GMSK receiver performance with narrowband FM interference on a cellular radio channel

This paper addresses GMSK receiver performance analysis for limiter discriminator detection with co-channel interference resulting from a combined cellular voice and packet radio network. A specific example is cellular digital packet data (CDPD) which shares spectrum with cellular voice users, thus the CDPD receiver will see both narrow-band FM voice and GMSK data interference. Previous studies by Elnoubi (1986) and Varshney and Kumar (1991) investigated the performance of a GMSK receiver with a single GMSK interferer and multipath delay. In this paper, we extend this earlier work to multiple Rayleigh fading interferers (up to six) having narrow-band FM (f_dm =12 kHz) analog modulation. Probability of bit error expressions are derived for the FM and GMSK interferer cases. Using central limit theorem arguments, one would expect that the interference approaches a Gaussian distribution as the number of interferers increases. Here we find that a single FM interferer is within 1.5 dB of Gaussian performance at P_b=10^-2 while six interferers is only 0.04 dB closer