A Multistage Space-Time Equalizer for Blind Source Separation

摘要

A multistage space-time equalizer (STE) is proposed to blindly separate signals received by an antenna array from different sources simultaneously. Neither the direction of arrival (DOA) nor a training sequence is assumed to be available at the receiver. The only assumption is that the transmitted signals satisfy the constant modulus property, which is valid for many modulation schemes, and can be exploited by the multi-modulus algorithm. Each stage consists of an adaptive beamformer, a DOA estimator and an equalizer. Its function is to jointly combat multi-user interference and the effect of fading channels between sources and the antenna. An adaptive version of the basic structure of generalized sidelobe canceller (GSC), called adaptive GSC, is presented which can track a user and strongly attenuate other users with different DOAs. The possibly time-varying DOA for each user is estimated using the phase shift between the outputs of two subarray beamformers at each stage. The estimated DOAs are used to improve multi-user interference rejection and to compute the input to the next stage. In order to significantly alleviate inter-stage error propagation and provide a fast convergence, a mean-square-error sorting algorithm is proposed which assigns detected sources to different stages according to the reconstruction error. Further, to speed up the convergence, a simple, yet efficient, DOA estimation algorithm is proposed which can provide good initial DOAs for the multistage STE. Simulation results illustrate the performance of the proposed STE and show that it can deal effectively with changing DOAs and time-varying channels.