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/sub b//N/sub o/ to achieve a bit error rate (BER) of P/sub e/=10/sup -2/ which is within 2 dB of the theoretical GMSK performance in a mobile channel with normalised Doppler spread of f/sub D/T=6.25/spl times/10/sup -3/. The corresponding E/sub b//N/sub 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.>

A novel block inversion code (BIC) which is both simple and effective in controlling low-frequency components of multilevel data signals is introduced, and its power spectrum is analyzed. The BIC's effect on the performance of QAM modems is studied, and an expression for the coded modem's symbol error rate is obtained. The code allows M-ary QAM system designs to incorporate unmodulated carrier-pilot insertion techniques using high-pass filters, for more robust, unambiguous carrier recovery and automatic gain control. The effect of BIC coding on the performance of a 256 QAM modem with carrier-pilot insertion using high-pass filters is investigated. It is found that, under some circumstances, BIC coding can significantly reduce the ill-effect of the high-pass filter on the modem's performance.>