Designof High-Frequency Spread Spectrum Communication System Based On SOPC

In comparison with the conventional communication system, the spreadspectrum communication system has strong capacities of resisting human disturbance,resisting narrowband interference and resisting multipath interference, with thecharacteristics of information hiding and multiple access secure communication.Under the inevitable development trend of digitization, integration and totalization ofthe civil air defense communication system, the spread spectrum communicationsystem can enhance the anti-interference ability, confidentiality, reliability andimperceptibility of civil air defense alarm communication, which has an epoch-making significance for the development of urban civil air defense alarmcommunication system.The paper focuses on the modulation and demodulation of digital DS-BPSKtransceiver, studies the SOPC technology based Nios II soft-core processor, andanalyzes the development demand of modern civil air defense alarm system.According to the design requirements of highly dynamic wireless communicationenvironment and embedded Nios II processors, it makes an in-depth study andanalysis on the principles and methods of signal modulation, despreading anddemodulation in the DSSS communication system, the key technologies of wirelessRF analog front end, and the design and development of embedded SOPC system.This paper adopts the program that the DSP processor or spread spectrum chip isreplaced by the large-scale FPGA and soft-core Nios II microprocessor, designs theDS-BPSK high-frequency spread spectrum communication system based on SOPC,and completes the designs for spread spectrum and modulation of digital signals, fastacquisition and tracking of spread spectrum codes, timing acquisition of carriers, datademodulation and other digital modules. Among them, the acquisition of spreadspectrum codes is realized by adopting sliding correlation acquisition methods,which meet the requirements for speed and logic resources; The non-coherent delay- locked loops are used to achieve the synchronous tracking function of spreadingcodes, which can improve the synchronous and accurate tracking performance of PNcode tracking circuits in a complex electromagnetic environment; The Costas loopmethod is used to demodulate BPSK signals, which further saves the FPGAprogrammable logic resources. Meanwhile, design high-performance digital-to-analog and analog-to-digital conversion circuits and wireless transceiver analogfront-end critical circuits in accordance with the civil air defense alarmcommunication system requirements. Soft-core Nios II processors which can be cut,are embedded in FPGA of Cyclone IV series, and an embedded SOPC system isconstructed, and the application softwares of spread spectrum communication systemare designed. The theoretical analysis and simulation verification for the system isperformed in this paper, and finally the program is realized in SOPC.The high-frequency spread spectrum communication system based on SOPC notonly has the characteristics of low power consumption and easy system upgrade, butalso can improve the communication capability of the civil air defense alarm system,and enhance the reliability, anti-interference ability and confidentiality ofcommunication system, which also has certain applicative value for the developmentof modern civil air defense alarm communication system.