A Constrained Maximum-SINR NBI-Resistant Receiver for OFDM Systems

In this paper, with reference to the problem of joint equalization and narrowband interference (NBI) suppression in orthogonal frequency-division multiplexing (OFDM) systems, synthesis and analysis of both unconstrained and constrained optimum equalizers are carried out, based on the maximum signal-to-noise-plus-interference (SINR) criterion. Specifically, a comparative performance analysis is provided from a theoretical point of view, either when the second-order statistics (SOS) of the received data are exactly known at the receiver, or when they are estimated from a finite number of data samples. Relying on the results of this analysis, a three-stage constrained maximum-SINR equalizer is then proposed, which outperforms existing receivers and, in comparison with its unconstrained counterpart, exhibits a significantly stronger robustness against errors in the estimated SOS. Moreover, a computationally efficient adaptive implementation of the three-stage equalizer is derived, and in connection with it, a simple and effective NBI-resistant channel estimation algorithm is proposed. Finally, numerical simulations are performed that aim to validate the theoretical analysis carried out and compare the performances of the considered equalizers with those of existing approaches