Novel SIR measurement method for modified closed loop transmit diversity in W-CDMA

Antenna verification, i.e., verification of the actual antenna weights of the dedicated physical channel (DPCH) is indispensable to closed loop transmit diversity mode 1 (CL-TD) dictated in the 3GPP specification for W-CDMA FDD. The accuracy of which is largely determined by the dedicated pilot power of corresponding DPCH. Transmitting the dedicated pilot channel from antenna 2 only, thus suspending the transmission of the dedicated pilot channel on antenna 1, improves the accuracy without any extra overhead since the transmit signal on antenna 1 is transmitted with constant antenna weight, thus precluding the need for antenna verification. However, this strategy exhibits worse performance when closed loop transmit power control (CL-TPC) is active due to large signal to interference power ratio (SIR) measurement error in the CL-TPC loop. Therefore, we propose a novel SIR measurement method in conjunction with the modified CL-TD scheme to facilitate CL-TPC. Computer simulation results show that our proposed scheme is capable of decreasing the required average transmit E_b/N₀ at average BER of 10^-3 by about 0.4-2.0 dB depending on the user equipment (UE) mobility speed and propagation conditions. Further, this proposal is attractive since it can be considered as add-on functionality to the current user equipment (UE) specification.