NLOS mitigation based on range estimation error characterization in an RTT-based IEEE 802.11, indoor location system

Ranging techniques have significant effects on localization accuracy, system complexity, and system cost, in most common wireless location systems. In such systems, loss of accuracy is most often caused by the lack of a direct line-of-sight (LOS) between a mobile user (MU) and a reference access point (AP). This drawback is increased when the location system is deployed in cluttered scenarios. Modeling the non-line-of-sight (NLOS) error formally represents one way to deal with this issue. However, a trade-off decision has to be made between the efficiency of the system and its complexity and computational cost. In this paper, NLOS error is confined to single-parameter distributions, specifically Exponential and Rayleigh. Both models are introduced in the prior NLOS measurements correction (PNMC) method, and compared in terms of range and position error, in a round-trip time (RTT)-based real location system. Furthermore, improvement of accuracy by dynamically estimating Exponential or Rayleigh parameters is likewise analyzed. The results show a high NLOS bias reduction after PNMC procedure, and even greater when using dynamic parameters.