Differential space-time modulation schemes for DS-CDMA systems

Differential space-time modulation (DSTM) schemes were recently proposed to fully exploit the receive and transmit antenna diversities without the need for channel state information. DSTM is attractive in fast flat fading channels since accurate channel estimation is difficult to achieve. We propose a new modulation scheme to improve the performance of DS-CDMA systems in fast time-dispersive fading channels, referred to as the differential space-time modulation for DS-CDMA (DST-CDMA). We present two new demodulation schemes, referred to as the differential space-time RAKE receiver (DSTR) and differential space-time deterministic receiver (DSTD), respectively. DSTD exploits the known information of the spreading sequences and their delayed paths deterministically besides the RAKE type combination. Consequently, it outperforms DSTR, which employs the RAKE type combination only. The new modulation and demodulation schemes are especially suited for the fast fading downlink transmission in DS-CDMA systems employing multiple transmit antennas and one receive antenna