A novel two-stage self correcting GPS-free localization algorithm for GSM mobiles

Extending emergency services like Enhanced 911 to a constantly increasing mobile population is becoming increasingly important for wireless providers. Localization service or position estimation with GPS in GSM based mobile phones is an expensive affair, both in terms of cost and energy consumption. Experiments have shown that GPS does not provide reliable location estimates of mobile terminals (MT) in indoor and dense urban environments. The principal contribution of this paper is the proposed novel algorithm that employs the existing GSM signal strength measurements as an alternative to GPS measurements, as the basis for position estimation in GSM based networks. The proposed algorithm is two-staged with a signal weight based positioning technique (SWBP) as the initial stage followed by a self-correction feedback mechanism (SCFM). In the SWBP, an initial position estimate is computed using the received signal strengths from the surrounding base stations. This initial estimate from SWBP is then fed into the SCFM to generate an accurate final location estimate based on previous history of location estimates. The second stage (SCFM) strives to negate the effects of erroneous signal strength measurements and abrupt changes in user direction. Simulation results demonstrate that the proposed algorithm yields better MT position estimates compared to conventional triangulation techniques.