| Link-16 data link is an important tactical data link used for reconnaissance,command,and control,which has the advantages of real-time transmission,high security,and strong anti-jamming capabilities.However,with the changes in communication countermeasures technology and application scenarios,the traditional Link-16 data link transmission waveform faces the shortcomings of low transmission rate and performance deterioration in complex electromagnetic environments.To address these issues,this thesis investigates Link-16 enhanced transmission waveform technology from three aspects:（1）frame synchronization technology,（2）carrier synchronization technology,（3）modulation/demodulation technology.The initial section of this thesis provides an introduction to the background and significance of the chosen topic.It presents an analysis of the current research status on Link-16 data links,frame synchronization algorithms,carrier synchronization algorithms,and Continuous Phase Modulation（CPM）signal modulation and demodulation technologies,both domestically and internationally.The purpose of this analysis is to introduce the research subject matter of this thesis.The second section of this thesis introduces the characteristics and key technologies of the traditional Link-16 data link transmission waveform.It also explains the direction of improvements to the traditional Link-16 data link transmission waveform.The third section of this thesis studies the key technologies of the Link-16 enhanced transmission waveform from three aspects:Firstly,this thesis investigates the enhanced frame synchronization technology for the Link-16 transmission waveform.The traditional methods for frame synchronization suffer from poor performance in complex electromagnetic environments.To address this issue,a decision scheme based on multi-channel matched filtering and interval peak detection is proposed.The scheme takes into account the specific characteristics of the Link-16 system and achieves accurate frame synchronization through multi-channel peak search and detection decision,allowing for both coarse and fine synchronization.Simulation results demonstrate that the proposed frame synchronization scheme achieves a capture success probability of over 99.9%when the signal-to-noise ratio（SNR）is greater than or equal to-10 d B.Moreover,when the relative velocity between the transmitter and receiver is 4 Mach and the carrier frequencies are 1.2 GHz,6 GHz,and18 GHz,corresponding to Doppler frequency shifts of 5.44 k Hz,27.2 k Hz,and 81.6 k Hz,respectively,the frame synchronization performance degrades by 1 d B,1.5 d B,and 2.5d B.In the presence of interference signals in both additive white Gaussian noise（AWGN）and fading channels,the proposed scheme can effectively suppress interference and maintain a frame synchronization performance degradation of less than 1.5 d B.Next,this thesis investigates the key technology of the Link-16 enhanced transmission waveform in terms of carrier synchronization.To address the problem of existing carrier synchronization schemes,which cannot simultaneously achieve estimation range and accuracy,this thesis proposes an improved carrier synchronization scheme suitable for the enhanced waveform.The scheme combines both time-domain and frequency-domain carrier synchronization algorithms.Firstly,the scheme estimates the frequency offset roughly through an Auto Correlation DFT（AC-DFT）algorithm in the frequency domain.Then,the scheme uses a Cross Correlation（CC）algorithm in the time domain to estimate the frequency offset accurately after carrier recovery.Simulation results show that under the AWGN channel condition with a frequency offset range of（-0.5f s,0.5fs）Hz,the Mean Square Error（MSE）of the proposed scheme can reach the order of10-9.Additionally,in the fading channel environment compared to directly cascading the frequency-domain and time-domain schemes,the MSE of the proposed scheme drops from the order of10-8to10-12.In the presence of interfering signals in the fading channel,after suppressing interference,the MSE of the frequency offset estimation can reach the order of10-6when the SNR is greater than or equal to-2d B.This thesis further investigates the enhanced modulation and demodulation technology for the Link-16 data link transmission waveform.To improve the transmission rate of the Link-16 link,this thesis introduces 4CPM non-spread spectrum waveform into the Link-16 transmission waveform.At the receiver,different demodulation methods are adopted for different waveforms:for spread spectrum waveforms,a soft-decision spread-spectrum demodulation scheme is used;for 4CPM modulation non-spread spectrum waveforms,a soft output Viterbi algorithm（SOVA）demodulation is used;for Minimum Shift Keying（MSK）modulation non-spread spectrum waveforms,SOVA algorithm and multi-symbol non-coherent soft-decision algorithms are used based on whether accurate carrier estimation can be achieved.Simulation results show that the performance of the multi-symbol non-coherent demodulation scheme is 1.3 d B worse than that of the SOVA algorithm.However,the multi-symbol non-coherent demodulation scheme is insensitive to frequency offset.Under fading channels with Doppler frequency shifts of 5.44 k Hz and27.2 k Hz,the performance of the multi-symbol non-coherent demodulation scheme is improved by 1.4 d B and 14 d B compared to the SOVA algorithm.The fourth part of this thesis designs the Link-16 datalink enhanced transmission waveform based on the three key technologies studied.This thesis first describes the system link structure of the Link-16 data link enhanced transmission waveform,then presents the parameter design of the Link-16 data link enhanced transmission waveform,and then simulates and analyzes the frame synchronization performance,carrier synchronization performance,and link error performance of the Link-16 data link enhanced transmission waveform.Finally,this thesis summarizes the performance of the Link-16 data link enhanced transmission waveform under different communication scenarios.The simulation results show that the BER performance of the enhanced link has a gain of more than 5d B compared with the conventional Link-16 system.In the fourth part of this thesis,the Link-16 data link enhanced transmission waveform is designed based on the three key technologies studied.This thesis first describes the structure of the Link-16 data link enhanced transmission waveform,summarizes and analyzes the frame synchronization performance and carrier synchronization performance of the Link-16 data link enhanced transmission waveform,and then simulates the performance of the Link-16 data link enhanced transmission waveform in different communication scenarios.Simulation results show that the enhanced waveform has a gain of more than 5 d B in error performance compared to the traditional Link-16 waveform.In addition,the maximum transmission data rate of the enhanced waveform is increased from 115.2 kbps to 2016.512kbps. |
