From bddaaee2d5c49e80cc6b40b9721e40677969634d Mon Sep 17 00:00:00 2001
From: Jens Ahrensfeld <jens@jayfield.org>
Date: Sun, 5 Apr 2015 14:07:25 +0000
Subject: [PATCH] - auto compensate cyclic prefix

git-svn-id: http://moon:8086/svn/matlab/trunk@25 801c6759-fa7c-4059-a304-17956f83a07c
---
 ofdm/fdet.m     |  9 ++++-----
 ofdm/fdet_wav.m | 30 +++++++++++++++++++++++++-----
 2 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/ofdm/fdet.m b/ofdm/fdet.m
index eca070d..bd5a1ed 100644
--- a/ofdm/fdet.m
+++ b/ofdm/fdet.m
@@ -1,8 +1,7 @@
-function [omega, err, dmod, omega_coarse, omega_est] = fdet(x, N, Ng, omega_min, omega_step, omega_max)
+function [omega, err, dmod, omega_coarse, omega_est] = fdet(x, N, Ng, off, omega_min, omega_step, omega_max)
 %
-% Example: fdet_eval(1200, pi/4, -10, [1100 1350 1])
 
-K = fix(length(x-Ng)/(N+Ng));
+K = fix((length(x)-Ng)/(N+Ng))-1;
 
 % Initial guess
 omega_coarse = fdet_coarse(x, N, omega_min, omega_step, omega_max);
@@ -10,12 +9,12 @@ omega_coarse = fdet_coarse(x, N, omega_min, omega_step, omega_max);
 phi_est = 0;
 omega_est = omega_coarse;
 
-off = 0;
 for k=1:K
 	omega(k) = omega_est;
     xp = x((k-1)*(N+Ng)+off+1:k*(N+Ng)+off);
     x_est = exp(-j*(2*pi*omega_est*(0:N-1)' + phi_est));
-    dmod(k) = sum(xp(Ng+1:N+Ng).*x_est);
+    iq = xp(Ng+1:N+Ng).*x_est;
+    dmod(k) = sum(iq);
     phi = angle(dmod(k));
     omega_f = phi/N/(2*pi);
     err(k) = omega_f;
diff --git a/ofdm/fdet_wav.m b/ofdm/fdet_wav.m
index 933e692..06e2f90 100644
--- a/ofdm/fdet_wav.m
+++ b/ofdm/fdet_wav.m
@@ -28,21 +28,41 @@ else
     x = xwav.*exp(-j*(2*pi*fc/fs*(0:len-1)'));
 end
 
+fprintf('Perform frequency correction\n');
 x = x.*exp(j*(2*pi*foff/fs*(0:len-1)'));
-[omega, err, dmod, omega_coarse, omega_est] = fdet(x, N, Ng, omega_min, omega_step, omega_max);
+
+% Remove cyclic prefix
+fprintf('Perform CP calculation\n');
+x0 = x(1:2*(N+Ng));
+x1 = x(N+Ng+1:3*(N+Ng));
+
+c = xcorr(x0, x1);
+[v, ii] = max(abs(c));
+cp_off = mod(ii, Ng+N)
+
+% Detect CFO
+fprintf('Perform frequency detection\n');
+[omega, err, dmod, omega_coarse, omega_est] = fdet(x, N, Ng, cp_off, omega_min, omega_step, omega_max);
 
 f_coarse = omega_coarse*fs
 f_est = omega_est*fs
 
 close all;
-subplot(4,1,1)
+
+plot(abs(c)); grid;
+figure;
+
+subplot(5,1,1)
 plot(1:lge(omega), real(dmod)/N, 1:lge(omega), imag(dmod)/N, 1:lge(omega), abs(dmod)/N); grid; legend('Re', 'Im', 'abs()');
 
-subplot(4,1,2)
+subplot(5,1,2)
 plot(1:lge(omega), err*fs, '-'); grid; legend('error');
 
-subplot(4,1,3)
+subplot(5,1,3)
 plot(1:lge(omega), omega*fs); grid; legend('f');
 
-subplot(4,1,4)
+subplot(5,1,4)
 plot(1:lge(omega), angle(dmod), '-', 1:lge(omega), diff(angle([0 dmod])), 'r-'); grid; legend('phi', 'dphi');
+
+subplot(5,1,5)
+plot(1:lge(omega), abs(dmod)/N - real(dmod)/N, '-'); grid; legend('diff');