Transceiver52M: Add dual channel diversity receiver option

This patch add support for dual channel diversity on the receive
path. This allows two antennas two shared antennas to be used for
each ARFCN handling channel in the receiver. This configuration
may improvde performance in multi-path fading environments,
however, noise andpotential interference levels are increased due
to the higher bandwidth used.

The receive path is oversampled by a factor of four for a rate
of 1.083333 Msps. If the receive paths are tuned within a
maximum channel spacing (currently set at 600 kHz), then both
ARFCN frequencies are processed by each channel of the receiver.
Otherwise, the frequency shifted diversity path is disabled and
standard non-diversity operation takes place.

Diversity processing is handled by selecting the path with the
higheset energy level and discarding the burst on the second
path. Selection occurs on a burst-by-burst basis.

Signed-off-by: Thomas Tsou <tom@tsou.cc>

1 files changed, 248 insertions, 0 deletions

diff --git a/Transceiver52M/radioInterfaceDiversity.cpp b/Transceiver52M/radioInterfaceDiversity.cpp
new file mode 100644
index 0000000..8e921b1
--- /dev/null
+++ b/Transceiver52M/radioInterfaceDiversity.cpp
@@ -0,0 +1,248 @@
+/*
+ * SSE Convolution
+ * Copyright (C) 2013 Thomas Tsou <tom@tsou.cc>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <radioInterface.h>
+#include <Logger.h>
+
+#include "Resampler.h"
+
+extern "C" {
+#include "convert.h"
+}
+
+/* Resampling parameters for 64 MHz clocking */
+#define RESAMP_64M_INRATE			20
+#define RESAMP_64M_OUTRATE			80
+
+/* Downlink block size */
+#define CHUNK					625
+
+/* Universal resampling parameters */
+#define NUMCHUNKS				48
+
+/*
+ * Resampling filter bandwidth scaling factor
+ *   This narrows the filter cutoff relative to the output bandwidth
+ *   of the polyphase resampler. At 4 samples-per-symbol using the
+ *   2 pulse Laurent GMSK approximation gives us below 0.5 degrees
+ *   RMS phase error at the resampler output.
+ */
+#define RESAMP_TX4_FILTER		0.45
+
+static size_t resamp_inrate = 0;
+static size_t resamp_inchunk = 0;
+static size_t resamp_outrate = 0;
+static size_t resamp_outchunk = 0;
+
+RadioInterfaceDiversity::RadioInterfaceDiversity(RadioDevice *wRadio,
+						 size_t sps, size_t chans)
+	: RadioInterface(wRadio, sps, chans, 2), outerRecvBuffer(NULL),
+	  mDiversity(false), mFreqSpacing(0.0)
+{
+}
+
+RadioInterfaceDiversity::~RadioInterfaceDiversity()
+{
+	close();
+}
+
+void RadioInterfaceDiversity::close()
+{
+	delete outerRecvBuffer;
+
+	outerRecvBuffer = NULL;
+
+	for (size_t i = 0; i < dnsamplers.size(); i++) {
+		delete dnsamplers[i];
+		dnsamplers[i] = NULL;
+	}
+
+	if (recvBuffer.size())
+		recvBuffer[0] = NULL;
+
+	RadioInterface::close();
+}
+
+bool RadioInterfaceDiversity::setupDiversityChannels()
+{
+	size_t inner_rx_len;
+
+	/* Inner and outer rates */
+	resamp_inrate = RESAMP_64M_INRATE;
+	resamp_outrate = RESAMP_64M_OUTRATE;
+	resamp_inchunk = resamp_inrate * 4;
+	resamp_outchunk = resamp_outrate * 4;
+
+	/* Buffer lengths */
+	inner_rx_len = NUMCHUNKS * resamp_inchunk;
+
+	/* Inside buffer must hold at least 2 bursts */
+	if (inner_rx_len < 157 * mSPSRx * 2) {
+		LOG(ALERT) << "Invalid inner buffer size " << inner_rx_len;
+		return false;
+	}
+
+	/* One Receive buffer and downsampler per diversity channel */
+	for (size_t i = 0; i < mMIMO * mChans; i++) {
+		dnsamplers[i] = new Resampler(resamp_inrate, resamp_outrate);
+		if (!dnsamplers[i]->init()) {
+			LOG(ALERT) << "Rx resampler failed to initialize";
+			return false;
+		}
+
+		recvBuffer[i] = new signalVector(inner_rx_len);
+	}
+
+	return true;
+}
+
+/* Initialize I/O specific objects */
+bool RadioInterfaceDiversity::init(int type)
+{
+	int tx_len, outer_rx_len;
+
+	if ((mMIMO != 2) || (mChans != 2)) {
+		LOG(ALERT) << "Unsupported channel configuration " << mChans;
+		return false;
+	}
+
+	/* Resize for channel combination */
+	sendBuffer.resize(mChans);
+	recvBuffer.resize(mChans * mMIMO);
+	convertSendBuffer.resize(mChans);
+	convertRecvBuffer.resize(mChans);
+	mReceiveFIFO.resize(mChans);
+	dnsamplers.resize(mChans * mMIMO);
+	phases.resize(mChans);
+
+	if (!setupDiversityChannels())
+		return false;
+
+	tx_len = CHUNK * mSPSTx;
+	outer_rx_len = resamp_outchunk;
+
+	for (size_t i = 0; i < mChans; i++) {
+		/* Full rate float and integer outer receive buffers */
+		convertRecvBuffer[i] = new short[outer_rx_len * 2];
+
+		/* Send buffers (not-resampled) */
+		sendBuffer[i] = new signalVector(tx_len);
+		convertSendBuffer[i] = new short[tx_len * 2];
+	}
+
+	outerRecvBuffer = new signalVector(outer_rx_len, dnsamplers[0]->len());
+
+	return true;
+}
+
+bool RadioInterfaceDiversity::tuneRx(double freq, size_t chan)
+{
+	double f0, f1;
+
+	if (chan > 1)
+		return false;
+
+	if (!mRadio->setRxFreq(freq, chan))
+		return false;
+
+	f0 = mRadio->getRxFreq(0);
+	f1 = mRadio->getRxFreq(1);
+
+	mFreqSpacing = f1 - f0;
+
+	if (abs(mFreqSpacing) <= 600e3)
+		mDiversity = true;
+	else
+		mDiversity = false;
+
+	return true;
+}
+
+/* Receive a timestamped chunk from the device */
+void RadioInterfaceDiversity::pullBuffer()
+{
+	bool local_underrun;
+	int rc, num, path0, path1;
+	signalVector *shift, *base;
+	float *in, *out, rate = -mFreqSpacing * 2.0 * M_PI / 1.08333333e6;
+
+	if (recvCursor > recvBuffer[0]->size() - resamp_inchunk)
+		return;
+
+	/* Outer buffer access size is fixed */
+	num = mRadio->readSamples(convertRecvBuffer,
+				  resamp_outchunk,
+				  &overrun,
+				  readTimestamp,
+				  &local_underrun);
+	if ((size_t) num != resamp_outchunk) {
+		LOG(ALERT) << "Receive error " << num;
+		return;
+	}
+
+	for (size_t i = 0; i < mChans; i++) {
+		convert_short_float((float *) outerRecvBuffer->begin(),
+			    convertRecvBuffer[i], 2 * resamp_outchunk);
+
+		if (!i) {
+			path0 = 0;
+			path1 = 2;
+		} else {
+			path0 = 3;
+			path1 = 1;
+		}
+
+		/* Diversity path 1 */
+		base = outerRecvBuffer;
+		in = (float *) base->begin();
+		out = (float *) (recvBuffer[path0]->begin() + recvCursor);
+
+		rc = dnsamplers[2 * i + 0]->rotate(in, resamp_outchunk,
+						   out, resamp_inchunk);
+		if (rc < 0) {
+			LOG(ALERT) << "Sample rate downsampling error";
+		}
+
+		/* Enable path 2 if Nyquist bandwidth is sufficient */
+		if (!mDiversity)
+			continue;
+
+		/* Diversity path 2 */
+		shift = new signalVector(base->size(), base->getStart());
+		in = (float *) shift->begin();
+		out = (float *) (recvBuffer[path1]->begin() + recvCursor);
+
+		rate = i ? -rate : rate;
+		if (!frequencyShift(shift, base, rate, phases[i], &phases[i])) {
+			LOG(ALERT) << "Frequency shift failed";
+		}
+
+		rc = dnsamplers[2 * i + 1]->rotate(in, resamp_outchunk,
+						   out, resamp_inchunk);
+		if (rc < 0) {
+			LOG(ALERT) << "Sample rate downsampling error";
+		}
+
+		delete shift;
+	}
+
+	underrun |= local_underrun;
+	readTimestamp += (TIMESTAMP) resamp_outchunk;
+	recvCursor += resamp_inchunk;
+}