Studies On Noise Reduction Methods For CI-DCSK Communication Systems

Since the carrier index differential chaos shift keying(CI-DCSK)communication system needs to transmit the reference and information-bearing signals over different subcarriers to the receiver,the received reference and informationbearing signals suffer from excessive noise interferences.This will inevitably degrade the bit error rate(BER)performance of the system seriously.To alleviate this problem in all existing CI-DCSK systems,this thesis proposes three novel CI-DCSK systems.The main work of this thesis is as follows:(1)Combining short reference modulation and carrier index modulation,a short reference carrier index differential chaotic shift keying(SR-CI-DCSK)modulation system is proposed.The energy efficiency of the proposed system is improved by shortening the length of the reference signal,and the averaging of the information signal is used to reduce the noise interference in received information-bearing signals and thus improve the BER performance of the system.A series of performance of the proposed system are analyzed.Using the theoretical analysis as a basis to compare computer simulation,the outcomes pointed out: The proposed system can achieve higher energy efficiency and BER performance with reduced system complexity.(2)Based on the system given in(1),a time-hopping short reference carrier index differential chaotic shift keying(TH SR-CI-DCSK)system is proposed,in which a PPM modulator is added to change the position of the reference signal in the reference time period.In this new system,the problem that the reference signals of the classical CI-DCSK system carry no data information is solved,meanwhile the spectrum efficiency of the system is also improved.A series of performance of the proposed system are analyzed,and comparisons are performed based on Monte Carlo simulations.Compared with the system given in(1),the new proposed system can further improve the spectrum efficiency as well as the bit transmission ratewithout affecting the original noise reduction effect.(3)A replicator and a moving average filter are added to the classical CI-DCSK system,and a noise reduction carrier index differential chaotic shift keying(NR-CI-DCSK)modulation system is proposed.In the proposed system,noises in both the received reference and information-bearing signals are reduced,which helps to improve the system's BER performance.A series of performance of the proposed system are analyzed,and Monte Carlo simulations are performed to show that this new method is effective in noise reduction.