%-- SEND.M: a complex-PAM transmitter --------------------------------------%
                                                                       clear;
%-- System parameters ------------------------------------------------------%
 
M = 16;  		% size of alphabet
Ltrain = 1000;          % number of training symbols to transmit
f0 = 2000;              % carrier frequency in Hz
q = 20;          	% q = number of samples per baud; baud rate = 8192/q.
timelag = 20;		% delay in symbol periods of transmit pulse g(t)
Rsample = 8192;         % computer sample period (in secs; can't be changed)
filename = 'Pics/eye.jpg';  % name of JPEG image to be transmitted

%-- Define alphabet --------------------------------------------------------%
%---------------------------------------------------------------------------%

sM = sqrt(M); [x,y] = meshgrid((-sM+1):2:(sM-1),(-sM+1):2:(sM-1));
alphabet = x(:) + 1i*y(:);	%M-QAM alphabet; sqrt(M) must be a power of 2

%-- Convert image to bits & scramble ---------------------------------------%
%---------------------------------------------------------------------------%

X = double(imread(filename));
clf; subplot(222); imshow(uint8(X)); clear bits;
for k=1:8, bits(:,k)=bitget(X(:),k); end;
bits = [bits(:); zeros(log2(M) - rem(length(bits(:)),log2(M)),1)];
rand('state',0); scrambler = rand(length(bits),1)>0.5;
bits = xor(bits, scrambler); 
clear scrambler;

%-- Convert bits to symbols ------------------------------------------------%
%---------------------------------------------------------------------------%
bits = reshape(bits,length(bits)/log2(M),log2(M));
a = alphabet(1 + bits*2.^(0:(log2(M)-1)).'); 
L = length(a);
%---------------------------------------------------------------------------%

disp(' ');
disp(['   At a baud rate of 8192/',num2str(q),' = ',num2str(8192/q), ...
     ' baud, it will take ']); 
disp(['   ', num2str((L + Ltrain)*q/Rsample),' secs to send ',  ...
num2str(Ltrain),' training and ',num2str(L),' data symbols.'])
disp(['   With ', num2str(M),'-ary complex PAM, the bit rate will be ', ...
	num2str(log2(M)*8192/q),' b/s.']); disp(' ');

%-- Generate QAM signal -------------------------------------------%
 
rand('state',0); train = alphabet(ceil(M*rand(Ltrain,1)));
chips = [[train.' a.']; zeros(q-1,Ltrain+L)]; 	% insert q-1 0's btwn ea symbl
tbyT = (-timelag*q : timelag*q) / q;	
g = sinc(tbyT); 
s_tilde = conv(g, chips(:)); 
s = real(s_tilde .* exp(1i*2*pi*f0*(1:length(s_tilde)).'/Rsample)); 
s = s/max(abs(s));
clear a s_tilde chips train;

%-- Transmit signal --------------------------------------------------------%
%---------------------------------------------------------------------------%

reply = [input('Transmit through speaker (y/n)? [y] : ','s'),' '];
if reply(1) ~= 'n',
    disp('Execute the following command at the receiver:');
    disp(' '); disp('              audiorecord > Share/recorded.au'); disp(' ');
    input('Then hit return to begin transmission ... ','s');
    sound(s)
    disp('Done.  Hit <cntrl-c> at receiver to stop recording.');
end;

%-- Save information to be Shared with receiver ----------------------------%
%---------------------------------------------------------------------------%

disp('Saving data ...');

parms = [Rsample/q; f0; Ltrain; L; timelag; size(X).']; 
save Share/parms parms -ascii
save Share/alphabet alphabet

save Cheating/bits bits
save Cheating/X X
save Cheating/s s -ascii
clear