Effects of ACI and nonlinearities on the performance of differentially detected GMSK signals

The effects on the performance of differentially detected Gaussian minimum shift keying (GMSK) signals operated in the presence of adjacent channel interference (ACI), modulator impairments, amplifier nonlinearities and additive white Gaussian noise is investigated. By means of computer simulation, the bit error rate (BER) performance of 1- and 2-bit conventional and decision feedback differentially detected (C-DD and DF-DD) GMSK systems in the presence of static and Rayleigh faded ACI is obtained. It is found that the best performance is achieved by the 2-bit DF-DD receiver and has resulted in BER performance improvements for the static ACI channel and error floor reductions for the Rayleigh faded ACI channel. The effects on the BER performance of a cascade of imperfect GMSK quadrature modulators and a nonlinear amplifier in conjunction with the resulting ACI are also investigated. The combination of ´typical´ and ´extreme´ operating conditions for the modulator are considered. For all combinations, it was found that the DF-DD receivers perform better than the C-DD receivers. However, for systems operating under ´typical´ Operating conditions, the 2-bit DF-DD receiver exhibits the best performance.