Comparative assessment of orthogonal and nonorthogonal multiplexing techniques for differentiated satellite broadcasting services

This paper presents a comparative assessment of two multiplexing techniques for providing differentiated classes of services over a realistic broadcasting satellite channel under variable link conditions. A distinctive characteristic of satellite broadcasting channels is the non-linear characteristics of high power amplifier on-board of the satellite. In this scenario, the conventional additive white Gaussian noise (AWGN) channel with average power limitation is no longer an accurate model and nonlinear characteristics have to be taken into account. Orthogonal multiplexing (time sharing) techniques combined with variable coding and modulation are compared with hierarchical modulations with the goal of maximizing the number of broadcast channels over a given transponder while maintaining a target service availability. Hierarchical modulations are shown to provide better performance than orthogonal time division multiplexing (time-sharing) schemes for the AWGN channel. Here we design a practical transmitter scheme based on the hierarchical modulation and maximize the throughput by optimizing the achievable mutual information for finite size constellations. This will provide a lower bound on throughput which can be achieved by non orthogonal multiplexing scheme. We compare the performance of hierarchical modulation (non-orthogonal multiplexing) and time sharing techniques (orthogonal multiplexing) supporting two different service quality and service availability requirements for broadcasting the same content.