One of the primary functions of a direct-sequence (DS) spread-spectrum (SS) receiver is to despread the received pseudonoise (PN) code. This is accomplished by generating a local replica of the PN code in the receiver and then synchronizing this local PN signal to the one which is superimposed on the incoming (received) waveform. Multiplication or remodulation of the incoming signal by the synchronized local PN code replica then produces the desired despreading process.

The process of synchronizing the local and received PN signals is ordinarily accomplished in two stages. Initially, a coarse alignment of the two PN signals is produced to within a small (typically less than a fraction of a chip) residual relative timing offset. The process of bringing the two codes into coarse alignment is referred to as PN acquisition . Once the incoming PN code has been acquired, a fine synchronization system takes over and continuously maintains the best possible waveform alignment by means of a closed loop operation. The process of maintaining the two codes in fine synchronism is referred to as PN tracking . In this chapter, we focus our attention on techniques and their performance for accomplishing PN acquisition. Chapter 2 deals with the companion problem of PN tracking.