Decimeter Level Indoor Localization Using Hybrid Measurements of a Distributed Single Receiver

Recently, indoor localization using a single receiver has received significant attention. Despite the improvement of this, developing an accurate and universal system is still heavily required. In this article, we design and implement BiLoc, a decimeter level indoor localization system with hybrid measurements of a distributed single receiver. Specifically, different from the existing single receiver-based localization system, in BiLoc, some antennas of the array on the single receiver are distributed at different locations. To this end, BiLoc is based on the fact that the paths recorded on the same receiver incur common phase errors that are caused by nonsynchronization between the transmitter and the receiver. In BiLoc, first, some antennas of the antenna array are moved to different locations to locate the target. Then, BiLoc uses the 2-D matrix pencil (MP) to estimate the Angle of Arrival (AoA) and Time of Flight (ToF) of the multipath signals, which reduces the computational complexity effectively. After that, BiLoc constructs a nonlinear localization model by using the ToFs of the paths received at different antennas and AoAs measured at the antenna array, and then, an iterative algorithm based on the gradient of the localization objective function is used to solve this nonlinear problem. Because of combining hybrid AoA and ToF measurements, the proposed localization method is no longer sensitive to the selection of the initial guess of the target location. Finally, we implement BiLoc on the software-defined radio (SDR) X310 devices, and the designed prototype has six antennas with a maximum signal bandwidth of 100 MHz. The extensive experiments conducted in the practical indoor environments show that BiLoc achieves a median accuracy of 5 dm, which is comparable to the existing localization systems with decimeter level accuracy, and the localization delay is less than 100 ms. We believe that BiLoc can perform better in the emerging networks, such as 5G, because wider bandwidth and more antennas can be provided.