Error Protection for the Access Code
Original Post: access code sensitivity to BER (SIG Forum)
Date: 2000-08-16
The access code
precedes every baseband packet , and is used to determine what packet is
destined for what piconet. However it is not protected (by such methods as FEC ,
CRC etc.). This then leads to the question why not?
As it is written in the spec, the intention of the access
code is for fast & robust identification.It can't be protected by HEC or
rate 1/3 because then it will probably always be wrong. The access code is
rather protected by a "heavy code" which allows for quite large
number of mistakes. It is also designed for good autocorrelation so that little
shifts gives large miss-correlation.
It doesn't have anything to do with RF VCO. The access
code itself is a very robust (relatively) code so it doesn't have to be
protected by other FEC .
It is possible to this by increasing the load of the DSP ,
this is because the DSP needs to do FEC then correlation, so shift one bit , do
FEC and then correlation. This is a very common practice in any type of
communication systems, you can see any Spread Spectrum book on the topic of
"PN code synchronization".
Note : see also 'Access
Code Sensitivity to BER'
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