Concurrent blind deconvolution for channel equalization

Concurrent constant modulus algorithm and soft decision directed scheme for fractionally-spaced blind equalization

“…A potential problem of (hard) decision-directed adaptation is that if the decision is wrong, error propagation occurs which subsequently degrades equalizer adaptation. As analyzed in [6], if the equalizer hard decisions before and after the CMA adaptation are the same, the decision probably is a right one. The DD adaptation, when is safe to perform, has a much faster convergence speed and is capable of lowering the steady state MSE, compared with the pure CMA.…”

“…De Castro and co-workers [6] proposed a blind equalization scheme that consists of a CMA equalizer and a DD equalizer operating concurrently. Specifically, let w = w c + w d .…”

“…To avoid error propagation due to incorrect decisions, the DD weight adaptation only takes place if the CMA adaptation is judged to have achieved a successful adjustment with high probability. At a cost of slightly more than doubling the complexity of the very simple CMA, this concurrent CMA+DD equalizer is reported to obtain a dramatical improvement in equalization performance over the CMA [6], and it represents a state-of-art technique for low-complexity blind equalization of high-order QAM channels. Another blind equalization scheme, which is relevant to the proposed concurrent CMA and soft decision-directed (SDD) blind equalizer, is the bootstrap maximum a posteriori probability (MAP) blind equalizer [7], [8].…”

“…De Castro and co-workers [6] have suggested an interesting solution to this problem. Rather than switching to a DD adaptation after the CMA has converged, they have proposed to operate a DD equalizer concurrently with a CMA equalizer.…”

“…A possible solution is to switch to a decision directed (DD) adaptation which should be able to minimize the residual CMA steady state MSE [5]. However, as pointed out in [6], in order for such a transfer to be successful, the CMA steady state MSE should be sufficiently low. In practice, such a low level of MSE may not always be achievable by the CMA.…”