The Digital Receiving Technology For Direct Sequence Spread Spectrum System

Direct Sequence Spread Spectrum (DS/SS) communication is the most wide in spread spectrum systemapplication. In this dissertation, synchronization, one of the key techniques of DS/SS communicationsystem, is investigated in theory and practice. Synchronization scheme and its hardware implementation arepresented for IS-95 CDMA mobile communication system.Firstly, for PN sequence acquisition scheme, this paper studies the parallel acquisition scheme and the serialacquisition scheme. The serial acquisition scheme has the less complexity at cost of increasing theacquisition time. The parallel acquisition scheme has the shorter acquisition time at cost of times ofcomplexity in hardware. For the limitation of the serial acquisition and the parallel acquisition, this paperbrings forward a mixed scheme. The mixed scheme splits the difference between the acquisitionperformance and the receiver complexity.For tracking the PN sequence , the synchronization system always adopts the phase lock loop. This paperresearches the theory and processes the simulation for the phase lock loop. The strength of signals caninfluence the performance of the loop. Especially under the condition of the little power and low SNR, theperformance of the loop is worse to make the lock time longer clearly. For this problem, this paper bringsforward the returning to one method to remove the influence which is brought by the change of signalpower. This method can make the tracking performance better.For multi-path fading channel, the structure of RAKE receiver, which uses PLL to estimate and compensatecarries phase, is given, and its advantage and disadvantage in realization are discussed. Another RAKEreceiver structure, which uses MAP phase estimation, is presented. Then automatic frequency correctionscheme is proposed for this RAKE receiver, and its performance is verified by computer simulation.In the end, according to the IS-95 standard, the hardware implementations of sequence acquisition unit andtiming tracking unit are given, and the hardware implementation of RAKE receiver has been accomplished.