channel_model2.h

Go to the documentation of this file.

/* -*- c++ -*- */
/*
 * Copyright 2009,2012,2013 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_CHANNELS_CHANNEL_MODEL2_H
#define INCLUDED_CHANNELS_CHANNEL_MODEL2_H

#include <gnuradio/channels/api.h>
#include <gnuradio/hier_block2.h>
#include <gnuradio/types.h>

namespace gr {
  namespace channels {
    
    /*!
     * \brief Basic channel simulator allowing time-varying frequency
     * and timing inputs.
     * \ingroup channel_models_blk
     *
     * \details
     * This block implements a basic channel model simulator that can
     * be used to help evaluate, design, and test various signals,
     * waveforms, and algorithms.
     *
     * This model allows the user to set the voltage of an AWGN noise
     * source (\p noise_voltage), an initial timing offset (\p
     * epsilon), and a seed (\p noise_seed) to randomize the AWGN
     * noise source.
     *
     * Multipath can be approximated in this model by using a FIR
     * filter representation of a multipath delay profile with the
     * parameter \p taps.
     *
     * Unlike gr::channels::channel_model, this block is designed to
     * enable time-varying frequency and timing offsets.
     * * Port 0: input signal to be run through the channel.
     * * Port 1: frequency function. A constant value between -0.5 and
     *           0.5 here will turn into a constant frequency offset
     *           from -fs/2 to fs/2 (where fs is the sample rate).
     * * Port 2: timing offset function. Sets the resampling rate of
     *           the channel model. A constant value here produces
     *           that value as the timing offset, so a constant 1.0
     *           input stream is the same as not having a timing
     *           offset.
     *
     * Since the models for frequency and timing offset may vary and
     * what we are trying to model may be different for different
     * simulations, we provide the time-varying nature as an input
     * function that is user-defined. If only constant frequency and
     * timing offsets are required, it is easier and less expensive to
     * use gr::channels::channel_model.
     */
    class CHANNELS_API channel_model2 : virtual public hier_block2
    {
    public:
      // gr::channels::channel_model2::sptr
      typedef boost::shared_ptr<channel_model2> sptr;

      /*! \brief Build the channel simulator.
       *
       * \param noise_voltage The AWGN noise level as a voltage (to be
       *                      calculated externally to meet, say, a
       *                      desired SNR).
       * \param epsilon The initial sample timing offset to emulate the
       *                different rates between the sample clocks of
       *                the transmitter and receiver. 1.0 is no difference.
       * \param taps Taps of a FIR filter to emulate a multipath delay profile.
       * \param noise_seed A random number generator seed for the noise source.
       * \param block_tags If true, tags will not be able to propagate through this block.
       */
      static sptr make(double noise_voltage=0.0,
                       double epsilon=1.0,
                       const std::vector<gr_complex> &taps=std::vector<gr_complex>(1,1),
                       double noise_seed=0,
                       bool block_tags=false);

      virtual void set_noise_voltage(double noise_voltage) = 0;
      virtual void set_taps(const std::vector<gr_complex> &taps) = 0;
      virtual void set_timing_offset(double epsilon) = 0;

      virtual double noise_voltage() const = 0;
      virtual std::vector<gr_complex> taps() const = 0;
      virtual double timing_offset() const = 0;
    };

  } /* namespace channels */
} /* namespace gr */

#endif /* INCLUDED_CHANNELS_CHANNEL_MODEL2_H */