Sudden Spread Spectrum Signal Synchronization Study

Recently spread spectrum technique has been used widely in wireless data communication, cellular mobile communication, military communication and telemetry monitor system with resistance to interference, high usage of spectrum, resistance to multi-path fading, so investigators in communications field pay more attention to the technique, especially direct sequence spread spectrum (DSSS) technique. Based on the theory of DSSS, the received signal can be despreaded and demodulated only when the phase of spread sequence in the receiver is equal to the phase of the received signal, or the useful signal would be overwhelmed by the noise. However in the practice spread spectrum communication system, the phase of the received signal is likely to be uncertain because of the instability of transmitter and receiver's clock, transmission delay and multi-path. Consequently PN synchronization is the key technique in spread spectrum system, and is an important element to influence the performance of the whole system.PN synchronization is usually achieved in two stages: PN acquisition and PN tracking. PN acquisition involves coarsely aligning the local replica generated in the receiver with that of the received signal and PN tracking is to realize the synchronization accurately, so PN acquisition is the emphasis and difficulty of PN synchronization. Presently a lot of PN acquisition schemes have been proposed, but there always is a contradiction between the system performance and the hardware complexity. It means that improving the acquisition performance would increase the system complexity, and vice versa. Because of the reason above, a novel PN acquisition method using auxiliary sequence and binary search is proposed. Because the cross correlation between auxiliary sequence and spread sequence is linear, some search algorism can be used to estimate the phase of incoming signal quickly without increasing the complexity of system. To validate the performance of the proposed scheme, the scheme is simulated with FPGA, and the simulation result indicates that compared with the conventional PN acquisition schemes, the PN acquisition using auxiliary sequence and binary search can decrease the acquisition time greatly on the same condition.