Worst case equalizer for noncoherent HIPERLAN receivers

Coherent detection of HIPERLAN Gaussian minimum-shift keying signals calls for complex and expensive receivers, However, when the channel delay spread is limited to at the most 50% of the symbol time and a reliable line-of-si ght component of the radiated signal exists (Rician fading model), noncoher ent detectors are capable of achieving a good performance, Based on the abo ve motivations, in this work we compare four different demodulation techniq ues, namely the following: 1) one-bit differential detector; 2) discriminat or detector; 3) limiter discriminator detector; and 4) limiter discriminato r integrator detector (LDID). The intersymbol interference introduced by th ese demodulators is nonlinear (with respect to the data symbols) and a deci sion-feedback equalizer (DFE) based on a mean square-error criterion mag no t be appropriate. Moreover, at this high speed, a DFE may be very complex t o implement. Hence, we propose a new DFE design method that increases the e ye-diagram aperture by removing the worst case interference. Performance of the above demodulators in the presence of a simple nonlinear DFE (with feedback part only) is computed in terms of the bit-error rate ( BER) by means of the saddle point approximation. This procedure, for static channels, turns out to be a very general tool with a simple and robust imp lementation. The same method can be applied, for multipath fading channels, to the BER evaluation as part of a semianalytic approach. The main conclusion from this work is that for LDID demodulators and in the presence of Rician fading channels with an average normalized root mean sq uare delay spread of 0.3 and dual antenna diversity, the new equalizer lowe rs the outage probability from 60 % to 10 % at a BER of 10(-4).