GNU Radio's AIS Package
gr::ais::corr_est_cc Class Referenceabstract

Correlate stream with a pre-defined sequence and estimate peak. More...

#include <corr_est_cc.h>

Inheritance diagram for gr::ais::corr_est_cc:

Public Types

typedef boost::shared_ptr< corr_est_ccsptr
 

Public Member Functions

virtual std::vector< gr_complex > symbols () const =0
 
virtual void set_symbols (const std::vector< gr_complex > &symbols)=0
 

Static Public Member Functions

static sptr make (const std::vector< gr_complex > &symbols, float sps, unsigned int mark_delay, float threshold=0.9)
 

Detailed Description

Correlate stream with a pre-defined sequence and estimate peak.

Input:

  • Stream of complex samples.

Output:

  • Output stream that just passes the input complex samples
  • tag 'phase_est': estimate of phase offset
  • tag 'time_est': estimate of symbol timing offset
  • tag 'corr_est': the correlation value of the estimates
  • tag 'corr_start': the start sample of the correlation and the value
  • Optional 2nd output stream providing the advanced correlator output

This block is designed to search for a sync word by correlation and uses the results of the correlation to get a time and phase offset estimate. These estimates are passed downstream as stream tags for use by follow-on synchronization blocks.

The sync word is provided as a set of symbols along with a baseband matched filter which we use to create the filtered and upsampled symbols that we will receive over-the-air.

The phase_est tag can be used by downstream blocks to adjust their phase estimatopm/correction loops, and is currently implemented by the gr::digital::costas_loop_cc block.

The time_est tag can be used to adjust the sampling timing estimate of any downstream synchronization blocks and is currently implemented by the gr::digital::pfb_clock_sync_ccf block.

The caller must provide a "time_est" and "phase_est" tag marking delay from the start of the correlated signal segment, in order to mark the proper point in the sync word for downstream synchronization blocks. Generally this block cannot know where the actual sync word symbols are located relative to "corr_start", given that some modulations have pulses with intentional ISI. The user should manually examine the primary output and the "corr_start" tag postition to determine the required tag delay settings for the particular modulation, sync word, and downstream blocks used.

For a discussion of the properties of complex correlations, with respect to signal processing, see: Marple, Jr., S. L., "Estimating Group Delay and Phase Delay via Discrete-Time 'Analytic' Cross-Correlation, IEEE_Transcations on_Signal_Processing, Volume 47, No. 9, September 1999

Member Typedef Documentation

◆ sptr

typedef boost::shared_ptr<corr_est_cc> gr::ais::corr_est_cc::sptr

Member Function Documentation

◆ make()

static sptr gr::ais::corr_est_cc::make ( const std::vector< gr_complex > &  symbols,
float  sps,
unsigned int  mark_delay,
float  threshold = 0.9 
)
static

Make a block that correlates against the symbols vector and outputs a phase and symbol timing estimate.

Parameters
symbolsSet of symbols to correlate against (e.g., a sync word).
spsSamples per symbol
mark_delaytag marking delay in samples after the corr_start tag
thresholdThreshold of correlator, relative to a 100% correlation (1.0). Default is 0.9.

◆ set_symbols()

virtual void gr::ais::corr_est_cc::set_symbols ( const std::vector< gr_complex > &  symbols)
pure virtual

Implemented in gr::ais::corr_est_cc_impl.

◆ symbols()

virtual std::vector< gr_complex > gr::ais::corr_est_cc::symbols ( ) const
pure virtual

Implemented in gr::ais::corr_est_cc_impl.


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