1    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    2    % Matlab code skeleton for Digital Transmitter
    3
    4    close all;clear;
    5
    6    % Generate random bits
    7    bits_per_symbol=2;
    8    num_symbols=64;
    9    numbits=bits_per_symbol*num_symbols;
    10    bits=rand(1,numbits)>0.5;
    11
    12    Tsymb=32;           % samples per symbol
    13
    14
    15    % These are the 4 frequencies to choose from                    
    16    % Note that 32 samples per symbol does not correspond to 
    17    % an integer number of periods at these frequencies
    18    omega1 =  9*pi/32;
    19    omega2 = 13*pi/32;
    20    omega3 = 17*pi/32;
    21    omega4 = 21*pi/32;
    22
    23
    24    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    25    % Transmitter section
    26
    27    % Initialize transmit sequence
    28    index=1;			% Initialize bit index
    29    n=1;				% Initialize sample index
    30    phi=0;				% Initialize phase offset
    31
    32    % Generate 64 32-sample symbols
    33    while (n<=num_symbols*Tsymb)
    34    
    35      if (bits(index:index+1) == [0 0])
    36         sig(n:n+Tsymb-1) = sin(omega1*[0:Tsymb-1]+phi);   
    37         phi = omega1*Tsymb+phi;	% Calculate phase offset for next symbol
    38         phi = mod(phi, 2*pi);	% Restrict phi to [0,2*pi)
    39          
    40     % -----------> Insert code here <-------------%
    41     
    42      end % end if-else statements
    43   
    44      index=index+2; % increment bit counter so we look at next 2 bits
    45    
    46      n=n+Tsymb;
    47    end   % end while
    48
    49
    50    % Show transmitted signal and its spectrum
    51    % ---------------> Insert code here <-----------------%