Wireless geolocation with TOA/AOA measurements using factor graph and sum-product algorithm

Wireless geolocation techniques make use of measurements of signal strength, time-of-arrival (TOA), angle-of-arrival (AOA), or their combinations. With different degrees of reliability of the measurement data, how to efficiently coordinate all the available information is crucial. The factor graph together with the sum-product algorithm, which makes the optimum use of the data statistics, is a perfect candidate for such a task. So far, most existing position location techniques focus on geometric approximations when looking for sub-optimal least-square solutions (W.H. Foy, IEEE Trans. Aerospace and Electron. Sys., vol. 12, no. 2, pp. 187-193, 1976; J. Caffery, IEEE Vehicular Tech. Conf., vol. 4. pp. 1943-1949, 2000; L. Cong and W. Zhang, IEEE Trans. on Wireless Comm, vol. 1, pp. 439-447, 2002). In this paper, with the stochastic properties of TOA/AOA measurement data, we propose a brand-new low-complexity high-accuracy algorithm to estimate the location of a target MS. In a factor graph framework, the proposed algorithm efficiently exchanges soft information among local processing units in the mobile switching center to iteratively purify the estimate of the MS location.