Effects of open-loop transmit diversity schemes with four antennas on control signals using cyclic-shift CDMA

This paper investigates the effects of open-loop transmit diversity schemes with four antennas on low-rate control signals using cyclic shift (CS)-CDMA for single-carrier (SC)-frequency division multiples access (FDMA). More specifically, we investigate the average block error rate (BLER) performance levels of space orthogonal-resource transmit diversity (SORTD) and a combination of space-time block code (STBC) and time-switched transmit diversity (TSTD) for N_Rx = 2 and 4 antenna diversity reception. Computer simulation results show that for N_Tx = 4 transmission antennas, SORTD significantly decreases the required average received signal-to-noise power ratio (SNR) that satisfies the target average BLER compared to the combination of STBC and TSTD due to the minimum mean-square error combining (MMSEC) gain from the 4 antennas. We show that for N_Rx = 2, the required average received SNR at the average BLER of 10^-2 and 10^-3 using SORTD with N_Tx = 4 antennas is decreased by approximately 0.6 and 1.5 dB, respectively, compared to that for SORTD with N_Tx = 2 antennas. Moreover, we show that even with N_Rx = 4-antenna receiver diversity, N_Tx = 4-antenna SORTD is effective in decreasing the required average received SNR when a large number of control channels such as K = 12 are multiplexed during a short cyclic shift, in which severe inter-code interference occurs.