Advice on long distance wireless links?

Bruno Lopes F. Cabral bruno at
Mon Sep 9 12:23:28 EST 2002

Hi there

I did a long distance point to point link here, 45km, 
30dBs 1.5meters antennaes on both sides (105m high on 
one side, 15m high on the other, no higher obstacles 
between the points)

the Link Quality shows 19/92, Signal level: -87 dBm 
Noise level:-99 dBm. auto bitrate states 1Mb, but 
fixing it at 11Mb also seems to "work" (i.e. pinging
the other side works -- most of the time)

the performance is poor in any case, about 64K/192K 
at best. lots of lost packets, very few or none DUP

I dig a bit and found indicattions that long distance
links need increasing ACKs timeouts to prevent "multi-
path" retransmissions, but I could'nt find exactly what
I need to change or any further indications of how to
calculate the parameters involved, so I'm seeking for 
advice of you fellows

do I need to increase/decrease one or more of the 
following or other parameters? do you have any tables/
formulas indicating the ranges x the distances between 
the points?

- Fragmentation threeshold
- Listen interval (or beacon interval)
- RTS threeshold

would be better to use ad-hoc mode instead of managed 
mode in this setup?? I'm using linux on the stations,
tried orinoco (orinoco_cs/kernel 2.2) and prism2
(hostap_cs, kernel 2.4) cards (drivers)

any help/FAQ/pointers on this would be greatelly 
appreciated :)

from Brazil

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