03.713GPPFunctional descriptionLocation Services (LCS)Release 1999Stage 2TS
The Radio Interface Timing determination system consists of functions in LMUs and in the SMLC. The system runs continuously offering base station synchronization information for mobile station location.
7.15.1 LMU Functions
The Radio Interface Timing functionality in the LMU must be capable of performing the following functions:
– The LMU performs necessary air interface measurements from signals transmitted by base stations (both serving and neighbor). These signals can be normal bursts, dummy bursts, and synchronization bursts on the BCCH frequency.
– If the LMU contains the common reference clock, it time stamps reception of BTS signals.
– If there is no reference clock available, the LMU makes Real Time Difference measurements, i.e. measures the time difference between arrival of bursts from two base stations (e.g. serving and one of neighbors)
– The LMU performs some processing of measurements, like averaging and filtering, using parameters delivered to it, or in their absence using default settings.
7.15.2 SMLC Functions
The SMLC must be capable of performing the following functions related to Radio Interface Timing determination:
– The SMLC sends to LMUs requests for Radio Interface Timing measurement information.
– The SMLC will communicate continuously with LMUs; thus, the SMLC can monitor operation of LMUs. If a LMU fails to send Radio Interface Timing information, the SMLC shall try to restart the LMU, and if this restarting fails, the SMLC shall inform O&M system. SMLC can use also diagnostics messages to query the status of LMUs.
– The SMLC receives Radio Interface Timing measurement results from LMUs.
– The SMLC stores or queries extra information required for base station synchronization determination, like base station and LMU coordinates, base station identity information (LAC, CI, BSIC, carrier), and burst length schemes.
– The SMLC determines synchronization differences between base stations using measurements and other information.
– Synchronization information is delivered for mobile station location purposes.
7.15.3 LMU-SMLC Interactions
The request for Radio Interface Timing measurement information from the SMLC to a LMU contains the following parameters:
– Measurement type. This indicates whether the SMLC wants the LMU to perform Absolute Time Difference (ATD) or Real Time Difference (RTD) measurements.
– Measurement result reporting frequency. This indicates how often the LMU should send Radio Interface Timing measurement results.
– Measurement duration. This indicates how long the LMU should make measurements and report results.
– Instructions about filtering of raw measurement data.
– Instructions about base stations to be measured. The LMU unit can measure autonomously a certain number of most strongly received base stations. Another possibility is that the SMLC tells which base stations it should measure.
– If the LMU measures signals from BTSs from other time slots than 0 or 4, it must be informed about the burst length scheme used by BTSs.
The Radio Interface Timing measurement response from a LMU to the SMLC contains:
– Location Area Code and Cell Identity of the serving base station.
– If the LMU can perform ATD measurements, and it is told to do them, the ATD measurement of the serving BTS is reported (i.e. time stamp for the reception of the burst from the serving BTS referred to the common reference clock).
– Time slot number of the burst(s) measured from the serving BTS.
– Frame number of the (last) burst measured from the serving BTS.
– For each measured neighbor BTS its identity as Location Area Code and Cell Identity or BSIC & carrier.
– For each measured neighbor BTS the possible ATD measurement is reported. This can be expressed relative to the ATD value of the serving BTS.
– If the LMU does not perform ATD measurements, for each measured neighbor BTS, Observed Time Difference value between the receptions of signals from the serving and the neighbor BTS is reported.
– For each measured neighbor BTS the time slot number of its burst(s).
– For each measured neighbor BTS the (last) frame number of its burst.
– For each measured BTS the quality of measurements. Also the RX level can be reported.