Code Orthogonality for Wideband CDMA Systems With Multiple Transmit Antennas

Code orthogonality is a useful indicator in determining the performance of the synchronous downlink of third generation Universal Mobile Telecommunication System (UMTS) Terrestrial Radio Access systems. In this paper, previous work on quantifying code orthogonality for single-antenna [or single-input single-output (SISO)] links is extended to fixed beamforming and transmit diversity schemes. Code orthogonality estimates from real measured channel data are extracted for typical outdoor radio environments. The results indicate that the spatial conditioning of fixed beamforming radio channels generally improves code orthogonality. In contrast, full code-rate transmit diversity schemes degrade code orthogonality.