Pipelined sequential acquisition in a direct sequence spread spectrum communication system

Direct sequence spread spectrum (DS/SS) technology has been proven very useful in various mobile communication and global positioning systems. In order to exploit the advantages of a DS/SS signal the receiver must first be to able synchronize the local pseudonoise (PN) code with the received PN code. This is usually done in two steps: acquisition and tracking. First, the acquisition process coarsely aligns the two PN codes to within a fraction of a chip duration. The tracking circuit then takes over and performs fine adjustment until the desired accuracy is achieved. Hybrid acquisition schemes have been shown to provide a useful tradeoff between the low complexity of serial schemes and the high speed of parallel schemes. We compare two hybrid active schemes both using sequential tests at the testing stage. The first scheme uses a test based on the M-ary sequential probability ratio test (MSPRT), while the second scheme uses a test based on the sequential probability ratio test (SPRT) that utilizes M SPRTs operating independently. The latter scheme can be viewed as a form of pipelining. Both coherent and noncoherent acquisition are considered. The system and channel models are presented, and the sequential decision rules and numerical results are given.