On the Optimality of WLAN Location Determination Systems

This report presents a general analysis for the performance of WLAN location determination systems. In particular, we present an analytical method for calculating the average distance error and probability of error of WLAN location determination systems. These expressions are obtained with no assumptions regarding the distribution of signal strength or the probability of the user being at a specific location, which is usually taken to be a uniform distribution over all the possible locations in current WLAN location determination systems. We use these expressions to find the optimal strategy to estimate the user location and to prove formally that probabilistic techniques give more accuracy than deterministic techniques, which has been taken for granted without proof for a long time. The analytical results are validated through simulation experiments. We also study the effect of the assumption that the user position follows a uniform distribution over the set of possible locations on the accuracy of WLAN location determination systems. The results show that knowing the probability distribution of the user position can reduce the number of access points required to obtain a given accuracy. However, with a high density of access points, the performance of a WLAN location determination system is consistent under different probability distributions for the user position.