ofdm_cyclic_prefixer.h

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/* -*- c++ -*- */
/*
 * Copyright 2013, 2018 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *
 */
 
#ifndef INCLUDED_DIGITAL_OFDM_CYCLIC_PREFIXER_H
#define INCLUDED_DIGITAL_OFDM_CYCLIC_PREFIXER_H
 
#include <gnuradio/digital/api.h>
#include <gnuradio/tagged_stream_block.h>
 
namespace gr {
namespace digital {
 
/*!
 * \brief Adds a cyclic prefix and performs optional pulse shaping on OFDM symbols.
 * \ingroup ofdm_blk
 *
 * \details
 * Input: OFDM symbols (in the time domain, i.e. after the IFFT). Optionally,
 *        entire frames can be processed. In this case, \p len_tag_key must be
 *        specified which holds the key of the tag that denotes how
 *        many OFDM symbols are in a frame.
 * Output: A stream of (scalar) complex symbols, which include the cyclic prefix
 *         and the pulse shaping.
 *         Note: If complete frames are processed, and \p rolloff_len is greater
 *         than zero, the final OFDM symbol is followed by the delay line of
 *         the pulse shaping.
 *
 * The pulse shape is a raised cosine in the time domain.
 *
 * Different CP lengths as for instance needed in LTE are supported. This
 * is why one of the inputs is std::vector<int>. After every CP given has
 * been prepended to symbols, each with the length of the IFFT operation,
 * the mechanism will wrap around and start over. To give an example, the
 * input tuple for LTE with an FFT length of 2048 would be (160,) +
 * (144,)*6, which is equal to (160, 144, 144, 144, 144, 144, 144). A
 * uniform CP would be indicated by (uniform_cp_length, ).
 *
 * This block does some sanity checking: 1. It is not allowed to have a
 * vector of CP lengths, which are only 0.  2. Not a single CP in the
 * vector must be longer than the rolloff. 3. Not a single CP is allowed to
 * be < 0.
 */
class DIGITAL_API ofdm_cyclic_prefixer : virtual public tagged_stream_block
{
public:
    typedef std::shared_ptr<ofdm_cyclic_prefixer> sptr;
 
    /*!
     * \param input_size IFFT length (i.e. length of the OFDM symbols).
     * \param output_size FFT length + cyclic prefix length (in samples).
     * \param rolloff_len Length of the rolloff flank in samples.
     * \param len_tag_key For framed processing the key of the length tag.
     */
    static sptr make(size_t input_size,
                     size_t output_size,
                     int rolloff_len = 0,
                     const std::string& len_tag_key = "");
 
    /*!
     * \param fft_len IFFT length (i.e. length of the OFDM symbols).
     * \param cp_lengths CP lengths. Wraps around after reaching the end.
     * \param rolloff_len Length of the rolloff flank in samples.
     * \param len_tag_key For framed processing the key of the length tag.
     */
    static sptr make(int fft_len,
                     const std::vector<int>& cp_lengths,
                     int rolloff_len = 0,
                     const std::string& len_tag_key = "");
};
 
} // namespace digital
} // namespace gr
 
#endif /* INCLUDED_DIGITAL_OFDM_CYCLIC_PREFIXER_H */