The Research Of Carrier Tracking For Direct Sequence Spread Spectrum Receiver

Spread spectrum communication system has the advantage of the safety of communication, concealment of information, anti-interference and so on. Therefore, the field of digital communication becomes popular in the environment of secrecy communication and bad electromagnetism, and becomes hotspot of wireless communication gradually. Therefore, people pay more and more attention to the research of the high-powered spread spectrum receiver. Because of the effect of Doppler, the frequency shift between the local carrier and receiving carrier fluctuates heavily, which have brought great difficulty of tracking synchronization of carrier. The paper has researched in allusion to the theoretical and practical problem which comes across in the process of researching direct sequence spread spectrum receiver, analyzed the influence which is brought along that Doppler to the tracking synchronization and tracking accuracy of local carrier and discussed the digital realization of phase locked loop.The paper has expounded the rationale of carrier resuming of spread spectrum receiver in the aspect of composition of carrier resuming system, mathematic model, prime capability index, tracking scheme, frequency locked loop, phase locked loop, and so on, and emphasize theoretical analysis and simulated study of AFC, Costas and two loops switch. The paper has analyzed the tracking scheme of FLL+PLL, and designs the loop filter for phase locked loop, meanwhile, explains its digital realized method. In the end, we have built the model of spread spectrum communication system for simulation, through SPW simulation software, designed carrier tracking model of direct sequence spread spectrum receiver, got the statistical error of carrier wave tracking in the situation of different Doppler frequency shift and Doppler change rates, and validated the above theoretical analysis and design. Result has indicated that this design scheme solved this problem well,which is brought by effect of Doppler, and is able to fulfill the request of tracking accuracy.