| With the rapid development of modern electronic technology,the typical applications in military and civil fields,such as satellite communication system,intelligent transportation system,earth and earth integration system,military electronic integrated system,etc.,are constantly putting forward new technical requirements.In these complex systems,there are a large number of multi-party cooperation scenarios,and the characteristics of resource use are developing in the direction of decentralization,sharing and intelligence.Among them,the radar communication integration scheme is an important technical means for efficient cooperative work of complex systems,but the problem of radar communication signal sharing and synchronization of the receiving system is still to be solved.Therefore,this paper takes LFM-CPM signal,which has been widely studied and discussed in recent years,as the radar communication shared signal,and focuses on the study of synchronization technology in signal processing.The main work done is as follows:First of all,the basic model of LFM-CPM signal is introduced.Its essence is based on linear frequency modulation signal,through continuous phase modulation technology to realize the loading of communication information,construction of integrated signal with both detection and communication functions,and analysis of the designed signal in the time domain and frequency domain characteristics,it has the characteristics of constant envelope and continuous phase,both communication and detection functions.Secondly,aiming at timing synchronization problem of integrated signal demodulation at communication receiver,a data-assisted matching correlation timing synchronization algorithm and a non-data-assisted fractional Fourier transform timing synchronization algorithm are proposed.Simulation results show that the proposed algorithm can realize timing synchronization of received signals with high accuracy under low computational complexity（log）.The accuracy of the former can reach more than 10-5at-15d B,and the accuracy of the latter can be stable at 10-4after-10d B.Then,the frequency synchronization problem of the integrated signal during demodulation at the receiving end of communication is studied.By analyzing the causes of frequency mismatch,a theoretical model of the first order frequency offset and the second order frequency offset is established.According to this characteristic,an improved iterative Fitz algorithm is proposed to make it suitable for the multi-parameter estimation scene of the integrated signal.At the same time,a frequency synchronization algorithm based on double pilot is proposed by using special frame structure design.Through simulation verification,both of them can realize frequency synchronization of received signals within the range of?∈-3KHz,3KHz and?∈-2 MHz s,2 MHz s.The frequency synchronization algorithm based on double pilot is simple in structure,easy in hardware implementation,and the synchronization accuracy is always more than 2 orders of magnitude ahead of the cyclic iterative Fitz algorithm under the condition of bad signal-to-noise ratio.Then,the phase synchronization technology of the integrated signal during demodulation at the communication receiver is studied.On the one hand,the maximum likelihood phase synchronization algorithm based on PAM decomposition is analyzed from the perspective of CPM modulation signal.On the other hand,the phase synchronization algorithm based on pilot sequence is proposed based on the good autocorrelation of the integrated signal.But at the same time,it is very dependent on the branch metric information of the data in the process of Viterbi decoding,and the estimated range is only-π2,π2,while the phase synchronization algorithm based on the pilot sequence can complete the phase bias estimation,which has a larger estimation range-π,π,and can be used for module reuse with the double pilot frequency synchronization algorithm,saving receiver design resources.Finally,a time-frequency-phase synchronization algorithm for the integrated signal of LFM-CPM radar communication is proposed.Simulation results show that the proposed algorithm can effectively reduce the bit error rate of the integrated signal receiving and demodulation.At the same time,the effectiveness and engineering of the proposed algorithm is verified by a semi-physical simulation platform built by software-defined radio equipment.The average bit error rate of the actual channel in the laboratory is 1.98×10-4,which lays a foundation for further optimization of the algorithm and hardware implementation. |
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