A low-complexity blind QAM receiver

We present a low complexity blind receiver tailored for QAM signals. Various simplifications are introduced in carrier/phase recovery and adaptive equalizer algorithms. For blind equalization, the multi-modulus algorithm (MMA) and its generalized version (GMMA) are very promising. They combine the benefits of the reduced constellation algorithm (RCA) and the constant modulus algorithm (CMA) (Yang, J. et al., IEEE J. Select. Areas Commun., vol.20, no.5, p.997-1015, 2002). We propose a low-complexity version of these algorithms by modifying the error function and applying the sign data LMS algorithm for coefficient adaptation. The proposed algorithms use fewer multiplication operations than conventional ones, and ensure a good rate of convergence with an acceptable steady state. Convergence analysis, in the mean sense, of the proposed algorithm is presented. For carrier/phase recovery, we propose an algorithm that has two modes of operation - acquisition and tracking. The overall proposed scheme is promising, especially for applications dealing with a high baud rate over a severe channel, such as VDSL systems, where the required number of taps for the equalizer is large. Computer simulations are presented to support our approach.