| In this research, the performance of two MCD (Multi-Carrier Demultiplexer) architectures, i.e. M-MCD (Multi-stage Multi-Carver Demultiplexer) and PPF (Polyphase FFT), for the on-board processing (OBP) satellite are analytically modeled and numerically evaluated in the presence of five critical degrading factors, i.e. narrow-band AWGN, carrier frequency offset, phase error, ISI (Intersymbol Interference) and quantization error. Cumulative effects of these factors on two different MCD structures are also assessed for comparison and tradeoff assuming MF-TDMA signal using QPSK modulation. Results show that phase error, ISI and narrow-band AWGN are the most critical degrading factors to both MCDs. However, combined effect of phase error under narrow-band AWGN is more critical to M-MCD than PPF. In addition, PPF proves to be more sensitive to quantization error than M-MCD. When all five degrading factors are considered, PPF method exhibits slightly better BER performance than M-MCD, especially when carrier phase error is significant. However system performance is not the only concern for choosing the preferred MCD architecture. Because of better filtering technique, modularity, flexibility, simple hardware implementation, and reliability, it is quite clear that M-MCD is the preferred MCD scheme to PPF.;In order to compensate the effect of critical impairment factors, further investigations are performed as to the synchronization methods of time delay, frequency offset and phase error for MF-TDMA OBP system. Corresponding estimates are obtained from a block of L symbols, transmitted through an Additive White Gaussian Noise (AWGN) channel. A new DA (data-aided) algorithm with reduced computational complexity and fast acquisition time is proposed, implemented and evaluated. Finally, the numerical results of new estimation are generated and corresponding system performances are illustrated. It is apparent that not only the proposed estimation algorithm is accurate and effective, but it also makes the communication system robust to critical impairment parameters considered. |
