digital: ofdm_equalizer_simpledfe: add enable_soft_output option

Enable outputting equalized symbols that are not exactly constellation symbols. This is useful for OFDM soft decoding/demodulation (e.g. optimal turbo or LDPC decoding). For compatibility, this new behaviour has to be enabled by setting the new option "enable_soft_output" to true (false by default).
author: japm48 <japm48@users.noreply.github.com> 2020-10-20 07:54:59 +0200
committer: mormj <34754695+mormj@users.noreply.github.com> 2020-10-28 14:15:25 -0400
commit: 1458b71d90310444e556f515ee86dde7c287ed79 (patch)
tree: 69ac890ede9ed5b5c9ebdf1e571d3d13ff5a0263 /gr-digital
parent: 15efb1ed8d089b3e5ef2aac7f55f483e36d4866d (diff)
4 files changed, 68 insertions, 20 deletions
diff --git a/gr-digital/include/gnuradio/digital/ofdm_equalizer_simpledfe.h b/gr-digital/include/gnuradio/digital/ofdm_equalizer_simpledfe.h
index 54c9c43fea..725ef7c6c8 100644
--- a/gr-digital/include/gnuradio/digital/ofdm_equalizer_simpledfe.h
+++ b/gr-digital/include/gnuradio/digital/ofdm_equalizer_simpledfe.h
@@ -44,9 +44,12 @@ namespace digital {
  * channel state is estimated incorrectly during equalization; after that,
  * all subsequent symbols will be completely wrong.
  *
- * Note that the equalized symbols are *exact points* on the constellation.
- * This means soft information of the modulation symbols is lost after the
+ * Note that, by default, the equalized symbols are *exact points* on the
+ * constellation.
+ * This means that soft information of the modulation symbols is lost after the
  * equalization, which is suboptimal for channel codes that use soft decision.
+ * If this behaviour is not desired, set the `enable_soft_output` parameter to
+ * true.
  *
  */
 class DIGITAL_API ofdm_equalizer_simpledfe : public ofdm_equalizer_1d_pilots
@@ -64,7 +67,8 @@ public:
                                  std::vector<std::vector<gr_complex>>(),
                              int symbols_skipped = 0,
                              float alpha = 0.1,
-                             bool input_is_shifted = true);
+                             bool input_is_shifted = true,
+                             bool enable_soft_output = false);
 
     ~ofdm_equalizer_simpledfe();
 
@@ -97,6 +101,9 @@ public:
      *                         the first input items is on the DC carrier.
      *                         Note that a lot of the OFDM receiver blocks operate on
      * shifted signals!
+     * \param enable_soft_output Output noisy equalized symbols instead of exact
+     *                           constellation symbols.
+     *                           This is useful for soft demodulation and decoding.
      */
     static sptr make(int fft_len,
                      const gr::digital::constellation_sptr& constellation,
@@ -108,12 +115,15 @@ public:
                          std::vector<std::vector<gr_complex>>(),
                      int symbols_skipped = 0,
                      float alpha = 0.1,
-                     bool input_is_shifted = true);
+                     bool input_is_shifted = true,
+                     bool enable_soft_output = false);
 
 private:
     gr::digital::constellation_sptr d_constellation;
     //! Averaging coefficient
     float d_alpha;
+    //! Do not output exact constellation symbols
+    bool d_enable_soft_output;
 };
 
 } /* namespace digital */
diff --git a/gr-digital/lib/ofdm_equalizer_simpledfe.cc b/gr-digital/lib/ofdm_equalizer_simpledfe.cc
index 6ba0ca1b6e..0bca3bdbf6 100644
--- a/gr-digital/lib/ofdm_equalizer_simpledfe.cc
+++ b/gr-digital/lib/ofdm_equalizer_simpledfe.cc
@@ -24,16 +24,19 @@ ofdm_equalizer_simpledfe::make(int fft_len,
                                const std::vector<std::vector<gr_complex>>& pilot_symbols,
                                int symbols_skipped,
                                float alpha,
-                               bool input_is_shifted)
+                               bool input_is_shifted,
+                               bool enable_soft_output)
 {
-    return ofdm_equalizer_simpledfe::sptr(new ofdm_equalizer_simpledfe(fft_len,
-                                                                       constellation,
-                                                                       occupied_carriers,
-                                                                       pilot_carriers,
-                                                                       pilot_symbols,
-                                                                       symbols_skipped,
-                                                                       alpha,
-                                                                       input_is_shifted));
+    return ofdm_equalizer_simpledfe::sptr(
+        new ofdm_equalizer_simpledfe(fft_len,
+                                     constellation,
+                                     occupied_carriers,
+                                     pilot_carriers,
+                                     pilot_symbols,
+                                     symbols_skipped,
+                                     alpha,
+                                     input_is_shifted,
+                                     enable_soft_output));
 }
 
 ofdm_equalizer_simpledfe::ofdm_equalizer_simpledfe(
@@ -44,7 +47,8 @@ ofdm_equalizer_simpledfe::ofdm_equalizer_simpledfe(
     const std::vector<std::vector<gr_complex>>& pilot_symbols,
     int symbols_skipped,
     float alpha,
-    bool input_is_shifted)
+    bool input_is_shifted,
+    bool enable_soft_output)
     : ofdm_equalizer_1d_pilots(fft_len,
                                occupied_carriers,
                                pilot_carriers,
@@ -52,7 +56,8 @@ ofdm_equalizer_simpledfe::ofdm_equalizer_simpledfe(
                                symbols_skipped,
                                input_is_shifted),
       d_constellation(constellation),
-      d_alpha(alpha)
+      d_alpha(alpha),
+      d_enable_soft_output(enable_soft_output)
 {
 }
 
@@ -69,6 +74,7 @@ void ofdm_equalizer_simpledfe::equalize(gr_complex* frame,
         d_channel_state = initial_taps;
     }
     gr_complex sym_eq, sym_est;
+    bool enable_soft_output = d_enable_soft_output;
 
     for (int i = 0; i < n_sym; i++) {
         for (int k = 0; k < d_fft_len; k++) {
@@ -92,7 +98,7 @@ void ofdm_equalizer_simpledfe::equalize(gr_complex* frame,
                                                &sym_est);
                 d_channel_state[k] = d_alpha * d_channel_state[k] +
                                      (1 - d_alpha) * frame[i * d_fft_len + k] / sym_est;
-                frame[i * d_fft_len + k] = sym_est;
+                frame[i * d_fft_len + k] = enable_soft_output ? sym_eq : sym_est;
             }
         }
         if (!d_pilot_carriers.empty()) {
diff --git a/gr-digital/python/digital/bindings/ofdm_equalizer_simpledfe_python.cc b/gr-digital/python/digital/bindings/ofdm_equalizer_simpledfe_python.cc
index 44bb7e5b42..fcd939057f 100644
--- a/gr-digital/python/digital/bindings/ofdm_equalizer_simpledfe_python.cc
+++ b/gr-digital/python/digital/bindings/ofdm_equalizer_simpledfe_python.cc
@@ -14,7 +14,7 @@
 /* BINDTOOL_GEN_AUTOMATIC(0)                                                       */
 /* BINDTOOL_USE_PYGCCXML(0)                                                        */
 /* BINDTOOL_HEADER_FILE(ofdm_equalizer_simpledfe.h) */
-/* BINDTOOL_HEADER_FILE_HASH(8091e37dbba4afc0b7a2fd9441996144)                     */
+/* BINDTOOL_HEADER_FILE_HASH(e484906ff9740a46f83b999ec69f511e)                     */
 /***********************************************************************************/
 
 #include <pybind11/complex.h>
@@ -47,6 +47,7 @@ void bind_ofdm_equalizer_simpledfe(py::module& m)
              py::arg("symbols_skipped") = 0,
              py::arg("alpha") = 0.10000000000000001,
              py::arg("input_is_shifted") = true,
+             py::arg("enable_soft_output") = false,
              D(ofdm_equalizer_simpledfe, make))
 
 
diff --git a/gr-digital/python/digital/qa_ofdm_frame_equalizer_vcvc.py b/gr-digital/python/digital/qa_ofdm_frame_equalizer_vcvc.py
index 6af2817685..a1b2a2e070 100644..100755
--- a/gr-digital/python/digital/qa_ofdm_frame_equalizer_vcvc.py
+++ b/gr-digital/python/digital/qa_ofdm_frame_equalizer_vcvc.py
@@ -167,6 +167,7 @@ class qa_ofdm_frame_equalizer_vcvc (gr_unittest.TestCase):
         # Check data
         self.assertComplexTuplesAlmostEqual(rx_expected, sink.data()[0], places=4)
 
+
     def test_002_static (self):
         """
         - Add a simple channel
@@ -229,6 +230,9 @@ class qa_ofdm_frame_equalizer_vcvc (gr_unittest.TestCase):
         expected_dict = {
                 'ofdm_sync_chan_taps': channel[-fft_len:]
         }
+        # Won't be exactly the same when compiled with -fcx-limited-range
+        self.assertTrue(numpy.allclose(tag_dict['ofdm_sync_chan_taps'], expected_dict['ofdm_sync_chan_taps']))
+        expected_dict['ofdm_sync_chan_taps'] = tag_dict['ofdm_sync_chan_taps']
         self.assertEqual(tag_dict, expected_dict)
 
     def test_002_static_wo_tags (self):
@@ -330,6 +334,9 @@ class qa_ofdm_frame_equalizer_vcvc (gr_unittest.TestCase):
         equalizer = digital.ofdm_equalizer_simpledfe(
             fft_len, cnst.base(), occupied_carriers, pilot_carriers, pilot_symbols, 0, 0.01
         )
+        equalizer_soft = digital.ofdm_equalizer_simpledfe(
+            fft_len, cnst.base(), occupied_carriers, pilot_carriers, pilot_symbols, 0, 0.01, enable_soft_output=True
+        )
         channel = [
             0, 0,  1,  1, 0,  1,  1, 0,
             0, 0,  1,  1, 0,  1,  1, 0, # These coefficients will be rotated slightly...
@@ -346,16 +353,40 @@ class qa_ofdm_frame_equalizer_vcvc (gr_unittest.TestCase):
         chan_tag.value = pmt.init_c32vector(fft_len, channel[:fft_len])
         src = blocks.vector_source_c(numpy.multiply(tx_signal, channel), False, fft_len, (chan_tag,))
         eq = digital.ofdm_frame_equalizer_vcvc(equalizer.base(), 0, self.tsb_key, True)
+        eq_soft = digital.ofdm_frame_equalizer_vcvc(equalizer_soft.base(), 0, self.tsb_key, True)
         sink = blocks.tsb_vector_sink_c(fft_len, tsb_key=self.tsb_key)
+        sink_soft = blocks.tsb_vector_sink_c(fft_len, tsb_key=self.tsb_key)
+        stream_to_tagged = blocks.stream_to_tagged_stream(gr.sizeof_gr_complex, fft_len, len(tx_data) // fft_len, self.tsb_key)
         self.tb.connect(
                 src,
-                blocks.stream_to_tagged_stream(gr.sizeof_gr_complex, fft_len, len(tx_data) // fft_len, self.tsb_key),
+                stream_to_tagged,
                 eq,
                 sink
         )
+        self.tb.connect(
+          stream_to_tagged,
+          eq_soft,
+          sink_soft
+        )
         self.tb.run ()
-        rx_data = [cnst.decision_maker_v((x,)) if x != 0 else -1 for x in sink.data()[0]]
+
+        out_syms = numpy.array(sink.data()[0])
+        out_syms_soft = numpy.array(sink_soft.data()[0])
+        demod = lambda syms: [cnst.decision_maker_v((x,)) if x != 0 else -1 for x in syms]
+        rx_data = demod(out_syms)
+        rx_data_soft = demod(out_syms_soft)
+
+        ## Uncomment to plot symbols
+        #import matplotlib.pyplot as plt
+        #def plot_syms(d): plt.figure(); plt.plot(d.real, d.imag, 'b.')
+        #
+        #plot_syms(out_syms)
+        #plot_syms(out_syms_soft)
+        #plt.show()
+
         self.assertEqual(tx_data, rx_data)
+        self.assertEqual(rx_data, rx_data_soft)
+        self.assertFalse(numpy.allclose(out_syms, out_syms_soft))
         self.assertEqual(len(sink.tags()), 1)
         tag = sink.tags()[0]
         self.assertEqual(pmt.symbol_to_string(tag.key), "ofdm_sync_chan_taps")
@@ -363,5 +394,5 @@ class qa_ofdm_frame_equalizer_vcvc (gr_unittest.TestCase):
 
 
 if __name__ == '__main__':
-    gr_unittest.run(qa_ofdm_frame_equalizer_vcvc, "qa_ofdm_frame_equalizer_vcvc.xml")
+    gr_unittest.run(qa_ofdm_frame_equalizer_vcvc)
author	japm48 <japm48@users.noreply.github.com>	2020-10-20 07:54:59 +0200
committer	mormj <34754695+mormj@users.noreply.github.com>	2020-10-28 14:15:25 -0400
commit	1458b71d90310444e556f515ee86dde7c287ed79 (patch)
tree	69ac890ede9ed5b5c9ebdf1e571d3d13ff5a0263 /gr-digital
parent	15efb1ed8d089b3e5ef2aac7f55f483e36d4866d (diff)