Fast tracking of pn synchronization in a direct-sequence spread-spectrum digital communications system

Abstract

In a direct sequence spread spectrum communication receiver, a system and method for recovering the timing of a pseudo-random noise (PN) sequence used for despreading the received signals. In one embodiment of the method, the receiver waits for detection of a SYNC field to confirm at least a coarse synchronization or the receiver's local PN sequence with the received PN sequence (in the received signal). The receiver then performs a fast tracking to finely synchronize the receiver's PN sequence with the received PN sequence, preferably for a fixed duration of time. One embodiment of a system for performing the synchronization with the fast tracking includes an input for receiving a received spread-spectrum data stream, an ML detection logic, a receiver PN clock, a despreading mixer that generates a narrowband signal from the spread-spectrum data stream, a testing logic that generates a PASS output if it identifies a SYNC field in the narrowband signal, and a fast-tracking logic. The fast-tracking logic temporarily advances and temporarily delays the receiver PN clock by a small shift and measures the resulting correlations between the receiver's PN sequence and the received PN sequence. If the advanced correlation is greater or less than the delayed correlation, then the fast-tracking logic accordingly makes a small adjustment to advance or delay the receiver PN clock. This temporary advancing, temporary delaying, and adjusting of the receiver PN clock is preferably repeated a fixed number of times.