Virtual Multi-Antenna Array for Estimating the Angle-of-Arrival of a RF Transmitter

We consider the problem of angle-of-arrival (AoA) estimation of a RF transmitter using a mobile receiver. We develop a method very similar to synthetic aperture radar which is compatible with cellular technology. By considering the successive packets received along the receiver trajectory, we implicitly create a virtual MIMO array, which allows us to utilize conventional MIMO theory for AoA estimation. For this method to work, the first major challenge is the need to separate the phase offset due to receiver movement from the phase offset due to local oscillator (LO) offset. Two approaches are proposed to do this: i) a stop-and-start approach, where the receiver first stands still long enough to estimate the LO offset and then estimates the AoA while moving, and ii) a joint nonlinear estimator where the AoA and LO offset are estimated simultaneously. The second major difficulty is the need to estimate the receiver's relative position with sub-wavelength accuracy. We solve this by using a three-dimensional inertial measurement unit, which provides reasonably good relative position estimates if the measurement period is sufficiently short. Simulations and experimental results based on a software-defined radio platform in an anechoic chamber show the feasibility of the proposed method.