Abstract
Passive tracking aims to track targets without assistant devices, that is, device-free targets. Passive tracking based on Radio Frequency (RF) Tomography in wireless sensor networks has recently been addressed as an emerging field. The passive tracking scheme using geometric theorems (GTs) is one of the most popular RF Tomography schemes, because the GT-based method can effectively mitigate the demand for a high density of wireless nodes. In the GT-based tracking scheme, the tracking scenario is considered as a two-dimensional geometric topology and then geometric theorems are applied to estimate crossing points (CPs) of the device-free target on line-of-sight links (LOSLs), which reveal the target’s trajectory information in a discrete form. In this paper, we review existing GT-based tracking schemes, and then propose a novel passive tracking scheme by exploiting the Intercept Theorem (IT). To create an IT-based CP estimation scheme available in the noisy non-parallel LOSL situation, we develop the equal-ratio traverse (ERT) method. Finally, we analyze properties of three GT-based tracking algorithms and the performance of these schemes is evaluated experimentally under various trajectories, node densities, and noisy topologies. Analysis of experimental results shows that tracking schemes exploiting geometric theorems can achieve remarkable positioning accuracy even under rather a low density of wireless nodes. Moreover, the proposed IT scheme can provide generally finer tracking accuracy under even lower node density and noisier topologies, in comparison to other schemes.
Highlights
The positioning technique of adopting received signal strength (RSS) plays a vital role in wireless sensor networks (WSNs), because the RSS is ubiquitous in radio frequency (RF) environments and can be acquired without extra hardware costs
We focused on utilizing geometric theorems for crossing points (CPs) estimation on the line-of-sight links (LOSLs) to track a device-free target under WSN scenarios
As the prerequisite of geometric theorems, we investigated the characteristics of the RF Tomography to distinguish traverse attenuation (TA) from non-traverse attenuation (NTA) in order to guarantee LOSL detection
Summary
The positioning technique of adopting received signal strength (RSS) plays a vital role in wireless sensor networks (WSNs), because the RSS is ubiquitous in radio frequency (RF) environments and can be acquired without extra hardware costs. The rest of this paper is organized as follows: Section 2 gives a comprehensive review of the work in the current passive tracking field; Section 3 investigates both spatial and temporal characteristics of RF Tomography to guarantee LOSL triggering detection; in Section 4, the IT scheme is proposed after two existing geometric theorem-based tracking schemes, including the LM scheme and GF scheme, are reviewed; for performance evaluation of the proposed IT scheme under assumed MP estimation deviation, the ERT algorithm is presented in Section 5; in Section 6, the properties of the three schemes are analyzed; their performance is evaluated through practical experiments under various trajectories and LOSL densities. For clarity, k X − Y k indicates the Euclidean distance between point X and Y, and lx ∩ ly presents the intersection of straight lines lx and ly
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