Noncoherent sequence estimation combined with noncoherent adaptive channelestimation

In this paper, M-ary differential phase-shift keying (MDPSK) transmission o ver possibly time-variant intersymbol interference (ISI) channels is consid ered. For equalization, we combine noncoherent sequence estimation (NSE) wi th noncoherent adaptive channel estimation. For this, an efficient noncoher ent least-mean-square (NLMS) algorithm is employed. It is shown that the re sulting noncoherent receiver is very robust against carrier phase variation s. For constant channel phase the convergence speed and the steady-state er ror of the noncoherent adaptive algorithm are similar to that of a conventi onal (coherent) LMS algorithm. However, the conventional LMS algorithm dive rges even for relatively small phase variations, whereas the proposed NLMS algorithm also converges for relatively large phase variations. Simulations confirm the good performance of various NSE combined with noncoherent adap tive channel estimation for both time-invariant and time-variant (fading) I SI channels.