MOBILE SATELLITE CDMA SYSTEM ROBUST TO DOPPLER-SHIFT

This paper suggests a dual-channel PSK demodulator for LEO satellite DS/CDMA communications, whose performance is absolutely invariant to time-variant Doppler offset of a carrier and local oscillator instability, The demodulator does not require any preamble (pilot signal) for carrier recovery, differential encoder/decoder, and carrier recovery circuit such as PLL and Costas loop, thereby resulting in high transmission efficiency and system complexity reduction, In aCDMA channel with the demodulator, the transmitted CDMA signal is composed of two orthogonal linear polarized components, which are spread by different spreading codes, and only one of which is modulated by the data stream, At the receiver, one of the two components despread by the corresponding matched-filter is utilized as a pilot reference carrier for the demodulation, Thereby, the Doppler offset is completely eliminated from the received signal since both these components exhibit the same Doppler and local oscillator instability.