The Research Of The Incoherent Chaotic Communications System In MIMO Multipath Channels

With the continuous development of wireless communication technology,the quality of communication system has been further improved.At the same time,it is becoming more and more important to improve the security and confidentiality of the information transmission.Chaotic signal is a kind of pseudo-random signal.It is non-periodic,irregular,nonconvergent but bounded and highly sensitive to initial values.Owing to these characteristics,the chaotic communication system has a wide developmental and applied prospect.Without any extra cost of signal bandwidth and transmitter power,MIMO technology can manyfold improve the communication system performance by using multi-antennas at both the transmitter and receiver.OFDM technology is a special multi-carrier communication system,in which the subcarriers are mutually orthogonal and the frequency spectrum of the sub-channels is overlapped.OFDM technology has high spectrum efficiency and strong ability to resist the wireless fading.Both MIMO technology and OFDM technology are the core technology in the field of modern wireless communication.Taking advantages of MIMO technology and OFDM technology,this paper makes some researches on the purpose of improving the bit error rate performance and transmission efficiency of the chaotic communication system.The main researches and contributions are as follows:1.We analyse the basic characteristics of the chaotic signal and the typical chaotic communication system CSK and DCSK.The traditional bit error rate formula is based on central limit theorem,which suffers from low precision when the spreading factor is low.Considering the dynamic characteristic of the chaotic signal,we deduce a more accurate analytical bit error rate expression.The results demonstrate that there is an excellent match between simulations and the bit error rate expression especially when the spreading factor is low.2.It is difficult to implement the coherent demodulation in the CSK system and the bit error rate performance of the DCSK system is not ideal under the wireless fading channel.In order to improve the capability against the fading,we design the SIMO-DCSK and MIMO-DCSK noncoherent chaotic communication systems by introducing the spatial diversity technology.The basic principle of the system is presented and the accurate analytical bit error rate expressions under AWGN channel and Rayleigh fading channel are derived.The result of simulations shows that the SIMO-DCSK and the MIMO-DCSK communication systems obtain apparent spatial diversity gain compare to the traditional DCSK communication system,and the bit error rate performance is significantly improved.3.In order to improve the bandwidth efficiency and the transmission rate of the DCSK system,a study of noncoherent chaotic communication system based on OFDM technology has been made.There is an obvious enhancement on the transmission rate when the number of subcarriers is high.Finally we make further research on the noncoherent chaotic communication system based on OFDM-MIMO technology.The accurate analytical bit error rate expressions are derived and the result of simulations demonstrates that the bit error rate performance of the system is substantially improved.