Ahmed Lutful Kabir Electronics and Telecommunication Engineering North South University, Dhaka, Bangladesh Dhaka, Bangladesh lutful_1985@hotmail.com Muhammad Arman Khan Electronics and Telecommunication Engineering North South University, Dhaka, Bangladesh Dhaka, Bangladesh armankhan007@hotmail.com Abstract – For the enhancement of Emergency Call services and Location Based Services (LBS), tracking Mobile Station (MS) has become one of the most urged needs within modern technologies. Moreover the act by Federal Communication Commission (FCC) on 1990 increased the requirement for finding a MS within a standard confined region. There are several approaches for tracking MS. The aim of this paper is to find a reduced area of approximation of a MS in a particular cell, by joining time of arrival (TOA) and angle of arrival (AOA) calculations. Keywords – Distance calculation, TOA, tracking, AOA, area of approximation. I. INTRODUCTION With the development of telecommunication technologies and increased amount of reliance on it, MS tracking is now essential. As an example, the emergency call service, such as Enhanced 991 (E911), the agency needs to locate the caller exactly for providing assistance. Moreover, a platform for profit projection businesses for the service providers is created. LBS, such as, in exchange of money a MS’s position will be provided by the operator to the user, by which the trail the MS holder can be obtained. Many mobile locating techniques have been proposed already using Time of Arrival (TOA), Timing Advance (TA), Time Difference of Arrival (TDOA), GPS etc. TOA is a technique, where the round trip time (RTT) of signal transmission to base station and back to mobile station or vice versa (i.e. initiated by base station) is estimated. GPS aided tracking uses signals transmitted by satellite to give a very precise location approximation. But, the high consumption of battery, time delay for the tracking, and unavailability in indoor environment and canyon situation (high walls and buildings) accounts for the disadvantages of GPS aided system [1]. Since GSM uses time division multiplexing (TDMA), it is hard to achieve accurate timing for TOA; hence there is every possible chance that the base station will ignore signal after the slotted time [2]. Moreover, “system delay” occurs, which means that the system has to take time to process the received signal and prepare for the transmitting signal [3]. For TDOA Rajeeb Saha Electronics and Telecommunication Engineering North South University, Dhaka, Bangladesh Dhaka, Bangladesh rajeeb_saha2003@yahoo.com Munawwar M Sohul Electronics and Telecommunication Engineering North South University, Dhaka, Bangladesh Dhaka, Bangladesh mmsohul@northsouth.edu location methods, the distance differences of the MS to at least three BSs are measured. Each TDOA measurement provides a hyperbolic locus on which the MS must lie and the position estimate is determined by the intersection of two or more hyperbolas. It has high rollout cost, due to the extra hardware at every BS, and yield only high-to-medium accuracy position estimates [4], [5]. There is also a technique where distance is calculated from the received signal strength (RSS) using HATA Mainly this technique doesn’t require synchronization, moreover, automatically it also accounts for the Doppler shift, Line of Sight (LOS), Non Line of Sight (NLOS), and scattering phenomenon included in radio transmission. But the main disadvantage is that it is an empirical formula so it is not always accurate for any area plus is in accuracy increases as the distance increases. In this paper we have use TOA for distance calculation and AOA using antenna array at the BTS. Here a technique is proposed which easily can remove the error in AOA and TOA calculation. Also a probability density statistics is shown for TOA error correction for NLOS environment. II. DISTANCE CALCULATION USING TOA TA can be used to approximate the distance between the serving BS and the MS. TA is available in GSM system. In the TDMA system TA is the time delay between the MS and the serving BS which must be known to avoid overlapping time slots. In the CDMA system, time delay can be estimated by coarse timing acquisition with a sliding correlator or fine timing acquisition with a delay loop lock (DLL). The later is better suited for a location system, as illustrated in [6]. Round trip delay (RTD) is a method to determine the distance between the transmitter and receiver; it needs a time stamp when the signal is transmitted and a time stamp when the signal is received. The range is approximated by the time difference of the two time stamps. In this paper, we have considered only two BSs that is, BS 1 and BS 2 as shown in Figure 1. BS 1 is the serving BS. In order to get the distance to the other BS, “force handover” could be a good choice [7].to initiate the process of locating MS, the network will force the MS to make a handover attempt from the serving BS 1 to the BS 2 . Usually BS 2 Locating Mobile Station Using Joint TOA/AOA 978-1-4244-5130-2/09/$26.00 © 2009 IEEE