| Scattering communication has become an important communication mode in modern wireless communication because of its advantages of long distance of transmission,high reliability,flexible communication mode and strong anti-interference ability.However,due to the existence of multipath effect and Doppler frequency shift in the scattering channel,frequency selective fading and time selective fading will be generated accordingly,so SC-FDMA technology is selected as the design scheme of scattering communication system in this paper.As a modulation scheme of LTE Uplink,SC-FDMA technology has the advantages of low PAPR and frequency domain equalization,and can realize multi-user communication scenarios by assigning subcarriers.At the same time,in multi-user communication system,preamble detection is an essential part.In the scattering communication scene with low SNR,in order to ensure good detection performance,the traditional direct correlation detection algorithm needs to consume a lot of hardware resources,which may cause chip resource overflow in the project.So it is necessary to study a low complexity and low SNR preamble detection algorithm.Therefore,the SC-FDMA baseband system is designed and implemented according to the characteristics of the scattering channel in this paper.On this basis,the preamble detection algorithm in the low SNR scene is studied and implemented.The main contents of this paper include:(1)For the current scattering channel,this paper designs the baseband parameters of the physical layer of the system,including the system bandwidth,communication mode,physical channel division and frame structure.On this basis,the processing flow of the baseband part of the uplink and downlink of the system is designed.The design principle of baseband algorithm module is analyzed,including constellation mapping,diversity and combination,subcarrier mapping,frequency offset estimation and compensation,SNR estimation,channel estimation and equalization.This paper focuses on the design method of the preamble sequence and the corresponding preamble detection algorithm.The simulation results show that when the SNR is-17d B,the false alarm probability and missed detection probability of the algorithm proposed in this paper are all below 10-4.(2)The fixed-point simulation scheme of baseband algorithm is designed in MATLAB.The simulation results show that the 9-bit quantization bit width is selected in the hardware design.At this time,the system performance is basically the same as that in the case of full precision,and the loss of signal-to-noise ratio can be ignored.Based on the theory of baseband algorithm,combined with the fixed-point simulation scheme,the hardware architecture of some modules is designed,including constellation mapping,diversity,FFT/IFFT,adding pilot,interleaving subcarrier mapping,adding CP,preamble detection,frequency offset estimation and compensation,SNR estimation,channel estimation and compensation,etc.By comparing the hardware simulation results of the algorithm module with the fixed-point simulation results in MATLAB,the correctness of the design of each algorithm hardware module is shown.(3)Combined with the current measured data of scattering channel,a single link loop simulation test scheme is designed and implemented by MATLAB and FPGA simulation tools.The simulation results show that the current SC-FDMA scattering communication system has a bit error rate of 0 when the SNR is 0 d B.According to the system architecture of DSP+FPGA,the interface protocol for data transmission between FPGA and DSP is designed,including the working mode of SRIO interface and the interaction information between FPGA and DSP.At the same time,the timing of hardware system is designed to facilitate the coordination between DSP and FPGA.Finally,the baseband part of SC-FDMA scattering communication system is realized by hardware.The results show that the current system can be used in the actual scattering communication engineering,and still has good communication performance in low SNR. |
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