On Polarization Transmit Diversity in CDMA Régimes

This paper considers transmit diversity schemes applied to cross-polarized linear antennas at cellular basestations, with a single linearly polarized antenna used by the mobile station receiver. The performance of SpaceTime Block Code (STBC) and Time-Delay Transmit Diversity (TDTD) is analyzed as a function of the relative orientation of the transmit and receive antennas. It is shown that power gain and diversity gain interplay as a function of the relative polarization orientation angle and affect the bit error-rate (BER) performance. The method of polarization matching is reviewed [8], and its power-BER performance advantage explained. Finally, a new method that combines polarization transmit diversity with polarization matching is presented. This new enhanced transmit diversity is suitable for 3G cellular systems without any further modifications required in the mobile station. The system performance for this new method is presented, and compared with the former polarization transmit diversity schemes.