%%*************************************************************************
%%此程序用來仿真OFDM系統在AWGN信道中的誤碼特性 
%%Function information:
%%
%%-------------------------------------------------------------------------
%%  Created by Wei Zhao           2003-04-17    (Version 1.0)                                       
%%-------------------------------------------------------------------------
%%  Recreated by Kunji Wang
%%*************************************************************************

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%%                                  MAIN PROGRAM 
%%～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～

clear;
clc;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%   System Parameters
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
NumOfSubcarrier = 64;
LengthOfGI = 16;  % the subcarriers GI(guard interval)contains
modulation_mode = 4;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Simulation Parameters
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
NumOfSymbolPerFrame=5;
NumOfFrames=100;
SNR_in_dB=[0:4:30];

fs=10000;
fd=100;
Rb=fs;
Ts=1/Rb;
dt=Ts;
n_delay=3;
t_delay=[0,100,200];
p_delay=[0.0,-2.0,-6.0];

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Simulation Starting!!!
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
tic;
for counter=1:length(SNR_in_dB) 
    P=1;				  	                      % energy per symbol
    snr=10^(SNR_in_dB(counter)/10);	 	      % signal to noise ratio
    sgma=sqrt(P/(snr));	  	  	              % noise variance
  
    %Clear the all the counters 
   
    NumOfErrorBit = 0;
    SampleIndex=0;
    for Frame_counter = 1:NumOfFrames
        %--------------------------------------------------------------------------------------------
        %                                        Tx
        %--------------------------------------------------------------------------------------------
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        %% Source Bit Sequence 
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%  
        Source_Bits=randint(1,2*NumOfSubcarrier*NumOfSymbolPerFrame);
        
        
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        %% QPSK Modulation
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        Modulated_Sequence=modulation(Source_Bits,modulation_mode);
        R_Modulated_Sequence=reshape(Modulated_Sequence,NumOfSubcarrier,NumOfSymbolPerFrame);
        
        
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        %% IFFT
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
        IFFT_Out_Data(:,:) =sqrt(NumOfSubcarrier)* ifft (R_Modulated_Sequence);
       
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        %% adding guard interval for DATA
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        GI_Added_Frame(1:LengthOfGI,:) = IFFT_Out_Data((NumOfSubcarrier-LengthOfGI+1):NumOfSubcarrier,:);
        GI_Added_Frame((LengthOfGI+1):(NumOfSubcarrier+LengthOfGI),:) = IFFT_Out_Data(1:NumOfSubcarrier,:);
    
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        %% P -> S
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        Serial_Signal = reshape(GI_Added_Frame,1,NumOfSymbolPerFrame*(NumOfSubcarrier+LengthOfGI));
        
        %%%------------------------------------------------------------------------------------------------------------
        %%                                              CHANNEL
        %%%------------------------------------------------------------------------------------------------------------
        %--------------------------------------------------------------------------------------------
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        %% AWGN channel
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        
            in=Serial_Signal;
            [out]=channel(in,fs,fd,n_delay,t_delay,p_delay);
            Serial_Signal_Ray=Serial_Signal*out;
            
        for i=1:NumOfSymbolPerFrame*(NumOfSubcarrier+LengthOfGI)
            [n_I n_Q]=gngauss(sgma);
            noise(i)=n_I+j*n_Q;
        end
        Noised_Transmited_Signal=Serial_Signal_Ray+noise(i);
        
        
        %--------------------------------------------------------------------------------------------
        %                                         Rx
        %--------------------------------------------------------------------------------------------
 
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        %%  Remove the GI 
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        for jj=1:NumOfSymbolPerFrame
            for ii=1:NumOfSubcarrier
                GI_Removed_Rx_Signal(ii+(jj-1)*NumOfSubcarrier)=Noised_Transmited_Signal(LengthOfGI*jj+ii+(jj-1)*NumOfSubcarrier);
            end
        end 
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        %%  S -> P
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        Parallel_Rx_Signal = reshape(GI_Removed_Rx_Signal,NumOfSubcarrier,NumOfSymbolPerFrame);
        
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        %% FFT
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%   
        Freq_Rx_Signal = fft(Parallel_Rx_Signal)/sqrt(NumOfSubcarrier);
        Demod_In_Data(1:NumOfSubcarrier,1:NumOfSymbolPerFrame) = Freq_Rx_Signal(1:NumOfSubcarrier,1:NumOfSymbolPerFrame);
        FFT_Out = conj(Demod_In_Data(:,1:NumOfSymbolPerFrame)');
        Serial_Output = reshape(Demod_In_Data,1,NumOfSubcarrier*NumOfSymbolPerFrame);
        
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        %% Demodulation
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        Demod_Sequence= demodulation(Serial_Output,modulation_mode);
        
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        %% Calculate the BER
        %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
        for jj = 1:(length(Source_Bits)) 
            if  Demod_Sequence(jj) ~= Source_Bits(jj) 
                NumOfErrorBit = NumOfErrorBit + 1; 
            end
        end
    end
        
    BER(counter) = NumOfErrorBit/(NumOfFrames*NumOfSubcarrier*2*NumOfSymbolPerFrame);
end
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    % Simulation Completed
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    
    elapse=toc
    
    clock_time = clock;
    present = fix(clock_time)  
    
%---------------------------------------------%
%% Draw BER figure
%---------------------------------------------% 
h=figure;
semilogy(SNR_in_dB,BER,'r*-');
xlabel('SNR(dB)');
ylabel('BER(bit error rate)');
title( 'BER performance of OFDM  in AWGN Channel');
grid on ;