改进型时间反转的多用户DCSK系统

Improved time reversal multi-user DCSK system

针对基于时间反转的多用户差分混沌移位键控系统误码率较大和传输速率较低的问题,提出了改进型时间反转的多用户DCSK系统,来提升系统的误码性能和信息传输速率。在发送端,混沌信号通过延迟和时间反转两种结构,传输两路参考信号。每一路信号利用正交沃尔什码组同时承载N个用户信息来达到提高传输速率和消除用户间干扰、降低误码率的目的;在接收端,利用滑动平均滤波器对参考信号做降噪处理,降低判决项方差来减小系统误码率,再进行相关解调。推导了系统误码率公式,并在加性高斯白噪声信道和多径瑞利衰落信道下进行了性能仿真分析。分析了用户数N、复制次数P、序列长度β、信噪比E_(b)/N_(0)和路径数L对系统误码率的影响,并与基于时间反转的多用户差分混沌移位键控系统的误码率进行比较。结果表明,在加性高斯白噪声信道中,当用户数为2、复制次数为8、β为512时,相较于基于时间反转的多用户差分混沌移位键控系统,该系统传输速率提升了约300%,误码性能提升近3 dB。这为该系统在实际工程应用提供了良好的理论意义和实用价值。

To overcome the shortcomings of high bit error rate and low transmission rate in the shift differential chaos shift keying system based on time reverse,an improved time reversal multi-user DCSK system is proposed to improve the system BER performance and transmission rate.At the transmitter,the chaotic signal generator adopts delaying and time reversing structures to send two orthogonal reference signals.Different orthogonal Walsh codes are used to bear users’information simultaneously to increase the transmission rate and eliminate the interference between the users,thus reducing the error rate.At the receiver,the reference signal is denoised by moving the average filter,the variance of the decision term is reduced to reduce the bit error rate of the system,and then the correlation demodulation is carried out.The new BER formula is deduced and simulated under the additive white Gaussian noise channel and the multi-path Rayleigh fading channel.The influences of the number of users N,the number of copies P,the sequence length,the SNR and the path number L on BER are analyzed.Compared with BER of the TRM-DCSK system,it is shown that in the AWGN channel,when the number of users is 2,the number of replications is 8,and is 512,the transmission rate of the system is increased by about 300%compared with the TRM-DCSK system,and that the error performance is improved by nearly 3dB,which provides a good theoretical significance and practical value for the practical engineering application of the system.