[Laser] Troposcatter and Information Theory-2

[TWOSIG at aol.com]

Andy K0SM/2 had a recent question to help setup a troposcatter system that 
got me puzzled about coding information.  He described the system "uses an 8.2 
second transmission length per character and incoherent averaging of the 
message as it loops 
around. "

I know that there has been success with moonbounce using long characters, but 
I don't understand the advantage.  Assume a 10 character message, that takes 
almost a minute and a half to transmit.  Doesn't information theory say that 
if you use 0.1 second character time and repeat the message 82 times you get 
the same benefit?

Is there something about troposcatter that would benefit from such long 
characters?

For a communications system, I would think that using short characters would 
allow you to count the number of repetitions needed to "detect" the correct 
value, and thus have a dynamic measure of the data rate that the channel will 
provide.  If the system is stable with excess channel capacity, it could then 
adapt by increasing the message rate ( send fewer repetitions ) or lowering the 
transmitted power

It could be that I just have a personal bias for faster communications.  I 
think PSK31 with every character repeated three times is as slow as I would want 
to try to work.  


Andy, I wish you success.


James
N5GUI