A SIMPLE MODULATION SCHEME FOR ERROR PERFORMANCE IMPROVEMENT OF LOW-DEVIATION DIGITAL FM

This paper proposes a simple digital modulation scheme named LF (Lowpa ss Filtered)-pi/2 TFSK. Since it is essentially a constant envelope mo dulation scheme, it can be applied to severely band-limited channels s uch as land mobile and satellite mobile radio channels, Its error perf ormance is superior to that of MSK modulation in band-limited channels at the cost of a slightly wider bandwidth (approximately 1.06 times) than GMSK, The required E(b)/N-o with 2-bit differential detection at the error rate of 10(-5) is 2.3 dB smaller than that of GMSK in an add itive Gaussian channel and 3 dB smaller at the average error rate of 1 0(-4) in a fast Rayleigh fading channel, The above result, obtained by an exact error rate analysis, was confirmed by laboratory experiments at a frequency of 880 MHz. The spectral characteristics were analyzed through computer simulations and the results were found to agree with those obtained from a hardware implementation.