Low complexity ultra-wideband ranging in indoor multipath environments

In this paper, the possibility of using UWB channel impulse response statistics, other than the TOA, for ranging applications, is investigated. Models for the total received signal power and for the first path power are proposed, based on an extensive UWB measurement campaign covering both LOS and NLOS propagation and conducted in typical office environments. The proposed models are subsequently used to estimate the distance between the transmitter and the receiver. The possibility of combining in an optimal way the range estimation provided by each single method, using a best linear unbiased estimator of the distance, is then analyzed. Finally, some implementation issues related to the proposed solution are discussed. First, a low complexity receiver implementation, able to estimate the power of the first path of the channel impulse response is suggested. Second, the bandwidth dependency of the described approach is considered and a model for the achieved standard deviation is proposed. Third, the possibility of using the strongest path power statistic, instead of the first path, is briefly discussed. In LOS, when large bandwidths are used, the first path power represents a reliable statistic, and it is able to achieve a standard deviation of the range error of 0.54 m, about half of that achieved with the classical signal strength estimation. To retrieve this statistic, no synchronization between the system nodes is needed and only modest sampling rates are required. For this reason, this approach represents a viable solution for low complexity positioning systems. In NLOS, the first path power statistic is useful to improve the accuracy provided by the signal strength approach.