Nonlinear Power Amplifier Effects on the Performance of CPFSK Systems

CPFSK signals with rectangular modulation pulse shaping are tested here in a transmission system including a nonlinear high-power amplifier (HPA), working at saturation. The effects of filtering followed by amplifying on power spectrum spreading of the transmitted signal and on error probability are determined. The results obtained show that, unlike other modulation systems (PSK, offset PSK, MSK), in the CPFSK case the power spectrum at HPA output can be efficiently controlled by means of filtering at the intermediate frequency (IF), if the duty-cycle τ/T of modulation pulses and the maximum angular frequency deviation ωd are suitably chosen. Moreover, by considering the transmission of a single radio frequency (RF) channel, they show that the nonlinear behavior of the transmitter has very little influence on error probability for all the ωd values of practical interest, other conditions being fixed.