Realization Of Logical Circuit Of Spread Specturm Communication System

According to theoretical research and practice,spread spectrum communication is a communication technology with superior performance,because it has the advantages of low signal-to-noise ratio,low interception rate,strong confidentiality,anti-interference and anti-fading ability.In the past,it was mainly used in military systems.In recent years,spread spectrum technology has also been involved in civilian fields,such as video surveillance,mobile communications,and remote sensing.However,with the development of science and technology,the bandwidth of data signal processing is increasing day by day.People put forward higher requirements on the real-time performance of the algorithm.Under the real-time requirement that the DSP can not meet the processing of the algorithm,there is an urgent need for a large throughput algorithm.Firstly,based on a Field Programmable Gate Array(FPGA),the direct spread spectrum spread spectrum communication algorithm is implemented by logic circuit.In the design,the whole spread spectrum algorithm is first divided according to the direction of the data stream.,respectively,a sync head generator module,a Hamming coding module,a spreader module,an m-sequence synchronizer module,a despreader module,and a Hamming decoding module.After completing the RTL(Register Transfer Level)design of each logic module,each module is simulated by logic function.Finally,the logical top layer of the logic algorithm is built,and finally the bit file is generated and burned into the test algorithm of the device,thus can test the algorithm.Secondly,the design also includes the logic circuit implementation of the improved modulation and demodulation algorithm pi/8DPSK(Differential Phase Shift Keying).Compared with the conventional PSK modulation,pi/8DPSK reduces the phase abrupt amount,making the modulated signal higher.The frequency band utilization,and since the modulation method is generated using differential phase encoding,the advantage of differential demodulation can be fully utilized at the receiving end.The pi/8DPSK uses non-coherent demodulation,and the coherent demodulation can't adapt to the scene where the carrier changes rapidly.Therefore,pi/8DPSK is very practical in the signal environment with fast carrier frequency or phase change.The design uses matlab as an auxiliary tool to design the filter and the local oscillator generator DDS(Direct Digital Synthesizer)required in the modulation and demodulation logic circuit,and generate the simulation excitation for the logic circuit verification,and analyze the demodulation and despreading algorithm output in the logic design.Finally,the design uses the loopback test method to verify the correctness of the logic algorithm.The input 10 MHz signal is sent by the signal source,and is collected by the ADC(Analog-to-Digital Converter)into the FPGA device,respectively,through the spread spectrum,modulation algorithm,and write After entering the DDR(Double Data Rate SDRAM)buffer on the board,the data is read out,and then demodulated and despreaded,sent to the DAC(Digital to analog converter),and then displayed by the oscilloscope after processing by the algorithm.Whether the signal can be normally restored to the signal of the source of the transmitting end,the algorithm completes the layout and wiring in the logic device XC7K325 T of XILINX Company,solves the related timing problem,and enables the host computer to perform parameter configuration on the relevant device,and then verify the point of the signal source.After the frequency signal is collected by the ADC,the data is processed by the spread spectrum module and the modulation module of the transmitting end and the demodulation and despreading module of the receiving end,and finally the data is returned to the oscilloscope through the DAC,and the oscilloscope can normally recover the signal from the source of the transmitting end,and the eye pattern is very clear and the frequency is almost frequency-free.