Performance analysis of mobile satellite noncoherent DS-CDMA systems with orthogonal signals

As noncoherent direct sequence code-division multiple-access (DS-CDMA) mobi le satellite communications, two typical transmission schemes are compared; one is a quasi-synchronous differential BPSK (QS-DBPSK) where orthogonal s ignals are used for reducing the multiple access interference and the other is M-ary orthogonal signaling (MOS) scheme where orthogonal signals are us ed for exploiting more efficient modulation. The performances are evaluated in additive white Gaussian noise (AWGN) and shadowed Rician fading (SRF) c hannels and the effects of timing misalignments in the QS-DBPSK system and the amount of Doppler shifts of a SRF channel are investigated. The results show that MOS much outperforms QS-DBPSK in the region of low system loadin g up to about 50% and a precise chip synchronization is required for QS-DBP SK. In a SRF channel, it is also shown that QS-DBPSK much outperforms MOS i n a slow fading channel but MOS has a performance gain against the large Do ppler shift.