Design And Performance Analysis Of Multiple-Access DCSK Communication System Based On Carrier Index Modulation

Chaotic signal is easy to generate and has good autocorrelation and cross-correlation characteristics.Besides,chaotic systems are very sensitive to initial values,and thus it is easy to obtain a large number of orthogonal chaotic spread spectrum codes suitable for multi-user systems.This makes chaotic signal a very competitive candidate carrier in spread spectrum communications.The existing carrier index differential chaos shift keying system(CI-DCSK)has some disadvantages,such as high rate of iddle carriers,low energy efficiency and spectrum efficiency,etc.For this reason,three schemes of multi-user carrier index differential chaotic shift keying systems are proposed in this paper.The main work is as follows:(1)A multi-user CI-DCSK communication system is proposed.In this system,all users share the same index subcarriers to transmit data signals for higher spectral efficiency.To reduce inter-user interferences,each user transmits a unique chaotic signal as the reference signal on its own private subcarrier.The spectrum efficiency,energy efficiency and complexity of the proposed system are discussed,and the approximate theoretical bit error rate of the system in additive Gaussian white noise channel and multipath Rayleigh fading channel is analyzed.Finally,Monte carlo simulations are performed to verify the feasibility and advantages of this new scheme.Results show that the system achieves not only higher spectral efficiency but also better bit error rate performance in comparison with other multi-user schemes.(2)Since there are collisions of data signals from different users in system(1),mutual interferences between users are not eliminated completely.In order to solve the above problem,a multi-user direct spread spectrum CI-DCSK system is proposed.The system uses Walsh codes and repeated short chaotic sequences to form the reference signal for each user(i.e.,spread spectrum code)so that the reference signals of all users are strictly orthogonal.The proposed system not only avoids user interference but also reduce the noise interferences,resulting in improved bit error rate performance.Gaussian approximation method is used to analyze the theoretical bit error rate of the system under different channel conditions,and Monte carlo simulations are performed to verify the feasibility and advantages of the scheme.Theoretical and simulated results show that this new system performs better than system(1)in bit error rate.(3)To further improve the spectral and energy efficiencies of system(2),a multi-user direct spread spectrum two-channel CI-DCSK system is proposed.This system uses the chaotic reference signal and its Hilbert transform in system(1)as two carriers,which allows each user to transmit two independent CI-DCSK signals simultaneously.The bit error rate,energy efficiency,spectrum efficiency and system complexity of this new system are analyzed.Theoretical and simulated results show that the system obtains higher energy and spectral efficiencies.