This paper investigates three code acquisition methods for direct sequence spread spectrum systems (DS/SS) utilizing smart antennas. The methods are suitable especially for receivers that consist of a smart antenna followed by a single correlator or a matched filter (IMF). The first method is the known fixed beam strategy where the whole angular uncertainty region is divided into small cells using conventional beamforming techniques. Therein, the receiver searches through all angular and delay cells via a serial search procedure. In the second method, the fixed division is made using advanced beamforming techniques, which provide improved tolerance against interference. In the third strategy, the direction-of-arrival (DOA) of incoming signals are estimated and utilized in the acquisition process. An advantage of this DOA estimation-based strategy, when compared to fixed beamforming methods, is a decrease in the region of uncertainty. Disadvantages are increased computational complexity and signal-to-noise ratio (SNR) limitations. The acquisition strategies are compared when the serial search acquisition of the code phase is made using either the correlator or the matched filter. The results indicate that a single antenna receiver gives the best acquisition performance when SNR is high. However, single antenna methods are sensitive to interference. On the other hand, DOA estimation-based methods offer shorter mean acquisition times than fixed beam methods, especially when the number of arriving signals is small.

In this paper, code synchronization probabilities of the direct sequence spread spectrum (DS/SS) system are investigated when the receiver utilizes an adaptive antenna array. Performance studies of three beam forming algorithms in the presence of direction-of-arrival (DOA) errors are presented. The investigated algorithms are the conventional, the minimum variance distortionless response (MVDR), and the MVDR+ADL where the MVDR algorithm is enhanced against DOA error via the adaptive diagonal loading (ADL). The paper includes a large number of analytical and simulation results where the effects of DOA errors are investigated. It can be concluded that the MVDR beam former is more sensitive to DOA errors than the conventional beam former, especially, at large DOA errors and high signal-to-noise-ratio (SNR) values. However, this sensitivity can be reduced notably by using the ADL.