GNU Radio Manual and C++ API Reference  3.7.9.2
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ofdm_frame_acquisition.h
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1 /* -*- c++ -*- */
2 /*
3  * Copyright 2006,2007,2011,2012 Free Software Foundation, Inc.
4  *
5  * This file is part of GNU Radio
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7  * GNU Radio is free software; you can redistribute it and/or modify
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22 
23 #ifndef INCLUDED_DIGITAL_OFDM_FRAME_ACQUISITION_H
24 #define INCLUDED_DIGITAL_OFDM_FRAME_ACQUISITION_H
25 
26 #include <gnuradio/digital/api.h>
27 #include <gnuradio/block.h>
28 #include <vector>
29 
30 namespace gr {
31  namespace digital {
32 
33  /*!
34  * \brief take a vector of complex constellation points in from an
35  * FFT and performs a correlation and equalization.
36  * \ingroup ofdm_blk
37  *
38  * \details
39  * This block takes the output of an FFT of a received OFDM symbol
40  * and finds the start of a frame based on two known symbols. It
41  * also looks at the surrounding bins in the FFT output for the
42  * correlation in case there is a large frequency shift in the
43  * data. This block assumes that the fine frequency shift has
44  * already been corrected and that the samples fall in the middle
45  * of one FFT bin.
46  *
47  * It then uses one of those known symbols to estimate the channel
48  * response over all subcarriers and does a simple 1-tap
49  * equalization on all subcarriers. This corrects for the phase
50  * and amplitude distortion caused by the channel.
51  */
52  class DIGITAL_API ofdm_frame_acquisition : virtual public block
53  {
54  public:
55  // gr::digital::ofdm_frame_acquisition::sptr
56  typedef boost::shared_ptr<ofdm_frame_acquisition> sptr;
57 
58  /*!
59  * Make an OFDM correlator and equalizer.
60  *
61  * \param occupied_carriers The number of subcarriers with data in the received symbol
62  * \param fft_length The size of the FFT vector (occupied_carriers + unused carriers)
63  * \param cplen The length of the cycle prefix
64  * \param known_symbol A vector of complex numbers representing a known symbol at the
65  * start of a frame (usually a BPSK PN sequence)
66  * \param max_fft_shift_len Set's the maximum distance you can look between bins for correlation
67  */
68  static sptr make(unsigned int occupied_carriers, unsigned int fft_length,
69  unsigned int cplen,
70  const std::vector<gr_complex> &known_symbol,
71  unsigned int max_fft_shift_len=4);
72 
73  /*!
74  * \brief Return an estimate of the SNR of the channel
75  */
76  virtual float snr() = 0;
77  };
78 
79  } /* namespace digital */
80 } /* namespace gr */
81 
82 #endif /* INCLUDED_DIGITAL_OFDM_FRAME_ACQUISITION_H */
#define DIGITAL_API
Definition: gr-digital/include/gnuradio/digital/api.h:30
Include this header to use the message passing features.
Definition: logger.h:131
boost::shared_ptr< ofdm_frame_acquisition > sptr
Definition: ofdm_frame_acquisition.h:56
take a vector of complex constellation points in from an FFT and performs a correlation and equalizat...
Definition: ofdm_frame_acquisition.h:52
The abstract base class for all 'terminal' processing blocks.A signal processing flow is constructed ...
Definition: block.h:60