Pilot-based calibration of dual-tuner SDR receivers

Multi-channel RF signal acquisition is a typical requirement in modern communications and radar applications. The use of multiple general-purpose Software-Defined-Radio receivers, connected to a host via USB interface, seems to be an attractive solution since it allows a high number of channels to be obtained with relatively low hardware cost and system weight. Unfortunately, such an architecture usually introduces some inter-channel phase-shifts and time-delays due to hardware limitations, and thus requires calibration routines. In this paper we present a calibration method that is based on pilot signals generated in additional hardware part and injected into the input RF signals. The system extended with such a calibration circuit was used during a field PCL measurement campaign and hours of the recorded signals have been processed offline with the proposed algorithm. The obtained results prove that it is possible to estimate the time delays and phase shifts in practice using the described solution even in the case of low SNR values and time-varying carrier frequency of the pilot signals.