Intermodulation Distortion in Multicarrier Satellite Systems: Analysis and Turbo Volterra Equalization

The urgent objective of transmitting high data rates over satellite, coupled with the challenge to maximize satellite mass efficiency, has necessitated that multiple carriers share the same transponder high-power amplifier (HPA). This paper presents analytical framework that characterizes the resulting intermodulation distortion (IMD) by utilizing Volterra series representation to account for the memory within the carrier itself and those associated with other carriers. Also provided is analytical evaluation of nonlinear IMD which involves computing statistical averages of higher-order products of Volterra series containing complex-valued symbols from multiple carriers. Using this theoretical characterization, novel algorithms are developed to overcome IMD in highly distortion-limited environments by employing the powerful Turbo equalization method with linear minimum mean-squared error criterion. Further, the solution is adaptive so compensation does not require prior knowledge of the HPA characteristics and can be rapidly responsive to variations in the environment. Through extensive simulations, it is shown that the proposed multicarrier analysis and Turbo Volterra techniques can be used to substantially remove IMD resulting from operating the nonlinear transponder HPA, shared by multiple carriers, near saturation. By applying more iterations of joint equalization and decoding, the solution can approach the ideal performance when feeding back correct decisions.