Re: gEDA-user: Anticapacitor -- step back a little from the problem

["Bert Douglas" <bertd@xxxxxxxxxxxxx>]

This is for Karel.

Part of your problem is that you are using baseband signalling over the 
optical link.  That is, if ethernet signal is high, LED is on, if ethernet 
signal is low, then LED is off.

Since this signal was not designed for an optical link, it is highly 
unlikely that it is optimum for the task.

An optical link is likely to have significant changes in signal strength 
over relatively short periods of time.  On ethernet this doesn't happen.

So you might want to consider re-encoding the ethernet bits to a different 
signal pattern on the LED.

If you apply direct spreading you can get some code gain.  And since the 
interesting cases are always at the margin where there is a lot of noise, 
you can add some FEC (forward error correction).

In really high noise cases, you can lower the effective data rate and use a 
longer spreading sequence.  It is better to get a little data through than 
to get no data through.  This document may be helpful:

http://public.ccsds.org/publications/archive/131x0b1.pdf