Efficient direct-sequence code acquisition in spread-spectrum communication systems

In order to exploit the advantages of a direct-sequence (DS) spread-spectrum (SS) signal in a code-division multiple access (CDMA) system, receivers must first be able to synchronize the local pseudo-noise (PN) code with the received PN code. Code acquisition is often carried out by a serial search procedure, particularly suited for the downlink of third generation mobile communication systems. The simplest of such techniques is the fixed dwell-time method. In this contribution, we deal with the more general multiple-dwell method. An interesting conclusion is that multiple dwells can result in a significant reduction of the mean acquisition time, while all the possible acquisition times are conversely bounded by a limited maximum waiting time. In order to perform an optimum search procedure, both non-detection and false-alarm probabilities of the multi-dwell test may be evaluated by means of the novel class of generalized Q (GQ) functions, characterized by a lower computational cost than numerical integration, that extend the well-known Marcum's Q-function. A number of operating examples of double-dwell serial search have been investigated. In all the considered examples, the devised testing procedure has significantly enhanced the performance of the acquisition system, reducing the mean acquisition time of the whole search.