matlab_实现弱信号条件下的检测，可以检测到较低信噪比条件下的信号

%忽视了频率偏移 clear; clc; close all; load 收到的射频信号.mat svnum=5; gpsmatch=IFSignal; IFSignal=[IFSignal IFSignal]; n=length(gpsmatch); m=25000; for i=1:m res(i)=gpsmatch*IFSignal(1,i:i+n-1)'; end plot(1:m,res); %找到GPS信号中的导航电文 %检验GPS信号最大值处是否有相位偏移 res2=abs(res); for i=1:100 [C I]=max(res2); res(1,I)=0; index(1,i)=I; end; w=length(gpsmatch); m=1; for i=index(1,1):w:(length(IFSignal)-w+1) navigationbit(m)=(IFSignal(i:i+w-1)*gpsmatch')/w; m=m+1; end navigationcode=zeros(1,1); navigationcode(1,1)=navigationbit(1,1); m=2;count=0; for i=2:length(navigationbit) if(navigationbit(1,i)~=navigationbit(1,i-1)) navigationcode(1,m)=navigationbit(1,i); m=m+1; count=0; else count=count+1; if(count>=5) navigationcode(1,m)=navigationbit(1,i); m=m+1; count=0 end end end %ND转化为数字 navigationcode=navigationcode./abs(navigationcode); index1=find(navigationcode<0); navigation(index1)=zeros(1,length(index1)); table2=[0 0 0 0;0 0 0 1;0 0 1 0;0 0 1 1;0 1 0 0;0 1 0 1;0 1 1 0;0 1 1 1; 1 0 0 0;1 0 0 1;1 0 1 0;1 0 1 1;1 1 0 0;1 1 0 1;1 1 1 0;1 1 1 1;]; Result=''; for i=1:4:length(navigationcode) tt=navigationcode(i:i+3); matchtable=table2(:,1:4)-[tt;tt;tt;tt;tt;tt;tt;tt;tt;tt;tt;tt;tt;tt; tt;tt]; matchtable=sum(abs(matchtable)'); tempchar='0'; bestmatch=find(matchtable==min(matchtable)); switch (bestmatch) case 1 tempchar='0'; case 2 tempchar='1'; case 3 tempchar='2'; case 4 tempchar='3'; case 5 tempchar='4'; case 6 tempchar='5'; case 7 tempchar='6'; case 8 tempchar='7'; case 9 tempchar='8'; case 10 tempchar='9'; case 11 tempchar='a'; case 12 tempchar='b'; case 13 tempchar='c'; case 14 tempchar='d'; case 15 tempchar='e'; case 16 tempchar='f'; otherwise end Result=strcat(Result,tempchar); end Num1=hex2num(Result(1:16)); Num2=hex2num(Result(17:32)); Num3=hex2num(Result(33:48));