Collaborative Positioning in Ad Hoc Networks Using Passive Time- Differences of Arrival

Accuracy and scalability contribute to the quality of location solutions in wireless networks. While accuracy is a parameter addressed in all location technologies, scalability is often relegated. However, scalability becomes an actual issue in positioning solutions based message exchange (e.g. measuring ranges from beacons). The passive TDOA algorithm is a solution designed to localize terminals in a mobile ad hoc network in a passive way. It is achieved by computing time-differences of arrival from messages being exchanged by other network nodes (i.e. the active nodes), but just listening to the radio channel. In advanced stages of the passive TDOA algorithm (i.e. autonomous passive TDOA recently patented), it is able to compute the position of the unknown node (i.e. the passive node) and of the nodes which the listened location messages belong to (i.e. the active nodes). Thus, the requirement of active nodes informing about its own position to passive nodes is fulfilled. From the network perspective, the impact of this joint-position computation: it boosts the scalability since less information is transmitted and it helps to improve the accuracy of the active nodes, because passive nodes can report several positions regarding a single active node. However, the accuracy of the positions computed by means of the passive TDOA algorithm needs to be good enough to attend the user’s demands. The aim of this work is analyzing the accuracy achieved by the passive TDOA, focusing on the loss of precision due to passivity if compared with conventional two-way time-of-arrival active solutions, which passive TDOA is rely on.