GNU Radio's AIS Package
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Correlate stream with a pre-defined sequence and estimate peak. More...
#include <corr_est_cc.h>
Public Types | |
typedef boost::shared_ptr< corr_est_cc > | sptr |
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) |
Correlate stream with a pre-defined sequence and estimate peak.
Input:
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
typedef boost::shared_ptr<corr_est_cc> gr::ais::corr_est_cc::sptr |
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static |
Make a block that correlates against the symbols
vector and outputs a phase and symbol timing estimate.
symbols | Set of symbols to correlate against (e.g., a sync word). |
sps | Samples per symbol |
mark_delay | tag marking delay in samples after the corr_start tag |
threshold | Threshold of correlator, relative to a 100% correlation (1.0). Default is 0.9. |
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pure virtual |
Implemented in gr::ais::corr_est_cc_impl.
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pure virtual |
Implemented in gr::ais::corr_est_cc_impl.