Collaborative space-time spreading scheme for higher than unity rate CDMA downlink

A novel scheme referred to as collaborative space-time spreading is proposed to provide a higher than unity rate with spatial diversity gain for the downlink of a CDMA system operating in a fading channel. This is achieved by performing collaborative coding and spreading over groups of T users, each of which is assigned a single orthogonal spreading sequence and followed by space-time encoding on the total composite signal of all groups. A user terminal simply despreads the incoming signal to recover the composite T-user group data and then extracts its intended data after space-time and collaborative decoding. Extensive comparisons with other relevant schemes are provided to show the superiority of this approach.