use long preamble for channel estimation and add lms equalizer

2015-04-17 10:23:25 +02:00
parent 5dd30e5e84
commit 48950a502b
9 changed files with 364 additions and 60 deletions
@@ -0,0 +1,63 @@
+/*
+ * Copyright (C) 2015 Bastian Bloessl <bloessl@ccs-labs.org>
+ *
+ * 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 <http://www.gnu.org/licenses/>.
+ */
+
+#include "linear_comb.h"
+
+using namespace gr::ieee802_11::equalizer;
+
+void linear_comb::equalize(const gr_complex *in, gr_complex *out, int n) {
+	if(n < 2)
+		return;
+
+	double avg_mag = (abs(in[11]) + abs(in[25]) + abs(in[39]) + abs(in[53])) / 4;
+
+	gr_complex p = POLARITY[(n - 2) % 127 ];
+
+	double p1 = arg( p * in[11]);
+	double p2 = arg( p * in[25] * conj(p * in[11])) + p1;
+	double p3 = arg( p * in[39] * conj(p * in[25])) + p2;
+	double p4 = arg(-p * in[53] * conj(p * in[39])) + p3;
+
+	double my = (p1 + p2 + p3 + p4) / 4;
+	double mx = (11.0 + 25 + 39 + 53) / 4;
+
+	double var = (((11.0 * 11.0) + (25.0 * 25.0) + (39.0 * 39.0) + (53.0 * 53.0)) / 4) - (mx * mx);
+	double cov =  (( (p1 * 11) + (p2 * 25) + (p3 * 39) + (p4 * 53) ) / 4) - (mx * my);
+	double beta = cov / var;
+	double alpha = my - beta * mx;
+
+	int c = 0;
+	for(int n = 0; n < 64; n++) {
+		if( (n == 11) || (n == 25) || (n == 32) || (n == 39) || (n == 53) || (n < 6) || ( n > 58)) {
+			continue;
+		} else {
+			out[c] = in[n] * exp(gr_complex(0, -n * beta - alpha)) * gr_complex(1 / avg_mag, 0);
+			c++;
+		}
+	}
+
+}
+
+const gr_complex linear_comb::POLARITY[127] = {
+		 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,
+		 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,
+		-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,
+		-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 };