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Mobile location estimation has attracted a significantamount of attention in recent years. The network-basedlocation estimation schemes have been widely adopted based onthe radio signals between the mobile device and the base stations.The two-step Least Square (LS) method has been studied inrelated research to provide efficient location estimation of themobile devices. However, the algorithm results in insufficientaccuracy for location estimation with the existence of the Non-Line-Of-Sight (NLOS) errors. A Geometry-Assisted LocationEstimation (GALE) algorithm is proposed in this paper with theconsideration of different geometric layouts between the mobiledevice and its associated base stations. In order to enhance theprecision of the location estimate, the GALE scheme is designedto incorporate the geometric constraints within the formulationof the two-step LS method. The algorithm can be utilized toestimate both the two-dimensional and the three-dimensionalpositions of a mobile device. The proposed GALE schemecan both preserve the computational efficiency from the twostepLS algorithm and obtain precise location estimation underNLOS environments. Moreover, the Cramér-Rao Lower Bound(CRLB) for various types of measurement signals is derived tofacilitate the performance comparison between different locationestimation schemes. Numerical results illustrate that the proposedGALE algorithm can achieve better accuracy, comparing withother existing network-based location estimation schemes.
Wireless location estimation, two-step least square method, Non-Line-Of-Sight (NLOS) errors, Time-Of-Arrival (TOA), Angle-Of-Arrival (AOA)

C. Chen, K. Feng and C. Chen, "GALE: An Enhanced Geometry-Assisted Location Estimation Algorithm for NLOS Environments," in IEEE Transactions on Mobile Computing, vol. 7, no. , pp. 199-213, 2007.
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