Orthogonal CDMA transmission for satellite-based mobile communications radio networks

Code division multiple access (CDMA) techniques have received a great deal of attention for mobile terrestrial/satellite communication systems. Primarily considered for the noteworthy features of low power flux density emission and robustness to interference and multipath, CDMA is known to provide reduced bandwidth and power efficiency when compared to traditional TDMA and FDMA due to the intrinsic co-channel self-noise. Practical solutions, under advanced development status in Europe and in the USA, respectively, propose to overcome such a shortcoming by implementing orthogonal CDMA signalling in the outbound link. The paper is focused on the comparative performance analysis of those two orthogonal CDMA schemes in the operating conditions of a mobile satellite communications system. In particular, starting from the analysis of the classical additive white Gaussian noise (AWGN) environment, the two CDMA systems are compared in the presence of carrier phase offset, frequency-selective multipath fading, and a typical satellite transponder nonlinearity.