The Effects of Transponder Nonlinearity on Binary CPSK Signal Transmission

An analytical approach is developed to investigate the performance of coherent phase-shift keying (CPSK) systems transmitted through a nonlinear satellite transponder. A novel quadrature model of the satellite nonlinearity is introduced, and is found to yield an excellent fit to the actual traveling wave tube (TWT) characteristics as commonly used in a satellite transponder, with the advantage of requiring the choosing of only a few parameter values. Based on this quadrature model an expression for the bit error rate is derived in the form of an infinite series where the leading term corresponds to the error-rate for a linear channel and the remaining terms are correction terms accounting for nonlinear effects. The performance of a binary PSK system is computed and presented as a function of the up-link and down-link carrier-to-noise-power ratios (CNR) and a bandwidth spread factor.