Research On Digital Modulation Technology Based On Chaos Keying And Its FPGA Implementation

As mankind fully enters the information age,communication technology has been fully integrated with all aspects of people's life,work and society.In this era of rapid social and economic development,and constant innovation and progress in science and technology,people are facing greater and greater hidden dangers in information security,which has led to the rapid development of communication technology security research.With its natural and outstanding characteristics,chaotic systems have become the darlings of confidential communication technology,and chaotic modulation communication technology has emerged as the times require.Faced with huge future business traffic and a large number of device accesses,it has become an urgent issue to improve the spectrum utilization of chaotic modulation technology to meet the increasingly scarce spectrum resources.Orthogonal Frequency Division Multiplexing(OFDM)has the advantage of being close to the ideal frequency band utilization.Therefore,the optimization of chaotic modulation technology using OFDM technology has become a research hotspot at this stage.Therefore,this paper studies the problem of low spectrum utilization of chaotic keying digital modulation technology,and uses FPGA to implement its key technology.The main findings are as follows:(1)Aiming at the problem of low spectrum utilization of traditional chaotic digital modulation technology,a new OFDM differential chaotic keying(OFDM-DCSK)system design scheme is proposed.The transmitted signal is DCSK-modulated and cascaded with the OFDM system to achieve multi-carrier modulation.A new type of Quadrature Amplitude Modulation(QAM)mapping is proposed to optimize the constellation diagram to ensure that the minimum Euclidean distance and minimum phase interval of the system are approximately unchanged,and the Peak-to-Average Power Ratio of the system is reduced.The simulation results show that under the same transmission conditions,the OFDM-DCSK system has extremely high frequency band utilization and Bit Error Rate performance advantages compared to the traditional DCSK system,and the design scheme has lower requirements for the length of the chaotic reference sequence,which improves Transmission rate of chaotic symbols.(2)Aiming at the problem of low information transmission rate of the OFDM-DCSK system,an High Efficient OFDM-DCSK(HE-OFDM-DCSK)system design scheme based on orthogonal coding technology is proposed.The system uses an orthogonal coding frame structure to increase the amount of information carried,and the new QAM mapping can increase the information transmission rate multiple times under the premise that the Bit Error Rate performance is approximately constant.The simulation results show that the information transmission rate of the HE-OFDM-DCSK system using the new QAM is nearly four times that of the OFDM-DCSK system,but the Bit Error Rate performance of the two is not much different.(3)Aiming at the problems of using FPGA to implement chaotic systems,the lack of precision of some chaotic systems,and inefficient development,a general design scheme for chaotic systems based on FPGA is proposed.This scheme not only has the advantages of high accuracy,easy error correction,and anti-chaos degradation,but also is compatible with all chaotic systems.This paper uses this scheme to implement logical implementation of one-dimensional Logistic and three-dimensional Lorenz chaotic systems and verify their correctness on the FPGA platform.Both can work at a clock frequency of 100 Mhz,and the correct chaotic system attractor phase can be seen from the oscilloscope Illustration.For the N-point FFT/IFFT technology of the OFDM-DCSK design scheme in this paper,a floatingpoint base-2 FFT/IFFT design scheme for a single-stage butterfly unit multiplex structure is optimized and proposed.This solution can save N times the butterfly unit,and has the advantages of high calculation accuracy and low transformation error,etc.Relative to the fixed-point implementation.The FPGA implementation of the communication system design scheme in this paper can be applied to application scenarios such as secure communication at the physical layer of the drone,and can provide a practical hardware implementation method for various secure communication systems using chaotic signals.