A transmitter diversity scheme for wideband CDMA systems based on space-time spreading

We present a transmit diversity technique for the downlink of (wideband) di rect-sequence (DS) code division multiple access (CDMA) systems. The techni que, called space-time spreading (STS), improves the downlink performance b y using a small number of antenna elements at the base and one or more ante nnas at the handset, in conjunction with a novel spreading scheme that is i nspired by space-time codes. It spreads each signal in a balanced way over the transmitter antenna elements to provide maximal path diversity at the r eceiver. In doing so, no extra spreading codes, transmit power, or channel information are required at the transmitter and only minimal extra hardware complexity at both sides of the link. Both our analysis and simulation:res ults show significant performance gains over conventional single-antenna sy stems and other open-loop transmit diversity techniques. Our approach is a practical way to increase the bit rate: and/or improve the quality and rang e in the downlink of either-mobile or fixed CDMA systems. ii STS-based prop osal for the case of two transmitter and single-receiver antennas was recen tly accepted and will be included as an optional diversity mode in release A of the IS-2000 wideband CDMA standard.