% 本程序用來估計 QPSK 誤碼率；
% 考慮了瑞利衰落和白噪聲，沒有考慮率多徑的影響；

% QPSK System Simulation,Pe evaluation
clear all; % close all;
% echo on;
SNRindB1=0:0.2:5;
SNRindB2=0:0.2:5;

% 瑞利信道；函數 cm_sm32 考慮了瑞利衰落和加性白噪聲的影響;
% rayleigh channel 
for i=1:length(SNRindB1)
    % simulated bit and symbol error rates
    [pb,ps]=cm_sm32(SNRindB1(i));             
    smld_bit_ray_err_prb(i)=pb;
    smld_symbol_ray_err_prb(i)=ps;
    disp([ps,pb]);
%     echo off;
end;

% awgn channel ,函數 cm_sm33 只考慮加性白噪聲的影響;
% echo on;
for i=1:length(SNRindB1)
    [pb1,ps1]=cm_sm33(SNRindB1(i));             
    smld_bit_awgn_err_prb(i)=pb1;
    smld_symbol_awgn_err_prb(i)=ps1;
    disp([ps1,pb1]);
%     echo off;
end;

% theory curve
% 理論曲線完全由公式推導得出;
% echo on;
for i=1:length(SNRindB2)
    % signal to noise ratio
    SNR=exp(SNRindB2(i)*log(10)/10);  
    % AWGN theoretical bit error rate
    theo_err_awgn_prb(i)=0.5*erfc(sqrt(SNR));
    % Rayleigh theoretical bit error rate
    theo_err_ray_prb(i)=0.5*(1-1/sqrt(1+1/SNR));    
%     echo off;
end;
echo on;

% Plotting commands follow
figure;
semilogy(SNRindB2,theo_err_awgn_prb,'r');

hold on; grid on;

semilogy(SNRindB1,smld_bit_awgn_err_prb,'rs-.'); hold on;

semilogy(SNRindB2,theo_err_ray_prb); hold on;

semilogy(SNRindB1,smld_bit_ray_err_prb,'b^-.'); hold on;
% semilogy(SNRindB2,0.3,'r*--');

title('BER curves');

xlabel('Eb/No');ylabel('BER');

legend('theory AWGN curve','simulated AWGN curve',...
    'theory Rayleigh curve','simulated Rayleigh curve');
echo off;