Noncoherent LMS algorithm for noncoherent sequence estimation

A novel noncoherent adaptive algorithm for channel estimation is introduced. The proposed noncoherent least-mean-square (NC-LMS) algorithm can be combined easily with noncoherent sequence estimation (NSE) for M-ary differential phase-shift keying (MDPSK) signals transmitted over intersymbol interference (ISI) channels. For zero frequency offset the convergence speed and the steady-state error of the novel noncoherent adaptive algorithm are similar to those of a conventional (coherent) LMS algorithm. However, the conventional LMS algorithm diverges even for relatively small frequency offsets, whereas the proposed NC-LMS algorithm also converges for relatively large frequency offsets. Simulations confirm the good performance of NSE combined with noncoherent adaptive channel estimation in time-variant (fading) ISI channels