Add LUT predistorter

9 files changed, 497 insertions, 209 deletions

diff --git a/dpd/README.md b/dpd/README.md
index b5a6b81..83a2986 100644
--- a/dpd/README.md
+++ b/dpd/README.md
@@ -8,7 +8,9 @@ Concept
 
 ODR-DabMod makes outgoing TX samples and feedback RX samples available for an external tool. This
 external tool can request a buffer of samples for analysis, can calculate coefficients for the
-polynomial predistorter in ODR-DabMod and load the new coefficients using the remote control.
+predistorter in ODR-DabMod and load the new coefficients using the remote control.
+
+The predistorter in ODR-DabMod supports two modes: polynomial and lookup table.
 
 The *dpd/main.py* script is the entry point for the *DPD Calculation Engine* into which these
 features will be implemented. The tool uses modules from the *dpd/src/* folder:
@@ -43,10 +45,21 @@ The coef file contains the polynomial coefficients used in the predistorter. The
 very similar to the filtertaps file used in the FIR filter. It is a text-based format that can
 easily be inspected and edited in a text editor.
 
-The first line contains the number of coefficients as an integer. The second and third lines contain
-the real, respectively the imaginary parts of the first coefficient. Fourth and fifth lines give the
-second coefficient, and so on. The file therefore contains 2xN + 1 lines if it contains N
-coefficients.
+The first line contains an integer that defines the predistorter to be used:
+1 for polynomial, 2 for lookup table.
+
+For the polynomial, the subsequent line contains the number of coefficients
+as an integer. The second and third lines contain the real, respectively the
+imaginary parts of the first coefficient. Fourth and fifth lines give the
+second coefficient, and so on. The file therefore contains 1 + 1 + 2xN lines if
+it contains N coefficients.
+
+For the lookup table, the subsequent line contains a float scalefactor that is
+applied to the samples in order to bring them into the range of 32-bit unsigned
+integer. Then, the next pair of lines contains real and imaginary part of the first
+lookup-table entry, which is multiplied to samples in first range. Then it's
+followed by 31 other pairs. The entries are complex values close to 1 + 0j.
+The file therefore contains 1 + 1 + 2xN lines if it contains N coefficients.
 
 TODO
 ----
diff --git a/dpd/dpd.ini b/dpd/dpd.ini
index 1bc51de..9a76393 100644
--- a/dpd/dpd.ini
+++ b/dpd/dpd.ini
@@ -10,8 +10,8 @@ filelog=1
 filename=/tmp/dabmod.log
 
 [input]
-transport=tcp
-source=localhost:9200
+transport=file
+source=/home/bram/dab/mmbtools-aux/eti/buddard.eti
 
 [modulator]
 gainmode=var
@@ -31,7 +31,7 @@ polycoeffile=dpd/poly.coef
 [output]
 # to prepare a file for the dpd/iq_file_server.py script,
 # use output=file
-output=uhd
+output=file
 
 [fileoutput]
 filename=dpd.iq
diff --git a/dpd/lut.coef b/dpd/lut.coef
new file mode 100644
index 0000000..a198d56
--- /dev/null
+++ b/dpd/lut.coef
@@ -0,0 +1,64 @@
+2
+4294967296
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
+1
+0
diff --git a/dpd/main.py b/dpd/main.py
index 5e67c90..de3453e 100755
--- a/dpd/main.py
+++ b/dpd/main.py
@@ -13,7 +13,7 @@ predistortion module of ODR-DabMod."""
 import datetime
 import os
 import time
-
+import sys
 import matplotlib
 matplotlib.use('GTKAgg')
 
@@ -82,8 +82,8 @@ parser.add_argument('--samps', default='81920',
 parser.add_argument('-i', '--iterations', default='1',
                     help='Number of iterations to run',
                     required=False)
-parser.add_argument('-l', '--load-poly',
-                    help='Load existing polynomial',
+parser.add_argument('-L', '--lut',
+                    help='Use lookup table instead of polynomial predistorter',
                     action="store_true")
 
 cli_args = parser.parse_args()
@@ -105,12 +105,13 @@ c = src.const.const(samplerate)
 meas = Measure.Measure(samplerate, port, num_req)
 
 adapt = Adapt.Adapt(port_rc, coef_path)
-coefs_am, coefs_pm = adapt.get_coefs()
-if cli_args.load_poly:
-    model = Model.Model(c, SA, MER, coefs_am, coefs_pm, plot=True)
+dpddata = adapt.get_predistorter()
+
+if cli_args.lut:
+    model = Model.LutModel(c, SA, MER, plot=True)
 else:
-    model = Model.Model(c, SA, MER, [1.0, 0, 0, 0, 0], [0, 0, 0, 0, 0], plot=True)
-adapt.set_coefs(model.coefs_am, model.coefs_pm)
+    model = Model.PolyModel(c, SA, MER, None, None, plot=True)
+adapt.set_predistorter(model.get_dpd_data())
 adapt.set_digital_gain(digital_gain)
 adapt.set_txgain(txgain)
 adapt.set_rxgain(rxgain)
@@ -118,13 +119,28 @@ adapt.set_rxgain(rxgain)
 tx_gain = adapt.get_txgain()
 rx_gain = adapt.get_rxgain()
 digital_gain = adapt.get_digital_gain()
-dpd_coefs_am, dpd_coefs_pm = adapt.get_coefs()
-logging.info(
-    "TX gain {}, RX gain {}, dpd_coefs_am {},"
-    " dpd_coefs_pm {}, digital_gain {}".format(
-        tx_gain, rx_gain, dpd_coefs_am, dpd_coefs_pm, digital_gain
+
+dpddata = adapt.get_coefs()
+if dpddata[0] == "poly":
+    coefs_am = dpddata[1]
+    coefs_pm = dpddata[2]
+    logging.info(
+        "TX gain {}, RX gain {}, dpd_coefs_am {},"
+        " dpd_coefs_pm {}, digital_gain {}".format(
+            tx_gain, rx_gain, coefs_am, coefs_pm, digital_gain
+        )
     )
-)
+elif dpddata[0] == "lut":
+    scalefactor = dpddata[1]
+    lut = dpddata[2]
+    logging.info(
+        "TX gain {}, RX gain {}, LUT scalefactor {},"
+        " LUT {}, digital_gain {}".format(
+            tx_gain, rx_gain, scalefactor, lut, digital_gain
+        )
+    )
+else:
+    logging.error("Unknown dpd data format {}".format(dpddata[0]))
 
 tx_agc = TX_Agc.TX_Agc(adapt)
 
@@ -141,8 +157,8 @@ for i in range(num_iter):
         if tx_agc.adapt_if_necessary(txframe_aligned):
             continue
 
-        coefs_am, coefs_pm = model.get_next_coefs(txframe_aligned, rxframe_aligned)
-        adapt.set_coefs(coefs_am, coefs_pm)
+        model.train(txframe_aligned, rxframe_aligned)
+        adapt.set_predistorter(model.get_dpd_data())
 
         off = SA.calc_offset(txframe_aligned)
         tx_mer = MER.calc_mer(txframe_aligned[off:off + c.T_U])
@@ -155,7 +171,8 @@ for i in range(num_iter):
 
 # The MIT License (MIT)
 #
-# Copyright (c) 2017 Andreas Steger, Matthias P. Braendli
+# Copyright (c) 2017 Andreas Steger
+# 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
diff --git a/dpd/poly.coef b/dpd/poly.coef
index f65e369..913507a 100644
--- a/dpd/poly.coef
+++ b/dpd/poly.coef
@@ -1,5 +1,6 @@
-5
 1
+5
+1.0
 0
 0
 0
diff --git a/dpd/src/Adapt.py b/dpd/src/Adapt.py
index b4042d6..f21bb87 100644
--- a/dpd/src/Adapt.py
+++ b/dpd/src/Adapt.py
@@ -13,6 +13,10 @@ import zmq
 import logging
 import numpy as np
 
+LUT_LEN=32
+FORMAT_POLY=1
+FORMAT_LUT=2
+
 class Adapt:
     """Uses the ZMQ remote control to change parameters of the DabMod
 
@@ -126,45 +130,74 @@ class Adapt:
         # TODO handle failure
         return float(self.send_receive("get gain digital")[0])
 
-    def _read_coef_file(self, path):
+    def get_predistorter(self):
         """Load the coefficients from the file in the format given in the README,
-        return ([AM coef], [PM coef])"""
-        coefs_am_out = []
-        coefs_pm_out = []
-        f = open(path, 'r')
+        return ("poly", [AM coef], [PM coef]) or ("lut", scalefactor, [LUT entries])"""
+        f = open(self.coef_path, 'r')
         lines = f.readlines()
-        n_coefs = int(lines[0])
-        coefs = [float(l) for l in lines[1:]]
-        i = 0
-        for c in coefs:
-            if i < n_coefs:
-                coefs_am_out.append(c)
-            elif i < 2*n_coefs:
-                coefs_pm_out.append(c)
-            else:
-                raise ValueError(
-                    "Incorrect coef file format: too many coefficients in {}, should be {}, coefs are {}"
-                        .format(path, n_coefs, coefs))
-            i += 1
-        f.close()
-        return (coefs_am_out, coefs_pm_out)
-
-    def get_coefs(self):
-        return self._read_coef_file(self.coef_path)
-
-    def _write_coef_file(self, coefs_am, coefs_pm, path):
+        predistorter_format = int(lines[0])
+        if predistorter_format == FORMAT_POLY:
+            coefs_am_out = []
+            coefs_pm_out = []
+            n_coefs = int(lines[1])
+            coefs = [float(l) for l in lines[2:]]
+            i = 0
+            for c in coefs:
+                if i < n_coefs:
+                    coefs_am_out.append(c)
+                elif i < 2*n_coefs:
+                    coefs_pm_out.append(c)
+                else:
+                    raise ValueError(
+                        "Incorrect coef file format: too many coefficients in {}, should be {}, coefs are {}"
+                            .format(path, n_coefs, coefs))
+                i += 1
+            f.close()
+            return ("poly", coefs_am_out, coefs_pm_out)
+        elif predistorter_format == FORMAT_LUT:
+            scalefactor = int(lines[1])
+            coefs = np.array([float(l) for l in lines[2:]], dtype=np.float32)
+            coefs = coefs.reshape((-1, 2))
+            lut = coefs[..., 0] + 1j * coefs[..., 1]
+            if len(lut) != LUT_LEN:
+                raise ValueError("Incorrect number of LUT entries ({} expected {})".format(len(lut), LUT_LEN))
+            return ("lut", scalefactor, lut)
+        else:
+            raise ValueError("Unknown predistorter format {}".format(predistorter_format))
+
+    def _write_poly_coef_file(self, coefs_am, coefs_pm, path):
         assert(len(coefs_am) == len(coefs_pm))
 
         f = open(path, 'w')
-        f.write("{}\n".format(len(coefs_am)))
+        f.write("{}\n{}\n".format(FORMAT_POLY, len(coefs_am)))
         for coef in coefs_am:
             f.write("{}\n".format(coef))
         for coef in coefs_pm:
             f.write("{}\n".format(coef))
         f.close()
 
-    def set_coefs(self, coefs_am, coefs_pm):
-        self._write_coef_file(coefs_am, coefs_pm, self.coef_path)
+    def _write_lut_file(self, scalefactor, lut, path):
+        assert(len(lut) == LUT_LEN)
+
+        f = open(path, 'w')
+        f.write("{}\n{}\n".format(FORMAT_LUT, scalefactor))
+        for coef in lut:
+            f.write("{}\n{}\n".format(coef.real, coef.imag))
+        f.close()
+
+    def set_predistorter(self, dpddata):
+        """Update the predistorter data in the modulator. Takes the same
+        tuple format as argument than the one returned get_predistorter()"""
+        if dpddata[0] == "poly":
+            coefs_am = dpddata[1]
+            coefs_pm = dpddata[2]
+            self._write_poly_coef_file(coefs_am, coefs_pm, self.coef_path)
+        elif dpddata[0] == "lut":
+            scalefactor = dpddata[1]
+            lut = dpddata[2]
+            self._write_lut_file(scalefactor, lut, self.coef_path)
+        else:
+            raise ValueError("Unknown predistorter '{}'".format(dpddata[0]))
         self.send_receive("set memlesspoly coeffile {}".format(self.coef_path))
 
 # The MIT License (MIT)
diff --git a/dpd/src/Model.py b/dpd/src/Model.py
index 827027a..a23f0ce 100644
--- a/dpd/src/Model.py
+++ b/dpd/src/Model.py
@@ -15,7 +15,7 @@ import numpy as np
 import matplotlib.pyplot as plt
 from sklearn import linear_model
 
-class Model:
+class PolyModel:
     """Calculates new coefficients using the measurement and the old
     coefficients"""
 
@@ -28,6 +28,7 @@ class Model:
                  learning_rate_am=1.,
                  learning_rate_pm=1.,
                  plot=False):
+        logging.debug("Initialising Poly Model")
         self.c = c
         self.SA = SA
         self.MER = MER
@@ -35,7 +36,10 @@ class Model:
         self.learning_rate_am = learning_rate_am
         self.learning_rate_pm = learning_rate_pm
 
-        self.coefs_am = coefs_am
+        if coefs_am is None:
+            self.coefs_am = [1.0, 0, 0, 0, 0]
+        else:
+            self.coefs_am = coefs_am
         self.coefs_am_history = [coefs_am, ]
         self.mses_am = []
         self.errs_am = []
@@ -43,116 +47,17 @@ class Model:
         self.tx_mers = []
         self.rx_mers = []
 
-        self.coefs_pm = coefs_pm
+        if coefs_pm is None:
+            self.coefs_pm = [0, 0, 0, 0, 0]
+        else:
+            self.coefs_pm = coefs_pm
         self.coefs_pm_history = [coefs_pm, ]
         self.errs_pm = []
 
         self.plot = plot
 
-    def sample_uniformly(self, tx_dpd, rx_received, n_bins=5):
-        """This function returns tx and rx samples in a way
-        that the tx amplitudes have an approximate uniform 
-        distribution with respect to the tx_dpd amplitudes"""
-        mask = np.logical_and((np.abs(tx_dpd) > 0.01), (np.abs(rx_received) > 0.01))
-        tx_dpd = tx_dpd[mask]
-        rx_received = rx_received[mask]
-
-        txframe_aligned_abs = np.abs(tx_dpd)
-        ccdf_min = 0
-        ccdf_max = np.max(txframe_aligned_abs)
-        tx_hist, ccdf_edges = np.histogram(txframe_aligned_abs,
-                                           bins=n_bins,
-                                           range=(ccdf_min, ccdf_max))
-        n_choise = np.min(tx_hist)
-        tx_choice = np.zeros(n_choise * n_bins, dtype=np.complex64)
-        rx_choice = np.zeros(n_choise * n_bins, dtype=np.complex64)
-
-        for idx, bin in enumerate(tx_hist):
-            indices = np.where((txframe_aligned_abs >= ccdf_edges[idx]) &
-                               (txframe_aligned_abs <= ccdf_edges[idx + 1]))[0]
-            indices_choise = np.random.choice(indices,
-                                              n_choise,
-                                              replace=False)
-            rx_choice[idx * n_choise:(idx + 1) * n_choise] = \
-                rx_received[indices_choise]
-            tx_choice[idx * n_choise:(idx + 1) * n_choise] = \
-                tx_dpd[indices_choise]
-
-        assert isinstance(rx_choice[0], np.complex64), \
-            "rx_choice is not complex64 but {}".format(rx_choice[0].dtype)
-        assert isinstance(tx_choice[0], np.complex64), \
-            "tx_choice is not complex64 but {}".format(tx_choice[0].dtype)
-
-        return tx_choice, rx_choice
-
-    def dpd_amplitude(self, sig, coefs=None):
-        if coefs is None:
-            coefs = self.coefs_am
-        assert isinstance(sig[0], np.complex64), "Sig is not complex64 but {}".format(sig[0].dtype)
-        sig_abs = np.abs(sig)
-        A_sig = np.vstack([np.ones(sig_abs.shape),
-                           sig_abs ** 1,
-                           sig_abs ** 2,
-                           sig_abs ** 3,
-                           sig_abs ** 4,
-                           ]).T
-        sig_dpd = sig * np.sum(A_sig * coefs, axis=1)
-        return sig_dpd, A_sig
-
-    def dpd_phase(self, sig, coefs=None):
-        if coefs is None:
-            coefs = self.coefs_pm
-        assert isinstance(sig[0], np.complex64), "Sig is not complex64 but {}".format(sig[0].dtype)
-        sig_abs = np.abs(sig)
-        A_phase = np.vstack([np.ones(sig_abs.shape),
-                             sig_abs ** 1,
-                             sig_abs ** 2,
-                             sig_abs ** 3,
-                             sig_abs ** 4,
-                             ]).T
-        phase_diff_est = np.sum(A_phase * coefs, axis=1)
-        return phase_diff_est, A_phase
-
-    def _next_am_coefficent(self, tx_choice, rx_choice):
-        """Calculate new coefficients for AM/AM correction"""
-        rx_dpd, rx_A = self.dpd_amplitude(rx_choice)
-        rx_dpd = rx_dpd * (
-            np.median(np.abs(tx_choice)) /
-            np.median(np.abs(rx_dpd)))
-        err = np.abs(rx_dpd) - np.abs(tx_choice)
-        mse = np.mean(np.abs((rx_dpd - tx_choice) ** 2))
-        self.mses_am.append(mse)
-        self.errs_am.append(np.mean(err**2))
-
-        reg = linear_model.Ridge(alpha=0.00001)
-        reg.fit(rx_A, err)
-        a_delta = reg.coef_
-        new_coefs_am = self.coefs_am - self.learning_rate_am * a_delta
-        new_coefs_am = new_coefs_am * (self.coefs_am[0] / new_coefs_am[0])
-        return new_coefs_am
-
-    def _next_pm_coefficent(self, tx_choice, rx_choice):
-        """Calculate new coefficients for AM/PM correction
-        Assuming deviations smaller than pi/2"""
-        phase_diff_choice = np.angle(
-            (rx_choice * tx_choice.conjugate()) /
-            (np.abs(rx_choice) * np.abs(tx_choice))
-        )
-        plt.hist(phase_diff_choice)
-        plt.savefig('/tmp/hist_' + str(np.random.randint(0,1000)) + '.svg')
-        plt.clf()
-        phase_diff_est, phase_A = self.dpd_phase(rx_choice)
-        err_phase = phase_diff_est - phase_diff_choice
-        self.errs_pm.append(np.mean(np.abs(err_phase ** 2)))
-
-        reg = linear_model.Ridge(alpha=0.00001)
-        reg.fit(phase_A, err_phase)
-        p_delta = reg.coef_
-        new_coefs_pm = self.coefs_pm - self.learning_rate_pm * p_delta
-
-        return new_coefs_pm, phase_diff_choice
-
-    def get_next_coefs(self, tx_dpd, rx_received):
+    def train(self, tx_dpd, rx_received):
+        """Give new training data to the model"""
         # Check data type
         assert tx_dpd[0].dtype == np.complex64, \
             "tx_dpd is not complex64 but {}".format(tx_dpd[0].dtype)
@@ -164,7 +69,7 @@ class Model:
                                   np.median(np.abs(tx_dpd)) + np.median(np.abs(rx_received)))
         assert normalization_error < 0.01, "Non normalized signals"
 
-        tx_choice, rx_choice = self.sample_uniformly(tx_dpd, rx_received)
+        tx_choice, rx_choice = self._sample_uniformly(tx_dpd, rx_received)
         new_coefs_am = self._next_am_coefficent(tx_choice, rx_choice)
         new_coefs_pm, phase_diff_choice = self._next_pm_coefficent(tx_choice, rx_choice)
 
@@ -255,8 +160,8 @@ class Model:
 
             ax = plt.subplot(4, 2, i_sub)
             rx_range = np.linspace(0, 1, num=100, dtype=np.complex64)
-            rx_range_dpd = self.dpd_amplitude(rx_range)[0]
-            rx_range_dpd_new = self.dpd_amplitude(rx_range, new_coefs_am)[0]
+            rx_range_dpd = self._dpd_amplitude(rx_range)[0]
+            rx_range_dpd_new = self._dpd_amplitude(rx_range, new_coefs_am)[0]
             i_sub += 1
             ax.scatter(
                 np.abs(tx_choice),
@@ -284,8 +189,8 @@ class Model:
             ax.set_ylabel("Coefficient Value")
 
             phase_range = np.linspace(0, 1, num=100, dtype=np.complex64)
-            phase_range_dpd = self.dpd_phase(phase_range)[0]
-            phase_range_dpd_new = self.dpd_phase(phase_range,
+            phase_range_dpd = self._dpd_phase(phase_range)[0]
+            phase_range_dpd_new = self._dpd_phase(phase_range,
                                                  coefs=new_coefs_pm)[0]
             ax = plt.subplot(4, 2, i_sub)
             i_sub += 1
@@ -330,11 +235,139 @@ class Model:
         self.coefs_am_history.append(self.coefs_am)
         self.coefs_pm = new_coefs_pm
         self.coefs_pm_history.append(self.coefs_pm)
-        return self.coefs_am, self.coefs_pm
+
+    def get_dpd_data(self):
+        return "poly", self.coefs_am, self.coefs_pm
+
+    def _sample_uniformly(self, tx_dpd, rx_received, n_bins=5):
+        """This function returns tx and rx samples in a way
+        that the tx amplitudes have an approximate uniform 
+        distribution with respect to the tx_dpd amplitudes"""
+        mask = np.logical_and((np.abs(tx_dpd) > 0.01), (np.abs(rx_received) > 0.01))
+        tx_dpd = tx_dpd[mask]
+        rx_received = rx_received[mask]
+
+        txframe_aligned_abs = np.abs(tx_dpd)
+        ccdf_min = 0
+        ccdf_max = np.max(txframe_aligned_abs)
+        tx_hist, ccdf_edges = np.histogram(txframe_aligned_abs,
+                                           bins=n_bins,
+                                           range=(ccdf_min, ccdf_max))
+        n_choise = np.min(tx_hist)
+        tx_choice = np.zeros(n_choise * n_bins, dtype=np.complex64)
+        rx_choice = np.zeros(n_choise * n_bins, dtype=np.complex64)
+
+        for idx, bin in enumerate(tx_hist):
+            indices = np.where((txframe_aligned_abs >= ccdf_edges[idx]) &
+                               (txframe_aligned_abs <= ccdf_edges[idx + 1]))[0]
+            indices_choise = np.random.choice(indices,
+                                              n_choise,
+                                              replace=False)
+            rx_choice[idx * n_choise:(idx + 1) * n_choise] = \
+                rx_received[indices_choise]
+            tx_choice[idx * n_choise:(idx + 1) * n_choise] = \
+                tx_dpd[indices_choise]
+
+        assert isinstance(rx_choice[0], np.complex64), \
+            "rx_choice is not complex64 but {}".format(rx_choice[0].dtype)
+        assert isinstance(tx_choice[0], np.complex64), \
+            "tx_choice is not complex64 but {}".format(tx_choice[0].dtype)
+
+        return tx_choice, rx_choice
+
+    def _dpd_amplitude(self, sig, coefs=None):
+        if coefs is None:
+            coefs = self.coefs_am
+        assert isinstance(sig[0], np.complex64), "Sig is not complex64 but {}".format(sig[0].dtype)
+        sig_abs = np.abs(sig)
+        A_sig = np.vstack([np.ones(sig_abs.shape),
+                           sig_abs ** 1,
+                           sig_abs ** 2,
+                           sig_abs ** 3,
+                           sig_abs ** 4,
+                           ]).T
+        sig_dpd = sig * np.sum(A_sig * coefs, axis=1)
+        return sig_dpd, A_sig
+
+    def _dpd_phase(self, sig, coefs=None):
+        if coefs is None:
+            coefs = self.coefs_pm
+        assert isinstance(sig[0], np.complex64), "Sig is not complex64 but {}".format(sig[0].dtype)
+        sig_abs = np.abs(sig)
+        A_phase = np.vstack([np.ones(sig_abs.shape),
+                             sig_abs ** 1,
+                             sig_abs ** 2,
+                             sig_abs ** 3,
+                             sig_abs ** 4,
+                             ]).T
+        phase_diff_est = np.sum(A_phase * coefs, axis=1)
+        return phase_diff_est, A_phase
+
+    def _next_am_coefficent(self, tx_choice, rx_choice):
+        """Calculate new coefficients for AM/AM correction"""
+        rx_dpd, rx_A = self._dpd_amplitude(rx_choice)
+        rx_dpd = rx_dpd * (
+            np.median(np.abs(tx_choice)) /
+            np.median(np.abs(rx_dpd)))
+        err = np.abs(rx_dpd) - np.abs(tx_choice)
+        mse = np.mean(np.abs((rx_dpd - tx_choice) ** 2))
+        self.mses_am.append(mse)
+        self.errs_am.append(np.mean(err**2))
+
+        reg = linear_model.Ridge(alpha=0.00001)
+        reg.fit(rx_A, err)
+        a_delta = reg.coef_
+        new_coefs_am = self.coefs_am - self.learning_rate_am * a_delta
+        new_coefs_am = new_coefs_am * (self.coefs_am[0] / new_coefs_am[0])
+        return new_coefs_am
+
+    def _next_pm_coefficent(self, tx_choice, rx_choice):
+        """Calculate new coefficients for AM/PM correction
+        Assuming deviations smaller than pi/2"""
+        phase_diff_choice = np.angle(
+            (rx_choice * tx_choice.conjugate()) /
+            (np.abs(rx_choice) * np.abs(tx_choice))
+        )
+        plt.hist(phase_diff_choice)
+        plt.savefig('/tmp/hist_' + str(np.random.randint(0,1000)) + '.svg')
+        plt.clf()
+        phase_diff_est, phase_A = self._dpd_phase(rx_choice)
+        err_phase = phase_diff_est - phase_diff_choice
+        self.errs_pm.append(np.mean(np.abs(err_phase ** 2)))
+
+        reg = linear_model.Ridge(alpha=0.00001)
+        reg.fit(phase_A, err_phase)
+        p_delta = reg.coef_
+        new_coefs_pm = self.coefs_pm - self.learning_rate_pm * p_delta
+
+        return new_coefs_pm, phase_diff_choice
+
+class LutModel:
+    """Implements a model that calculates lookup table coefficients"""
+
+    def __init__(self,
+                 c,
+                 SA,
+                 MER,
+                 learning_rate=1.,
+                 plot=False):
+        logging.debug("Initialising LUT Model")
+        self.c = c
+        self.SA = SA
+        self.MER = MER
+        self.learning_rate = learning_rate
+        self.plot = plot
+
+    def train(self, tx_dpd, rx_received):
+        pass
+
+    def get_dpd_data(self):
+        return ("lut", np.ones(32, dtype=np.complex64))
 
 # The MIT License (MIT)
 #
 # Copyright (c) 2017 Andreas Steger
+# 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
diff --git a/src/MemlessPoly.cpp b/src/MemlessPoly.cpp
index d7f9a96..f223d34 100644
--- a/src/MemlessPoly.cpp
+++ b/src/MemlessPoly.cpp
@@ -8,7 +8,8 @@
 
     http://opendigitalradio.org
 
-   This block implements a memoryless polynom for digital predistortion.
+   This block implements both a memoryless polynom for digital predistortion,
+   and a lookup table predistorter.
    For better performance, multiplying is done in another thread, leading
    to a pipeline delay of two calls to MemlessPoly::process
  */
@@ -67,7 +68,7 @@ MemlessPoly::MemlessPoly(const std::string& coefs_file, unsigned int num_threads
 
     if (num_threads == 0) {
         const unsigned int hw_concurrency = std::thread::hardware_concurrency();
-        etiLog.level(info) << "Polynomial Predistorter will use " <<
+        etiLog.level(info) << "Digital Predistorter will use " <<
             hw_concurrency << " threads (auto detected)";
 
         for (size_t i = 0; i < hw_concurrency; i++) {
@@ -80,7 +81,7 @@ MemlessPoly::MemlessPoly(const std::string& coefs_file, unsigned int num_threads
         }
     }
     else {
-        etiLog.level(info) << "Polynomial Predistorter will use " <<
+        etiLog.level(info) << "Digital Predistorter will use " <<
             num_threads << " threads (set in config file)";
 
         for (size_t i = 0; i < num_threads; i++) {
@@ -100,54 +101,93 @@ MemlessPoly::MemlessPoly(const std::string& coefs_file, unsigned int num_threads
 
 void MemlessPoly::load_coefficients(const std::string &coefFile)
 {
-    std::vector<float> coefs_am;
-    std::vector<float> coefs_pm;
     std::ifstream coef_fstream(coefFile.c_str());
     if (!coef_fstream) {
         throw std::runtime_error("MemlessPoly: Could not open file with coefs!");
     }
-    int n_coefs;
-    coef_fstream >> n_coefs;
 
-    if (n_coefs <= 0) {
-        throw std::runtime_error("MemlessPoly: coefs file has invalid format.");
-    }
-    else if (n_coefs != NUM_COEFS) {
-        throw std::runtime_error("MemlessPoly: invalid number of coefs: " +
-                std::to_string(n_coefs) + " expected " + std::to_string(NUM_COEFS));
-    }
+    uint32_t file_format_indicator;
+    const uint8_t file_format_odd_poly = 1;
+    const uint8_t file_format_lut = 2;
+    coef_fstream >> file_format_indicator;
 
-    const int n_entries = 2 * n_coefs;
+    if (file_format_indicator == file_format_odd_poly) {
+        int n_coefs;
+        coef_fstream >> n_coefs;
+
+        if (n_coefs <= 0) {
+            throw std::runtime_error("MemlessPoly: coefs file has invalid format.");
+        }
+        else if (n_coefs != NUM_COEFS) {
+            throw std::runtime_error("MemlessPoly: invalid number of coefs: " +
+                    std::to_string(n_coefs) + " expected " + std::to_string(NUM_COEFS));
+        }
 
-    etiLog.log(debug, "MemlessPoly: Reading %d coefs...", n_entries);
+        const int n_entries = 2 * n_coefs;
 
-    coefs_am.resize(n_coefs);
-    coefs_pm.resize(n_coefs);
+        std::vector<float> coefs_am;
+        std::vector<float> coefs_pm;
+        coefs_am.resize(n_coefs);
+        coefs_pm.resize(n_coefs);
 
-    for (int n = 0; n < n_entries; n++) {
-        float a;
-        coef_fstream >> a;
+        for (int n = 0; n < n_entries; n++) {
+            float a;
+            coef_fstream >> a;
 
-        if (n < n_coefs) {
-            coefs_am[n] = a;
-        }
-        else {
-            coefs_pm[n - n_coefs] = a;
+            if (n < n_coefs) {
+                coefs_am[n] = a;
+            }
+            else {
+                coefs_pm[n - n_coefs] = a;
+            }
+
+            if (coef_fstream.eof()) {
+                etiLog.log(error, "MemlessPoly: file %s should contains %d coefs, "
+                        "but EOF reached after %d coefs !",
+                        coefFile.c_str(), n_entries, n);
+                throw std::runtime_error("MemlessPoly: coefs file invalid !");
+            }
         }
 
-        if (coef_fstream.eof()) {
-            etiLog.log(error, "MemlessPoly: file %s should contains %d coefs, "
-                    "but EOF reached after %d coefs !",
-                    coefFile.c_str(), n_entries, n);
-            throw std::runtime_error("MemlessPoly: coefs file invalid !");
+        {
+            std::lock_guard<std::mutex> lock(m_coefs_mutex);
+
+            m_dpd_type = dpd_type_t::odd_only_poly;
+            m_coefs_am = coefs_am;
+            m_coefs_pm = coefs_pm;
+            m_dpd_settings_valid = true;
         }
+        etiLog.log(info, "MemlessPoly loaded %zu poly coefs",
+                m_coefs_am.size() + m_coefs_pm.size());
     }
+    else if (file_format_indicator == file_format_lut) {
+        float scalefactor;
+        coef_fstream >> scalefactor;
 
-    {
-        std::lock_guard<std::mutex> lock(m_coefs_mutex);
+        std::array<complexf, lut_entries> lut;
 
-        m_coefs_am = coefs_am;
-        m_coefs_pm = coefs_pm;
+        for (size_t n = 0; n < lut_entries; n++) {
+            float a;
+            coef_fstream >> a;
+
+            lut[n] = a;
+        }
+
+        {
+            std::lock_guard<std::mutex> lock(m_coefs_mutex);
+
+            m_dpd_type = dpd_type_t::lookup_table;
+            m_lut_scalefactor = scalefactor;
+            m_lut = lut;
+            m_dpd_settings_valid = true;
+        }
+
+        etiLog.log(info, "MemlessPoly loaded %zu LUT entries", m_lut.size());
+    }
+    else {
+        etiLog.log(error, "MemlessPoly: coef file has unknown format %d",
+                file_format_indicator);
+        m_dpd_settings_valid = false;
     }
 }
 
@@ -195,6 +235,39 @@ static void apply_coeff(
     }
 }
 
+static void apply_lut(
+        const complexf *__restrict lut, const float scalefactor,
+        const complexf *__restrict in,
+        size_t start, size_t stop, complexf *__restrict out)
+{
+    for (size_t i = start; i < stop; i++) {
+        const float in_mag = std::abs(in[i]);
+
+        // The scalefactor is chosen so as to map the input magnitude
+        // to the range of uint32_t
+        const uint32_t scaled_in = lrintf(in_mag * scalefactor);
+
+        // lut_ix contains the number of leading 0-bits of the
+        // scaled value, starting at the most significant bit position.
+        //
+        // This partitions the range 0 -- 0xFFFFFFFF into 32 bins.
+        //
+        // 0x00000000 to 0x07FFFFFF go into bin 0
+        // 0x08000000 to 0x0FFFFFFF go into bin 1
+        // 0x10000000 to 0x17FFFFFF go into bin 2
+        // ...
+        // 0xF0000000 to 0xF7FFFFFF go into bin 30
+        // 0xF8000000 to 0xFFFFFFFF go into bin 31
+        //
+        // The high 5 bits are therefore used as index.
+        const uint8_t lut_ix = (scaled_in >> 27);
+
+        // The LUT contains a complex correction factor that is close to
+        // 1 + 0j
+        out[i] = in[i] * lut[lut_ix];
+    }
+}
+
 void MemlessPoly::worker_thread(MemlessPoly::worker_t *workerdata)
 {
     while (true) {
@@ -205,9 +278,18 @@ void MemlessPoly::worker_thread(MemlessPoly::worker_t *workerdata)
             break;
         }
 
-        apply_coeff(in_data.coefs_am, in_data.coefs_pm,
-                in_data.in, in_data.start, in_data.stop,
-                in_data.out);
+        switch (in_data.dpd_type) {
+            case dpd_type_t::odd_only_poly:
+                apply_coeff(in_data.coefs_am, in_data.coefs_pm,
+                        in_data.in, in_data.start, in_data.stop,
+                        in_data.out);
+                break;
+            case dpd_type_t::lookup_table:
+                apply_lut(in_data.lut, in_data.lut_scalefactor,
+                        in_data.in, in_data.start, in_data.stop,
+                        in_data.out);
+                break;
+        }
 
         workerdata->out_queue.push(1);
     }
@@ -221,6 +303,7 @@ int MemlessPoly::internal_process(Buffer* const dataIn, Buffer* dataOut)
     complexf* out = reinterpret_cast<complexf*>(dataOut->getData());
     size_t sizeOut = dataOut->getLength() / sizeof(complexf);
 
+    if (m_dpd_settings_valid)
     {
         std::lock_guard<std::mutex> lock(m_coefs_mutex);
         const size_t num_threads = m_workers.size();
@@ -232,6 +315,9 @@ int MemlessPoly::internal_process(Buffer* const dataIn, Buffer* dataOut)
             for (auto& worker : m_workers) {
                 worker_t::input_data_t dat;
                 dat.terminate = false;
+                dat.dpd_type = m_dpd_type;
+                dat.lut_scalefactor = m_lut_scalefactor;
+                dat.lut = m_lut.data();
                 dat.coefs_am = m_coefs_am.data();
                 dat.coefs_pm = m_coefs_pm.data();
                 dat.in = in;
@@ -245,8 +331,16 @@ int MemlessPoly::internal_process(Buffer* const dataIn, Buffer* dataOut)
             }
 
             // Do the last in this thread
-            apply_coeff(m_coefs_am.data(), m_coefs_pm.data(),
-                    in, start, sizeOut, out);
+            switch (m_dpd_type) {
+                case dpd_type_t::odd_only_poly:
+                    apply_coeff(m_coefs_am.data(), m_coefs_pm.data(),
+                            in, start, sizeOut, out);
+                    break;
+                case dpd_type_t::lookup_table:
+                    apply_lut(m_lut.data(), m_lut_scalefactor,
+                            in, start, sizeOut, out);
+                    break;
+            }
 
             // Wait for completion of the tasks
             for (auto& worker : m_workers) {
@@ -255,10 +349,21 @@ int MemlessPoly::internal_process(Buffer* const dataIn, Buffer* dataOut)
             }
         }
         else {
-            apply_coeff(m_coefs_am.data(), m_coefs_pm.data(),
-                    in, 0, sizeOut, out);
+            switch (m_dpd_type) {
+                case dpd_type_t::odd_only_poly:
+                    apply_coeff(m_coefs_am.data(), m_coefs_pm.data(),
+                            in, 0, sizeOut, out);
+                    break;
+                case dpd_type_t::lookup_table:
+                    apply_lut(m_lut.data(), m_lut_scalefactor,
+                            in, 0, sizeOut, out);
+                    break;
+            }
         }
     }
+    else {
+        memcpy(dataOut->getData(), dataIn->getData(), sizeOut);
+    }
 
     return dataOut->getLength();
 }
diff --git a/src/MemlessPoly.h b/src/MemlessPoly.h
index 57c0924..612934f 100644
--- a/src/MemlessPoly.h
+++ b/src/MemlessPoly.h
@@ -49,6 +49,12 @@
 
 typedef std::complex<float> complexf;
 
+enum class dpd_type_t {
+    odd_only_poly,
+    lookup_table
+};
+
+
 class MemlessPoly : public PipelinedModCodec, public RemoteControllable
 {
 public:
@@ -71,8 +77,16 @@ private:
         struct input_data_t {
             bool terminate = false;
 
+            dpd_type_t dpd_type;
+
+            // Valid for polynomial types
             const float *coefs_am = nullptr;
             const float *coefs_pm = nullptr;
+
+            // Valid for LUT
+            float lut_scalefactor = 0.0f;
+            const complexf *lut = nullptr;
+
             const complexf *in = nullptr;
             size_t start = 0;
             size_t stop = 0;
@@ -112,8 +126,16 @@ private:
 
     static void worker_thread(worker_t *workerdata);
 
+    bool m_dpd_settings_valid = false;
+    dpd_type_t m_dpd_type;
     std::vector<float> m_coefs_am; // AM/AM coefficients
     std::vector<float> m_coefs_pm; // AM/PM coefficients
+
+    float m_lut_scalefactor; // Scale value applied before looking up in LUT
+
+    static constexpr size_t lut_entries = 32;
+    std::array<complexf, lut_entries> m_lut; // Lookup table correction factors
+
     std::string m_coefs_file;
     mutable std::mutex m_coefs_mutex;
 };