Complex noncoherent receivers for GMSK signals

Noncoherent demodulators are very attractive for high performance radio LAN (HIPERLAN) systems because of their low implementation costs and their inh erent robustness against frequency and carrier phase offsets. However, when the channel is time dispersive, the nonlinear intersymbol interference (IS I) introduced by these demodulators precludes the use of conventional linea r equalization strategies. We present an alternative noncoherent receiver s tructure followed by a nonlinear equalizer, which includes a RAM and a Vite rbi detector, capable of equalizing nonlinear multipath fading channels. In addition, we also present a new algorithm specifically for noncoherent dem odulators, which allows estimation of all useful signal values at the input of the equalizer to be stored in the RAM. By means of computer simulations , we report the performance and computational complexity tradeoffs of the r eceiver/equalizer structure, including antenna diversity. We show that demo dulators which consist of a complex receiver and a Viterbi detector are muc h more robust against multipath fading channels than traditional real nonco herent demodulators. The results suggest that in a typical HIPERLAN scenari o, where the channel delay spread is less than 50 ns and a reliable line of sight component exists, it is feasible to combat multipath effects using n oncoherent demodulation.