GPS Adaptive Array Phase Compensation using a Software Radio Architecture

Digital Beam Forming and nulling are viable means of GPS array signal processing that enable multipath mitigation and provide protection against interference. As reported in the literature [1], nulling causes errors in the carrier phase and code phase measurements. The output of multi element antenna arrays (Controlled Reception Pattern Antennas – CRPAs) are subject to significant variations in their phase patterns that arise from the application of time varying adaptive array weights. This phase error can be compensated in the carrier phase tracking domain in the baseband GPS receiver. Classical approaches implement a constrained beam steering mechanism to control the phase response of the array in the look direction. An alternative approach using unconstrained adaptive array processing with compensation for the subsequent phase distortion of the GPS signal is demonstrated using a software defined GPS radio.