Widely-linear fractionally-spaced blind equalization of frequency-selective channels

This paper deals with the problem of designing widely-linear (WL) fractionally-spaced (FS) finite-impulse response equalizers for both real- and complex-valued improper modulation schemes. Specifically, the synthesis of both WL-FS minimum mean-square error and zero-forcing equalizers is discussed, by deriving the mathematical conditions assuring perfect symbol recovery in the absence of noise. In a general framework, the feasibility of designing WL-FS blind equalizers based on the constant modulus criterion is also investigated, and both unconstrained and constrained designs are provided. The effectiveness of the proposed equalizers is corroborated by means of computer simulation results.