One-Hop Location Estimation
This chapter discusses how to transform physical measurements to locations of nodes. This step is a basic and essential building block of all localization approaches. Typically, it takes place among a target node and its neighboring beacons. Thus, we name it one-hop location estimation. Various kinds of optimization techniques are used in this step for accuracy. In particular, we discuss the positioning methods for measurements of distance, TDoA, AoA, and RSS-profiling. The distances from an unknown node to several references constrain the presence of this node, which is the basic idea of the so-called multilateration. TDoA measurement gives the difference of the time receiving the same signal on different reference nodes. Given a TDoA measurement Dtij and the coordinates of reference nodes i and j, they define one branch of a hyperbola whose foci are at the locations of reference nodes i and j. Hence, the unknown node must lie on the hyperbola. AoA measurement gives the bearing information of the two nodes. By combining the AoA estimates of two reference nodes, an estimate of the position can be obtained. RSS-profiling-based methods directly utilize RSS measurement data for location estimation. Since the RSS distribution of a set of anchor nodes is relatively stable over the spatial space, the RSS vector measured at an unknown node, defined as RSS finger print, reveals the physical location of the node.