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A non-coherent serial acquisition scheme for direct sequence spread spectrum communication systems is analyzed and discussed in this paper. The adaptive thresholding based on constant false alarm rate and multilayer perceptron neural network (MLP-NN) techniques are combined to improve the performance of code division multiple access systems. One of the most important problems in code acquisition of pseudo-noise sequences for multiuser detection is the presence of interferences caused by the multiple access technique and multipath replicas. To solve this problem, an MLP-NN is trained and adapted to work as a constant false alarm rate detector using the error back propagation gradient descendent algorithm.It is named MLP-NN adaptive processor. The performance of this proposed algorithm is presented using the serial search acquisition system, which is chosen because of its simple hardware implementation. The performance of the MLP-NN adaptive processor algorithm in homogeneous and non-homogenous environments for additive white Gaussian noise and Rayleigh fading channels is evaluated via computer simulations. The obtained results are compared to other serial acquisition schemes using the cell-averaging adaptive processor, the order statistics adaptive processor, and the automatic censoring adaptive processor algorithms.

In this paper, we propose an adaptive non-coherent serial pseudo-noise (PN) acquisition scheme for code division multiple access (CDMA) communication systems. Acquisition systems based on a fixed threshold may not be able to adapt to varying mobile communication environments leading to a high false alarm rate and/or a low detection probability. Accordingly, an adaptively varying threshold scheme based on artificial neural networks, namely the artificial neural networks constant false alarm rate (ANNíCFAR) algorithm for the serial system under consideration to improve the detection performance. The performance of the proposed system in terms of probability of detection, false alarm rate and mean acquisition time in a nonhomogenous Gaussian channel is studied and compared with those of the conventional adaptive acquisition scheme based on CA-CFAR and OS-CFAR detectors.

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