Optimum transmit antenna weight generation method for adaptive antenna array transmit diversity in W-CDMA forward link

This paper investigates the optimum transmit antenna weight generation method for adaptive antenna array transmit diversity (AAA-TD) with 6 antennas in the W-CDMA forward link: AAA-TD with beam and null steering (BNST), AAA-TD with beam steering (BST), or multi-beam transmit diversity with fixed weights (MBTD-FW). The BER performance after carrier frequency calibration in the transmit beam pattern is compared among the three methods in frequency division duplex (FDD) system 2 GHz band with carrier separation of 184.5 MHz based on computer simulation. The simulation results show that the achievable BER performance in the forward link using AAA-TD with BNST is almost identical to that using AAA-TD with BST when the number of interfering users is much larger than that of the array antennas, except for the special case when a small number of higher rate users exits in the reverse link. This is because by performing carrier frequency calibration, the directions of the beam nulls are shifted from the real directions of arrival (DOA) of the interfering users. However, we also show that the required transmit E _b/N₀ at the average BER of 10^-3 using AAA-TD with BST is decreased by approximately 1.0-1.2 dB compared to that using MBTD-FW with 12 beams