Research On Reference Removal Technology Of Code Shifted Differential Chaos Shift Keying Communication System

Reference signals that carry no data bits are transmitted in Code Shifted Differential Chaos Shift Keying(CS-DCSK)communication system,which seriously affects the energy efficiency.Besides,the attainable data rate is relatively low as only one data bit is transmitted during one symbol duration.In order to solve these problems,three CS-DCSK-based schemes which avoid the transmission of reference signals are proposed in this thesis.The main innovations and contributions of this thesis are as follows:(1)Based on the CS-DCSK system,the reference signal is removed,and two separate information signals are transmitted instead.These two signals are generated by weighting two different Walsh code sequences on the chaotic sequence.Indices of different Walsh code sequences are determined by different index bits.In addition,the second information signal also carries an extra modulated bit.Since these two information signals are coupled by using the same chaotic message bearer,data bits can be easily recovered according to the correlation of these two signals,and thus the transmission of reference signals can be completely avoided.Theoretical bit error rate(BER)expressions are derived over the additive white Gaussian noise and multipath Rayleigh fading channels.Furthermore,theoretical analysis and Monte Carlo simulations indicate that the proposed system can achieve better BER performance with lower complexity.The data show that the BER performance of the new system is 2d B better than that of the same type of system when the number of bits transmitted in a symbol period is the same.(2)Based on the scheme in(1),the binary DCSK modulation is extended to the M-ary DCSK modulation.The two orthogonal basis functions in M-ary DCSK modulation are generated by weighting the chaotic sequence with two second-order Walsh code sequences.The proposed system obtains a higher energy efficiency and data rate as more data bits are transmitted during one symbol duration with no increase in energy consuming.Theoretical BER expressions are derived,and factors that affect the BER performance are also analyzed by Monte Carlo simulations.Compared to the scheme in(1),the BER performance of the new system has the advantage of 1d B when the order of Walsh code is the same.(3)Based on the scheme in(1),the number of information signals that are transmitted in a symbol duration is extended from two to M.Each information signal is generated by weighting the chaotic sequence with different Walsh code sequences determined by index bits.Except the first one,almost every information signal also carries an additional modulated bit.Not only the utilization of the Walsh code matrix is maximized but also the data rate is improved greatly.Theoretical BER expressions are derived,and simulated BER performances are compared with other CS-DCSK-based modulation systems.Results show that not only the data rate of the new system is improved but also the BER performance of the system is enhanced.