bkmxxtp.m

巴克码和线性调频混合雷达信号仿真

close all;clear all;clc;
%%%%%%%%%产生雷达发射信号%%%%%%%%%%%%%%%%%%%
code=[1,1,1,1,1,-1,-1,1,1,-1,1,-1,1];
tao=10e-6;               %脉宽
f0=30e6;                 %频率
B=4e6;                   %调频带宽 
fc=f0-B/2;               %起始频率
fs=100e6;                %采样频率
ts=1/fs;
t_tao=0:1/fs:tao-1/fs;
N=length(t_tao);
n=length(code);
k=B/fs*2*pi/max(t_tao);
pha=0;

s=zeros(1,n*N);
for i=1:n
    if code(i)==1
        pha=0;
    else
        pha=pi;
    end
    s(1,(i-1)*N+1:i*N)=cos(2*pi*fc*t_tao+k*cumsum(t_tao)+pha);
end
t=0:1/fs:n*tao-1/fs;
figure(1),subplot(3,1,1),plot(t,s),xlabel('t/s'),
title('脉内线性调频脉间相位编码信号(13bit bark code)');
s_fft_result=abs(fft(s(1:N)));
subplot(3,1,2),plot((0:fs/N:fs/2-fs/N),s_fft_result(1:N/2)),xlabel('f/Hz'),
title('脉内信号频谱');
s1_fft_result=abs(fft(s));
subplot(3,1,3),plot((0:fs/(n*N):fs/2-fs/(n*N)),s1_fft_result(1:N*n/2)),xlabel('f/Hz'),
title('信号频谱');


%%%%%%%%%%%产生脉冲压缩系数%%%%%%%%%%%%%%%%
%-----------正交解调---------------------%
N=tao/ts;
n=0:N-1;
s1=s(1:N);
loacal_oscillator_i=cos(n*f0/fs*2*pi);        %i路本振
loacal_oscillator_q=sin(n*f0/fs*2*pi);        %q路本振
fbb_i=loacal_oscillator_i.*s1;                %i路解调
fbb_q=loacal_oscillator_q.*s1;                %q路解调
window=chebwin(51,40);                      %50阶cheby窗的fir低通滤波器
[b,a]=fir1(50,2*B/fs,window);
fbb_i=[fbb_i,zeros(1,25)];
fbb_q=[fbb_q,zeros(1,25)];
fbb_i=filter(b,a,fbb_i);
fbb_q=filter(b,a,fbb_q);
fbb_i=fbb_i(26:end);                        %截取有效信息
fbb_q=fbb_q(26:end);                        %截取有效信息
fbb=fbb_i+j*fbb_q;

%-------产生理想线性调频脉冲压缩匹配系数----------%
M=131126 ;
D=B*tao;
match_filter_1=ts*fliplr(conj(fbb))*sqrt(D)*2/tao;
match_filter_1_fft=fft(match_filter_1,M);   %第一次脉冲压缩处理匹配系数
figure(2),subplot(2,1,1),plot(real(match_filter_1_fft)),title('脉冲压缩系数（实部）');
subplot(2,1,2),plot(imag(match_filter_1_fft)),title('脉冲压缩系数（虚部）');

N=length(s);
n=0:N-1;
loacal_oscillator_i=cos(n*f0/fs*2*pi);   %I 路本振信号
loacal_oscillator_q=sin(n*f0/fs*2*pi);   %q路本振信号
fbb_i=loacal_oscillator_i.*s;
fbb_q=loacal_oscillator_q.*s;
window=chebwin(51,40);
[b,a]=fir1(50,0.5,window);
fbb_i=[fbb_i,zeros(1,25)];
fbb_q=[fbb_q,zeros(1,25)];
fbb_i=filter(b,a,fbb_i);
fbb_q=filter(b,a,fbb_q);
fbb_i=fbb_i(26:end);
fbb_q=fbb_q(26:end);
signal=fbb_i+j*fbb_q;
clear fbb_i;
clear fbb_q;

signal_fft=fft(signal,M);
pc_result_fft=signal_fft.*match_filter_1_fft;
pc_result=ifft(pc_result_fft,M);
figure(3),plot((0:ts:length(signal)*ts-ts),pc_result(1:length(signal))),
xlabel('时间，单位：S'),title('回波脉冲压缩处理结果');
clear loacal_oscillator_i;
clear loacal_oscillator_q;

t=tao*length(code);
match_filter_2=2*ts*fliplr(conj(pc_result))*2/t;
match_filter_2_fft=fft(match_filter_2,M); 
figure,subplot(2,1,1),plot(real(match_filter_2_fft)),title('脉冲压缩系数（实部）');
subplot(2,1,2),plot(imag(match_filter_2_fft)),title('脉冲压缩系数（虚部）');
clear fbb;
clear match_filter_1;
clear match_filter_2;
clear signal;
clear signal_fft;
clear pc_result;
clear pc_result_fft;
%%%%%%%%%%%%产生雷达回波%%%%%%%%%%%%
f_frame=1e3;
T_frame=1/f_frame;
N_echo_frame=18;

f_doppler=3.5e3;
t_frame=0:ts:T_frame-ts;
t_mobj=200e-6;
echo_mobj_pulse=[zeros(1,t_mobj/ts),s,zeros(1,(T_frame-t_mobj)/ts-length(s))];
echo_mobj=repmat(echo_mobj_pulse,1,N_echo_frame);
t_doppler=0:ts:N_echo_frame*T_frame-ts;
s_doppler=cos(2*pi*f_doppler*t_doppler);
s_echo_mobj=echo_mobj.*s_doppler;

t_fobj=450e-6;
echo_fobj_pulse=[zeros(1,t_fobj/ts),s,zeros(1,(T_frame-t_fobj)/ts-length(s))];
s_echo_fobj=repmat(echo_fobj_pulse,1,N_echo_frame);

t_clutter=700e-6;
t_clutter_pulse=39e-6;
sigma=2;
t1=0:ts:t_clutter_pulse-ts;
rand('state',0);
u=rand(1,length(t1));
echo_clutter=0.08*sqrt(2*log(1./u))*sigma;%.*s;  %可能有错
s_echo_clutter_pulse=[zeros(1,t_clutter/ts),echo_clutter,zeros(1,(T_frame-t_clutter)/ts-length(echo_clutter))];
s_echo_clutter=repmat(s_echo_clutter_pulse,1,N_echo_frame);

s_noise=0.1*rand(1,N_echo_frame*T_frame/ts);

s_echo=s_echo_mobj+s_echo_fobj+s_echo_clutter+s_noise;
clear s_echo_mobj;
clear s_echo_fobj;
clear s_echo_clutter;
clear s_echo_clutter_pulse;
clear s_noise;
clear echo_mobj_pulse;
clear echo_mobj;
clear echo_fobj_pulse;
clear echo_clutter;
clear s_doppler;
clear t_doppler;

%-------正交解调------------------%
N=N_echo_frame*T_frame/ts;
n=0:N-1;
loacal_oscillator_i=cos(n*f0/fs*2*pi);        %i路本振
loacal_oscillator_q=sin(n*f0/fs*2*pi);        %q路本振
s_echo_i=loacal_oscillator_i.*s_echo;                %i路解调
s_echo_q=loacal_oscillator_q.*s_echo;                %q路解调
window=chebwin(51,40);                      %50阶cheby窗的fir低通滤波器
[b,a]=fir1(50,2*B/fs,window);
s_echo_i=[s_echo_i,zeros(1,25)];
s_echo_q=[s_echo_q,zeros(1,25)];
s_echo_i=filter(b,a,s_echo_i);
s_echo_q=filter(b,a,s_echo_q);
s_echo_i=s_echo_i(26:end);                        %截取有效信息
s_echo_q=s_echo_q(26:end);                        %截取有效信息
s_echo_mf=s_echo_i+j*s_echo_q;
clear s_echo;
clear loacal_oscillator_i;
clear loacal_oscillator_q;
clear s_echo_i;
clear s_echo_q;
clear n;

%%%%%%%%%%%%脉冲压缩处理%%%%%%%%%%%%%
for i=1:N_echo_frame
    s_echo_fft_result=fft(s_echo_mf(1,(i-1)*T_frame/ts+1:i*T_frame/ts),M);
    s_pc_fft_1=s_echo_fft_result.*match_filter_1_fft;
    s_pc_fft_2=s_pc_fft_1.*match_filter_2_fft;
end
clear s_echo_mf;

s_pc_result_1=s_pc_result;
s_pc_result_1=reshape(s_pc_result_1,1,N_echo_frame*M);
figure,subplot(2,1,1),plot(0:ts:N_echo_frame*T_ftame-ts,real(s_pc_result_1)),
xlabel('t/s'),title('脉冲压缩处理后结果（实部）');
subplot(2,1,2),plot(0:ts:N_echo_frame*T_ftame-ts,imag(s_pc_result_1)),
xlabel('t/s'),title('脉冲压缩处理后结果（虚部）');

%%%%%%%%%%%固定杂波对消处理%%%%%%%%%%%%%%%%%
for i=1:16;
    s_MTI_result(i,:)=s_pc_result(i,:)+s_pc_result(i+2,:)-2*s_pc_result(i+1,:);
end

clear s_pc_result;
clear s_pc_result_1;
s_MTI_result_1=s_MTI_result';
s_MTI_result_1=reshape(s_MTI_result_1,1,(N_echo_frame-2)*M);
figure,subplot(2,1,1),plot(0:ts:N_echo_frame*T_ftame-ts,real(s_MTI_result_1)),
xlabel('t/s'),title('固定杂波对消后结果（实部）');
subplot(2,1,2),plot(0:ts:N_echo_frame*T_ftame-ts,imag(s_MTI_result_1)),
xlabel('t/s'),title('固定杂波对消后结果（虚部）');
clear s_MTI_result_1;

%%%%%%%%%%%%%MTD处理和求模%%%%%%%%%%%%%%%%%%
for i=1:T_frame/ts
    s_MTD_result_1(:,i)=fft(s_MTI_result(:,i),16);
end
for i=1:T_frame/ts
    s_MTD_result(i)=abs(max(s_MTD_result_1));
end

figure,plot(0:ts:N_echo_frame*T_ftame-ts,s_MTD_result),
xlabel('t/s'),title('MTD处理后求模结果（信号最大通道）');

%%%%%%%%%%%CFAR处理%%%%%%%%%%%%%%%%%%%
N=T_frame/ts;
                %第1点恒虚警处理时噪声均值由其后面的16点噪声决定
    cfar_result(1,1)=s_MTD_result(1,1)/(sqrt(2)/pi*mean(s_MTD_result(1,2:17)));
                
for i=2:16
                %第2点到第16点恒虚警处理时噪声均值由其后面的和后面的16点噪声共同决定
    noise_mean=sqrt(2)/pi*(mean(s_MTD_result(1,1:i-1))+mean(s_MTD_result(1,i+1:i+16)))/2;
    cfar_result(1,i)=s_MTD_result(1,i)/noise_mean;
end

for i=17:N-17
                %正常数据点恒虚警处理时噪声均值由其前面和后面的16点噪声中的大者决定
    noise_mean=sqrt(2)/pi*max(mean(s_MTD_result(1,i-16:i-1)),mean(s_MTD_result(1,i+1:i+16)));
    cfar_result(1,i)=s_MTD_result(1,i)/noise_mean;
end

for k=N-16:N-1
                %倒数第16点到倒数第2点恒虚警处理时噪声均值由其前面的16和后面噪声共同决定
    noise_mean=sqrt(2)/pi*(mean(s_MTD_result(1,k-16:k-1))+mean(s_MTD_result(1,k+1:N)))/2;
    cfar_result(1,k)=s_MTD_result(1,k)/noise_mean;
end
               %最后一点的恒虚警处理时噪声均值由其前面的16点噪声决定
    cfar_result(1,N)=s_MTD_result(1,N)/(sqrt(2)/pi*mean(s_MTD_result(1,N-16:N-1)));
    
figure,plot(0:ts:N_echo_frame*T_ftame-ts,cfar_result),
xlabel('t/s'),title('采用恒虚警处理后的结果');