ofdm_carrier_allocator_cvc.h

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/* -*- c++ -*- */
/*
 * Copyright 2013 Free Software Foundation, Inc.
 *
 * This file is part of GNU Radio
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *
 */
 
 
#ifndef INCLUDED_DIGITAL_OFDM_CARRIER_ALLOCATOR_CVC_H
#define INCLUDED_DIGITAL_OFDM_CARRIER_ALLOCATOR_CVC_H
 
#include <gnuradio/digital/api.h>
#include <gnuradio/tagged_stream_block.h>
 
namespace gr {
namespace digital {
 
/*!
 * \brief Create frequency domain OFDM symbols from complex values, add pilots.
 * \ingroup ofdm_blk
 *
 * \details
 * This block turns a stream of complex, scalar modulation symbols into vectors
 * which are the input for an IFFT in an OFDM transmitter. It also supports the
 * possibility of placing pilot symbols onto the carriers.
 *
 * The carriers can be allocated freely, if a carrier is not allocated, it is set
 * to zero. This allows doing OFDMA-style carrier allocations.
 *
 * Input: A tagged stream of complex scalars. The first item must have a tag
 *        containing the number of complex symbols in this frame.
 * Output: A tagged stream of complex vectors of length fft_len. This can directly
 *         be connected to an FFT block. Make sure to set this block to 'reverse'
 *         for the IFFT. If \p output_is_shifted is true, the FFT block must activate
 *         FFT shifting, otherwise, set shifting to false. If given, sync words are
 *         prepended to the output. Note that sync words are prepended verbatim,
 *         make sure they are shifted (or not).
 *
 * Carrier indexes are always such that index 0 is the DC carrier (note: you should
 * not allocate this carrier). The carriers below the DC carrier are either indexed
 * with negative numbers, or with indexes larger than \p fft_len/2. Index -1 and index
 * \p fft_len-1 both identify the carrier below the DC carrier.
 *
 * There are some basic checks in place during initialization which check that the
 * carrier allocation table is valid. However, it is possible to overwrite data symbols
 * with pilot symbols, or provide a carrier allocation that has mismatching pilot symbol
 * positions and -values.
 *
 * Tags are propagated such that a tag on an incoming complex symbol is mapped to the
 * corresponding OFDM symbol. There is one exception: If a tag is on the first OFDM
 * symbol, it is assumed that this tag should stay there, so it is moved to the front
 * even if a sync word is included (any other tags will never be attached to the
 * sync word). This allows tags to control the transmit timing to pass through in the
 * correct position.
 */
class DIGITAL_API ofdm_carrier_allocator_cvc : virtual public tagged_stream_block
{
public:
    typedef std::shared_ptr<ofdm_carrier_allocator_cvc> sptr;
 
    virtual std::string len_tag_key() = 0;
    virtual int fft_len() const = 0;
    virtual std::vector<std::vector<int>> occupied_carriers() = 0;
 
    /*
     * \param fft_len FFT length, is also the maximum width of the OFDM symbols, the
     *                output vector size and maximum value for elements in
     *                \p occupied_carriers and \p pilot_carriers.
     * \param occupied_carriers A vector of vectors of indexes. Example: if
     *                          occupied_carriers = ((1, 2, 3), (1, 2, 4)), the first
     *                          three input symbols will be mapped to carriers 1, 2
     *                          and 3. After that, a new OFDM symbol is started. The next
     *                          three input symbols will be placed onto carriers 1, 2
     *                          and 4 of the second OFDM symbol. The allocation then
     *                          starts from the beginning.
     *                          Order matters! The first input symbol is always mapped
     *                          onto occupied_carriers[0][0].
     * \param pilot_carriers The position of the pilot symbols. Same as occupied_carriers,
     *                       but the actual symbols are taken from pilot_symbols instead
     *                       of the input stream.
     * \param pilot_symbols The pilot symbols which are placed onto the pilot carriers.
     *                      pilot_symbols[0][0] is placed onto the first OFDM symbol, on
     *                      carrier index pilot_carriers[0][0] etc.
     * \param sync_words OFDM symbols that are prepended to the OFDM frame (usually for
     *                   synchronisation purposes, e.g. OFDM symbols with every second
     *                   sub-carrier being idle). Is a vector of complex vectors of length
     *                   \p fft_len
     * \param len_tag_key The key of the tag identifying the length of the input packet.
     * \param output_is_shifted whether to 'fftshift' the output OFDM symbols. If used,
     * the followup FFT should be instantaited such that it knows that the input is
     * shifted. Default is true.
     */
    static sptr make(int fft_len,
                     const std::vector<std::vector<int>>& occupied_carriers,
                     const std::vector<std::vector<int>>& pilot_carriers,
                     const std::vector<std::vector<gr_complex>>& pilot_symbols,
                     const std::vector<std::vector<gr_complex>>& sync_words,
                     const std::string& len_tag_key = "packet_len",
                     const bool output_is_shifted = true);
};
 
} // namespace digital
} // namespace gr
 
#endif /* INCLUDED_DIGITAL_OFDM_CARRIER_ALLOCATOR_CVC_H */