Intelligent Serving Mobile Location Centre (iSMLC) - Overview
PertSol iSMLC is part of PertSol iLcoator product suite which caters CSP’s location service requirements. iSMLC manages the overall coordination and scheduling of resources required for the location of a UE (User Equipment) that is attached to RAN. It calculates the final location of the subscribers along with their velocity estimates and also determines the degree of uncertainty/error in the final location. iSMLC supports both UE based and Network Based positioning methods. It interacts with both UEs as well as BSC/RNC/MME to retrieve location information as required by UE or Network Based positioning methods respectively. iSMLC either receives the location request from the UE (in the case of mobile-initiated location requests) or relays the the location requests to the UE (in the case of network-initiated location requests).
iSMLC along with iGMLC can fulfil complete location service requirement of an operator across all technologies.
For GSM and UMTS network, iSMLC resides in RAN (GERAN and UTRAN) and integrates with BSC and RNC/SGSN over Lb interface Iu interface respectively. The communication with the BSC or RNC is done through PCAP for tunneling RRLP (Radio Resource LCS Protocol) messages. Results are sent back via RANAP between the RNC and MSC/SGSN or BSSAP between the BSC and the MSC/SGSN.
Whereas for LTE network, iSMLC is attached to E-UTRAN and integrated with MME over SLs interface. The SLs interface is used to transmit LCS-AP messages and parameters between the MME and E-SMLC.
Control Plane Positioning Methods
iSMLC is capable of performing control plane and user plane localization methods. iSMLC selects the methods to be used for getting location information depending upon the location request requirement defined by the LCS clients or the capability of the network like the number of available LMUs, cell size and other paramteres.
Cell ID is the most rudimentary method of identifying location of the subscribers. Cell Identity (Cell-ID) localization method returns the geo- coordinates of the serving sector as the location estimate of the subscriber.
It is dependent upon the cell radius and the angle of coverage (if available). Its accuracy can vary from few hundred meters to few Kilometers depending upon the size of the cell.
This positioning method is an enhancement of Cell-ID method and is used in GSM network. This method uses Timing Advance parameter which restrict the location of subscriber by pointing the subscriber within a 550 meter wide angular ring. The accuracy of this method will decrease as the device moves farther away from the serving cell.
In UMTS & LTE network Round Trip Time (RTT) parameter is used which corresponds to Timing Advance in GSM. Cell Identitiy with RTT achieves a much higher precision in UMTS than in GSM networks, due to its much higher bandwidth. This improves the spatial resolution of RTT values due to which the system is able to reduce the confidence region and generate location coordinates with higher positioning accuracy.
It is a hyperbolic multilateration positioning method. It relies on the time difference of arrival (TDOA) measurements to estimate the location of the target subscriber/UE.
There is a TDOA measurement for each pair of reference nodes, yielding a hyperbolic line-of-position, with multiple refernce stations as focuses. The accuracy of this method depends upon the number of reference nodes.
It is a multilateration based positioning method. In this method the User Equipment (UE) measures the time of arrival (TOA) of signals received from multiple base stations.
The TOAs from several neighbouring base stations are subtracted from a TOA of a reference base station to form Observed Time Differnece of Arrival.
Assited GPS (A-GPS) – It is an enhancement of standalone GNSS/GPS. It provides the most accurate location information of a UE with an approximate
range of 10 meters. This methods depends upon the radio signals sent by satellite to user’s mobile device.
The cellular network assists the GPS receiver by providing assistance data for the visible satellites. This method works best when used outdoors as it need a good view of sky to work properly.