The Research Of Code Acquisition Scheme In DS/CDMA Spread Spectrum Communication Systems

With the communication technique development, spread spectrumcommunication system demonstrated his doughty strength of life by rightof special dominance. Especially in the day of electron opposition, itwill become the most advanced communication system in the war. This modeof spread spectrum communication have a lot of advantages, such asanti-jamming,secrecy,robust against noise and the effects of multi-pathfading, performing very well in the low power density. Therefore, itbecome a kind of technique which develop very fast in recent year, togetherwith fiber communication and satellite communication, they went by thename of three high tech communication in the information era. The otherscannot replace such dominance not only in military communication, but alsoin every social field, for instance, telemetry,monitoring,alarm,navigation, and so on.Synchronization of spreading sequence is an important and radicalproblem in spread spectrum communication system. If data demodulation ispossible, the receiver needs to synchronize the local spreading sequencewith the received one, otherwise, the useful information become noise.Synchronization of spreading sequence is usually achieved in two steps:acquisition and tracking. At present, there are a lot of schemes ofacquisition, which make use of favorable correlation of spreadingsequence, and whose performance is improved in different aspects.This paper analyses disadvantage of existing scheme of acquisition,and it proposes a new one. This improved scheme is developed from matchedfilter, and adopts a kind of delay circuit to remove influence ofmodulation or random data, thus it solves this problem that thetransmitter cannot transmit information data before achievingacquisition; at the same time, in order to improve signal to noise ratioat the receiver, the paper adopts method of feedback circuit to suppress noise influence. The theoretical analysis and simulation results showthat the improved scheme can remove influence of information data andimprove detection probability of acquisition system, in this way, fastcode acquisition come true.