Hybrid TOA/RSSI Wireless Location with Unconstrained Nonlinear Optimization for Indoor UWB Channels

In this paper, a hybrid TOA/RSSI wireless positioning technique is proposed for gaining favorable position accuracy in indoor UWB systems. One major problem encountered in indoor wireless location is the effects caused by non-line of sight (NLOS) propagation. To mitigate the NLOS effects, an unconstrained nonlinear optimization approach is utilized to process time-of-arrival (TOA) and received signal strength (RSSI) in the location system. Path loss models and geometrical cell layout based on the TOA's are used in formulating the LOS/NLOS decision boundary. The weighting factors, used in solving the objective function in the unconstrained nonlinear optimization approach, are related to the credibility of the TOA measurements, and are determined from the LOS/NLOS identification. Computer simulations are conducted to investigate the performance of the proposed technique in different scenarios of the NLOS errors. The results show that the proposed technique outperforms other algorithms and achieves improved location accuracy under severe NLOS conditions.