| The rapid development of information technology has provided strong support for military warfare,and communication countermeasures have gradually become one of the most important means of modern electronic warfare,so its development is extremely important.In order to win an electronic war,effective jamming of communication systems has become crucial,it is of great practical importance to study the jamming effectiveness of communication systems.The minimum frequency shift keying(MSK)modulation is widely used in military communications because of its constant envelope,high spectral efficiency and high antiinterference ability.Based on communication reconnaissance,with the ultimate research goal of evaluating the jamming effectiveness of MSK coherent demodulation systems,this thesis focuses on three aspects.The first is an analysis of the jamming effectiveness of MSK coherent reception under conventional jamming.The second is the analysis of jamming effectiveness under ideal correlated jamming.And the third is the analysis of jamming effectiveness under non-ideal correlated jamming.In this thesis,correlated jamming means that the jammer has already obtained part of the key information of the communication system by means of communication reconnaissance,and sends jamming signals with modulation scheme similar to the communication link,and does not specifically refer to the jamming modulation scheme identical to the communication link.The detailed research is carried out in the following three aspects.Firstly,for the conventional jamming of MSK coherent demodulation system,the jamming effectiveness of noise amplitude modulation interference,noise frequency modulation interference and single tone jamming on the communication system is studied.Noise amplitude modulation interference and noise frequency modulation interference are analyzed theoretically to study the jamming effectiveness of the interference at different frequencies and bandwidths.In particular,the jamming effectiveness of single-tone jamming is analyzed,the theoretical bit error rare(BER)of MSK system under single-tone jamming is derived,and the effect of frequency as well as phase variation of single-tone jamming is also studied in depth.The analysis shows that the optimal jamming frequency for single-tone jamming is not a fixed value,and the appropriate jamming frequency should be selected according to the signal-to-noise ratio(SNR)of the communication signal to achieve more efficient jamming.The phase change of single-tone jamming also effect the jamming effectiveness,and the power of the jamming should be increased appropriately in order to effectively the communication system at some special phase.Secondly,for the correlated jamming of MSK coherent reception,the jamming effectiveness of jammers with modulation scheme similar to the MSK link is investigated.The theoretical BERs of MSK system under binary amplitude shift keying(2ASK),binary phase shift keying(2PSK),binary frequency shift keying(2FSK)and MSK are derived respectively,and the jamming effectiveness is analyzed in detail.The analysis demonstrates that the jamming effectiveness of interference with the same modulation as the communication link is not always optimal,and a suitable jamming style should be selected according to the SNR of the transmitted signal.Finally,for the non-ideal MSK correlated jamming,the jamming effectiveness of the MSK coherent reception is investigated when there are frequency difference,phase difference and time delay difference between the jamming signal and the communication signal respectively.The minimum value of BER in these three non-ideal situations is derived and analyzed,and the jammer should adjust the power of the jamming signal appropriately to ensure effective jamming in some special phase difference and time delay difference. |
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