LF: Re: Op-32 correlation results online

["Markus Vester" <markusvester@aol.com>]

Andy,

 

yes I am using the second method. The predefined list of callsigns is converted to prestored Opera 01 sequences, based on the protocol description published by Guido PE1NNZ. For any 35 minute time slot, the received signal is correlated to each of the candidates, and the winning correlation peak is displayed if it exceeds an SNR threshold (14 dB). There is no attempt to decode anything, and the program will never come up with a callsign which was not in the list. In that sense it is really only a detection tool, but it does provide more than one bit due to unique identification (eg. 5 bits worth for 32 candidates), along with precise frequency and time information. 

 

Experiments with simulated incoherent signals (ie. random phase for each dash) indicate that the correlation process in itself is about 6 dB more sensitive than the standard 28 bit decoding. This is more or less paid for by the reduced information content. For coherent transmissions, another 5 or 6 db are gained by being able to sum up the real complex amplitude rather than the power of all dashes. Loosely speaking, this can reduce the equivalent noise bandwidth from the inverse length of a single symbol (0.125 Hz), down to something proportional to the inverse of the whole sequence (0.5 mHz). 

 

Best 73,

Markus (DF6NM)

 

  

 

Re: [rsgb_lf_group] Re: 0p-32 correlation results online

What I am not sure about, Markus...

 

In your software do you actually decode the data in some way, therefore using knowledge of the Opera signal coding OR....

 

Do you precode a callsign (your "precalculated templates from a limited list of callsigns") then correlate the received data against the pattern generated for that callsign.    If this latter is the case, then really you are decoding just one bit of infomration.  The presence or absence of a known call.  

 

I suspect many readers hoping for an independent Opera are thinking the first option; but your description makes me think its the latter.  In which case, its certainly not a generalised data communication protocol, but a weak signal error corrected path checker.

 

Andy

G4JNT

Den 22.02.2013 11:55, skrev Markus:

Steinar,

yes this is an independent development. It's still very experimental, but I intend to make it public after I have fixed a few more issues.
 
The functional difference is that I don't try to decode individual bits, but correlate the message as a whole against precalculated templates from a limited list of callsigns. The benefit is that these detections can be up to 10 to 12 dB more sensitive than the incoherent decoding in the original software. 
 
Best 73,
 Markus