From 5cd7c299e4f8e1f18bc6304638e6f4456ed8976f Mon Sep 17 00:00:00 2001
From: Jens Ahrensfeld <jens@jayfield.org>
Date: Sun, 17 Jan 2021 18:11:47 +0000
Subject: [PATCH] - added

git-svn-id: http://moon:8086/svn/matlab/trunk@151 801c6759-fa7c-4059-a304-17956f83a07c
---
 iridium.m | 111 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)
 create mode 100644 iridium.m

diff --git a/iridium.m b/iridium.m
new file mode 100644
index 0000000..5f22dab
--- /dev/null
+++ b/iridium.m
@@ -0,0 +1,111 @@
+## Copyright (C) 2021 Jens
+## 
+## This program is free software: you can redistribute it and/or modify it
+## under the terms of the GNU General Public License as published by
+## the Free Software Foundation, either version 3 of the License, or
+## (at your option) any later version.
+## 
+## This program is distributed in the hope that it will be useful, but
+## WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+## 
+## You should have received a copy of the GNU General Public License
+## along with this program.  If not, see
+## <https://www.gnu.org/licenses/>.
+
+## -*- texinfo -*- 
+## @deftypefn {} {@var{retval} =} iridium (@var{input1}, @var{input2})
+##
+## @seealso{}
+## @end deftypefn
+
+## Author: Jens <jens@orion>
+## Created: 2021-01-16
+
+function iridium (name)
+[x, fs] = audioread(name);
+xc = (x(:,1) + i*x(:,2))';
+
+close all;
+N = length(x);
+
+phi = angle(xc);
+phi_uw = phi_unwrap(phi);
+dphi = [0 diff(phi_uw)];
+[lo] = losc(dphi);
+xc_cfo = xc .* lo;
+#xc_cfo = xc_cfo .* conj(xc_cfo);
+phi_cfo_uw = phi_unwrap(angle(xc_cfo));
+dphi_cfo = [0 diff(phi_cfo_uw)];
+foff = dphi_cfo*48000;
+found = find_preamble(dphi_cfo)
+
+alpha_mean = 0.1;
+dphi_mean = filter([0 alpha_mean], [1  -(1-alpha_mean)], dphi_cfo);
+
+#plot(1:N, abs(xc), 1:N, atan(xc)); grid;
+#plot(1:N, dphi, 1:N, phi_uw, 1:N, real(lo)); grid;
+
+subplot(3,1,1)
+#plot(1:N, dphi, 1:N, dphi_cfo); legend('dphi','dphi_{cfo}'); grid;
+plot(1:N, real(xc_cfo), 1:N, imag(xc_cfo)); legend('xc_cfo_{re}','xc_cfo_{im}'); grid;
+
+subplot(3,1,2)
+plot(1:N, phi_cfo_uw, "-o"); legend('phi'); grid;
+
+subplot(3,1,3)
+plot(1:N, dphi_cfo, "-o", 1:N, dphi_mean, 'r-'); legend('dphi'); grid;
+
+start=found(1)
+ende=start + 128
+step=2
+
+figure
+plot(real(xc_cfo(start:step:ende)), imag(xc_cfo(start:step:ende)), 'x'); grid;
+
+function found = find_preamble(phi)
+	thr = 0.5;
+	nsmp = 16;
+	last = phi(1);
+	count = 0;
+	found = [];
+	for n=1:length(phi)
+		count = count + 1;
+		if abs(phi(n) - last) > thr;
+			count = 0;
+		endif
+		if count == nsmp
+			found = [found n - nsmp];
+		endif
+		last = phi(n);
+	endfor
+endfunction
+
+function [res] = losc(dphi)
+	alpha_sm = 0.995;
+	dphi_sm = dphi(1);
+	phi = 0;
+	for n=1:length(dphi)
+		res(n) = exp(-j*phi);
+		phi = phi + dphi_sm;
+		dphi_sm = (1-alpha_sm)*dphi_sm + alpha_sm*dphi(n);
+	endfor
+endfunction
+
+function res = phi_unwrap(phi)
+	offset = 0;
+	last = phi(1);
+	for n=1:length(phi)
+		if (phi(n) - last) > pi	
+			offset = offset - 2*pi;
+		end
+		if (phi(n) - last) < -pi	
+			offset = offset + 2*pi;
+		end
+		res(n) = phi(n) + offset;
+		last = phi(n);
+	endfor
+endfunction
+
+endfunction