HiLoc: Sub-Meter Level Indoor Localization Using a Single Access Point With Distributed Antennas in Wireless Sensor Networks

Indoor localization as one of the visions of the Internet of Things (IoTs) receives much attention in Wireless Sensor Networks (WSNs). Many prior indoor localization technologies concentrated on multiple Access Points (APs), so developing a system that uses a single AP with high accuracy is indispensable, especially for households or small businesses. To this end, we present HiLoc, a single AP-based indoor localization system with sub-meter accuracy. The key insight of HiLoc is to estimate the relative Time of Flight (ToF) between the target and the distributed antennas and localize the target using the convex optimization accurately. Specifically, HiLoc utilizes the combination of Orthogonal Matching Pursuit (OMP) and Maximum Likelihood (ML) to estimate relative ToF. Then, by applying the semi-definite relaxation technique, the localization process can be transformed into an SDP problem. Unlike the methods that use the iterative least-square, in which an accurate guess of the target location is required, we can find the target location accurately without any initializations. Furthermore, we design the prototype AP using Software-Defined Radio (SDR) platform with Orthogonal Frequency Division Multiplexing (OFDM) signals. Our implementation in extensive indoor environments shows that HiLoc achieves a median localization error of 0.72m at 100MHz signal bandwidth, comparable to the state-of-the-art prior systems.