From 7fd15b67afa5abd20c0982bdd6bcb7191831bf73 Mon Sep 17 00:00:00 2001
From: Martin Braun <martin.braun@kit.edu>
Date: Fri, 15 Mar 2013 02:12:20 -0700
Subject: Squash/rebased martin/ofdm-master onto trial merge branch
Conflicts:
gr-blocks/include/blocks/CMakeLists.txt
---
.../include/digital_ofdm_equalizer_simpledfe.h | 126 +++++++++++++++++++++
1 file changed, 126 insertions(+)
create mode 100644 gr-digital/include/digital_ofdm_equalizer_simpledfe.h
(limited to 'gr-digital/include/digital_ofdm_equalizer_simpledfe.h')
diff --git a/gr-digital/include/digital_ofdm_equalizer_simpledfe.h b/gr-digital/include/digital_ofdm_equalizer_simpledfe.h
new file mode 100644
index 0000000000..9fd6395904
--- /dev/null
+++ b/gr-digital/include/digital_ofdm_equalizer_simpledfe.h
@@ -0,0 +1,126 @@
+/* -*- c++ -*- */
+/* Copyright 2012 Free Software Foundation, Inc.
+ *
+ * This file is part of GNU Radio
+ *
+ * GNU Radio 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, or (at your option)
+ * any later version.
+ *
+ * GNU Radio 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 GNU Radio; see the file COPYING. If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef INCLUDED_DIGITAL_OFDM_EQUALIZER_SIMPLEDFE_H
+#define INCLUDED_DIGITAL_OFDM_EQUALIZER_SIMPLEDFE_H
+
+#include <digital_api.h>
+#include <digital_constellation.h>
+#include <digital_ofdm_equalizer_base.h>
+
+class digital_ofdm_equalizer_simpledfe;
+typedef boost::shared_ptr<digital_ofdm_equalizer_simpledfe> digital_ofdm_equalizer_simpledfe_sptr;
+
+/*
+ * \param fft_len FFT length
+ * \param constellation The constellation object describing the modulation used
+ * on the subcarriers (e.g. QPSK). This is used to decode
+ * the individual symbols.
+ * \param occupied_carriers List of occupied carriers, see ofdm_carrier_allocator
+ * for a description.
+ * \param pilot_carriers Position of pilot symbols, see ofdm_carrier_allocator
+ * for a description.
+ * \param pilot_symbols Value of pilot symbols, see ofdm_carrier_allocator
+ * for a description.
+ * \param alpha Averaging coefficient (in a nutshell, if \f$H_{i,k}\f$ is the channel
+ * state for carrier i and symbol k,
+ * \f$H_{i,k+1} = \alpha H_{i,k} + (1 - \alpha) H_{i,k+1}\f$. Make this
+ * larger if there's more noise, but keep in mind that larger values
+ * of alpha mean slower response to channel changes).
+ * \param symbols_skipped Starting position within occupied_carriers and pilot_carriers.
+ * If the first symbol of the frame was removed (e.g. to decode the
+ * header), set this make sure the pilot symbols are correctly
+ * identified.
+ * \param input_is_shifted Set this to false if the input signal is not shifted, i.e.
+ * the first input items is on the DC carrier.
+ * Note that a lot of the OFDM receiver blocks operate on shifted
+ * signals!
+ */
+DIGITAL_API digital_ofdm_equalizer_simpledfe_sptr
+digital_make_ofdm_equalizer_simpledfe(
+ int fft_len,
+ const digital_constellation_sptr &constellation,
+ const std::vector<std::vector<int> > &occupied_carriers = std::vector<std::vector<int> >(),
+ const std::vector<std::vector<int> > &pilot_carriers = std::vector<std::vector<int> >(),
+ const std::vector<std::vector<gr_complex> > &pilot_symbols = std::vector<std::vector<gr_complex> >(),
+ int symbols_skipped = 0,
+ float alpha = 0.1,
+ bool input_is_shifted = true);
+
+/* \brief Simple decision feedback equalizer for OFDM.
+ * \ingroup ofdm_blk
+ * \ingroup eq_blk
+ *
+ * Equalizes an OFDM signal symbol by symbol using knowledge of the
+ * complex modulations symbols.
+ * For every symbol, the following steps are performed:
+ * - On every sub-carrier, decode the modulation symbol
+ * - Use the difference between the decoded symbol and the received symbol
+ * to update the channel state on this carrier
+ * - Whenever a pilot symbol is found, it uses the known pilot symbol to
+ * update the channel state.
+ *
+ * This equalizer makes a lot of assumptions:
+ * - The initial channel state is good enough to decode the first
+ * symbol without error (unless the first symbol only consists of pilot
+ * tones)
+ * - The channel changes only very slowly, such that the channel state
+ * from one symbol is enough to decode the next
+ * - SNR low enough that equalization will always suffice to correctly
+ * decode a symbol
+ * If these assumptions are not met, the most common error is that the
+ * 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
+ * equalization, which is suboptimal for channel codes that use soft decision.
+ *
+ */
+class DIGITAL_API digital_ofdm_equalizer_simpledfe : public digital_ofdm_equalizer_1d_pilots
+{
+ public:
+ digital_ofdm_equalizer_simpledfe(
+ int fft_len,
+ const digital_constellation_sptr &constellation,
+ const std::vector<std::vector<int> > &occupied_carriers = std::vector<std::vector<int> >(),
+ const std::vector<std::vector<int> > &pilot_carriers = std::vector<std::vector<int> >(),
+ const std::vector<std::vector<gr_complex> > &pilot_symbols = std::vector<std::vector<gr_complex> >(),
+ int symbols_skipped = 0,
+ float alpha = 0.1,
+ bool input_is_shifted = true);
+
+ ~digital_ofdm_equalizer_simpledfe();
+
+ void equalize(gr_complex *frame,
+ int n_sym,
+ const std::vector<gr_complex> &initial_taps = std::vector<gr_complex>(),
+ const std::vector<gr_tag_t> &tags = std::vector<gr_tag_t>());
+
+ private:
+ digital_constellation_sptr d_constellation;
+ //! Averaging coefficient
+ float d_alpha;
+
+};
+
+#endif /* INCLUDED_DIGITAL_OFDM_EQUALIZER_SIMPLEDFE_H */
+
--
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