Research On CPM Signal Demodulation Algorithm

As the rapid development of wireless communication has caused an increasingly scarcity of spectrum resources,people have begun to realize the importance of wireless spectrum resources.Continuous Phase Modulation(CPM)is a constant envelope modulation with continuous phase,which has attracted much attention due to its high frequency spectrum and power utilization.However,the excellent characteristics of CPM signals come at the cost of high-complexity receivers,which is the main reason why CPM signals have not been widely used.This article mainly focuses on the demodulation algorithm of CPM signals,and the main work and innovation points are as follows:The modulation parameters of CPM signal are estimated,which is the basis of correct demodulation of CPM signal.The main modulation parameters are modulation index,modulation order and association length,etc.In order to solve the problem that the association length estimation algorithm based on autocorrelation is greatly affected by the SNR,the performance of association length estimation is improved by changing the threshold according to different SNR.The simulation results show that the correct recognition rate of the optimized association length estimation algorithm is greatly improved.A synchronization parameter estimation algorithm based on burst signal detection is proposed for CPM signal synchronization.The algorithm uses the related results generated during burst signal detection to directly estimate the frequency offset and timing deviation,thus greatly reducing the complexity of the algorithm.The simulation results show that the frequency offset estimation algorithm has the same accuracy as the Fitz and L&R algorithms and approximates the modified Cramero bound(MCRB).The timing estimation algorithm is not only more accurate than the traditional methods,but also has better anti-frequency offset ability.After completing the synchronization of CPM signals,the demodulation algorithm based on Laurent decomposition and the iterative decoding algorithm are used to demodulate the CPM signals and Serially Concatenated CPM(SCCPM)signals respectively.Offset-quadrature phase shift keying(OQPSK)demodulation algorithm is studied and implemented on FPGA.The phase of the QOSPK signal after the forming pulse also has continuity,so it can be regarded as a special CPM signal.The synchronization parameter estimation of OQPSK is similar to the general CPM mentioned above,except that its burst signal detection adopts a segment correlation algorithm with lower complexity.When the number of segments of the segment correlation algorithm is selected appropriately,the accuracy of the frequency offset estimation algorithm is close to that of the Fitz and L&R algorithms,and it has a wider range of frequency offset estimation.In addition,the timing estimation algorithm has the advantages of high accuracy,not being affected by the rolling factor and resisting frequency offset.In order to improve the demodulation performance of OQPSK signal,the phase-locked synchronization module is added after completing the estimation of synchronization parameters.After the simulation and verification of the OQPSK signal demodulation algorithm,the FPGA hardware circuit design and debugging of the algorithm are finally implemented on Xilinx Vivado2018 platform.