apply the results. Following this, we shall return to our introductory classification of PN acquisition systems to dis- cuss and give the performance of the conventional multiple dwell serial search system with immediate rejection verification mode [7], [8]. Next, we will present a unified approach [14] to serial stepped search acquisition with fixed dwell times in which the previously discussed single dwell and multiple dwell schemes appear as special cases. Another special case of this general approach is the rapid acquisition matched filter system whose behavior and performance are the subject of the following section. The treatment of fixed dwell time systems is completed with a discussion of some optimum PN sync search procedures and sweep strategies for appli- cations where the a priori probability density function of the uncertainty region is not necessarily uniform [20]-[24], [26]. Here again the unified approach of [14] along with its equivalent circular state diagram are invalu- able in assessing the acquisition performance of these non-uniform step- ping strategies [24]. Next comes a combination of analytical and computer simulation results [27]-[30] pertaining to the performance of variable dwell time systems based on the classical method of sequential detection. Finally, as a bridge to the next chapter, we conclude with a discussion of the handover process between acquisition and tracking including some sug- gestions for search/lock strategies [9], and a brief consideration of paral- lel search. 1.2 THE SINGLE DWELL SERIAL PN ACQUISITION SYSTEM Consider the simple model of a single dwell serial PN acquisition system illustrated in Figure 1.6. Since our interest is in the case where the PN code is acquired without knowledge of the carrier phase, the model employs a standard type, non-coherent (square-law) detector. Briefly, the received sig- nal plus noise is actively correlated with a local replica of the PN code and SAMPLE AT t=itd RECEIVED SIGNAL SQUARE-LAW ENVELOPE THRESHOLD PLUS NOISE DETECTOR 1/