Adjacent Channel and Cochannel Interferences in CPFSK Systems with Nonlinear Transmitters and Limiter-Discriminator Detection

The performance of continuous-phase FSK (frequency-shift keying) systems with rectangular modulation pulse shaping and limiter-discriminator detection is analytically evaluated in the presence of transmission nonlinearities as well as adjacent channel and cochannel interference. Consideration of modulation pulses with length τ, shorter than symbol time, T, is investigated. The algorithm developed to evaluate bit-error probability shows that the choice τ/T<1 is more convenient than the conventional one, τ/T=1, and even moreso in the presence of adjacent channel interference. Moreover, for τ/T=0.5, numerical results are reported that describe system performance under different working conditions (type and bandwidth of the filters, frequency deviations of the signals, channel spacing,...) and can be used to develop design criteria