A simple modulation scheme for error performance improvement of low-deviation digital FM

The paper proposes a simple digital modulation scheme named LF (lowpass filtered)-π/2 TFSK. Since it is essentially a constant envelope modulation scheme, it can be applied to severely band-limited channels such as land mobile and satellite mobile radio channels. Its error performance 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/N₀ with 2-bit differential detection at the error rate of 10^-5 is 2.3 dB smaller than that of GMSK in an additive Gaussian channel and 3 dB smaller at the average error rate of 10^-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