Research On Code Index Modulation Technology Based On Chaotic Sequence

Following the large-scale commercial and civilian use of 5G technology,today’s society has entered a high-speed and high-capacity communication era.In order to further alleviate the contradiction between the increasing traffic demand and the shortage of spectrum resources,it is necessary to explore a high spectrum efficient information transmission method.Code Index Modulation(CIM)is based on direct sequence spread spectrum technology.Each transmission time slot is divided into modulation bits and mapping bits,which are mapped into modulation symbols and the indexes of spread spectrum codes respectively.Using the index,the respective spread spectrum codes are selected for the in-phase and orthogonal components of modulation symbols to realize spread spectrum modulation.In this way,the mapping bits are transmitted implicitly in the communication link.Compared with the traditional direct spread spectrum technology,the advantage of CIM is not only high concealment,but also higher spectral efficiency.On the other hand,chaotic sequence has the advantages of no period,rich quantity,good correlation and difficult to predict.Therefore,the combination of chaos and Code Index Modulation technology is studied in order to pursue higher spectral efficiency,lower implementation cost and better secure transmission performance of communication link.The work of this paper are as follows:(1)Aiming at the problem that the behavior of traditional single scroll and double scroll chaotic systems is not complex enough,a construction method of controllable odd number multi scroll chaotic system family based on combined symbolic function is proposed.The chaotic characteristics of the system are verified by simulating and analyzing the Lyapunov exponent spectrum,power spectrum,Poincare and stability of the system;At the same time,based on the discretization method,the FPGA(Field Programmable Gate Array)design mode of odd multi scroll chaotic system family is proposed,and the hardware implementation of 3 scroll,5 scroll and 7 scroll chaotic attractors based on ZYNQ7000 development platform is given.The simulation and hardware experimental results show that the proposed controllable odd number multi scroll chaotic system family has more complex nonlinear dynamic characteristics and richer phase space trajectories,which can be used in the fields of spread spectrum communication and secure communication.(2)In order to further improve the BER performance of traditional Code Index Modulation and reduce the consumption of pseudo noise(PN)code index resources,a chaotic spread spectrum Nonorthogonal Grouping-Code Index Modulation(NG-CIM)scheme is proposed.NG-CIM divides each transmission slot into modulation block and mapping block in parallel at the transmitting end.The modulation block is mapped into multiple groups of modulation symbols after bit grouping.The mapping block selects the same PN code for the orthogonal component and in-phase component of each group of modulation symbols for direct sequence spread spectrum transmission.The simulation results show that in the Additive White Gaussian Noise channel,when the spectrum efficiency is improved by increasing the modulation orders,the BER performance of NG-CIM is about 2.5 ～ 7d B better than that of CIM;When the spectrum efficiency is improved by increasing the number of PN code,the BER performance of NG-CIM is about 2 ～ 4d B better than that of CIM,and the consumption of PN code resources is greatly reduced.(3)Based on the data link characteristics of NG-CIM technology,a secure transmission scheme of Chaotic Unite Constellation Scrambling(CUCS)is proposed by combining the pseudo randomness and long-term unpredictability of chaotic sequence.For each transmission slot,the data stream at the transmitting end is divided into modulation block and mapping block in parallel.The modulation block is divided into multiple groups of modulation bits.The chaotic sequence after quantization grouping is used to scramble the original constellation mapping matrix corresponding to each group of modulation bits,and the unite index rearrangement is carried out between the constellation mapping matrices after scrambling.The modulation block is mapped into modulation symbols according to the final transformed constellation mapping matrix;The mapping block is selected to XOR with the final transformed constellation mapping matrix.Simulation analysis shows that each transmission slot of CUCS scheme corresponds to different chaotic constellation mapping matrix.With the increase of signal-to-noise ratio,this scheme can transmit information securely and effectively improve the security of NG-CIM link without affecting the BER performance.