A comparative study of transmit diversity schemes for 3G-CDMA system with correlation and power discrimination between diversity branches

Abstract

Most research on transmit antenna diversity assumes ideal diversity branches, which is not true in practice. In addition, comparative studies on different transmit diversity schemes for 3G-CDMA are available, but mainly through simulation. In this paper, we compare the performance of spacetime spreading (STS), orthogonal transmit diversity (OTD), and transmit adaptive array (TxAA) in different channel and diversity conditions in the presence of cross correlation and cross-polarization discrimination (XPD), through analysis of the Chernoff bound of the pair-wise error probability. We show that the design criterion of the outer code for all the schemes is the same as that of the coded transmission with one transmit antenna for both fast and slow fading channels, and not affected by non-ideal diversity branches. The interleaver design is shown to be important. STS outperforms OTD for both slow and fast fading conditions. STS and OTD are relatively robust to crosscorrelation, but sensitive to the power discrimination between diversity branches. TxAA outperforms all the other schemes, but its power gain over STS reduces with cross-correlation.