Performance Analysis of Orthogonal Transmit Diversity Over Intra-Cell Interference in WCDMA Downlinks

This paper extends the traditional orthogonal transmit diversity (OTD) analyses to the multipath intra-cell interference presented in a realistic wideband code-division multiple access (WCDMA) downlink channel. A generic OTD system model is proposed for analyses permitting maximizing the spatial and temporal diversity dimensions for multiple transmit antennas and space-time block code (STBC) respectively. Analytical expressions are derived to evaluate the Chernoff upper bounds on the bit-error rate (BER) for the OTD system under a variety of channel parameters. The expression shows that the BER upper bound can be simplified and determined using an attained signal-to-interference-plus-noise power ratio (SINK) obtained in terms of the number of transmit antennas, the phase difference between two transmit antennas, the channel orthogonality, and the relative cross-correlations of the desired signal to the intra-cell interferers power ratio when equal power allocation at each intra-cell user and perfect channel state information (CSI) are applied in the closed-loop TD system.