ccsds_encoder.h

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/* -*- c++ -*- */
/*
 * Copyright 2014 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *
 */
 
#ifndef INCLUDED_FEC_CCSDS_ENCODER_H
#define INCLUDED_FEC_CCSDS_ENCODER_H
 
#include <gnuradio/fec/api.h>
#include <gnuradio/fec/cc_common.h>
#include <gnuradio/fec/encoder.h>
#include <map>
#include <string>
 
namespace gr {
namespace fec {
namespace code {
 
/*!
 * \brief CCSDS Encoding class for convolutional encoding with
 * rate 1/2, K=7, and polynomials [109, 79].
 * \ingroup error_coding_blk
 *
 * \details
 *
 * Uses Phil Karn's (KA9Q) implementation of the CCSDS encoder
 * for rate 1/2, K=7, and CC polynomial [109, 79]. These are
 * non-adjustable in this encoder. For an adjustable CC encoder
 * where we can set the rate, constraint length, and polynomial,
 * see gr::fec::code::cc_encoder.
 *
 * The encoder is set up with a number of bits per frame in the
 * constructor. When not being used in a tagged stream mode,
 * this encoder will only process frames of the length provided
 * here. If used in a tagged stream block, this setting becomes
 * the maximum allowable frame size that the block may process.
 *
 * The \p mode is a cc_mode_t that specifies how the convolutional
 * encoder will behave and under what conditions.
 *
 * \li 'CC_STREAMING': mode expects an uninterrupted flow of
 * samples into the encoder, and the output stream is
 * continually encoded.
 *
 * \li 'CC_TERMINATED': is a mode designed for packet-based
 * systems. This mode adds rate*(k-1) bits to the output as a
 * way to help flush the decoder.
 *
 * \li 'CC_TAILBITING': is another packet-based method. Instead of
 * adding bits onto the end of the packet, this mode will
 * continue the code between the payloads of packets by
 * pre-initializing the state of the new packet based on the
 * state of the last packet for (k-1) bits.
 *
 * \li 'CC_TRUNCATED': a truncated code always resets the registers
 * to the \p start_state between frames.
 *
 * A common convolutional encoder uses K=7, Rate=1/2,
 * Polynomials=[109, 79]. This is the Voyager code from NASA:
 * \li   109: b(1101101) --> 1 + x   + x^3 + x^4 + x^6
 * \li   79:  b(1001111) --> 1 + x^3 + x^4 + x^5 + x^6
 */
class FEC_API ccsds_encoder : virtual public generic_encoder
{
public:
    /*!
     * Build the CCSDS (rate=1/2, K=7, polys=[109,79]
     * convolutional code FECAPI object.
     *
     * \param frame_size Number of bits per frame. If using in the
     *        tagged stream style, this is the maximum allowable
     *        number of bits per frame.
     * \param start_state Initialization state of the shift register.
     * \param mode cc_mode_t mode of the encoding.
     */
    static generic_encoder::sptr
    make(int frame_size, int start_state = 0, cc_mode_t mode = CC_STREAMING);
 
    /*!
     * Sets the uncoded frame size to \p frame_size. If \p
     * frame_size is greater than the value given to the
     * constructor, the frame size will be capped by that initial
     * value and this function will return false. Otherwise, it
     * returns true.
     */
    bool set_frame_size(unsigned int frame_size) override = 0;
 
    /*!
     * Returns the coding rate of this encoder.
     */
    double rate() override = 0;
};
 
} /* namespace code */
} /* namespace fec */
} /* namespace gr */
 
#endif /* INCLUDED_FEC_CCSDS_ENCODER_H */