throughput and tx rate in marginal signal conditions

don don at
Tue Jun 3 14:04:19 EDT 2003

I,ve just set up a link over 3.3km with an Actiontec pci card and hostap
drivers (2002-10-12) at one end and a Dlink dwl900ap+ in client mode at
the other. The signal is 4 to 5db above noise level and the link always
gets a few send errors. The Dlink end transmits at 11 meg solid, but the
hostap end drops down to 1 meg and stays there. If I force the hostap
end to operate at different rates and count the errors, it turns out
that the error rate goes up as the bit rate comes down. So it can't
always be presumed that lowering the bit rate will get the error rate

The hostap driver (as I read the code) drops the bit rate each time that
there is a transmit error and puts it up if 50 good packets are sent. If
the bit rate setting was based on the errors to good transmit ratio of
each bit rate, then I think that the throughput under marginal signal
conditions would improve considerably.

Don Magee

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