%-- SEND.M: a 256-QAM transmitter for ECE4601, Fall 2003 PROJECT ------------%
 
Rsample = 22050;        % computer sample period, in seconds
Ltrain = 1000;          % number of training symbols to transmit
f0 = 6000;              % carrier frequency in Hz
q = 8;          	% q = number of samples per baud; baud rate = Rsample/q.

[re,im] = meshgrid(-15:2:15,-15:2:15); alphabet = re(:) + 1i*im(:);

image = imread('mystery.jpg');

Lmsg = prod(size(image));

bits = dec2bin(double(image(:)),8)-'0';

rand('state',0); scramble = round(rand(Lmsg,8));

bits = rem(bits + scramble, 2);

a = alphabet(1 + bits*2.^(0:7).'); 

rand('state',0); train = alphabet(ceil(256*rand(Ltrain,1)));

chips = [[train.' a.']; zeros(q-1,Ltrain+Lmsg)]; % insert q-1 0's btwn ea symbl

g = sinc((-20*q : 20*q) / q);

s_tilde = conv(g, chips(:));

vco = exp(2i*pi*f0*(1:length(s_tilde)).'/Rsample);

s = real(s_tilde .* vco);

s = s/max(abs(s));

input('Start recording at receiver, then hit return to begin transmission ... ','s');

sound(s, Rsample)

disp('Done.  Stop recording at receiver.');