main.m

对衰落以及AGWN信道进行仿真

% qpsk_fading.m
%
% Simulation program to realize QPSK transmission system
% (under four path fading)
%
% Programmed by BangzengHe
%

%******************** Preparation part *************************************

sr=256000.0; % Symbol rate
ml=2;        % ml:Number of modulation levels (BPSK:ml=1, QPSK:ml=2, 16QAM:ml=4)
br=sr .* ml; % Bit rate
nd = 20;    % Number of symbols that simulates in each loop
ebn0=10;     % Eb/N0
IPOINT=10;    % Number of oversamples

%************************* Filter initialization ***************************

irfn=21;                  % Number of taps
alfs=0.5;                 % Rolloff factor
[xh] = hrollfcoef(irfn,IPOINT,sr,alfs,1);   %Transmitter filter coefficients 
[xh2] = hrollfcoef(irfn,IPOINT,sr,alfs,0);  %Receiver filter coefficients 

%******************* Fading initialization ********************

% Time resolution

tstp=1/sr/IPOINT; 

% Arrival time for each multipath normalized by tstp
% In this simulation four-path Rayleigh fading are considered
itau = [0, 2, 3, 4];

% Mean power for each multipath normalized by direct wave.
% In this simulation four-path Rayleigh fading are considered.
% This means that the second path is -10dB less than the first direct path.
dlvl = [0 ,10 ,20 ,25];

% Number of waves to generate fading for each multipath.
% In this simulation four-path Rayleigh fading are considered.
% In normal case, more than six waves are needed to generate Rayleigh fading
n0=[6,7,6,7];

% Initial Phase of delayed wave
% In this simulation four-path Rayleigh fading are considered.
th1=[0.0,0.0,0.0,0.0];

% Number of fading counter to skip (50us/0.5us)
% In this case we assume to skip 50 us
itnd0=nd*IPOINT*100;

% Initial value of fading counter
% In this simulation four-path Rayleigh fading are considered.
% Therefore four fading counter are needed.
  
itnd1=[1000,2000, 3000, 4000];

% Number of directwave + Number of delayed wave
% In this simulation four-path Rayleigh fading are considered
now1=4;        

% Maximum Doppler frequency [Hz]
% You can insert your favorite value
fd=200;       

% You can decide two mode to simulate fading by changing the variable flat
% flat     : flat fading or not 
% (1->flat (only amplitude is fluctuated),0->nomal(phase and amplitude are fluctutated)
flat =1;

%******************** START CALCULATION *************************************
nloop=100;
for iii=1:nloop
    
%*************************** Data generation ********************************  
	
    data1=rand(1,nd*ml)>0.5;  % rand: built in function
    [data2] = oversamp( data1, nd , IPOINT) ;
    
%*************************** QPSK Modulation ********************************  

    [ich,qch]=qpskmod(data1,1,nd,ml);
	[ich1,qch1]= compoversamp(ich,qch,length(ich),IPOINT); 
	[ich2,qch2]= compconv(ich1,qch1,xh); 
     
%**************************** Attenuation Calculation ***********************
	
    spow=sum(ich2.*ich2+qch2.*qch2)/nd;  % sum: built in function
	attn=0.5*spow*sr/br*10.^(-ebn0/10);
	attn=sqrt(attn);  % sqrt: built in function
     
%********************** Fading channel **********************

  % Generated data are fed into a fading simulator
    [ifade,qfade]=sefade(ich2,qch2,itau,dlvl,th1,n0,itnd1,now1,length(ich2),tstp,fd,flat);
  
  % Updata fading counter
    itnd1 = itnd1+ itnd0;

%********************* Add White Gaussian Noise (AWGN) **********************
	
    [ich3,qch3]= comb(ifade,qfade,attn);% add white gaussian noise
	[ich4,qch4]= compconv(ich3,qch3,xh2);

    syncpoint=irfn*IPOINT+1;
    ich5=ich4(syncpoint:IPOINT:length(ich4));
    qch5=qch4(syncpoint:IPOINT:length(qch4));
        
%**************************** QPSK Demodulation *****************************

    [demodata]=qpskdemod(ich5,qch5,1,nd,ml); 
    [data3] = oversamp( demodata, nd , IPOINT) ;
    
    figure(7);
    plot(ich2,qch2);
    title('signal constellation before the  Rayleigh channel');
    hold on;
    
    figure(8);
    plot(ifade,qfade);
    title('signal constellation after the Rayheigh channel');
    hold on;
end
%********************** Output result ***************************
    figure(1);
    plot(data2);
    axis([0 200 -0.5 1.5]);
    title('source signal');
    xlabel('Time');
    
    T=1;                        % symbol duration
    delta_T=T/(nd*ml);              % sampling interval
    t=-0.5*T+delta_T:delta_T:0.5*T; % time axis
    N=length(t);                % number of samples
    for i=1:N,                  % calculation of raised cosine pulse
        g_T(i)=data1(i);
    end;
    G_T=abs(fft(g_T));          % spectrum of g_T
    f=-0.5/delta_T:1/(delta_T*(N-1)):0.5/delta_T;
    figure(2);
   % plot(f,fftshift(G_T));
    psd(G_T);
    [Pxx,fr]=psd(G_T);
    plot(fr-0.5,fftshift(Pxx));
   

    figure(3);
    plot(ich2);
    title('modulated signal');
    xlabel('Time');
    
    figure(4);
    psd(ich2);
    [Pxx,fr]=psd(ich2);
    plot(fr-0.5,fftshift(Pxx));
   
    figure(5);
    plot(ich4);
    title('AWGN channel output signal');
    xlabel('Time');
    
    figure(6);
    psd(ich4);
    [Pxx,fr]=psd(ich4);
    %pause; 
    plot(fr-0.5,fftshift(Pxx));
%******************** end of file ***************************