:

– identification and spreading codes of the neighbouring cells (the channels that are used for measurements);

– Relative Time Difference (RTD), i.e. the timing offsets, asynchronicity between base stations, could be based on measurement results obtained by LMUs;

– roundtrip delay estimates in connected mode;

– the geographic position co-ordinates of the neighbouring Node B;

– the idle period places within the frame structure for multiple cells;

– the local time-of-day;

– reference time, reference position, DGNSS corrections, ephemeris and clock data, and almanac data.

– request UE Positioning related measurements from its associated Node Bs and LMUs:
The measurements requested by CRNC from its associated Node Bs and LMUs is dependant on the positioning method used. The following measurement returned by a LMU to a CRNC has a general status and may be used for more than one positioning method:

– radio interface timing information.

Signalling between Node B or LMU and CRNC is transferred using Iub signalling.

5.2.1.2.2 Drift RNC

The DRNC is a UTRAN element that has an active link to the UE that shall be located. The DRNC, of course, also provides CRNC functionality regarding UE Positioning for its associated Node Bs and LMUs.

5.2.2 Node B

Node B is a network element of UTRAN that may provide measurement results for position estimation and makes measurements of radio signals and communicates these measurements to the CRNC.

The Node B may make its measurements in response to requests (e.g. from the CRNC), or it may autonomously measure and report regularly or when there are significant changes in radio conditions (e.g. changes in the UTRAN GPS timing of cell frames or SFN-SFN Observed Time Difference).

5.2.3 Location measurement unit (LMU)

Location Measurement Units (LMU) are associated with either the CRNC or the SAS. LMUs associated with the SAS are outside the scope of this specification.

The Location Measurement Unit (LMU) entity makes measurements (e.g. of radio signals) and communicates these measurements to a RNC. The LMU may also perform calculations associated with the measurements.

All positioning and assistance measurements obtained by an LMU are supplied to a particular CRNC associated with the LMU. Instructions concerning the timing, the nature and any periodicity of these measurements are either provided by the CRNC or are pre-administered in the CRNC (e.g. using O&M).

The LMU may make its measurements in response to requests (e.g. from the CRNC), or it may autonomously measure and report regularly (e.g. timing of Node B transmissions) or when there are significant changes in radio conditions (e.g. changes in the UTRAN GPS timing of cell frames or SFN-SFN Observed Time Difference).

There may be one or more LMU associated with the UTRAN and an UE Positioning request may involve measurements by one or more LMU. The LMU may be of several types and the CRNCs will select the appropriate LMUs depending on the UE Positioning method being used.

The LMU may be used, for example, to measure UTRAN transmissions either UL or DL. These measurements may be made either, for example, to locate the UE or to measure a system parameter needed by the UE Positioning such as the timing offset (UTRAN GPS timing of cell frames or SFN-SFN Observed Time Difference) of transmissions Node Bs. The LMU may also measure other transmissions, such as those of satellite navigation systems (i.e. GPS) and either report the measurements for use by the CRNC, or report the positioning results as determined by internal calculations of the LMU. The details of the measurements to be made by the LMU will be defined by the chosen UE Positioning method.

An LMU makes radio measurements to support one or more positioning methods. These measurements fall into one of two categories:

(a) positioning measurements specific to one UE and used to compute its position;

(b) assistance measurements applicable to all UEs in a certain geographic area.

There are two classes of LMU:

– Stand-Alone LMU: communicates with RNCs via the Uu interface;

– Associated LMU: communicates with RNCs via the Iub interface.

The associated LMU signalling protocol is the NBAP. The protocol for stand-alone LMU UTRAN signalling will be the RRC protocol.

Stand-Alone LMU

A stand-alone LMU is accessed exclusively over the UTRAN air interface (Uu interface). There is no other connection from the stand-alone LMU to any other UTRAN network element.

NOTE 1: This does not preclude a stand-alone LMU from also communicating with other access networks (e.g. GSM) through interfaces that are not part of the present document.

A stand-alone LMU has a serving Node B that provides signalling access to its CRNC. A stand-alone LMU also has a serving 3G-MSC, VLR and a subscription profile in an HLR. A stand-alone LMU always has a unique IMSI and supports all radio resource and mobility management functions of the UTRAN radio interface that are necessary to support signalling. A stand-alone LMU shall support those connection management functions necessary to support UE Positioning signalling transactions with the CRNC and may support certain call control functions of to support signalling to an CRNC using a circuit switched data connection.

NOTE 2: A network operator may assign specific ranges of IMSI for its LMUs and may assign certain digits within the IMSI to indicate the associated CRNC. Certain digits in the IMSI may also be used as a local identifier for an LMU within an CRNC.

To ensure that a Stand-alone LMU and its associated CRNC can always access one another, an LMU may be homed (camped) on a particular cell site or group of cell sites belonging to one 3G-MSC. For any Stand-alone LMU with a subscription profile in an HLR, a special profile may be used to indicate the assigned supplementary services (e.g. the SMS-PP MT for data download via the SIM application toolkit, and barring of all incoming and possibly outgoing calls). An identifier in the HLR profile also distinguishes an LMU from a normal UE. All other data specific to an LMU is administered in the LMU and in its associated CRNC.

Associated LMU

An associated LMU is accessed over the Iub interface from an RNC. An associated LMU may make use of the radio apparatus and antennas of its associated Node B. The LMU may be either a logically separate network element addressed using some pseudo-cell ID, or connected to or integrated in a Node B. Signalling to an associated LMU is by means of messages routed through the controlling Node B.

An associated LMU may be separated from the Node B, but still communicate with the CRNC via the Node B Iub interface. The interface between the associated LMU and its Node B is not part of the present document.

NOTE 3: An associated LMU is not precluded from also communicating with other access networks (e.g. GSM) through interfaces that are not part of the present document.

Measurements

The assistance measurements obtained by an LMU are generic and are usable by more than one positioning method. These include:

– Radio Interface Timing measurements: include UTRAN GPS timing of cell frames or SFN-SFN Observed Time Difference of the signals transmitted by Node B, where timing differences are measured relative to either some common reference clock (UTRAN GPS timing of cell frames) or the signals of another Node B (SFN-SFN Observed Time Difference);

– Inter-System Timing measurements: include timing measurements between the UTRAN radio signals transmitted by a Node B and an external system such as the GPS or GSM.

5.2.4 User Equipment (UE)

The UE may transmit the needed signals for uplink based UE Positioning measurements and to make measurements of downlink signals. The measurements to be made will be determined by the chosen positioning method.

The UE may also contain LCS applications, or access an LCS application through communication with a network accessed by the UE or an application residing in the UE. This application may include the needed measurement and calculation functions to determine the UE’s position with or without assistance of the UTRAN UE Positioning entities. This is outside of the scope of this specification.

The UE may also, for example, contain an independent positioning function (e.g., GPS, WLAN, Bluetooth, Barometric Pressure, TBS) and thus be able to report its position, independent of the UTRAN transmissions. The UE with an independent positioning function may also make use of information broadcast by the UTRAN that assists the function.

5.2.5 Stand-alone SMLC

An SAS performs one or more of the following procedures:

– Provide GNSS assistance data to the RNC, for both UE-assisted and UE-based method types, to be delivered through point-to-point or broadcast channels to UE;

– Act as a location calculation server if the location estimates are not to be calculated in the RNC;

– Performs a U-TDOA positioning of a particular UE on request of the SRNC;

– Optionally, the SAS may determine the most appropriate positioning method or combination of positioning methods. When the SAS location method determination option is seleted:

o The SAS is responsible to select the set of GNSS assistance data to be sent to the UE for A-GNSS based positioning and provide that assistance data to the SRNC within the PCAP Position Activation Request message;

o The SAS is responsible to request UE positioning related information from the SRNC, e.g. channel information or round trip time;

o The SAS is responsible for coordination of simultaneous UE positioning requests from the CN.

– Selecting the set of U-TDOA capable LMUs to be involved in a U-TDOA location determination.

The SAS communicates with the RNC over the Iupc interface enabling it to forward UE Positioning assistance data to UEs and to receive UE Positioning measurement data from the RNC.

When timing assistance is needed, the SAS may rely on associated LMUs or on the RNC (and on the possibility to have GNSS receivers co-located with the RNC, the Node Bs and/or present in the UEs) to obtain that.