The Waveform Design And Receiver Techinques Reserach For CPM-based Direct Sequence Spread Spectrum

Direct sequence spread spectrum(DSSS)using continuous phase modulation(CPM)is a new type of modulation emerging in recent years.The so-called DSSS-CPM signals inherit the continuous phase,constant envelop and spectral properties of CPM as while as the narrowband interference suppression,low probability of intercept and multiple-access communication of DSSS.DSSS-CPM has research value in CDMA employing CPM,large capacity multi-access telemetry communication,efficienct cellular mobile communication and military secret communication.The analysis contained herein is the waveform design and receiver techniques reserach of DSSS-CPM signals.The main contributions are as follows.1.We summarized the DSSS-CPM signal formats and modulation schemes.And We studied the common expression,phase state trellis structure and power spectral density of DSSS-CPM and investigates the performance of DSSS-CPM from bandeidth efficiency,according to which we can design the waveform and choose porper modulation parameters.2.By introducing chip branch metric to the receiver scheme,de-spreading and data detection can be done meanwhile based on Maximum Likelihood Sequence Detection(MLSD),which can solve the problem that spreading sequences and data symbols are not separable.The synchronous de-spreading and demodulation algorithm has no performance loss compared to CPM system that employs MLSD algorithm under the same test conditions.low complexity algorithm is proposed based on PAM decomposition for conventional CPM.3.Based on the diversity technique and conventional ARKE receiver over a Rayleigh-fading multipath channel,a new class of coherent RAKE receiver for DSSS-CPM is proposed in this work,which accumulates symbol branch metric increments over every phase state of multiple paths with Viterbi algorithm.The proposed coherent RAKE receiver significantly outperforms conventional RAKE receiver of standard DSSS-BPSK and achieves a remarkable diversity gain of bit error rate(BER)under the Rayleigh-fading multipath channel.4.By partitioning the spreading sequence so that differing patterns of plus and minus chips are multiplied onto successive data bits,a new class of Multi-h CPM signals format based on Tamed Spread Spectrum technique is proposed,which can obtain similar phase state trellis structure and performance gain as conventional Multi-h CPM signal with Single-h.The modulation index synchronization can be completed while the pseudo random spreading sequence is synchronized.we have provided numerical examples of BER and Euclidean distance.And it shows that the proposed signal format has advantages of BER and complexity.5.Based on the theoretical analysis and computer simulation of low complexity synchronous de-spreading and demodulation algorithm,we finish the design and realization of the Viterbi demodulator for IF receiver.The Viterbi demodulator can reach symbol rate of 6Mcps with One-Pointer algorithm.The simulation and testing result show that the test performance and theoretical analysis are nearly identical.