21-11-2012, 02:35 PM
Mobile Tracking and Positioning In Telecommunication Industry
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ABSTRACT
Mobile positioning technology has become an important area of research, for emergency as well as for commercial services. Mobile positioning in cellular networks will provide several services such as, locating stolen mobiles, emergency calls, different billing tariffs depending on where the call is originated, and methods to predict the user movement inside a region. The evolution to location-dependent services and applications in wireless systems continues to require the development of more accurate and reliable mobile positioning technologies. The major challenge to accurate location estimation is in creating techniques that yield acceptable performance when the direct path from the transmitter to the receiver is intermittently blocked. This is the Non-Line-Of-Sight (NLOS) problem, and it is known to be a major source of error since it systematically causes mobile to appear farther away from the base station (BS) than it actually is, thereby increasing the positioning error.
In this paper, we present a simple method for mobile telephone tracking and positioning with high accuracy. Through this we will discuss some technology used for mobile positioning and tracking
NEED FOR GEOLOCATION
One of the most powerful ways to personalize mobile services is based on location. The location based services, provides the subscribers very best of the service. Recent demands from new applications require positioning capabilities of mobile telephones or other devices. The ability to obtain the geo-location of the Mobile Telephone (MT) in the cellular system allows the network operators to facilitate new services to the mobile users. The most immediate motivation for the cellular system to provide MT position is enhanced in accident emergency services. The geolocation of the mobile user could provide services like
ARCHITECTURE OF A GEOLOCATION SYSTEM
An example of geolocation system architecture [KOS00] is shown in Figure. As we said earlier, in order to fix a call the subscriber we are calling must be located accurately. A geolocation service provider provides location information and location aware services to subscribers.
Upon a request from a subscriber for location information about an MS, the service provider will contact a location control center querying it for the coordinates of the MS. This subscriber could be a commercial subscriber desiring to track a mobile device or a PSAP trying to answer an E-911 call. The location control center will gather information required to compute the MS’s location. This information could be parameters such as received signal strength, BTS ID, TOA of signals, and so on that we discuss later. Depending on past information about the MS, a set of BS’s could be used to page the MS, and directly or indirectly obtain the location parameters. These are sometimes called Geolocation base stations (GBSs). Once this information is collected, the location control center can determine the location of the mobile with certain accuracy and convey this information to the service provider. The service provider will then use this information to visually display the MS’s location to the subscriber. Sometimes the subscriber could be the MS itself, in which case the messaging and architecture will be simplified, especially if the application involves self-positioning.
Reference circle selection
The variances of the TOAs of a signal which arrives at the two BSs T1 and T2 from different paths are used to find the curve on which the actual location of the mobile telephone is determined. If the TOAs of the signal at the first BS T1 from N propagation paths are t1, t2, . . . , tN, the first BS T1 calculates the variances σ of t1, t2, . . . , tN. The location data processor compares the variances calculated by the first BS T1 with the variances calculated by the second BS T2 and considers that the mobile telephone is near to that BS with the larger variances (the first BS T2 in Figure 6). Hence, the reference circle has its center near to the BS with the smaller variances (the second BS T2 in Figure 6) on the line ST.With the larger variances, the center of a reference circle gets farther to the right from the center of the second BS T2. In order to select the desired curve, the location data processor initializes the reference circles with predetermined radii and the variances of TOAs of a signal transmitted from the mobile telephone located on the reference circles, and compare the preset variances with real variance measurements.