Adaptive Rayleigh fading compensation for coherent GMSK signals in digital mobile communications

A new fading compensation scheme for coherent Gaussian minimum shift keying (GMSK) in a fast Rayleigh fading mobile environment is described. The proposed scheme employs the adaptive extended Kalman filter (EKF) and a new decision-aided predictive algorithm to achieve accurate channel fading estimation and cancellation even when the Doppler spread is large. Our study shows that the proposed scheme requires only 18 dB E_b/N_o to achieve a bit error rate (BER) of P_e=10^-2 which is within 2 dB of the theoretical GMSK performance in a mobile channel with normalised Doppler spread of f_DT=6.25×10^-3. The corresponding E _b/N_o requirement for the conventional Costas loop coherent receiver is 28 dB. In addition, the proposed scheme achieves a residual error rate which is more than one order of magnitude lower than that of the conventional receivers. Our scheme is particularly attractive for mobile communications where a high Doppler spread is expected