Research On Synchronizaton And Demodulate Technology Of Continuous Phase Modulation

Continuous phase modulation is a kind of frequency modulation signal with constant envelope and continuous phase.Because of its high spectrum efficiency and the strong ability of anti-interference,it is an effective way to solve the resource shortage of frequency band.However,the modulation parameters of CPM signals are numerous which makes the modulation complexity increase and restricts the development of CPM.Therefore,it is significant to study the synchronization and demodulation algorithms of this modulation mode.Firstly,according to the signal mathematical model the advantages of CPM and the influence of the modulation parameters are analyzed respectively in time domain and frequency domain.These analysis set the basement for the following research on the synchronization and demodulation technology.Secondly,the synchronization algorithm including timing synchronization,carrier frequency synchronization and carrier phase synchronization is studied.Among them the NDA feed-forward timing synchronization based on maximum likelihood theory and the recursive NDA algorithm are deeply studied,and the performance of the algorithm is analyzed in detail.In the aspect of carrier frequency synchronization,this paper presents an improved algorithm based on the analysis of the delay-and-multiply frequency offset estimation algorithm.Compared with the original algorithm,the improved method not only applies to partial response CPM signal but also improves the performance by about 4d B.The research of phase synchronization algorithm focuses on the 2P-Power algorithm,and also gives a detailed analysis of the performance through theoretical simulation.Finally,the demodulation algorithm of CPM signal is studied,and the BER performance and the difference of each algorithm is analyzed in detail.Among them,the differential detection and the discriminator detection which belong to non-coherent detection is simple in structure and easy to implement,but their BER performance is worse than coherent detection,therefore they are better suited for high SNR channels.In the aspect of coherent detection,this paper studies the maximum likelihood receiver,the Viterbi demodulation and the demodulation algorithm based on PAM decomposition.The maximum likelihood receiver is the optimal Receiver,but much complicated.The Viterbi algorithm reduces the complexity of the maximum likelihood algorithm by preserving the survivor path,but its computation exponentially increase with minor modulation index.Therefore an improved algorithm of Viterbi is proposed in this paper which reduces the computational complexity to original 1/2 with little sacrifice on performance.When studying the optimal and suboptimal receivers based on PAM decomposition we compared the performance between these two algorithm and the maximum likelihood receiver.The demodulation algorithm based on PAM decomposition greatly reduces the complexity of the receiver,and the performance has no loss.