Research Of Modulation/Demodulation System For Burst-mode DS/2DBPSK

In modern communication, direct sequence spread Spectrum communications was widely used in the fields of military communication, because of high noise resistance, low interception probability, it can realize CDMA and countermine multipath effect. In tactics communication, DBPSK direct sequence spread Spectrum signals, which adopt differential modulation, especially integrate channel coding and soft decision Viterbi decoding, which have been testified more and more effective.DS/2DBPSK just about a sort of DBPSK direct sequence spread Spectrum signals, which equivalent DQPSK modulation. The paper firstly introduces the rationale of DS/2DBPSK modem and design & realization of each module, such as pulse shaping filter, DDC, carrier synchronization, bit synchronization, differential coding and decoding, Viterbi decoding and so on. Secondly, author has done algorithm simulation with Matlab. In the way of demodulation, the paper provides a new thought and solution, which is different from traditionary demodulation technique for DQPSK; In frame synchronization module, a technique for frame synchronization has been used, which doesn't need carrier synchronization; In bit synchronization module, according to the system's character, we have designed a simple adding window technique, which can adjust bit synchronization, consequently ,the synchronization spending of system is greatly decreased. Those algorithm, which not only decrease the operation of the system,but also reduce the hardware resource of the system, relative to the common modulation/demodulation algorithm. Research results prove that the algorithm completely appeases the capability and requirement of system.