PERFORMANCE OF GMSK MODULATION IN LAND MOBILE RADIO CHANNELS

Abstract

Cellular communication systems which provide telephone communication service to mobile users have experienced a rapid growth during the last five years. The current cellular systems are analog in nature. These systems employ frequency modulation. As the spectrum gets crowded, bandwidth efficient digital systems will find increasing application. Gaussian Minimum Shift Keying (GMSK) has been identified as the modulation scheme for future European digital cellular systems. The communication channel for the cellular systems is commonly referred to as the land mobile channel. The land mobile channel can be modelled as a frequency selective fast Rayleigh channel corrupted by additive white Gaussian noise. In addition to cochannel interference, delayed signals and doppler effects have to be considered. Performance of GMSK in this environment has not been analysed before. This thesis addresses this problem. A closed form expression for the bit-error-rate performance of GMSK is derived taking into account all the degradations in a land mobile channel. Numerical computation is used to obtain GMSK bit-error-rate results for various combinations of channel parameters. Both limiter-discriminator and one-bit delay detection methods for GMSK demodulation are considered. The computed bit-error-rate results indicate that limiter-discriminator method has a slight advantage when the delayed signals and the cochannel interference signal are significant.