Combined effect of coherent adaptive antenna array diversity receiver and fast transmit power control in W-CDMA reverse link

Abstract

Wideband direct sequence code division multiple access (W-CDMA), employing an adaptive antenna array is a very promising technique to reduce severe multiple access interference (MAI) from high rate users. We previously proposed a pilot symbol-assisted coherent adaptive antenna array diversity (PSA-CAAAD) receiver comprising an adaptive antenna array based on a minimum mean square error (MMSE) criterion and a RAKE combiner. In this scheme, the adaptive antenna array forms an antenna beam that tracks only slow changes in the directions of arrival and average powers of the desired and interfering user signals, while the RAKE combiner maximize the instantaneous signal-to-interference plus background noise power ratio (SINR). Although the PSA-CAAAD receiver has a significant effect on interference suppression in low signal-to-interference power ratio (SIR) (interference is large) channels, it is inferior to space diversity (SD) with maximal ratio combining (MRC) in a noise limited channel (high SIR) since the fading correlation of PSA-CAAAD receiver is almost 1 due to the small antenna separation. Therefore, we apply SINR-based fast transmit power control (TPC) in order to overcome this degradation. This paper presents an evaluation of the combined effect of the PSA-CAAAD receiver and SINR-based fast TPC in the W-CDMA reverse link based on laboratory and field experiments. The experimental results show that the combination of PSA-CAAAD and fast TPC is a powerful means to reduce severe MAI from high rate users in a low-to-high SIR environment and is more effective than using a SD receiver with the same number of antennas, i.e., the measured average bit error rate (BER) is improved by approximately one order of magnitude in the field experiment, when the target SINR of the desired user is 8 dB with 2 antennas at the average received SIR=-12 dB.