transmitter.m

clear all;
close all;
%----------------------------------------------------
%---------------- Initial Parameters ----------------
%----------------------------------------------------

numberOfBits = 100;                            %number of bits
QAM = 4;                              %4-QAM
BitsPerSymbol = log2(QAM);                        %number of bits in one symbol

if mod(numberOfBits, BitsPerSymbol) ~= 0
    error('numberOfBits must be a multiple of log2(M).');
end

Fc_tx = 400;                        %carrier frequency
phase_tx = 0;                       %carrier phase
phase_tx = 2*pi*0.13;

Fs = 10000;                          %sampling frequency
dt = 1/Fs;                          %simulation time differential
Rs = 100;                            %Symbol rate
Ns = Fs/Rs;                         %Number of samples per symbol

%----------------------------------------------------
%----------------Creation of the bitstream ----------
%----------------------------------------------------

dataIn = randi(2,1,numberOfBits) - 1;  % Generate vector of binary data
%dataIn = [0 0 0 0 1 1];

%----------------------------------------------------
%----------------- QAM Mapper -----------------------
%----------------------------------------------------

numberOfSymbols = length(dataIn)/BitsPerSymbol; %number of symbols in the FIFO

% Define mapping table applying Gray mapping

if QAM == 4
  mappingTable(1) =  1 + 1*j;
  mappingTable(2) = -1 + 1*j;
  mappingTable(3) =  1 - 1*j;
  mappingTable(4) = -1 - 1*j;
endif
      


mappedSymbols = zeros(1, numberOfSymbols);

% Map bits to symbols
for i = 1 : BitsPerSymbol : length(dataIn)  
    symbolBits = dataIn(i:i+BitsPerSymbol-1);
    symbolIndex = 2^1 * symbolBits(1) + 2^0 * symbolBits(2);
    
     % Mapping
    mappedSymbols((i - 1)/BitsPerSymbol + 1) = mappingTable( symbolIndex + 1);   
endfor

%----------------------------------------------------
%----------------- Upsampling -----------------------
%----------------------------------------------------
%% Adding zeros between symbols

for i = 1:length(mappedSymbols)
    mappedSymbols_upsampled( (i-1)*Ns+1 : i*Ns) = [mappedSymbols(i) zeros(1, Ns-1)];
end

%----------------------------------------------------
%----------------- Pulse shaping --------------------
%----------------------------------------------------
% Sqrt-Raised-Cosine Impulse Response Filter
alpha = 0.35;     % excess bandwidth factor = 0.35 for IS 136
G = 4;            % Group delay (how many symbols are delayed)
                  % Order of filter is N = Ns * G + 1

A_SRRC = 1;
                  
n = -Ns*G : Ns*G;
for i = 1 : length(n)
    if(n(i) == 0)
      B_SRRC(i) = (1/Ns) * ( 1 - alpha + 4 * (alpha/pi));
      
    elseif (abs(n(i)) == Ns/(4*alpha))
      B_SRRC(i) = (1 + (2/pi)) * sin(pi / (4*alpha)) + (1 - (2/pi)) * cos(pi / (4*alpha));
      B_SRRC(i) = (1/Ns) * (alpha/sqrt(2)) * B_SRRC(i);
      
    else
      B_SRRC(i) = sin(pi * (1-alpha) * n(i)/Ns) + 4*alpha*n(i)/Ns * cos(pi * (1+alpha) * n(i)/Ns);
      B_SRRC(i) = B_SRRC(i) / (pi * n(i)/Ns * (1 - (4*alpha*n(i)/Ns)^2) );
      B_SRRC(i) = (1/Ns) * B_SRRC(i);
    end 
end

% Normalize by the energy
B_SRRC = B_SRRC/sqrt(B_SRRC*B_SRRC');

%Adding zeros at the end to take into account the delay given by the filters (at the transmitter and the receiver)
mappedSymbols_upsampled_and_padded = [mappedSymbols_upsampled zeros(1, 2*Ns*(G+2))];

Tx_I_BB = filter(B_SRRC, A_SRRC, real(mappedSymbols_upsampled_and_padded)); 
Tx_Q_BB = filter(B_SRRC, A_SRRC, imag(mappedSymbols_upsampled_and_padded));

%----------------------------------------------------
%----------------- Modulation: Baseband to RF -------
%----------------------------------------------------

%t = 0 : dt : ((length(mappedSymbols) + 2*G) * Ns - 1) * dt;
t = 0 : dt : (length(Tx_I_BB) - 1) * dt;

Tx_I = Tx_I_BB .* (sqrt(2)*cos(2*pi*Fc_tx*t+phase_tx));
Tx_Q = Tx_Q_BB .* (sqrt(2)*sin(2*pi*Fc_tx*t+phase_tx));

Tx = Tx_I - Tx_Q;

%----------------------------------------------------
%----------------- Figures --------------------------
%----------------------------------------------------
##figure(1);
##stem(dataIn,"filled");
##title('Data In');
##xlabel('Bit Index');
##ylabel('Binary Value');

##figure(2);
##subplot(2,1,1);
##stem(real(mappedSymbols));
##title("Real part")
##subplot(2,1,2);
##stem(imag(mappedSymbols));
##title("Imaginary part");

##figure(3);
##scatter(real(mappedSymbols), imag(mappedSymbols) , "filled");
##axis([-2 2 -2 2]);
##title("Symbols");

##figure(4);
##subplot(3,1,1);
##stem(real(mappedSymbols));
##subplot(3,1,2);
##stem(real(mappedSymbols_upsampled));
##subplot(3,1,3);
##plot(Tx_I);

##figure(5);
##subplot(3,1,1);
##plot(Tx_I);
##subplot(3,1,2);
##plot(Tx_Q);
##subplot(3,1,3);
##plot(Tx);
##
##figure(6);
##stem(imag(mappedSymbols_upsampled));
##figure(7);
##plot(Tx_Q_BB);
##hold on
##stem(Tx_Q_BB);
##hold on
##stem(1:4:length(Tx_Q_BB), Tx_Q_BB(1:4:end), 'filled');

%----------------------------------------------------
%----------------- Clear ----------------------------
%----------------------------------------------------

%clear Tx_I Tx_Q Tx_I_BB Tx_Q_BB 
clear alpha i dt n
%clear mappedSymbols mappedSymbols_upsampled_and_padded mappedSymbols_upsampled
clear symbolBits symbolIndex