%-OS-CFAR检测器均匀背景与杂波干扰目标背景下性能仿真-
clc;
clear all;
N=32; 

r=3;     %CMLD_CFAR检测器筛除掉r个较大的参考样本单元
R=N-r;   %参考单元长度
n=N/2;            %半滑窗长度
k=3*N/4;
T=16.2933;        %标称系数
Pfa=1e-6;         %虚警概率
syms T0
g=Pfa-k*nchoosek(R,k)*gamma(R-k+1+T0)*gamma(k)/gamma(R+T0+1);
x=solve(g);
T0=double(x);
M=1e4;             %蒙特卡洛仿真次数
SNR_dB=5:1:35;        %信噪比
SNR=10.^(SNR_dB./10);
Simul_len=length(SNR);  %仿真长度

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%OS-CFAR ideal%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
for i=1:Simul_len
    Pd(i)=OS_Pd_Fun(N,k,T,SNR(i));
end
plot(SNR_dB,Pd,'b');
hold on
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%OS-CFAR simulation%%%%%%%%%%%%%%%%%%%%%%%%
for i=1:Simul_len
    count=0;
    for j=1:M
        lambda=1;       %产生噪声，长度为N
        u=rand(1,N);
        exp_noise=log(u)*(-lambda);
        lambda=SNR(i);  %产生待检测单元
        u=rand(1,2);
        CUT=log(u(1))*(-lambda);
        exp_noise(N)=log(u(2))*(-lambda);
        exp_noise=sort(exp_noise);
        if(CUT>T*exp_noise(k))
            count=count+1;
        end
    end
    Pd_sim(i)=count/M;
end
plot(SNR_dB,Pd_sim,'-*r');
hold on
%%%%%%%%%%%%%%%CMLD_CFAR检测器筛除掉r个较大的参考样本单%%%%%%%%%%%%%%%%%%
for i=1:Simul_len
    count=0;
    for j=1:M
        lambda=1;       %产生噪声，长度为N-1
        u=rand(1,N-1);
        exp_noise(1:N-1)=log(u)*(-lambda);
        
        lambda=SNR(i);  %产生待检测单元及一个干扰目标
        u=rand(1,2);
        CUT=log(u(1))*(-lambda);
        exp_noise(N)=log(u(2))*(-lambda);
        exp_noise=sort(exp_noise);
         exp_noise1(1:N-r)=exp_noise(1:N-r);
        if(CUT>T0*exp_noise1(k))
            count=count+1;
        end
    end
    Pd_sim_1(i)=count/M;
end
plot(SNR_dB,Pd_sim_1,'--g');
hold on

title('OS-CFAR 检测概率曲线,N=32,Pf=1e-6');
xlabel('信噪比(dB)');ylabel('检测概率');
legend('OS-ideal','OS-simulation','OS-1interference');