| Link-16 is an anti-jamming and high-security datalink system based on time division multiple access.Synchronization is one of the critical technologies of Link-16 datalink communication waveform.Excessive synchronization errors will lead to deterioration of system transmission performance and seriously affect the information interaction capability of Link-16.Therefore,designing an efficient synchronization algorithm to enhance the reliability of waveform synchronization in complex electromagnetic environments is an important part of Link-16 datalink technology research.Based on the Link-16 datalink specification,this thesis studies its frame and carrier synchronization algorithm.The main contents are as follows:The first part introduces the features of Link-16 system and analyzes the waveform synchronization requirements.Firstly,the link structure,transmission format,transmission waveform,and other characteristics of Link-16 are introduced,and then the channel and jamming models targeted by this thesis' s research are given.Finally,the synchronization requirements of Link-16 and the construction method of the synchronization header are explained.The second part studies the Link-16 waveform frame synchronization technology.Firstly,the classical sequence correlation synchronization algorithm and the synchronization method of the frequency hopping system are introduced.Several commonly used accumulation algorithms are discussed,including coherent accumulation,non-coherent accumulation,and differential accumulation algorithms,and the detection decision strategy is described.On this basis,according to the characteristics of Link-16 as a direct sequence spread spectrum and frequency hopping hybrid spread spectrum system,the frequency hopping pattern of the sync header is studied,and a Link-16 frame synchronization algorithm based on matched filtering is designed,including two steps of coarse synchronization and fine synchronization.The algorithm has a strong antijamming ability and fast synchronization speed by receiving the synchronization heads in multiple frequency points.It processes the synchronization heads using incoherent accumulation after delay,removes the influence of phase information,and improves the correlation peak.Finally,the improved P Q method or the maximum value method is used to make a decision,which improves the reliability of synchronization.The simulation results in different scenarios show that: under the Gaussian channel,the success rate of the frame synchronization algorithm is close to 100% when the Signal to Noise Ratio(SNR)is greater than-7d B;under the single-path Rice fading channel,when the maximum Doppler frequency shift is 4k Hz,the synchronization performance loses1?2d B compared with that of Gaussian channel,and it has a strong anti-fading ability;under suppression jamming,by adding jamming detection and suppression before synchronization,the synchronization performance between high Jamming-to-Signal Ratio(JSR)and no jamming is different by 1?3d B.The third part studies the Link-16 carrier synchronization technology.Firstly,the theoretical performance bound of the carrier synchronization algorithm is introduced,and Mean Square Error(MSE)and Modified Cramer-Rao Bound(MCRB)are given as the standard to measure the merits of the algorithm.Then the typical frequency estimation algorithms are compared and studied.The simulation results show that: when the frequency offset is small,the Fitz or L?R algorithm can be selected;when the frequency offset is large,the M?M algorithm can be selected,but it is not suitable for low SNR.In order to adapt to low SNR and large frequency offset environment under high dynamics,the F?F algorithm is proposed by combining the FFT algorithm and Fitz algorithm.The simulation results show that the SNR threshold of the F?F algorithm is 5d B lower than that of the M?M algorithm,and the estimation range is large.Under the Gaussian channel,after the large frequency offset of the system is estimated and compensated by the F?F algorithm,its bit error rate performance is close to that of ideal synchronization.Next,the thesis conducts a comparative study on data-aided and non-data-aided phase estimation algorithms.Through simulation and analysis,the data-aided algorithm with MSE close to MCRB and with a larger estimation range is selected as the phase synchronization algorithm for Link-16 waveform.The pilot sequence is added as auxiliary data in the silent period of Link-16 pulse.Under the Gaussian channel,the bit error rate performance of the system after phase estimation and compensation is about1 d B worse than that of ideal synchronization. |
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