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Reduced-complexity digital satellite CDMA systems robust to Doppler

This paper presents two digital satellite CDMA systems which are invariant to Doppler shift. Their performances in a subsampling front-end with a 1-bit A/D converter are evaluated by both theoretical analyses and simulations. The subsampling is done after the received signal is downconverted to an intermediate frequency (i.e. IF subsampling). Both systems are based on PSK DS/CDMA communication and do not require either an extra circuit or a pilot transmission for frequency tracking. The use of 1-bit A/D at front-end allows large power consuming circutries such as automatic gain control (AGC), phase-lock loop (PLL) and mixer be eliminated or simply replaced with digital ones. Hardware realizations of each system model are also discussed. After the 1-bit A/D converter, the whole system including the PN code synchronization, the carrier synchronization and timing synchronization can be implemented digitally with the use of application specific integrated circuit (ASIC) technology.