Effect of spatial fading correlation on CDMA code-acquisition performance

The effect of correlations among the fading signals at the multiple antennas on the code-acquisition performance for preamble search in a code-division multiple-access (CDMA) uplink is investigated. Previous results for frequency-selective fading assumed independent fading at each antenna. A general case of spatial fading correlation as a function of antenna spacing and azimuth spread is presented for the performance analysis of code-acquisition systems. The correlated antennas are exploited to derive the probability density function of a decision variable. The performance of a maximum-likelihood (ML) code-acquisition technique based on spatially correlated antennas is analysed by considering the detection, miss, and false-alarm probabilities. The result of performance analysis of a code-acquisition scheme utilising uncorrelated diversity antennas is also described. The detection performance and mean acquisition time given by partial correlation in spatial fading are presented and compared with those offered by antenna decorrelation via numerical evaluation. It is shown that without exploiting time diversity, the code-acquisition approach with multiple antennas provides much better detection performance than the corresponding scheme with a single antenna in a frequency-selective fading channel and that the performance enhancement depends on the degree of spatial fading correlation.