Research On Differential Chaotic Shift Keying System Based On Non-Orthogonal Modulation

As more and more terminal devices are connected to the Internet,the frequency spectrum efficiency and real-time requirement of communication system are improved.Meanwhile,faced with the access of a large number of terminals,communication networks begin to carry more privacy information,and the problem of user information confidentiality becomes increasingly prominent.Therefore,it is of great practical significance to research a communication system with high spectral efficiency,good confidentiality and strong real-time performance.Chaotic communication system is widely considered as one of the competitive technologies in secure communication system because of its simple implementation and good security performance.As a classical chaotic security system,Differential Chaos Shift Keying(DCSK)has the advantages of strong robustness,simple implementation and no need for chaos synchronization.As a result,it has a good application prospect.However,there are obvious drawbacks in DCSK system,such as low energy efficiency and low spectral efficiency,indicating that the application scope of DCSK system in today’s communication scene is very limited.Therefore,a multi-carrier chaotic communication system with high spectral efficiency is proposed in this thesis,which is called the Non-Orthogonal DCSK(NO-DCSK)system,and in-depth theoretical research and simulation verification are carried out for this system.The main work of this thesis is as follows:(1)The modulation and demodulation principle of NO system is described in detail.In addition,two notations that may constitute NO symbols are simulated in Additive White Gaussian Noise(AWGN)channel and multi-path Rayleigh fading channel.The results show that the NO system has better Bit Error Rate(BER)performance when the symbols are formed by the intra-group frequency division.(2)NO-DCSK system is proposed in this thesis to improve the spectral efficiency of the existing Multi-Carrier DCSK(MC-DCSK)system.Its technical characteristics are that the subcarriers in the time domain are superimposed after pre-defined delayed to form system symbols.The multi-carrier characteristic enables a chaotic reference sequence to be shared by multiple information data,which improves the energy efficiency of the DCSK system.In the frequency domain,each subchannel overlaps and the frequency interval is less than the reciprocal of the subcarrier duration(or even 0),which makes the subcarrier break through the orthogonal constraint and greatly improves the spectral efficiency of the system.Because each subchannel in frequency domain is not orthogonal,the method of solving linear equations is used to demodulate in this system.In this thesis the BER expression of NO-DCSK system in AWGN channel is derived,and the factors affecting BER performance of NO-DCSK system in AWGN channel and multipath Rayleigh fading channel are studied.The simulation results agree well with the theoretical derivation in this thesis.Meanwhile,the performance comparison with Multi-Carrier DCSK(MC-DCSK)system proves the superiority of the proposed system.(3)In order to adapt to the development trend of increasing multi-user communication scenarios,based on NO-DCSK system,a multi-user NO-DCSK(MU NO-DCSK)system with multiple access function based on carrier non-orthogonal modulation technology is proposed.To achieve multiple access,each user uses an unrelated chaotic reference sequence to reduce the destructive effects of multiple access interference.The ill-conditioned matrix of the system is analyzed theoretically and the BER performance of the system is improved by using wavelet preprocessing.Secondly,the improvement of energy efficiency and spectral efficiency of the system compared with traditional chaos technology is analyzed theoretically.Finally,various parameters affecting BER performance of the system are simulated in AWGN and multipath Rayleigh fading channel.Compared with MU MC-DCSK system,the simulation results show that MU NO-DCSK has better anti-noise performance and anti-multipath fading performance,which reflects the superiority of MU NO-DCSK system.