mcbts: Add multi-ARFCN channelizing filters

Introduce polyphase channelizer (Rx) and synthesis (Tx) filterbanks,
which serve as the signal processing backend for multi-carrier GSM.

Fast Fourier Transform (FFT) is used internally. FFTW is added as
a new build dependency.

Signed-off-by: Tom Tsou <tom.tsou@ettus.com>

1 files changed, 121 insertions, 0 deletions

diff --git a/Transceiver52M/Synthesis.cpp b/Transceiver52M/Synthesis.cpp
new file mode 100644
index 0000000..0f8197a
--- /dev/null
+++ b/Transceiver52M/Synthesis.cpp
@@ -0,0 +1,121 @@
+/*
+ * Polyphase synthesis filter
+ * 
+ * Copyright (C) 2012-2014 Tom Tsou <tom@tsou.cc>
+ * Copyright (C) 2015 Ettus Research LLC
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ * See the COPYING file in the main directory for details.
+ */
+
+#include <stdlib.h>
+#include <math.h>
+#include <assert.h>
+#include <string.h>
+#include <cstdio>
+
+#include "Logger.h"
+#include "Synthesis.h"
+
+extern "C" {
+#include "common/fft.h"
+#include "common/convolve.h"
+}
+
+static void interleave(float **in, size_t ilen,
+		       float *out, size_t m)
+{
+	size_t i, n;
+
+	for (i = 0; i < ilen; i++) {
+		for (n = 0; n < m; n++) {
+			out[2 * (i * m + n) + 0] = in[n][2 * i + 0];
+			out[2 * (i * m + n) + 1] = in[n][2 * i + 1];
+		}
+	}
+}
+
+size_t Synthesis::inputLen() const
+{
+	return blockLen;
+}
+
+size_t Synthesis::outputLen() const
+{
+	return blockLen * m;
+}
+
+float *Synthesis::inputBuffer(size_t chan) const
+{
+	if (chan >= m)
+		return NULL;
+
+	return hOutputs[chan];
+}
+
+bool Synthesis::resetBuffer(size_t chan)
+{
+	if (chan >= m)
+		return false;
+
+	memset(hOutputs[chan], 0, blockLen * 2 * sizeof(float));
+
+	return true;
+}
+
+/* 
+ * Implementation based on material found in:
+ *
+ * "harris, fred, Multirate Signal Processing, Upper Saddle River, NJ,
+ *     Prentice Hall, 2006."
+ */
+bool Synthesis::rotate(float *out, size_t len)
+{
+	size_t hSize = 2 * hLen * sizeof(float);
+
+	if (!checkLen(blockLen, len)) {
+		std::cout << "Length fail" << std::endl;
+		exit(1);
+		return false;
+	}
+
+	cxvec_fft(fftHandle);
+
+	/* 
+	 * Convolve through filterbank while applying and saving sample history 
+	 */
+	for (size_t i = 0; i < m; i++) {
+		memcpy(&hInputs[i][2 * -hLen], hist[i], hSize);
+		memcpy(hist[i], &hInputs[i][2 * (blockLen - hLen)], hSize);
+
+		convolve_real(hInputs[i], blockLen,
+			      subFilters[i], hLen,
+			      hOutputs[i], blockLen,
+			      0, blockLen, 1, 0);
+	}
+
+	/* Interleave into output vector */
+	interleave(hOutputs, blockLen, out, m);
+
+	return true;
+}
+
+Synthesis::Synthesis(size_t m, size_t blockLen, size_t hLen)
+	: ChannelizerBase(m, blockLen, hLen)
+{
+}
+
+Synthesis::~Synthesis()
+{
+}