Analytical characterization of non-linear effects in satellite CDMA systems

Code DivisionMultipleAccess (CDMA) technique has recently gained a particular interest for the design of satellite systems. The aim of this paper is to develop a theoretical characterization of non-linear distortion effects in CDMA systems for satellite communications, with reference to the effects of in-band interference. It is shown that the non-linear effects can be simply described by a complex scale factor and an additive noise on the decision variable at the receiver. In order to evaluate performance degradation, the curve of Total Degradation as a function of Output Back-Off (OBO) is taken as a reference. Two well known classes of High Power Amplifier (HPA) model are considered to obtain numerical results: Traveling Wave Tube Amplifier (TWTA) and Solid State Power Amplifier (SSPA)models. Both synchronous (orthogonal) and asynchronous systems are considered and, with regard to non-linear effects, the numerical results show a sort of equivalence between orthogonal CDMA and the OFDM technique.