Low complexity predistortion method for higher order APK modulation in nonlinear power amplifier channels

In 1974 Thomas et al. conducted a thorough study on the use of higher order Amplitude-Phase-Shift keying (APK) modulation in order to attain higher bit rate over a satellite channel containing a nonlinear power amplifier. Predistortion over this power amplifier was not considered. To overcome the nonlinearity of the power amplifier, many analog and digital predistortion techniques were proposed in the literature. However, they were basically too complicated to be applied in the practical satellite system. The goal of this research project is to design a simpler predistortion technique for APK modulations.; In this thesis, a very simple amplitude/phase predistortion technique involving the simple parameters of a circle is designed and tested for all the important APK modulations, which are expressed by a three-circle model. Both single- and two-link models are considered, where the latter corresponds to the bent-pipe satellite transmission model. Transmitter and receiver filters with 100% and 40% excess bandwidth are considered. By computing the symbol error rate (SER) with an extended Craig's method, the proposed predistortion technique is shown as a simple and effective method to counteract the nonlinear distortion of the power amplifier.