On the MAX/TC criterion for code acquisition and its application to DS-SSMA systems

In this paper, we analyze in depth the MAX/TC criterion for code acquisition in spread-spectrum transmissions. The uncertainty region is divided into sectors: inside each sector, the cell with associated maximum test variable is selected (MAX criterion), and sectors are serially tested according to the threshold crossing (TC) criterion. The most commonly used analysis tools for code acquisition, namely the direct and the flow-graph approaches, are extended to the MAX/TC criterion. An accurate but simple approximation to the acquisition time probability density function is found in terms of a gamma distribution, which is shown to yield much better accuracy than the Gaussian distribution. The general formulation is applied to the particular case of direct-sequence spread-spectrum multiple-access (DS-SSMA) systems, showing that sector size is a fundamental parameter to be optimized in the minimization of acquisition time, and that in some cases MAX/TC with parallel architecture performs marginally better than MAX/TC with serial architecture.