Transmitter diversity for a digital FM paging system

Multipath fading is one of the most serious problems for the signal transmission in mobile radio. To combat this problem, the application of transmitter diversity to a digital FM paging system is described. The method is to transmit two digital FM paging signals with different modulation indices, each of which is modulated by an identical binary signal, from separate antennas. It is shown that the same action obtained with the well-known selection diversity can be achieved when the difference between the modulation indices is equal to two. The diversity effect on the bit-error-rate (BER) performance is theoretically analyzed. The diversity effect on the BER performance in a 600-bit/s Manchester-coded digital FM system is verified by the laboratory simulation tests using a Rayleigh fading simulator.