GPS信号捕获

实验二GPS信号捕获一、实验目的1.熟悉GPS信号捕获基本概念；2.掌握串行搜索算法、并行频率搜索算法和并行码相位搜索捕获算法的基本思想、特点及算法流程；3.训练在实际当中分析问题、解决问题的能力。二、实验内容1.编写GPS信号捕获子程序，算法自选。2.将实验一最终生成的信号延迟时间，并加上大小为Df的多普勒频移，使用以上编写的信号捕获子程序对该信号进行捕获。3.画出三维捕获结果图（要求至少画出两幅，一幅对应信号成功捕获，一幅对应未捕获到信号）。三、实验结果成功捕获未成功捕获四、总结与反思在实验一的基础之上进行本次试验，感觉有了新的理解和领悟。但是在实验过程中还是遇到了很多的问题，通过上网搜索、询问教员、和同学探讨等方式最终做了出来。虽然程序代码多是网上搜索得来的，但在读程序的过程中还是收获一些知识。五、程序代码clearall;clc;%发射端%设置是否有信号TxCodeOnOff=1;%1-On,0-Off%设置仿真时间TxTotalTime=1e-3;%1ms%设置伪码频率TxCodeFrequency=1.023e6;%1.023MHz%设置载波频率TxCarrierFrequency=2*1.023e6;%2.046MHz%设置采样频率TxSampleFrequency=16*1.023e6;%MHz%发射端产生伪码并计算码长TxGoldSequence0=dyc_gold_gen_v3();TxGoldSequence0Len=length(TxGoldSequence0);%用载波调制TxTemp1=TxSampleFrequency/TxCodeFrequency;%将伪码序列扩展TxGoldSequence1=repmat(TxGoldSequence0,TxTemp1,1);TxGoldSequence1=reshape(TxGoldSequence1,1,TxTemp1*TxGoldSequence0Len);TxGoldSequence2=TxCodeOnOff*TxGoldSequence1;TxTiming=0:(1/TxSampleFrequency):(TxTotalTime-1/TxSampleFrequency);TxSignalSequence=sin(2*pi*TxCarrierFrequency*TxTiming+TxGoldSequence2*pi);%信道%设置多普勒频移ChDiffFrequency=-15000;%Hz%设置信噪比ChSN=-20;%dB%设置码相移ChDelayValue=800;%码片相移量ChDelay=ChDelayValue*TxTemp1;%此值为采样结果的码相移，是伪码相移的TxTemp1倍%将序列进行移位（需要先移位在加多普勒频移，否则的话移位操作会影响多普勒频移）ChGoldSequence=circshift(TxGoldSequence2,[0,ChDelay]);%生成带有多普勒频移的序列ChTiming=TxTiming;ChSignalSequence1=sin(2*pi*(TxCarrierFrequency+ChDiffFrequency)*ChTiming+ChGoldSequence*pi);%加入噪声ChSingalSequence3=awgn(ChSignalSequence1,ChSN,'measured');%(此函数还可添加更多参数)%接收端%设置频率搜索步长RxCarrierFrequencyDelta=500;%Hz%设置频率搜索范围RxDiffFrequencyMax=20*RxCarrierFrequencyDelta;%Hz%设置码相位搜索步长RxDelayDelta=10;%设采样率和码速率之比与发送端一致RxDelayRatio=TxTemp1;%设接收端采样率与发送端一致RxTiming=TxTiming;%计算接收端频率搜索次数RxFrequencySearchTimes=fix(2*RxDiffFrequencyMax/RxCarrierFrequencyDelta)+1;%(可能有误)%计算码相位搜索次数RxGoldLen=TxGoldSequence0Len;RxGoldSearchTimes=ceil(RxGoldLen/RxDelayDelta);RxSignalAmplitude=zeros(RxGoldSearchTimes,RxFrequencySearchTimes);forRxTemp11=1:RxGoldSearchTimesdisplay(['Processing...'num2str(RxTemp11/RxGoldSearchTimes*100,'%.2f')'%']);RxTemp12=RxTemp11-1;%产生接收伪码RxGoldSequence1=TxGoldSequence1;RxGoldSequence2=circshift(RxGoldSequence1,[0,RxTemp12*RxDelayDelta*RxDelayRatio]);%移动码相位RxGoldSequence3=RxGoldSequence2.*2-1;%%计算码相关RxSignalSequence1=ChSingalSequence3.*RxGoldSequence3;RxCarrierFrequency1=TxCarrierFrequency-RxDiffFrequencyMax;forRxTemp21=1:RxFrequencySearchTimesRxTemp22=RxTemp21-1;%产生接收载波RxCarrierFrequency=RxCarrierFrequency1+RxTemp22*RxCarrierFrequencyDelta;RxCarrierSequenceI=cos(2*pi*RxCarrierFrequency*RxTiming);RxCarrierSequenceQ=sin(2*pi*RxCarrierFrequency*RxTiming);%I/Q两路分别与接收载波做相关RxSignalXcorr2I=RxSignalSequence1*RxCarrierSequenceI';RxSignalXcorr2Q=RxSignalSequence1*RxCarrierSequenceQ';%幅度检波(平方相加再开根号)RxSignalAmplitude(RxTemp11,RxTemp21)=sqrt(RxSignalXcorr2I^2+RxSignalXcorr2Q^2);endend%生成坐标轴%纵坐标（行）RxLabelCode=((1:RxGoldSearchTimes)-1)*RxDelayDelta;%横坐标（列）RxLabelFrequency=((1:RxFrequencySearchTimes)-1)*RxCarrierFrequencyDelta-RxDiffFrequencyMax;%生成三维捕捉结果figure(31);mesh(RxLabelFrequency,RxLabelCode,RxSignalAmplitude);RxSignalAmplitude1=RxSignalAmplitude(:);%(将结果转化为一维向量便于后续计算)%计算捕捉到的最大幅度RxSignalResMax=max(RxSignalAmplitude1);%计算捕捉结果的平均幅度RxSignalResAverage=mean(RxSignalAmplitude1);%RxSignalResDeviation=std(RxSignalAmplitude1);%判断是否捕获%设置门限RxCatchThreshold=RxSignalResAverage+5*RxSignalResDeviation;%ifRxSignalResMaxRxCatchThreshold%捕获成功display('Success!!!');%查找最大值对应的坐标[RxResRowRxResColumn]=find(RxSignalAmplitude==RxSignalResMax);%(此方法仅限二位数组)display(['DopplerFrequency:'num2str(RxLabelFrequency(RxResColumn),'%.0f')'Hz']);display(['CodePhase:'num2str(RxLabelCode(RxResRow),'%.0f')]);else%捕获失败display('Fail!!!');End附录Bfunction[GoldSeq]=dyc_gold_gen_v3()M_base=8;M1=[2011];M2=[2415];Mfb_len=11;Mfinal_len=1023;M1origin_len=length(M1);M2origin_len=length(M2);Mfb_ratio=log2(M_base);M1fb_raw_len=M1origin_len*Mfb_ratio;M1fb_raw=zeros(1,M1fb_raw_len);forM1fb_reg_i=1:M1origin_lenforM1fb_bit_i=1:Mfb_ratioM1fb_raw((M1fb_reg_i-1)*Mfb_ratio+M1fb_bit_i)=mod(fix(M1(M1fb_reg_i)/(2^(Mfb_ratio-M1fb_bit_i))),2);endendM1fb=M1fb_raw((M1fb_raw_len-Mfb_len+1):M1fb_raw_len);M2fb_raw_len=M2origin_len*Mfb_ratio;M2fb_raw=zeros(1,M2fb_raw_len);forM2fb_reg_i=1:M2origin_lenforM2fb_bit_i=1:Mfb_ratioM2fb_raw((M2fb_reg_i-1)*Mfb_ratio+M2fb_bit_i)=mod(fix(M2(M2fb_reg_i)/(2^(Mfb_ratio-M2fb_bit_i))),2);endendM2fb=M2fb_raw((M2fb_raw_len-Mfb_len+1):M2fb_raw_len);M1regs_len=length(M1fb);M2regs_len=length(M2fb);M1len_period=Mfinal_len;M2len_period=Mfinal_len;M1regs_s=zeros(1,M1regs_len);M1regs_s(M1regs_len)=1;M2regs_s=zeros(1,M2regs_len);M2regs_s(M2regs_len)=1;M1regs_m1=M1regs_s;M1regs_m2=zeros(1,M1regs_len);M2regs_m1=M2regs_s;M2regs_m2=zeros(1,M2regs_len);M1regs_e=zeros(1,M1len_period);M2regs_e=zeros(1,M2len_period);M1regs_e(1)=M1regs_s(M1regs_len);forM1_ri=2:M1len_periodM1regs_m2(1)=mod(sum(M1fb.*M1regs_m1),2);M1regs_m2(2:M1regs_len)=M1regs_m1(1:(M1regs_len-1));M1regs_m1=M1regs_m2;M1regs_e(M1_ri)=M1regs_m1(M1regs_len);endM2regs_e(1)=M2regs_s(M2regs_len);forM2_ri=2:M2len_periodM2regs_m2(1)=mod(sum(M2fb.*M2regs_m1),2);