gr::digital::ofdm_chanest_vcvc Class Reference

Estimate channel and coarse frequency offset for OFDM from preamblesInput: OFDM symbols (in frequency domain). The first one (or two) symbols are expected to be synchronisation symbols, which are used to estimate the coarse freq offset and the initial equalizer taps (these symbols are removed from the stream). The following n_data_symbols are passed through unmodified (the actual equalisation must be done elsewhere). Output: The data symbols, without the synchronisation symbols. The first data symbol passed through has two tags: 'ofdm_sync_carr_offset' (integer), the coarse frequency offset as number of carriers, and 'ofdm_sync_eq_taps' (complex vector). Any tags attached to the synchronisation symbols are attached to the first data symbol. All other tags are propagated as expected. More...

#include <ofdm_chanest_vcvc.h>

Inheritance diagram for gr::digital::ofdm_chanest_vcvc:

List of all members.

Public Types
typedef boost::shared_ptr < ofdm_chanest_vcvc >	sptr
Static Public Member Functions
static sptr	make (const std::vector< gr_complex > &sync_symbol1, const std::vector< gr_complex > &sync_symbol2, int n_data_symbols, int eq_noise_red_len=0, int max_carr_offset=-1, bool force_one_sync_symbol=false)

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Detailed Description

Estimate channel and coarse frequency offset for OFDM from preambles

Input: OFDM symbols (in frequency domain). The first one (or two) symbols are expected to be synchronisation symbols, which are used to estimate the coarse freq offset and the initial equalizer taps (these symbols are removed from the stream). The following n_data_symbols are passed through unmodified (the actual equalisation must be done elsewhere). Output: The data symbols, without the synchronisation symbols. The first data symbol passed through has two tags: 'ofdm_sync_carr_offset' (integer), the coarse frequency offset as number of carriers, and 'ofdm_sync_eq_taps' (complex vector). Any tags attached to the synchronisation symbols are attached to the first data symbol. All other tags are propagated as expected.

Note: The vector on ofdm_sync_eq_taps is already frequency-corrected, whereas the rest is not.

This block assumes the frequency offset is even (i.e. an integer multiple of 2).

[1] Schmidl, T.M. and Cox, D.C., "Robust frequency and timing synchronization for OFDM", Communications, IEEE Transactions on, 1997. [2] K.D. Kammeyer, "Nachrichtenuebertragung," Chapter. 16.3.2.

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Member Typedef Documentation

typedef boost::shared_ptr<ofdm_chanest_vcvc> gr::digital::ofdm_chanest_vcvc::sptr

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Member Function Documentation

static sptr gr::digital::ofdm_chanest_vcvc::make	(	const std::vector< gr_complex > &	sync_symbol1,
		const std::vector< gr_complex > &	sync_symbol2,
		int	n_data_symbols,
		int	eq_noise_red_len = 0,
		int	max_carr_offset = -1,
		bool	force_one_sync_symbol = false
	)		[static]

Parameters:

sync_symbol1	First synchronisation symbol in the frequency domain. Its length must be the FFT length. For Schmidl & Cox synchronisation, every second sub-carrier has to be zero.
sync_symbol2	Second synchronisation symbol in the frequency domain. Must be equal to the FFT length, or zero length if only one synchronisation symbol is used. Using this symbol is how synchronisation is described in [1]. Leaving this empty forces us to interpolate the equalizer taps. If you are using an unusual sub-carrier configuration (e.g. because of OFDMA), this sync symbol is used to identify the active sub-carriers. If you only have one synchronisation symbol, set the active sub-carriers to a non-zero value in here, and also set force_one_sync_symbol parameter to true.
n_data_symbols	The number of data symbols following each set of synchronisation symbols. Must be at least 1.
eq_noise_red_len	If non-zero, noise reduction for the equalizer taps is done according to [2]. In this case, it is the channel influence time in number of samples. A good value is usually the length of the cyclic prefix.
max_carr_offset	Limit the number of sub-carriers the frequency offset can maximally be. Leave this zero to try all possibilities.
force_one_sync_symbol	See sync_symbol2.

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The documentation for this class was generated from the following file:

• ofdm_chanest_vcvc.h