From d5d5df21f912da6a2d84f645f3db36b45550a268 Mon Sep 17 00:00:00 2001
From: Jens Ahrensfeld <jens@jayfield.org>
Date: Sat, 26 Jul 2014 07:54:29 +0000
Subject: [PATCH] Initial version

git-svn-id: http://moon:8086/svn/matlab/trunk@2 801c6759-fa7c-4059-a304-17956f83a07c
---
 ofdm/ofdm_tx.m | 107 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)
 create mode 100644 ofdm/ofdm_tx.m

diff --git a/ofdm/ofdm_tx.m b/ofdm/ofdm_tx.m
new file mode 100644
index 0000000..ceea0b5
--- /dev/null
+++ b/ofdm/ofdm_tx.m
@@ -0,0 +1,107 @@
+% function ofdm_tx(N_data)
+function yv = ofdm_tx(N_data)
+
+j = sqrt(-1);
+WORK_BANDPASS = 1;
+do_evaluate = 0;
+
+% Params
+fa = 48000;
+fc = fa/4;
+F1 = 750;
+F2 = 2250;
+F3 = 3000;
+
+N_Carrier = 226;
+M_qam = 64;
+N_lp = 301;
+TSym = 21.3330E-3
+TGrd = 5.333E-3
+TFrm = TSym+TGrd
+NGrd = round(TGrd*fa)
+NSym = round(TSym*fa)
+NFrm = round(TFrm*fa)
+N_fft = NSym
+
+bin_c = fix(N_fft*fc/fa)+1;
+bin_f1 = fix(N_fft*(fc+F1)/fa)+1;
+bin_f2 = fix(N_fft*(fc+F2)/fa)+1;
+bin_f3 = fix(N_fft*(fc+F3)/fa)+1;
+
+% Source
+qlut = qamtable(M_qam);
+s = round(M_qam*rand(N_data,1)+0.5);
+
+% Band pass for transmission
+f_lp = N_Carrier*fa/N_fft
+hbp = cos(2*pi*(0:N_lp-1)*fc/fa).*sinc((-(N_lp-1)/2:(N_lp-1)/2)*f_lp/fa);
+hbp = hbp/sum(hbp.^2).*Hanning(N_lp)';
+hlp = sinc((-(N_lp-1)/2:(N_lp-1)/2)*f_lp/fa);
+hlp = hlp/sum(hlp.^2).*Hanning(N_lp)';
+
+t = 1;
+if (WORK_BANDPASS == 1)
+    bin_range = N_fft/4-N_Carrier/2:N_fft/4+N_Carrier/2;
+else
+    bin_range = 1:N_Carrier;
+end;
+
+N_bins = length(bin_range);
+for k=1:N_data/N_bins,
+
+    % DC
+    X = zeros(N_fft,1);
+    X(1) = 0;
+
+    for m=1:N_bins,
+        % Data
+        X(bin_range(m)) = qlut(s(t));
+        t = t + 1;
+    end;
+
+    % Additional carrier
+    if (WORK_BANDPASS == 1)
+        X(bin_c) = 1.0;
+        X(bin_f1) = 1.0 + j*1.0;
+        X(bin_f2) = 1.0 - j*1.0;
+        X(bin_f3) = -1.0 + j*1.0;
+    end;
+
+    % Make conj. symmetric in F => real in T
+    X(N_fft:-1:N_fft/2+1) =  conj(X(2:N_fft/2+1));
+
+    % Modulate
+    x = ifft(X);
+    xgrd = x(NSym-NGrd+1:NSym);
+    xt = [xgrd' x']';
+    xv((k-1)*(NFrm)+1:k*(NFrm)) = xt;
+    
+    if (do_evaluate == 1)
+        xf = fft(xt(NGrd+1:NSym+NGrd), N_fft);
+        plot(xf, '+'); grid;
+        pause;
+    end;    
+
+end;
+
+k_fft = 0.3333*sqrt(N_fft);
+
+% Pulse shape
+if (WORK_BANDPASS == 1)
+    yv = real(filter(hbp,1,k_fft*xv));
+   % yv = k_fft*xv;
+else
+    yc = cos(2*pi*(0:length(xv)-1)*fc/fa);
+    yF1 = 1.0/N_fft*cos(2*pi*(0:length(xv)-1)*F1/fa);
+    yF2 = 1.0/N_fft*cos(2*pi*(0:length(xv)-1)*F2/fa);
+    yF3 = 1.0/N_fft*cos(2*pi*(0:length(xv)-1)*F3/fa);
+    yv = yc.*(0.025 + filter(hlp,1,k_fft*xv) + yF1 + yF2 + yF3);
+end;
+
+% Output
+close all;
+
+figure;
+freqz(hlp);
+
+wavwrite(yv,fa,16,'yv.wav')
\ No newline at end of file