Mobile Positioning Techniques in GSM Cellular Networks: A ...

ISSN 2249-6343International Journal of Computer Technology and Electronics Engineering (IJCTEE)Volume 2, Issue 6, December 2012This paper makes a comparative and analytic study of thevarious techniques for mobile positioning and presentsthe limitations of each and the performance of eachmethod based on some performance indices that will beused in the analysis.II. PERFORMANCE INDICES FOR MOBILE LOCATIONTECHNIQUESThe comparative analysis of the techniques will be doneunder the following matrices:Reliability: simply put is the mean time between failuresand the mean time to repair.Generally a uniform measurement for reliability isdifficult to define due to the variations in technologies. InGPS systems, reliability is defined as a measure of howconsistent a GPS horizontal error levels can bemaintained below a specified reliability threshold. Inmobile positioning methods, we can simply definereliability as the ratio of successful positioning attemptsout of all attempts made. Systems used in personalpositioning should uncompromisingly give extremelyreliable performance especially in emergency cases sincefailure could be very detrimental. This is an importantindicator of performance because a positioning devicethat frequently fails or gives false positions will not beseen as trustworthy by the users [4].Latency:Latency measure is basically the time from power-up tothe instant when the first location measurement isobtained. In GPS, this is known as the time-to-first-fix(TTFF). The high demand for low or short latency is notonly realized in the emergency cases but also from theLBS point of view. Example, the QoS and usability ofguidance and tracking applications decreases if onecannot guarantee a real-time operation. Short latency alsosaves power. It is measured in seconds. Latency is furtherbroken down into three main components by defining thecall set-up delay, network delay and the processing delay.Briefly, call set-up delay is the time elapsed between callinitiation at the MS and receiving the first response fromthe network. Network delay is defined as the time neededto transmit all messages excluding call set-up delay.Processing delay as the name implies is the time neededby the positioning device to measure and calculate theposition [5].Applicability:Basically applicability measures the physical limitationsand requirements associated with the implementation anduse of certain technology in terms of technical andfinancial issues]. The key issues affecting theapplicability of mobile positioning methods are powerconsumption, hardware size, software size, processingload, supported positioning modes, network dependency,signal load, cost and standardization. [6].22Accuracy and Precision: Location accuracy of ageolocation method is defined to be the distance betweenthe estimated location and the true location of the mobilestation. It defines how close the location measurementsare to the actual location of the mobile station beinglocated. Accuracy is expressed in meters.A location system should report locations accurately andconsistently from measurement to measurement. Inevaluating the accuracy of a positioning device, one hasto consider how many location measurements are made,how location measurements are scored and in what formthe results are presented. There are a number ofperformance metrics for location accuracy in theliterature. Root Mean Square Error (RMSE), MeanSquared Error (MSE), Circular Error Probability (CEP),and Cramer-Rao Lower Bound (CRLB). A widely usedscore function in accuracy evaluation of multiple locationmeasurements is the square root of the mean of squarederrors (RMSE), where RMSE is given by:AndWhere (X est , Y est ) is the estimated coordinates, and(X true ,Y true ) is the true location coordinates of the mobilestation. Where d is are distance errors and n denotes thenumber of location estimates. RMSE is the mostapplicable location accuracy performance metric in theliterature. It is the most used and a simple metric.Table 1.Grading of accuracy levelsAccuracyMargin of errorLowGreater than 150mMedium50 to 150mHigh Less than 50m.Cost: We can assess the cost of a location-sensing systemin several ways. Time costs include factors such as theinstallation process's length and the system administrationneeds. Space costs involve the amount of installedinfrastructure and the hardware's size and form factor.Limitations: Some systems will not function in certainenvironments. This limitation has implications for thekind of applications we can build.Coverage: coverage in telecommunications systems isrelated to the service area where, at a bare minimum,access to the wireless network is possible. For the mobilelocation techniques under consideration in this paper,coverage corresponds to the availability of a sufficientnumber of measurements to perform a locationcomputation