In this letter, we propose modifications to existing transmit-diversity techniques to provide transmit diversity in code-division multiple-access cellular systems which must support both second-generation and third-generation mobiles on a common carrier. The proposed method, which we call symmetric-sweep transmit diversity, combines phase-sweep transmit diversity (PSTD) and space-time spreading (STS) in a way that allows second-generation and non-STS-capable mobiles to obtain the full advantage of PSTD, while third-generation mobiles obtain the full advantage of STS.

With the advent of new wireless mobile Internet technologies, there has been a significant increase in demand for capacity on the forward link of cellular systems. While significant enhancements to the system have improved the performance of the system, there continues to be a greater need for even more capacity on the forward link. Further capacity can only be derived by exploiting the spatial distribution of users. By intelligently steering energy related to a mobile only in the direction of a mobile, capacity can be increased. Use of intelligent antenna techniques coupled with transmit diversity techniques offer the most robust performance gains across a variety of environments. This paper discusses an antenna array architecture which exploits a combination of diversity and coherent antenna arrays to achieve peak performance in a cdma2000 environment. Performance results are given for this antenna architecture under a number of fading conditions.