SYNCHRONIZATION REQUIREMENTS FOR MULTIUSER OFDM ON SATELLITE MOBILE AND 2-PATH RAYLEIGH FADING CHANNELS

The performance of multi-user Orthogonal Frequency Division Multiplexing (OFDM) with raised cosine time domain pulse shaping is studied on the Satellite Mobile channel (SMC) and the two-path Rayleigh Fading channel. A multi-user time and carrier frequency synchronization scheme is discussed. The relationship between the synchronization requirement and the roll-off rate (beta) of the pulse shaping is explored. In Gaussian and typical Rician (K=10) channels, multi-user OFDM with beta=0.2 requires timing and carrier frequency synchronization accuracies of 4% and 2% respectively, in order to avoid severe degradation due to multi-user adjacent channel interference, while on the two-path Rayleigh channel these values must be better than 2% for error floors less than 10(-3). Timing and carrier frequency accuracies are normalized to T and 1/T respectively, where T is the symbol duration. Multi-user OFDM is less affected by the multipath time delay and slightly more severely affected by the Doppler frequency shift than traditional FDM with root Nyquist filtering (FDM/RNF) for the same value of beta.