Reception of QAM Signals with Pilots in Fast Fading Channels Using Partial GLRT

A reception method is proposed to improve error rate performance of quadrature amplitude modulation (QAM) signals transmitted over fast fading channels. The method can be treated as a simplified version of generalized likelihood ratio test (GLRT). Instead of exhaustive search that is necessary in GLRT, the search in the proposed method is performed over possible values of only one QAM symbol located in the middle between two pilot symbols. This searched symbol is used as an additional pilot symbol to improve channel estimation quality in the case of fast fading. For other QAM symbols of the received block, hard decisions of the demodulator are used instead of complete search. In such a manner, all data symbols are involved in the process of channel state estimation. Simulation results showed that the proposed method can notably reduce error floor with error rate reduction factor from 3.5 to 8 for 16- and 64QAM at Doppler spread up to 0.01 of symbol rate.