On Sat, 14 Aug 2004 14:18:22 GMT, "Bob Alston" <bobalston9
(E-Mail Removed)> wrote:
>Our marina has wireless internet b/g available to 170 boats. It is also
>available to immediately adjacent condos. If you are willing to use your PC
>next to the front window, a USB tin cantenna or a Hawking USB wireless g
>device with small directional antenna (about $70) works well.
>
>For a condo owner who would like to use wireless within their condo, the
>signal is not strong enough. For them I am thinking of recommending some
>kind of wireless bridge with a directional antenna connected via Ethernet
>cable to a standard WAP such as the Linksys WRT54G which I use.
>
>My question is what wireless bridge or device that can function as a
>bridge - mfg and model - would you suggest? Also what directional antenna
>would you suggest?
>
>Of course, low cost is good!
Good, fast, cheap. Pick two.
The basic decision is whether to use a store and forwared repeater, or
two back to back radios.
For example, a pair of back to back DLink DWL-900AP+ or Linksys WAP54G
wireless bridges would work. The one connecting to the marina system
would be set in the "client" mode, while the other one would be set to
the "access point" mode. This is what you describe above. This is
nice because you can position the access point end at some conventient
location within the condo. You can still use a directional antenna
toward the marina on the client radio, and use an omni on the access
point. Of course, they should be on different channels. However, you
will need a CAT5 ethernet cable between units.
The DWL-900AP+ and WAP54G also do the repeater thing, so you can
experiment. However, I expect problems. Store and forward repeaters
cut your bandwidth in half. Since it's on the same frequency as the
marina system, your inside condo laptops will constitute a source of
interference. With a repeater, you may need to construct a single
antenna that will provide both directional gain towards the marina,
and also cover the inside of the condo. With a dual antenna
(diversity) unit, such as the WAP54G in repeater mode, you could have
one antenna pointed at the marina, and the other an omni for covering
the condo[1]. However, location of the access point may still be a
challenge.
My limited experience with the repeater mode on DWL-810+ and
DWL-900AP+ has not been good. Performance was erratic and tended to
"lurch" in bursts due to the interference caused by the client radios
and other users on the "backhaul" channel. However, I never bothered
to troubleshoot the exact cause or find a solution as this was just my
tinkering.
I would go with the back to back radios. As for cheap, well... what's
your time worth? Two radios are a no brainer that's known to work. A
repeater strikes me as a challenge.
[1] A problem with using two antennas directional in a repeater is
that it might be even slower than the theoretical half your bandwidth.
That's because the algorithm for diversity reception is based upon
which antenna has received the last packet. If nothing is received,
then the radio times out and starts scanning both antennas
alternately. My guess is the timeout delay is about 100msec. You
would never notice it in access point mode when moving around the
house, as it would not switch very often. However, running as a
repeater, where the destination is always on one antenna, and the
client is always on the other, requires that it switch back and forth
for every last lousy packet. It wasn't made to do that and will add
the switching delay to every packet. I've only tried this only once
and found that I could barely get 50kbits/sec thruput on an 11Mbit/sec
association. In other words, the dual antenna repeater idea may not
work as expected. However, I may have screwed up somewhere, so it's
worth trying.
--
Jeff Liebermann
(E-Mail Removed)
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 AE6KS 831-336-2558
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