/* -*- c++ -*- */ /* * Copyright 2011,2012 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_LMS_DD_EQUALIZER_CC_H #define INCLUDED_DIGITAL_LMS_DD_EQUALIZER_CC_H #include <digital/api.h> #include <gr_sync_decimator.h> #include <digital/constellation.h> namespace gr { namespace digital { /*! * \brief Least-Mean-Square Decision Directed Equalizer (complex in/out) * \ingroup eq_blk * \ingroup digital * * This block implements an LMS-based decision-directed equalizer. * It uses a set of weights, w, to correlate against the inputs, * u, and a decisions is then made from this output. The error in * the decision is used to update teh weight vector. * * y[n] = conj(w[n]) u[n] * d[n] = decision(y[n]) * e[n] = d[n] - y[n] * w[n+1] = w[n] + mu u[n] conj(e[n]) * * Where mu is a gain value (between 0 and 1 and usualy small, * around 0.001 - 0.01. * * This block uses the digital_constellation object for making the * decision from y[n]. Create the constellation object for * whatever constellation is to be used and pass in the object. * In Python, you can use something like: * * self.constellation = digital.constellation_qpsk() * * To create a QPSK constellation (see the digital_constellation * block for more details as to what constellations are available * or how to create your own). You then pass the object to this * block as an sptr, or using "self.constellation.base()". * * The theory for this algorithm can be found in Chapter 9 of: * S. Haykin, Adaptive Filter Theory, Upper Saddle River, NJ: * Prentice Hall, 1996. */ class DIGITAL_API lms_dd_equalizer_cc : virtual public gr_sync_decimator { protected: virtual gr_complex error(const gr_complex &out) = 0; virtual void update_tap(gr_complex &tap, const gr_complex &in) = 0; public: // gr::digital::lms_dd_equalizer_cc::sptr typedef boost::shared_ptr<lms_dd_equalizer_cc> sptr; /*! * Make an LMS decision-directed equalizer * * \param num_taps Numer of taps in the equalizer (channel size) * \param mu Gain of the update loop * \param sps Number of samples per symbol of the input signal * \param cnst A constellation derived from class * 'constellation'. Use base() method to get a shared pointer to * this base class type. */ static sptr make(int num_taps, float mu, int sps, constellation_sptr cnst); virtual void set_taps(const std::vector<gr_complex> &taps) = 0; virtual std::vector<gr_complex> taps() const = 0; virtual float gain() const = 0; virtual void set_gain(float mu) = 0; }; } /* namespace digital */ } /* namespace gr */ #endif /* INCLUDED_DIGITAL_LMS_DD_EQUALIZER_CC_H */