Joint Estimation on the Reflector Velocity and Normal Direction Through NLOS Echo Signals.

This paper studies sensing through the non-line-of-sight (NLOS) paths to obtain the channel information. We assume that the reflector is in the near-field of the base station (BS), while the user equipment (UE) is in the far-field. We demonstrate that the normal direction of the reflector is necessary for the localization of the UE and the estimation of the Downlink (DL) angle of arrival (AOA). Moreover, the movement of the reflectors could cause the channel information to be fast varying. To solve these problems, we propose an algorithm to jointly estimate the magnitude of velocity and the normal direction of the reflector. We first derive the expression of the NLOS echo signal considering the dual Doppler effect caused by the transmitter, the UE and the reflector. We then propose an optimization problem to estimate the parameters, and propose to use the Levenberg-Marquardt (LM) method to solve the problem. We derive the Cramer-Rao lower bound (CRLB) for parameter estimations of the proposed algorithm. Simulation results validates the performance of our proposed algorithm for varying signal-to-noise-ratios (SNRs) and snapshot durations.