Merge branch 'next_memless' into next

18 files changed, 1315 insertions, 62 deletions

diff --git a/Makefile.am b/Makefile.am
index f4e8e00..12dfe6e 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,7 +1,7 @@
 # Copyright (C) 2007, 2008, 2009, 2010 Her Majesty the Queen in Right
 # of Canada (Communications Research Center Canada)
 #
-#  Copyright (C) 2016
+#  Copyright (C) 2017
 #  Matthias P. Braendli, matthias.braendli@mpb.li
 
 #   http://opendigitalradio.org
@@ -62,6 +62,8 @@ odr_dabmod_SOURCES  = src/DabMod.cpp \
 					  src/FicSource.h \
 					  src/FIRFilter.cpp \
 					  src/FIRFilter.h \
+					  src/MemlessPoly.cpp \
+					  src/MemlessPoly.h \
 					  src/PuncturingRule.cpp \
 					  src/PuncturingRule.h \
 					  src/PuncturingEncoder.cpp \
@@ -80,6 +82,8 @@ odr_dabmod_SOURCES  = src/DabMod.cpp \
 					  src/TimestampDecoder.cpp \
 					  src/OutputUHD.cpp \
 					  src/OutputUHD.h \
+					  src/OutputUHDFeedback.cpp \
+					  src/OutputUHDFeedback.h \
 					  src/OutputSoapy.cpp \
 					  src/OutputSoapy.h \
 					  src/InputMemory.cpp \
diff --git a/doc/example.ini b/doc/example.ini
index 1b4a2b4..425dfa4 100644
--- a/doc/example.ini
+++ b/doc/example.ini
@@ -136,6 +136,21 @@ enabled=1
 ; If filtertapsfile is not given, the default taps are used.
 ;filtertapsfile=simple_taps.txt
 
+[poly]
+;Predistortion using memoryless polynom
+enabled=1
+polycoeffile=polyCoefs
+;eg:
+;echo "8
+;0.1
+;0
+;0
+;0
+;0
+;0
+;0
+;0" > polyCoefs
+
 [output]
 ; choose output: possible values: uhd, file, zmq, soapysdr
 output=uhd
@@ -245,6 +260,11 @@ behaviour_refclk_lock_lost=ignore
 ; default value: 0
 max_gps_holdover_time=600
 
+; Enable the TCP server to communicate TX and RX feedback for
+; digital predistortion.
+; Set to 0 to disable
+dpd_port=50055
+
 ; section defining ZeroMQ output properties
 [zmqoutput]
 
diff --git a/doc/zmq-ctrl/zmq_remote.py b/doc/zmq-ctrl/zmq_remote.py
index dffe53e..3a54b20 100755
--- a/doc/zmq-ctrl/zmq_remote.py
+++ b/doc/zmq-ctrl/zmq_remote.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python
 
 import sys
 import zmq
@@ -18,7 +18,7 @@ message_parts = sys.argv[2:]
 # first do a ping test
 
 print("ping")
-sock.send("ping")
+sock.send(b"ping")
 data = sock.recv_multipart()
 print("Received: {}".format(len(data)))
 for i,part in enumerate(data):
@@ -32,7 +32,7 @@ for i, part in enumerate(message_parts):
 
     print("Send {}({}): '{}'".format(i, f, part))
 
-    sock.send(part, flags=f)
+    sock.send(part.encode(), flags=f)
 
 data = sock.recv_multipart()
 
diff --git a/dpd/README.md b/dpd/README.md
new file mode 100644
index 0000000..ec7cec2
--- /dev/null
+++ b/dpd/README.md
@@ -0,0 +1,20 @@
+Digital Predistortion for ODR-DabMod
+====================================
+
+This folder contains work in progress for digital predistortion. It requires:
+
+- USRP B200.
+- Power amplifier.
+- A feedback connection from the power amplifier output, at an appropriate power level for the B200.
+  Usually this is done with a directional coupler.
+- ODR-DabMod with enabled dpd_port, and with a samplerate of 8192000 samples per second.
+- Synchronous=1 so that the USRP has the timestamping set properly, internal refclk and pps
+  are sufficient for this example.
+- A live mux source with TIST enabled.
+
+See dpd/dpd.ini for an example.
+
+TODO
+----
+
+Implement a PA model that updates the predistorter.
diff --git a/dpd/dpd.ini b/dpd/dpd.ini
new file mode 100644
index 0000000..5e809e5
--- /dev/null
+++ b/dpd/dpd.ini
@@ -0,0 +1,44 @@
+[remotecontrol]
+telnet=1
+telnetport=2121
+zmqctrl=1
+zmqctrlendpoint=tcp://127.0.0.1:9400
+
+[log]
+syslog=0
+filelog=0
+filename=/dev/stderr
+
+[input]
+transport=tcp
+source=localhost:9200
+
+[modulator]
+digital_gain=0.8
+rate=8192000
+
+[firfilter]
+enabled=0
+
+[output]
+output=uhd
+
+[uhdoutput]
+device=
+master_clock_rate=32768000
+type=b200
+txgain=75
+channel=13C
+refclk_source=internal
+pps_source=none
+behaviour_refclk_lock_lost=ignore
+max_gps_holdover_time=600
+dpd_port=50055
+rxgain=0
+
+[delaymanagement]
+; Use synchronous=1 so that the USRP time is set. This works
+; even in the absence of a reference clk and PPS
+synchronous=1
+mutenotimestamps=1
+offset=4.0
diff --git a/dpd/show_spectrum.py b/dpd/show_spectrum.py
new file mode 100755
index 0000000..e92c1d0
--- /dev/null
+++ b/dpd/show_spectrum.py
@@ -0,0 +1,180 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+#
+# This is an example tool that shows how to connect to ODR-DabMod's dpd TCP server
+# and get samples from there.
+#
+# Since the TX and RX samples are not perfectly aligned, the tool has to align them properly,
+# which is done in two steps: First on sample-level using a correlation, then with subsample
+# accuracy using a FFT approach.
+#
+# It requires SciPy and matplotlib.
+#
+# Copyright (C) 2017 Matthias P. Braendli
+# http://www.opendigitalradio.org
+# Licence: The MIT License, see notice at the end of this file
+
+import sys
+import socket
+import struct
+import numpy as np
+import matplotlib.pyplot as pp
+from matplotlib.animation import FuncAnimation
+import argparse
+
+SIZEOF_SAMPLE = 8 # complex floats
+
+def main():
+    parser = argparse.ArgumentParser(description="Plot the spectrum of ODR-DabMod's DPD feedback")
+    parser.add_argument('--samps', default='10240', help='Number of samples to request at once',
+            required=False)
+    parser.add_argument('--port', default='50055',
+            help='port to connect to ODR-DabMod DPD (default: 50055)',
+            required=False)
+
+    parser.add_argument('--animated', action='store_true', help='Enable real-time animation')
+
+    cli_args = parser.parse_args()
+
+    port = int(cli_args.port)
+    num_samps_to_request = int(cli_args.samps)
+
+    if cli_args.animated:
+        plot_spectrum_animated(port, num_samps_to_request)
+    else:
+        plot_spectrum_once(port, num_samps_to_request)
+
+def recv_exact(sock, num_bytes):
+    bufs = []
+    while num_bytes > 0:
+        b = sock.recv(num_bytes)
+        if len(b) == 0:
+            break
+        num_bytes -= len(b)
+        bufs.append(b)
+    return b''.join(bufs)
+
+def get_samples(port, num_samps_to_request):
+    """Connect to ODR-DabMod, retrieve TX and RX samples, load
+    into numpy arrays, and return a tuple
+    (tx_timestamp, tx_samples, rx_timestamp, rx_samples)
+    where the timestamps are doubles, and the samples are numpy
+    arrays of complex floats, both having the same size
+    """
+
+    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    s.connect(('localhost', port))
+
+    print("Send version");
+    s.sendall(b"\x01")
+
+    print("Send request for {} samples".format(num_samps_to_request))
+    s.sendall(struct.pack("=I", num_samps_to_request))
+
+    print("Wait for TX metadata")
+    num_samps, tx_second, tx_pps = struct.unpack("=III", recv_exact(s, 12))
+    tx_ts = tx_second + tx_pps / 16384000.0
+
+    if num_samps > 0:
+        print("Receiving {} TX samples".format(num_samps))
+        txframe_bytes = recv_exact(s, num_samps * SIZEOF_SAMPLE)
+        txframe = np.fromstring(txframe_bytes, dtype=np.complex64)
+    else:
+        txframe = np.array([], dtype=np.complex64)
+
+    print("Wait for RX metadata")
+    rx_second, rx_pps = struct.unpack("=II", recv_exact(s, 8))
+    rx_ts = rx_second + rx_pps / 16384000.0
+
+    if num_samps > 0:
+        print("Receiving {} RX samples".format(num_samps))
+        rxframe_bytes = recv_exact(s, num_samps * SIZEOF_SAMPLE)
+        rxframe = np.fromstring(rxframe_bytes, dtype=np.complex64)
+    else:
+        rxframe = np.array([], dtype=np.complex64)
+
+    print("Disconnecting")
+    s.close()
+
+    return (tx_ts, txframe, rx_ts, rxframe)
+
+def get_spectrum(port, num_samps_to_request):
+    tx_ts, txframe, rx_ts, rxframe = get_samples(port, num_samps_to_request)
+
+    # convert to complex doubles for more dynamic range
+    txframe = txframe.astype(np.complex128)
+    rxframe = rxframe.astype(np.complex128)
+
+    print("Received {} & {} frames at {} and {}".format(
+        len(txframe), len(rxframe), tx_ts, rx_ts))
+
+    print("Calculate TX and RX spectrum assuming 8192000 samples per second")
+    tx_spectrum = np.fft.fftshift(np.fft.fft(txframe, fft_size))
+    tx_power = 20*np.log10(np.abs(tx_spectrum))
+
+    rx_spectrum = np.fft.fftshift(np.fft.fft(rxframe, fft_size))
+    rx_power = 20*np.log10(np.abs(rx_spectrum))
+    return tx_power, rx_power
+
+
+sampling_rate = 8192000
+fft_size = 4096
+freqs = np.fft.fftshift(np.fft.fftfreq(fft_size, d=1./sampling_rate))
+
+def plot_spectrum_once(port, num_samps_to_request):
+    tx_power, rx_power = get_spectrum(port, num_samps_to_request)
+    fig = pp.figure()
+
+    fig.suptitle("TX and RX spectrum")
+    ax1 = fig.add_subplot(211)
+    ax1.set_title("TX")
+    ax1.plot(freqs, tx_power, 'r')
+    ax2 = fig.add_subplot(212)
+    ax2.set_title("RX")
+    ax2.plot(freqs, rx_power, 'b')
+    pp.show()
+
+def plot_spectrum_animated(port, num_samps_to_request):
+    fig, axes = pp.subplots(2, sharex=True)
+    line1, = axes[0].plot(freqs, np.ones(len(freqs)), 'r', animated=True)
+    axes[0].set_title("TX")
+    line2, = axes[1].plot(freqs, np.ones(len(freqs)), 'b', animated=True)
+    axes[1].set_title("RX")
+    lines = [line1, line2]
+
+    axes[0].set_ylim(-30, 50)
+    axes[1].set_ylim(-60, 40)
+
+    def update(frame):
+        tx_power, rx_power = get_spectrum(port, num_samps_to_request)
+
+        lines[0].set_ydata(tx_power)
+        lines[1].set_ydata(rx_power)
+        return lines
+
+    ani = FuncAnimation(fig, update, blit=True)
+    pp.show()
+
+main()
+
+# The MIT License (MIT)
+#
+# Copyright (c) 2017 Matthias P. Braendli
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
diff --git a/dpd/store_received.py b/dpd/store_received.py
new file mode 100755
index 0000000..902f607
--- /dev/null
+++ b/dpd/store_received.py
@@ -0,0 +1,157 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+#
+# This is an example tool that shows how to connect to ODR-DabMod's dpd TCP server
+# and get samples from there.
+#
+# Since the TX and RX samples are not perfectly aligned, the tool has to align them properly,
+# which is done in two steps: First on sample-level using a correlation, then with subsample
+# accuracy using a FFT approach.
+#
+# It requires SciPy and matplotlib.
+#
+# Copyright (C) 2017 Matthias P. Braendli
+# http://www.opendigitalradio.org
+# Licence: The MIT License, see notice at the end of this file
+
+import sys
+import socket
+import struct
+import numpy as np
+import matplotlib.pyplot as pp
+from matplotlib.animation import FuncAnimation
+import argparse
+import os
+import time
+import src.dab_util as du
+
+SIZEOF_SAMPLE = 8 # complex floats
+
+def main():
+    parser = argparse.ArgumentParser(description="Plot the spectrum of ODR-DabMod's DPD feedback")
+    parser.add_argument('--samps', default='10240', help='Number of samples to request at once',
+            required=False)
+    parser.add_argument('--port', default='50055',
+            help='port to connect to ODR-DabMod DPD (default: 50055)',
+            required=False)
+    parser.add_argument('--out_dir', default='/tmp/record', help='Output directory',
+            required=False)
+    parser.add_argument('--count', default='1', help='Number of recordings',
+            required=False)
+    parser.add_argument('--verbose', type=int, default=0, help='Level of verbosity',
+            required=False)
+
+    parser.add_argument('--animated', action='store_true', help='Enable real-time animation')
+
+
+    cli_args = parser.parse_args()
+
+    if not os.path.isdir(cli_args.out_dir):
+        os.mkdir(cli_args.out_dir)
+
+    port = int(cli_args.port)
+    num_samps_to_request = int(cli_args.samps)
+
+    for i in range(int(cli_args.count)):
+        if i>0:
+            time.sleep(0.1)
+
+        tx_ts, txframe, rx_ts, rxframe = get_samples(port, num_samps_to_request)
+
+        txframe_aligned, rxframe_aligned = du.subsample_align(txframe, rxframe)
+
+        if cli_args.verbose >= 1:
+            n_up = 32
+            lag = du.lag_upsampling(txframe, rxframe, n_up)
+            lag_aligned = du.lag_upsampling(txframe_aligned, rxframe_aligned, n_up)
+            print("Lag from %d times oversampled signal:" % n_up)
+            print("Before alignment: %.2f" % lag)
+            print("After alignment: %.2f" % lag_aligned)
+            print("")
+
+        txframe_aligned.tofile("%s/%d_tx_record.iq" % (cli_args.out_dir, i))
+        rxframe_aligned.tofile("%s/%d_rx_record.iq" % (cli_args.out_dir, i))
+
+
+def recv_exact(sock, num_bytes):
+    bufs = []
+    while num_bytes > 0:
+        b = sock.recv(num_bytes)
+        if len(b) == 0:
+            break
+        num_bytes -= len(b)
+        bufs.append(b)
+    return b''.join(bufs)
+
+def get_samples(port, num_samps_to_request):
+    """Connect to ODR-DabMod, retrieve TX and RX samples, load
+    into numpy arrays, and return a tuple
+    (tx_timestamp, tx_samples, rx_timestamp, rx_samples)
+    where the timestamps are doubles, and the samples are numpy
+    arrays of complex floats, both having the same size
+    """
+
+    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    s.connect(('localhost', port))
+
+    print("Send version");
+    s.sendall(b"\x01")
+
+    print("Send request for {} samples".format(num_samps_to_request))
+    s.sendall(struct.pack("=I", num_samps_to_request))
+
+    print("Wait for TX metadata")
+    num_samps, tx_second, tx_pps = struct.unpack("=III", recv_exact(s, 12))
+    tx_ts = tx_second + tx_pps / 16384000.0
+
+    if num_samps > 0:
+        print("Receiving {} TX samples".format(num_samps))
+        txframe_bytes = recv_exact(s, num_samps * SIZEOF_SAMPLE)
+        txframe = np.fromstring(txframe_bytes, dtype=np.complex64)
+    else:
+        txframe = np.array([], dtype=np.complex64)
+
+    print("Wait for RX metadata")
+    rx_second, rx_pps = struct.unpack("=II", recv_exact(s, 8))
+    rx_ts = rx_second + rx_pps / 16384000.0
+
+    if num_samps > 0:
+        print("Receiving {} RX samples".format(num_samps))
+        rxframe_bytes = recv_exact(s, num_samps * SIZEOF_SAMPLE)
+        rxframe = np.fromstring(rxframe_bytes, dtype=np.complex64)
+    else:
+        rxframe = np.array([], dtype=np.complex64)
+
+    print("Disconnecting")
+    s.close()
+
+    return (tx_ts, txframe, rx_ts, rxframe)
+
+
+sampling_rate = 8192000
+fft_size = 4096
+freqs = np.fft.fftshift(np.fft.fftfreq(fft_size, d=1./sampling_rate))
+
+main()
+
+# The MIT License (MIT)
+#
+# Copyright (c) 2017 Matthias P. Braendli
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
diff --git a/src/ConfigParser.cpp b/src/ConfigParser.cpp
index 393f58a..459811f 100644
--- a/src/ConfigParser.cpp
+++ b/src/ConfigParser.cpp
@@ -168,6 +168,12 @@ static void parse_configfile(
             pt.get<std::string>("firfilter.filtertapsfile", "default");
     }
 
+    // Poly coefficients:
+    if (pt.get("poly.enabled", 0) == 1) {
+        mod_settings.polyCoefFilename =
+            pt.get<std::string>("poly.polycoeffile", "default");
+    }
+
     // Output options
     std::string output_selected;
     try {
@@ -212,6 +218,7 @@ static void parse_configfile(
         }
 
         outputuhd_conf.txgain = pt.get("uhdoutput.txgain", 0.0);
+        outputuhd_conf.rxgain = pt.get("uhdoutput.rxgain", 0.0);
         outputuhd_conf.frequency = pt.get<double>("uhdoutput.frequency", 0);
         std::string chan = pt.get<std::string>("uhdoutput.channel", "");
         outputuhd_conf.dabMode = mod_settings.dabMode;
@@ -249,6 +256,8 @@ static void parse_configfile(
 
         outputuhd_conf.maxGPSHoldoverTime = pt.get("uhdoutput.max_gps_holdover_time", 0);
 
+        outputuhd_conf.dpdFeedbackServerPort = pt.get<long>("uhdoutput.dpd_port", 0);
+
         mod_settings.outputuhd_conf = outputuhd_conf;
         mod_settings.useUHDOutput = 1;
     }
diff --git a/src/ConfigParser.h b/src/ConfigParser.h
index 2f49595..22a4fc5 100644
--- a/src/ConfigParser.h
+++ b/src/ConfigParser.h
@@ -74,6 +74,8 @@ struct mod_settings_t {
 
     std::string filterTapsFilename = "";
 
+    std::string polyCoefFilename = "";
+
 
 #if defined(HAVE_OUTPUT_UHD)
     OutputUHDConfig outputuhd_conf;
diff --git a/src/DabMod.cpp b/src/DabMod.cpp
index 88c7524..7c342a2 100644
--- a/src/DabMod.cpp
+++ b/src/DabMod.cpp
@@ -327,7 +327,8 @@ int launch_modulator(int argc, char* argv[])
                 mod_settings.digitalgain,
                 mod_settings.normalise,
                 mod_settings.gainmodeVariance,
-                mod_settings.filterTapsFilename);
+                mod_settings.filterTapsFilename,
+                mod_settings.polyCoefFilename);
 
         if (format_converter) {
             flowgraph.connect(modulator, format_converter);
@@ -431,7 +432,8 @@ int launch_modulator(int argc, char* argv[])
                     mod_settings.digitalgain,
                     mod_settings.normalise,
                     mod_settings.gainmodeVariance,
-                    mod_settings.filterTapsFilename);
+                    mod_settings.filterTapsFilename,
+                    mod_settings.polyCoefFilename);
 
             if (format_converter) {
                 flowgraph.connect(modulator, format_converter);
diff --git a/src/DabModulator.cpp b/src/DabModulator.cpp
index c41b8fc..4e0bc33 100644
--- a/src/DabModulator.cpp
+++ b/src/DabModulator.cpp
@@ -47,6 +47,7 @@
 #include "Resampler.h"
 #include "ConvEncoder.h"
 #include "FIRFilter.h"
+#include "MemlessPoly.h"
 #include "TII.h"
 #include "PuncturingEncoder.h"
 #include "TimeInterleaver.h"
@@ -61,7 +62,8 @@ DabModulator::DabModulator(
         unsigned dabMode, GainMode gainMode,
         float& digGain, float normalise,
         float gainmodeVariance,
-        const std::string& filterTapsFilename
+        const std::string& filterTapsFilename,
+        const std::string& polyCoefFilename
         ) :
     ModInput(),
     myOutputRate(outputRate),
@@ -74,6 +76,7 @@ DabModulator::DabModulator(
     myEtiSource(etiSource),
     myFlowgraph(NULL),
     myFilterTapsFilename(filterTapsFilename),
+    myPolyCoefFilename(polyCoefFilename),
     myTiiConfig(tiiConfig)
 {
     PDEBUG("DabModulator::DabModulator(%u, %u, %u, %zu) @ %p\n",
@@ -203,7 +206,8 @@ int DabModulator::process(Buffer* dataOut)
                 (1 + myNbSymbols), myNbCarriers, mySpacing);
 
         auto cifGain = make_shared<GainControl>(
-                mySpacing, myGainMode, myDigGain, myNormalise, myGainmodeVariance);
+                mySpacing, myGainMode, myDigGain, myNormalise, 
+                myGainmodeVariance);
 
         rcs.enrol(cifGain.get());
 
@@ -215,6 +219,19 @@ int DabModulator::process(Buffer* dataOut)
             cifFilter = make_shared<FIRFilter>(myFilterTapsFilename);
             rcs.enrol(cifFilter.get());
         }
+
+        shared_ptr<MemlessPoly> cifPoly;
+        if (not myPolyCoefFilename.empty()) {
+            cifPoly = make_shared<MemlessPoly>(myPolyCoefFilename);
+            etiLog.level(debug) << myPolyCoefFilename << "\n";
+            etiLog.level(debug) << cifPoly->m_coefs[0] << " " <<
+                cifPoly->m_coefs[1] << " "<< cifPoly->m_coefs[2] << " "<<
+                cifPoly->m_coefs[3] << " "<< cifPoly->m_coefs[4] << " "<<
+                cifPoly->m_coefs[5] << " "<< cifPoly->m_coefs[6] << " "<<
+                cifPoly->m_coefs[7] << "\n";
+            rcs.enrol(cifPoly.get());
+        }
+
         auto myOutput = make_shared<OutputMemory>(dataOut);
 
         shared_ptr<Resampler> cifRes;
@@ -306,7 +323,8 @@ int DabModulator::process(Buffer* dataOut)
             auto subchConv = make_shared<ConvEncoder>(subchSizeIn);
 
             // Configuring puncturing encoder
-            auto subchPunc = make_shared<PuncturingEncoder>(subchannel->framesizeCu());
+            auto subchPunc =
+                make_shared<PuncturingEncoder>(subchannel->framesizeCu());
 
             for (const auto& rule : subchannel->get_rules()) {
                 PDEBUG(" Adding rule:\n");
@@ -342,34 +360,44 @@ int DabModulator::process(Buffer* dataOut)
         if (useCicEq) {
             myFlowgraph->connect(cifSig, cifCicEq);
             myFlowgraph->connect(cifCicEq, cifOfdm);
-        } else {
+        }
+        else {
             myFlowgraph->connect(cifSig, cifOfdm);
         }
         myFlowgraph->connect(cifOfdm, cifGain);
         myFlowgraph->connect(cifGain, cifGuard);
 
+        auto cifOut = cifPoly ?
+            static_pointer_cast<ModPlugin>(cifPoly) :
+            static_pointer_cast<ModPlugin>(myOutput);
+
         if (cifFilter) {
             myFlowgraph->connect(cifGuard, cifFilter);
             if (cifRes) {
                 myFlowgraph->connect(cifFilter, cifRes);
-                myFlowgraph->connect(cifRes, myOutput);
-            } else {
-                myFlowgraph->connect(cifFilter, myOutput);
+                myFlowgraph->connect(cifRes, cifOut);
+            }
+            else {
+                myFlowgraph->connect(cifFilter, cifOut);
             }
         }
-        else { //no filtering
+        else {
             if (cifRes) {
                 myFlowgraph->connect(cifGuard, cifRes);
-                myFlowgraph->connect(cifRes, myOutput);
-            } else {
-                myFlowgraph->connect(cifGuard, myOutput);
+                myFlowgraph->connect(cifRes, cifOut);
             }
+            else {
+                myFlowgraph->connect(cifGuard, cifOut);
+            }
+        }
 
+        if (cifPoly) {
+            myFlowgraph->connect(cifPoly, myOutput);
         }
     }
 
     ////////////////////////////////////////////////////////////////////
-    // Proccessing data
+    // Processing data
     ////////////////////////////////////////////////////////////////////
     return myFlowgraph->run();
 }
diff --git a/src/DabModulator.h b/src/DabModulator.h
index c9bdbe1..0c691dd 100644
--- a/src/DabModulator.h
+++ b/src/DabModulator.h
@@ -55,7 +55,8 @@ public:
             unsigned dabMode, GainMode gainMode,
             float& digGain, float normalise,
             float gainmodeVariance,
-            const std::string& filterTapsFilename);
+            const std::string& filterTapsFilename,
+            const std::string& polyCoefFilename);
     DabModulator(const DabModulator& other) = delete;
     DabModulator& operator=(const DabModulator& other) = delete;
     virtual ~DabModulator();
@@ -80,6 +81,7 @@ protected:
     Flowgraph* myFlowgraph;
     OutputMemory* myOutput;
     std::string myFilterTapsFilename;
+    std::string myPolyCoefFilename;
     tii_config_t& myTiiConfig;
 
     size_t myNbSymbols;
diff --git a/src/MemlessPoly.cpp b/src/MemlessPoly.cpp
new file mode 100644
index 0000000..7e074eb
--- /dev/null
+++ b/src/MemlessPoly.cpp
@@ -0,0 +1,187 @@
+/*
+   Copyright (C) 2007, 2008, 2009, 2010, 2011 Her Majesty the Queen in
+   Right of Canada (Communications Research Center Canada)
+
+   Copyright (C) 2017
+   Matthias P. Braendli, matthias.braendli@mpb.li
+   Andreas Steger, andreas.steger@digris.ch
+
+    http://opendigitalradio.org
+
+   This block implements a memoryless polynom for digital predistortion.
+   For better performance, multiplying is done in another thread, leading
+   to a pipeline delay of two calls to MemlessPoly::process
+ */
+/*
+   This file is part of ODR-DabMod.
+
+   ODR-DabMod 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.
+
+   ODR-DabMod 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 ODR-DabMod.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "MemlessPoly.h"
+#include "PcDebug.h"
+#include "Utils.h"
+
+#include <stdio.h>
+#include <stdexcept>
+
+#include <array>
+#include <iostream>
+#include <fstream>
+#include <memory>
+
+using namespace std;
+
+
+// By default the signal is unchanged
+static const std::array<float, 8> default_coefficients({
+        1, 0.0, 0.0, 0.0,
+        0.0, 0.0, 0.0, 0.0
+        });
+
+
+MemlessPoly::MemlessPoly(const std::string& coefs_file) :
+    PipelinedModCodec(),
+    RemoteControllable("memlesspoly"),
+    m_coefs_file(coefs_file)
+{
+    PDEBUG("MemlessPoly::MemlessPoly(%s) @ %p\n",
+            coefs_file.c_str(), this);
+
+    RC_ADD_PARAMETER(ncoefs, "(Read-only) number of coefficients.");
+    RC_ADD_PARAMETER(coeffile, "Filename containing coefficients. When written to, the new file gets automatically loaded.");
+
+    load_coefficients(m_coefs_file);
+
+    start_pipeline_thread();
+}
+
+void MemlessPoly::load_coefficients(const std::string &coefFile)
+{
+    std::vector<float> coefs;
+    if (coefFile == "default") {
+        std::copy(default_coefficients.begin(), default_coefficients.end(),
+                std::back_inserter(coefs));
+    }
+    else {
+        std::ifstream coef_fstream(coefFile.c_str());
+        if(!coef_fstream) {
+            fprintf(stderr, "MemlessPoly: file %s could not be opened !\n", coefFile.c_str());
+            throw std::runtime_error("MemlessPoly: Could not open file with coefs! ");
+        }
+        int n_coefs;
+        coef_fstream >> n_coefs;
+
+        if (n_coefs <= 0) {
+            fprintf(stderr, "MemlessPoly: warning: coefs file has invalid format\n");
+            throw std::runtime_error("MemlessPoly: coefs file has invalid format.");
+        }
+
+        if (n_coefs != 8) {
+            throw std::runtime_error( "MemlessPoly: error: coefs file does not have 8 coefs\n");
+        }
+
+        fprintf(stderr, "MemlessPoly: Reading %d coefs...\n", n_coefs);
+
+        coefs.resize(n_coefs);
+
+        int n;
+        for (n = 0; n < n_coefs; n++) {
+            coef_fstream >> coefs[n];
+            PDEBUG("MemlessPoly: coef: %f\n",  coefs[n] );
+            if (coef_fstream.eof()) {
+                fprintf(stderr, "MemlessPoly: file %s should contains %d coefs, but EOF reached "\
+                        "after %d coefs !\n", coefFile.c_str(), n_coefs, n);
+                throw std::runtime_error("MemlessPoly: coefs file invalid ! ");
+            }
+        }
+    }
+
+    {
+        std::lock_guard<std::mutex> lock(m_coefs_mutex);
+
+        m_coefs = coefs;
+    }
+}
+
+
+int MemlessPoly::internal_process(Buffer* const dataIn, Buffer* dataOut)
+{
+        const float* in = reinterpret_cast<const float*>(dataIn->getData());
+        float* out      = reinterpret_cast<float*>(dataOut->getData());
+        size_t sizeIn   = dataIn->getLength() / sizeof(float);
+
+        {
+             std::lock_guard<std::mutex> lock(m_coefs_mutex);
+             for (size_t i = 0; i < sizeIn; i += 1) {
+                 float mag = std::abs(in[i]);
+                 //out[i] = in[i];
+                 out[i] = in[i] * (
+                     m_coefs[0] +
+                     m_coefs[1] * mag +
+                     m_coefs[2] * mag*mag +
+                     m_coefs[3] * mag*mag*mag +
+                     m_coefs[4] * mag*mag*mag*mag +
+                     m_coefs[5] * mag*mag*mag*mag*mag +
+                     m_coefs[6] * mag*mag*mag*mag*mag*mag +
+                     m_coefs[7] * mag*mag*mag*mag*mag*mag*mag
+                     );
+            }
+        }
+
+    return dataOut->getLength();
+}
+
+void MemlessPoly::set_parameter(const string& parameter, const string& value)
+{
+    stringstream ss(value);
+    ss.exceptions ( stringstream::failbit | stringstream::badbit );
+
+    if (parameter == "ncoefs") {
+        throw ParameterError("Parameter 'ncoefs' is read-only");
+    }
+    else if (parameter == "coeffile") {
+        try {
+            load_coefficients(value);
+            m_coefs_file = value;
+        }
+        catch (std::runtime_error &e) {
+            throw ParameterError(e.what());
+        }
+    }
+    else {
+        stringstream ss;
+        ss << "Parameter '" << parameter <<
+            "' is not exported by controllable " << get_rc_name();
+        throw ParameterError(ss.str());
+    }
+}
+
+const string MemlessPoly::get_parameter(const string& parameter) const
+{
+    stringstream ss;
+    if (parameter == "ncoefs") {
+        ss << m_coefs.size();
+    }
+    else if (parameter == "coefFile") {
+        ss << m_coefs_file;
+    }
+    else {
+        ss << "Parameter '" << parameter <<
+            "' is not exported by controllable " << get_rc_name();
+        throw ParameterError(ss.str());
+    }
+    return ss.str();
+}
+
diff --git a/src/MemlessPoly.h b/src/MemlessPoly.h
new file mode 100644
index 0000000..210b4b4
--- /dev/null
+++ b/src/MemlessPoly.h
@@ -0,0 +1,78 @@
+/*
+   Copyright (C) 2007, 2008, 2009, 2010, 2011 Her Majesty the Queen in
+   Right of Canada (Communications Research Center Canada)
+
+   Copyright (C) 2017
+   Matthias P. Braendli, matthias.braendli@mpb.li
+
+    http://opendigitalradio.org
+ */
+/*
+   This file is part of ODR-DabMod.
+
+   ODR-DabMod 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.
+
+   ODR-DabMod 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 ODR-DabMod.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#ifdef HAVE_CONFIG_H
+#   include <config.h>
+#endif
+
+
+#include "RemoteControl.h"
+#include "ModPlugin.h"
+#include "PcDebug.h"
+#include "ThreadsafeQueue.h"
+
+#include <sys/types.h>
+#include <complex>
+#include <thread>
+#include <vector>
+#include <time.h>
+#include <cstdio>
+#include <string>
+#include <memory>
+
+#define MEMLESSPOLY_PIPELINE_DELAY 1
+
+typedef std::complex<float> complexf;
+
+class MemlessPoly : public PipelinedModCodec, public RemoteControllable
+{
+public:
+    MemlessPoly(const std::string& coefs_file);
+
+    virtual const char* name() { return "MemlessPoly"; }
+
+    /******* REMOTE CONTROL ********/
+    virtual void set_parameter(const std::string& parameter,
+            const std::string& value);
+
+    virtual const std::string get_parameter(
+            const std::string& parameter) const;
+
+//TODO to protected
+    std::vector<float> m_coefs;
+
+
+protected:
+    int internal_process(Buffer* const dataIn, Buffer* dataOut);
+    void load_coefficients(const std::string &coefFile);
+
+    std::string m_coefs_file;
+
+    mutable std::mutex m_coefs_mutex;
+};
+
diff --git a/src/OutputUHD.cpp b/src/OutputUHD.cpp
index 3a5225b..c2f985b 100644
--- a/src/OutputUHD.cpp
+++ b/src/OutputUHD.cpp
@@ -50,7 +50,7 @@
 using namespace std;
 
 // Maximum number of frames that can wait in uwd.frames
-static const size_t FRAMES_MAX_SIZE = 2;
+static const size_t FRAMES_MAX_SIZE = 8;
 
 typedef std::complex<float> complexf;
 
@@ -80,6 +80,36 @@ void uhd_msg_handler(uhd::msg::type_t type, const std::string &msg)
     }
 }
 
+static void tune_usrp_to(
+        uhd::usrp::multi_usrp::sptr usrp,
+        double lo_offset,
+        double frequency)
+{
+    if (lo_offset != 0.0) {
+        etiLog.level(info) << std::fixed << std::setprecision(3) <<
+            "OutputUHD:Setting freq to " << frequency <<
+            "  with LO offset " << lo_offset << "...";
+
+        const auto tr = uhd::tune_request_t(frequency, lo_offset);
+        uhd::tune_result_t result = usrp->set_tx_freq(tr);
+
+        etiLog.level(debug) << "OutputUHD:" <<
+            std::fixed << std::setprecision(0) <<
+            " Target RF: " << result.target_rf_freq <<
+            " Actual RF: " << result.actual_rf_freq <<
+            " Target DSP: " << result.target_dsp_freq <<
+            " Actual DSP: " << result.actual_dsp_freq;
+    }
+    else {
+        //set the centre frequency
+        etiLog.level(info) << std::fixed << std::setprecision(3) <<
+            "OutputUHD:Setting freq to " << frequency << "...";
+        usrp->set_tx_freq(frequency);
+    }
+
+    usrp->set_rx_freq(frequency);
+}
+
 // Check function for GPS TIMELOCK sensor from the ODR LEA-M8F board GPSDO
 bool check_gps_timelock(uhd::usrp::multi_usrp::sptr usrp)
 {
@@ -165,6 +195,7 @@ OutputUHD::OutputUHD(
 
     /* register the parameters that can be remote controlled */
     RC_ADD_PARAMETER(txgain, "UHD analog daughterboard TX gain");
+    RC_ADD_PARAMETER(rxgain, "UHD analog daughterboard RX gain for DPD feedback");
     RC_ADD_PARAMETER(freq,   "UHD transmission frequency");
     RC_ADD_PARAMETER(muting, "Mute the output by stopping the transmitter");
     RC_ADD_PARAMETER(staticdelay, "Set static delay (uS) between 0 and 96000");
@@ -223,31 +254,14 @@ OutputUHD::OutputUHD(
         throw std::runtime_error("Cannot set USRP sample rate. Aborted.");
     }
 
-    if (myConf.lo_offset != 0.0) {
-        etiLog.level(info) << std::fixed << std::setprecision(3) <<
-            "OutputUHD:Setting freq to " << myConf.frequency <<
-            "  with LO offset " << myConf.lo_offset << "...";
-
-        const auto tr = uhd::tune_request_t(myConf.frequency, myConf.lo_offset);
-        uhd::tune_result_t result = myUsrp->set_tx_freq(tr);
-
-        etiLog.level(debug) << "OutputUHD:" <<
-            std::fixed << std::setprecision(0) <<
-            " Target RF: " << result.target_rf_freq <<
-            " Actual RF: " << result.actual_rf_freq <<
-            " Target DSP: " << result.target_dsp_freq <<
-            " Actual DSP: " << result.actual_dsp_freq;
-    }
-    else {
-        //set the centre frequency
-        etiLog.level(info) << std::fixed << std::setprecision(3) <<
-            "OutputUHD:Setting freq to " << myConf.frequency << "...";
-        myUsrp->set_tx_freq(myConf.frequency);
-    }
+    tune_usrp_to(myUsrp, myConf.lo_offset, myConf.frequency);
 
     myConf.frequency = myUsrp->get_tx_freq();
     etiLog.level(info) << std::fixed << std::setprecision(3) <<
-        "OutputUHD:Actual frequency: " << myConf.frequency;
+        "OutputUHD:Actual TX frequency: " << myConf.frequency;
+
+    etiLog.level(info) << std::fixed << std::setprecision(3) <<
+        "OutputUHD:Actual RX frequency: " << myUsrp->get_tx_freq();
 
     myUsrp->set_tx_gain(myConf.txgain);
     MDEBUG("OutputUHD:Actual TX Gain: %f ...\n", myUsrp->get_tx_gain());
@@ -284,13 +298,18 @@ OutputUHD::OutputUHD(
 
     SetDelayBuffer(myConf.dabMode);
 
-    MDEBUG("OutputUHD:UHD ready.\n");
-}
+    myUsrp->set_rx_rate(myConf.sampleRate);
+    MDEBUG("OutputUHD:Actual RX Rate: %f sps...\n", myUsrp->get_rx_rate());
 
+    myUsrp->set_rx_antenna("RX2");
+    MDEBUG("OutputUHD:Set RX Antenna: %s ...\n", myUsrp->get_rx_antenna().c_str());
 
-OutputUHD::~OutputUHD()
-{
-    MDEBUG("OutputUHD::~OutputUHD() @ %p\n", this);
+    myUsrp->set_rx_gain(myConf.rxgain);
+    MDEBUG("OutputUHD:Actual RX Gain: %f ...\n", myUsrp->get_rx_gain());
+
+    uhdFeedback.setup(myUsrp, myConf.dpdFeedbackServerPort, myConf.sampleRate);
+
+    MDEBUG("OutputUHD:UHD ready.\n");
 }
 
 
@@ -424,12 +443,11 @@ int OutputUHD::process(Buffer* dataIn)
                 "OutputUHD: dropping one frame with invalid FCT";
         }
         else {
-            while (true) {
-                size_t num_frames = uwd.frames.push_wait_if_full(frame,
-                        FRAMES_MAX_SIZE);
-                etiLog.log(trace, "UHD,push %zu", num_frames);
-                break;
-            }
+            uhdFeedback.set_tx_frame(frame.buf, frame.ts);
+
+            size_t num_frames = uwd.frames.push_wait_if_full(frame,
+                    FRAMES_MAX_SIZE);
+            etiLog.log(trace, "UHD,push %zu", num_frames);
         }
     }
 
@@ -915,9 +933,13 @@ void OutputUHD::set_parameter(const string& parameter, const string& value)
         ss >> myConf.txgain;
         myUsrp->set_tx_gain(myConf.txgain);
     }
+    else if (parameter == "rxgain") {
+        ss >> myConf.rxgain;
+        myUsrp->set_rx_gain(myConf.rxgain);
+    }
     else if (parameter == "freq") {
         ss >> myConf.frequency;
-        myUsrp->set_tx_freq(myConf.frequency);
+        tune_usrp_to(myUsrp, myConf.lo_offset, myConf.frequency);
         myConf.frequency = myUsrp->get_tx_freq();
     }
     else if (parameter == "muting") {
@@ -956,6 +978,9 @@ const string OutputUHD::get_parameter(const string& parameter) const
     if (parameter == "txgain") {
         ss << myConf.txgain;
     }
+    else if (parameter == "rxgain") {
+        ss << myConf.rxgain;
+    }
     else if (parameter == "freq") {
         ss << myConf.frequency;
     }
diff --git a/src/OutputUHD.h b/src/OutputUHD.h
index d42245f..c966c7e 100644
--- a/src/OutputUHD.h
+++ b/src/OutputUHD.h
@@ -2,7 +2,7 @@
    Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Her Majesty the
    Queen in Right of Canada (Communications Research Center Canada)
 
-   Copyright (C) 2016
+   Copyright (C) 2017
    Matthias P. Braendli, matthias.braendli@mpb.li
 
     http://opendigitalradio.org
@@ -56,6 +56,7 @@ DESCRIPTION:
 #include "TimestampDecoder.h"
 #include "RemoteControl.h"
 #include "ThreadsafeQueue.h"
+#include "OutputUHDFeedback.h"
 
 #include <stdio.h>
 #include <sys/types.h>
@@ -188,6 +189,7 @@ struct OutputUHDConfig {
     double frequency = 0.0;
     double lo_offset = 0.0;
     double txgain = 0.0;
+    double rxgain = 0.0;
     bool enableSync = false;
     bool muteNoTimestamps = false;
     unsigned dabMode = 0;
@@ -210,14 +212,15 @@ struct OutputUHDConfig {
 
     // static delay in microseconds
     int staticDelayUs = 0;
-};
 
+    // TCP port on which to serve TX and RX samples for the
+    // digital pre distortion learning tool
+    uint16_t dpdFeedbackServerPort = 0;
+};
 
 class OutputUHD: public ModOutput, public RemoteControllable {
     public:
-
         OutputUHD(OutputUHDConfig& config);
-        ~OutputUHD();
 
         int process(Buffer* dataIn);
 
@@ -235,11 +238,7 @@ class OutputUHD: public ModOutput, public RemoteControllable {
         virtual const std::string get_parameter(
                 const std::string& parameter) const;
 
-
     protected:
-        OutputUHD(const OutputUHD& other) = delete;
-        OutputUHD& operator=(const OutputUHD& other) = delete;
-
         EtiSource *myEtiSource;
         OutputUHDConfig& myConf;
         uhd::usrp::multi_usrp::sptr myUsrp;
@@ -248,6 +247,7 @@ class OutputUHD: public ModOutput, public RemoteControllable {
         bool gps_fix_verified;
         struct UHDWorkerData uwd;
         UHDWorker worker;
+        OutputUHDFeedback uhdFeedback;
 
     private:
         // Resize the internal delay buffer according to the dabMode and
diff --git a/src/OutputUHDFeedback.cpp b/src/OutputUHDFeedback.cpp
new file mode 100644
index 0000000..2a99e6b
--- /dev/null
+++ b/src/OutputUHDFeedback.cpp
@@ -0,0 +1,377 @@
+/*
+   Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Her Majesty the
+   Queen in Right of Canada (Communications Research Center Canada)
+
+   Copyright (C) 2017
+   Matthias P. Braendli, matthias.braendli@mpb.li
+
+    http://opendigitalradio.org
+
+DESCRIPTION:
+   This presents a TCP socket to an external tool which calculates
+   a Digital Predistortion model from a short sequence of transmit
+   samples and corresponding receive samples.
+*/
+
+/*
+   This file is part of ODR-DabMod.
+
+   ODR-DabMod 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.
+
+   ODR-DabMod 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 ODR-DabMod.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifdef HAVE_CONFIG_H
+#   include <config.h>
+#endif
+
+#ifdef HAVE_OUTPUT_UHD
+
+#include <vector>
+#include <complex>
+#include <cstring>
+#include <uhd/types/stream_cmd.hpp>
+#include <sys/socket.h>
+#include <errno.h>
+#include <poll.h>
+#include "OutputUHDFeedback.h"
+#include "Utils.h"
+
+using namespace std;
+typedef std::complex<float> complexf;
+
+OutputUHDFeedback::OutputUHDFeedback()
+{
+    m_running.store(false);
+}
+
+void OutputUHDFeedback::setup(uhd::usrp::multi_usrp::sptr usrp, uint16_t port, uint32_t sampleRate)
+{
+    m_usrp = usrp;
+    m_sampleRate = sampleRate;
+    burstRequest.state = BurstRequestState::None;
+
+    if (port) {
+        m_port = port;
+        m_running.store(true);
+
+        rx_burst_thread = boost::thread(&OutputUHDFeedback::ReceiveBurstThread, this);
+        burst_tcp_thread = boost::thread(&OutputUHDFeedback::ServeFeedbackThread, this);
+    }
+}
+
+OutputUHDFeedback::~OutputUHDFeedback()
+{
+    m_running.store(false);
+
+    rx_burst_thread.interrupt();
+    burst_tcp_thread.interrupt();
+
+    rx_burst_thread.join();
+    burst_tcp_thread.join();
+}
+
+void OutputUHDFeedback::set_tx_frame(
+        const std::vector<uint8_t> &buf,
+        const struct frame_timestamp &buf_ts)
+{
+    boost::mutex::scoped_lock lock(burstRequest.mutex);
+
+    assert(buf.size() % sizeof(complexf) == 0);
+
+    if (burstRequest.state == BurstRequestState::SaveTransmitFrame) {
+        const size_t n = std::min(
+                burstRequest.num_samples * sizeof(complexf), buf.size());
+
+        burstRequest.num_samples = n / sizeof(complexf);
+
+        burstRequest.tx_samples.clear();
+        burstRequest.tx_samples.resize(n);
+        // A frame will always begin with the NULL symbol, which contains
+        // no power. Instead of taking n samples at the beginning of the
+        // frame, we take them at the end and adapt the timestamp accordingly.
+
+        const size_t start_ix = buf.size() - n;
+        copy(buf.begin() + start_ix, buf.end(), burstRequest.tx_samples.begin());
+
+        frame_timestamp ts = buf_ts;
+        ts += (1.0 * start_ix) / (sizeof(complexf) * m_sampleRate);
+
+        burstRequest.tx_second = ts.timestamp_sec;
+        burstRequest.tx_pps = ts.timestamp_pps;
+
+        // Prepare the next state
+        burstRequest.rx_second = ts.timestamp_sec;
+        burstRequest.rx_pps = ts.timestamp_pps;
+        burstRequest.state = BurstRequestState::SaveReceiveFrame;
+
+        lock.unlock();
+        burstRequest.mutex_notification.notify_one();
+    }
+    else {
+        lock.unlock();
+    }
+}
+
+void OutputUHDFeedback::ReceiveBurstThread()
+{
+    set_thread_name("uhdreceiveburst");
+
+    uhd::stream_args_t stream_args("fc32"); //complex floats
+    auto rxStream = m_usrp->get_rx_stream(stream_args);
+
+    while (m_running) {
+        boost::mutex::scoped_lock lock(burstRequest.mutex);
+        while (burstRequest.state != BurstRequestState::SaveReceiveFrame) {
+            if (not m_running) break;
+            burstRequest.mutex_notification.wait(lock);
+        }
+
+        if (not m_running) break;
+
+        uhd::stream_cmd_t cmd(
+                uhd::stream_cmd_t::stream_mode_t::STREAM_MODE_NUM_SAMPS_AND_DONE);
+        cmd.num_samps = burstRequest.num_samples;
+        cmd.stream_now = false;
+
+        double pps = burstRequest.rx_pps / 16384000.0;
+        cmd.time_spec = uhd::time_spec_t(burstRequest.rx_second, pps);
+
+        // We need to free the mutex while we recv(), because otherwise we block the
+        // TX thread
+        lock.unlock();
+
+        const double usrp_time = m_usrp->get_time_now().get_real_secs();
+        const double cmd_time = cmd.time_spec.get_real_secs();
+
+        rxStream->issue_stream_cmd(cmd);
+
+        uhd::rx_metadata_t md;
+
+        std::vector<uint8_t> buf(cmd.num_samps * sizeof(complexf));
+
+        const double timeout = 60;
+        size_t samples_read = rxStream->recv(&buf[0], cmd.num_samps, md, timeout);
+
+        lock.lock();
+        burstRequest.rx_samples = std::move(buf);
+        burstRequest.rx_samples.resize(samples_read * sizeof(complexf));
+
+        // The recv might have happened at another time than requested
+        burstRequest.rx_second = md.time_spec.get_full_secs();
+        burstRequest.rx_pps = md.time_spec.get_frac_secs() * 16384000.0;
+
+        etiLog.level(debug) << "DPD: acquired " << samples_read << " RX feedback samples " <<
+            "at time " << burstRequest.tx_second << " + " <<
+            std::fixed << burstRequest.tx_pps / 16384000.0 <<
+            " Delta=" << cmd_time - usrp_time;
+
+        burstRequest.state = BurstRequestState::Acquired;
+
+        lock.unlock();
+        burstRequest.mutex_notification.notify_one();
+    }
+}
+
+static int accept_with_timeout(int server_socket, int timeout_ms, struct sockaddr_in *client)
+{
+    struct pollfd fds[1];
+    fds[0].fd = server_socket;
+    fds[0].events = POLLIN | POLLOUT;
+
+    int retval = poll(fds, 1, timeout_ms);
+
+    if (retval == -1) {
+        throw std::runtime_error("TCP Socket accept error: " + to_string(errno));
+    }
+    else if (retval) {
+        socklen_t client_len = sizeof(struct sockaddr_in);
+        return accept(server_socket, (struct sockaddr*)&client, &client_len);
+    }
+    else {
+        return -2;
+    }
+}
+
+static ssize_t sendall(int socket, const void *buffer, size_t buflen)
+{
+    uint8_t *buf = (uint8_t*)buffer;
+    while (buflen > 0) {
+        ssize_t sent = send(socket, buf, buflen, 0);
+        if (sent < 0) {
+            return -1;
+        }
+        else {
+            buf += sent;
+            buflen -= sent;
+        }
+    }
+    return buflen;
+}
+
+void OutputUHDFeedback::ServeFeedbackThread()
+{
+    set_thread_name("uhdservefeedback");
+
+    try {
+        if ((m_server_sock = socket(PF_INET, SOCK_STREAM, 0)) < 0) {
+            throw std::runtime_error("Can't create TCP socket");
+        }
+
+        struct sockaddr_in addr;
+        addr.sin_family = AF_INET;
+        addr.sin_port = htons(m_port);
+        addr.sin_addr.s_addr = htonl(INADDR_ANY);
+
+        if (bind(m_server_sock, (struct sockaddr*)&addr, sizeof(addr)) < 0) {
+            throw std::runtime_error("Can't bind TCP socket");
+        }
+
+        if (listen(m_server_sock, 1) < 0) {
+            throw std::runtime_error("Can't listen TCP socket");
+        }
+
+        etiLog.level(info) << "DPD Feedback server listening on port " << m_port;
+
+        while (m_running) {
+            struct sockaddr_in client;
+            int client_sock = accept_with_timeout(m_server_sock, 1000, &client);
+
+            if (client_sock == -1) {
+                throw runtime_error("Could not establish new connection");
+            }
+            else if (client_sock == -2) {
+                continue;
+            }
+
+            uint8_t request_version = 0;
+            ssize_t read = recv(client_sock, &request_version, 1, 0);
+            if (!read) break; // done reading
+            if (read < 0) {
+                etiLog.level(info) <<
+                    "DPD Feedback Server Client read request version failed: " << strerror(errno);
+                break;
+            }
+
+            if (request_version != 1) {
+                etiLog.level(info) << "DPD Feedback Server wrong request version";
+                break;
+            }
+
+            uint32_t num_samples = 0;
+            read = recv(client_sock, &num_samples, 4, 0);
+            if (!read) break; // done reading
+            if (read < 0) {
+                etiLog.level(info) <<
+                    "DPD Feedback Server Client read num samples failed";
+                break;
+            }
+
+            // We are ready to issue the request now
+            {
+                boost::mutex::scoped_lock lock(burstRequest.mutex);
+                burstRequest.num_samples = num_samples;
+                burstRequest.state = BurstRequestState::SaveTransmitFrame;
+
+                lock.unlock();
+            }
+
+            // Wait for the result to be ready
+            boost::mutex::scoped_lock lock(burstRequest.mutex);
+            while (burstRequest.state != BurstRequestState::Acquired) {
+                if (not m_running) break;
+                burstRequest.mutex_notification.wait(lock);
+            }
+
+            burstRequest.state = BurstRequestState::None;
+            lock.unlock();
+
+            burstRequest.num_samples = std::min(burstRequest.num_samples,
+                    std::min(
+                        burstRequest.tx_samples.size() / sizeof(complexf),
+                        burstRequest.rx_samples.size() / sizeof(complexf)));
+
+            uint32_t num_samples_32 = burstRequest.num_samples;
+            if (sendall(client_sock, &num_samples_32, sizeof(num_samples_32)) < 0) {
+                etiLog.level(info) <<
+                    "DPD Feedback Server Client send num_samples failed";
+                break;
+            }
+
+            if (sendall(client_sock,
+                        &burstRequest.tx_second,
+                        sizeof(burstRequest.tx_second)) < 0) {
+                etiLog.level(info) <<
+                    "DPD Feedback Server Client send tx_second failed";
+                break;
+            }
+
+            if (sendall(client_sock,
+                        &burstRequest.tx_pps,
+                        sizeof(burstRequest.tx_pps)) < 0) {
+                etiLog.level(info) <<
+                    "DPD Feedback Server Client send tx_pps failed";
+                break;
+            }
+
+            const size_t frame_bytes = burstRequest.num_samples * sizeof(complexf);
+
+            assert(burstRequest.tx_samples.size() >= frame_bytes);
+            if (sendall(client_sock,
+                        &burstRequest.tx_samples[0],
+                        frame_bytes) < 0) {
+                etiLog.level(info) <<
+                    "DPD Feedback Server Client send tx_frame failed";
+                break;
+            }
+
+            if (sendall(client_sock,
+                        &burstRequest.rx_second,
+                        sizeof(burstRequest.rx_second)) < 0) {
+                etiLog.level(info) <<
+                    "DPD Feedback Server Client send rx_second failed";
+                break;
+            }
+
+            if (sendall(client_sock,
+                        &burstRequest.rx_pps,
+                        sizeof(burstRequest.rx_pps)) < 0) {
+                etiLog.level(info) <<
+                    "DPD Feedback Server Client send rx_pps failed";
+                break;
+            }
+
+            assert(burstRequest.rx_samples.size() >= frame_bytes);
+            if (sendall(client_sock,
+                        &burstRequest.rx_samples[0],
+                        frame_bytes) < 0) {
+                etiLog.level(info) <<
+                    "DPD Feedback Server Client send rx_frame failed";
+                break;
+            }
+
+            close(client_sock);
+        }
+    }
+    catch (runtime_error &e) {
+        etiLog.level(error) << "DPD Feedback Server fault: " << e.what();
+    }
+
+    m_running = false;
+
+    if (m_server_sock != -1) {
+        close(m_server_sock);
+        m_server_sock = -1;
+    }
+}
+
+#endif
diff --git a/src/OutputUHDFeedback.h b/src/OutputUHDFeedback.h
new file mode 100644
index 0000000..32668b6
--- /dev/null
+++ b/src/OutputUHDFeedback.h
@@ -0,0 +1,118 @@
+/*
+   Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Her Majesty the
+   Queen in Right of Canada (Communications Research Center Canada)
+
+   Copyright (C) 2017
+   Matthias P. Braendli, matthias.braendli@mpb.li
+
+    http://opendigitalradio.org
+
+DESCRIPTION:
+   This presents a TCP socket to an external tool which calculates
+   a Digital Predistortion model from a short sequence of transmit
+   samples and corresponding receive samples.
+*/
+
+/*
+   This file is part of ODR-DabMod.
+
+   ODR-DabMod 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.
+
+   ODR-DabMod 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 ODR-DabMod.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#ifdef HAVE_CONFIG_H
+#   include <config.h>
+#endif
+
+#ifdef HAVE_OUTPUT_UHD
+
+#include <uhd/utils/thread_priority.hpp>
+#include <uhd/utils/safe_main.hpp>
+#include <uhd/usrp/multi_usrp.hpp>
+#include <boost/thread.hpp>
+#include <memory>
+#include <string>
+#include <atomic>
+
+#include "Log.h"
+#include "TimestampDecoder.h"
+
+enum class BurstRequestState {
+    None, // To pending request
+    SaveTransmitFrame, // The TX thread has to save an outgoing frame
+    SaveReceiveFrame, // The RX thread has to save an incoming frame
+    Acquired, // Both TX and RX frames are ready
+};
+
+struct UHDReceiveBurstRequest {
+    // All fields in this struct are protected
+    mutable boost::mutex mutex;
+    boost::condition_variable mutex_notification;
+
+    BurstRequestState state;
+
+    // In the SaveTransmit states, num_samples complexf samples are saved into
+    // the vectors
+    size_t num_samples;
+
+    // The timestamp of the first sample of the TX buffers
+    uint32_t tx_second;
+    uint32_t tx_pps; // in units of 1/16384000s
+
+    // Samples contain complexf, but since our internal representation is uint8_t
+    // we keep it like that
+    std::vector<uint8_t> tx_samples;
+
+    // The timestamp of the first sample of the RX buffers
+    uint32_t rx_second;
+    uint32_t rx_pps;
+
+    std::vector<uint8_t> rx_samples; // Also, actually complexf
+};
+
+// Serve TX samples and RX feedback samples over a TCP connection
+class OutputUHDFeedback {
+    public:
+        OutputUHDFeedback();
+        OutputUHDFeedback(const OutputUHDFeedback& other) = delete;
+        OutputUHDFeedback& operator=(const OutputUHDFeedback& other) = delete;
+        ~OutputUHDFeedback();
+
+        void setup(uhd::usrp::multi_usrp::sptr usrp, uint16_t port, uint32_t sampleRate);
+
+        void set_tx_frame(const std::vector<uint8_t> &buf,
+                const struct frame_timestamp& ts);
+
+    private:
+        // Thread that reacts to burstRequests and receives from the USRP
+        void ReceiveBurstThread(void);
+
+        // Thread that listens for requests over TCP to get TX and RX feedback
+        void ServeFeedbackThread(void);
+
+        boost::thread rx_burst_thread;
+        boost::thread burst_tcp_thread;
+
+        UHDReceiveBurstRequest burstRequest;
+
+        std::atomic_bool m_running;
+        int m_server_sock = -1;
+        uint16_t m_port = 0;
+        uint32_t m_sampleRate = 0;
+        uhd::usrp::multi_usrp::sptr m_usrp;
+};
+
+
+#endif // HAVE_OUTPUT_UHD