clear all;

freq = 1000e3;  %freq of carrier is 1Mhz
P = 1/sqrt(4);
N = 32;
n_b = 10;
n_fft = 32*n_b;

time = 0: (1/(N*freq)): (n_b/freq);
time = time(1:length(time)-1);

% for long simulations, store results in output file
[fid_o1,message]  = fopen('bpskmod.bin','w');
if(fid_o1 == -1)
   message
end




% initialization
last_i = 0;
last_q = 0;
current_i = 0;
current_q = 0;
b = dec2bin(0,10);


%data that will be transmitted, xt
%xt_ip = 2*(rand(1,n_b) > .5) - 1
%xt_ip = ones(1,n_b);
%xt = kron(xt_ip, ones(1,N))

%PN code
gt = [1 -1 1 1  -1 -1 1 -1  1 -1 -1 1  1 1 -1 1  1 1 -1 -1  1 -1 1 -1  1 1 1 -1  1 -1 1 -1];
gt_new = kron(ones(1,n_b), gt);


%------------------------------------------------------
% MAIN LOOP
%------------------------------------------------------


% loop signal processing (cannot use vectors)
for j = 1:length(time)
	i = j;  
xt(i) = 1;
%gt_new(i) = 1;

%carrier freq, ct
cti = sqrt(2*P)*cos(2*pi*freq*time(i));
ctq = sqrt(2*P)*sin(2*pi*freq*time(i));

%BPSK mod data, sxt
sxtiout = cti*xt(i);
sxtqout = ctq*xt(i);

test1(i) = sxtiout;
test2(i) = sxtqout;

%BPSK code mod data, st
sti = sxtiout .* gt_new(i);
stq = sxtqout .* gt_new(i);

test3(i) = sti;
test4(i) = stq;

% convert samples to 10-bit unsigned format
sigt2i = min(max((floor((sti+1.)*511.5)),0.),1023);
sigt2q = min(max((floor((stq+1.)*511.5)),0.),1023);
   
%invert bit order because of pinout
   a = dec2bin(sigt2i, 10);
   b(1) = a(10);
   b(2) = a(9);
   b(3) = a(8);
   b(4) = a(7);
   b(5) = a(6);
   b(6) = a(5);
   b(7) = a(4);
   b(8) = a(3);
   b(9) = a(2);
   b(10) = a(1);
   outputi = bin2dec(b);
   
   
   a = dec2bin(sigt2q, 10);
   b(1) = a(10);
   b(2) = a(9);
   b(3) = a(8);
   b(4) = a(7);
   b(5) = a(6);
   b(6) = a(5);
   b(7) = a(4);
   b(8) = a(3);
   b(9) = a(2);
   b(10) = a(1);
   outputq = bin2dec(b);
   
      % pack samples
   % wait until two complex samples are collected before writing into file
   if(mod(j,2) == 0)
      % even sample
      current_i = outputi;
      current_q = outputq;
      
      a = bitand(bitshift(last_q,-2), 255);
	   fprintf(fid_o1,'%c',a);
      a = bitand(bitor(bitshift(last_q,6),bitshift(last_i,-4)),255);
      fprintf(fid_o1,'%c',a);
      a = bitand(bitor(bitshift(last_i,4),bitshift(current_q,-6)),255);
      fprintf(fid_o1,'%c',a);
      a = bitand(bitor(bitshift(current_q,2),bitshift(current_i,-8)),255);
      fprintf(fid_o1,'%c',a);
      a = bitand(current_i,255);
      fprintf(fid_o1,'%c',a);
      
      % keep track of simulation progress
      if(mod(j,10000) == 0)
         j/10000
     	end;
      
   else
      % odd sample
	   % remember last sample
      last_i = outputi;
      last_q = outputq;
   end;
end   





%plot(sxtiout);
%hold on;
%plot(sxtqout, 'r');

subplot(5,1,1)
plot(time,xt,'b');
axis([0 time(length(time)) -1.5 1.5]);
grid on;
legend('x(t) - binary data');
%xlabel('time (us)');
%ylabel('Amplitude')
title('BPSK DSSS Transmitter - Time Domain Waveforms');

subplot(5,1,2)
plot(time,test1);
axis([0 time(length(time)) -1.5 1.5]);
grid on;
legend('sx(t) - BPSK i waveform');
%xlabel('time (us)');
%ylabel('Amplitude')
%title('sxti')

subplot(5,1,3)
plot(time,test2);
axis([0 time(length(time)) -1.5 1.5]);
grid on;
legend('sx(t) - BPSK q Waveform');
%xlabel('time (us)');
ylabel('Amplitude')
%title('sxtq')

subplot(5,1,4)
plot(time,test3);
axis([0 time(length(time)) -1.5 1.5]);
grid on;
legend('s(t) - BPSK DSSS i Waveform');
%xlabel('time (us)');
%ylabel('Amplitude')
%title('sxti')

subplot(5,1,5)
plot(time,test4);
axis([0 time(length(time)) -1.5 1.5]);
grid on;
legend('s(t) - BPSK DSSS q Waveform');
%xlabel('time (us)');
ylabel('Amplitude')
title('sxtq')

% close opened files
fclose(fid_o1);