CALCULATION OF THE NOISE-IMMUNITY OF APSK SIGNALS IN NONLINEAR CIRCUITS

Amplitude-phase shift keying (APSK) is used to improve the specific information transmission rate in communications channels. Such keying makes it possible to obtain a compact signal spectrum when transmitting digital signals [1]. However, the nonlinearity of the transmission circuit considerably reduces the noise immunity of APSK signals. The method of calculating the effect of nonlinearity on the noise immunity proposed in [1] was based on multiple statistical tests by means of computer simulation [3]. In the case of multiposition APSK signals and for a low error probability, the number of tests required and, therefore, the cost in terms of computer time become so large that this method is no longer suitable. Below, we describe a method of calculation that enables these drawbacks to be avoided.