Initial and Post-Initial Acquisition in the Serial Search Based Noncoherent Multiple Transmit/Receive Antenna Aided DS-CDMA Downlink

Abstract

In this paper we investigate the issues of both initial and post-initial acquisition schemes in the multiple transmit/receive antenna aided DS-CDMA downlink, when communicating over uncorrelated Rayleigh channels. The associated Mean Acquisition Time (MAT) performance trends are characterised as a function of the number of transmit/receive antennas. Furthermore, we characterise both the initial and post-initial acquisition performance as a function of the relevant system parameters. It is demonstrated that in contrast to our expectations, the achievable MAT degrades at low Ec/Io values, except for the case of P = 2 transmit antennas operating in conjunction with R=1 receive antenna over the specific Signal-to-Interference plus Noise Ratio (SINR) per chip (Ec/Io) range considered, as the number of transmit antennas is increased. Ironically, our findings suggest that increasing the number of transmit antennas in a MIMO-aided CDMA system results in combining the low-energy, noise-contaminated signals of the transmit antennas, which ultimately increases the MAT by an order of magnitude, when the SINR is relatively low. This phenomenon has a detrimental effect on the performance of Rake receiver based synchronisation schemes, when the perfectly synchronised system is capable of attaining its target bit error rate performance at reduced SINR values, as a benefit of employing multiple transmit antennas. Therefore our future research will be focused on specifically designing acquisition schemes for MIMO systems