[Discuss-gnuradio] choosing start of frame bits, studies?

[George Nychis]

Hi all,

The gr_correlate_access_code_bb block takes a 64-bit access code as 
input to detect the start of incoming frames using a hamming distance 
with a threshold.  The packet utilities has a default access code and 
uses a threshold of 12.

I'm not sure who wrote the code and who picked the default access code 
and threshold, but my instinct tells me Eric :)

Was the access code picked randomly, or was there some basic rule of 
thumb for generating it?  What about the threshold of 12?  What about 
choosing a 64bit access as opposed to 32bit?

Does anyone know of any studies done on these variables that I could 
read about?  They have obvious impacts on false positives and negatives.

When it comes down to fully decoding the frame, false positives can 
easily be picked out by examining the frame header.  But, I'm working on 
something that is attempting to perform actions without fully decoding 
the frame header and frame, so the access code itself has a strong impact.

Thanks!
George