We are having problems in a significant number of large lecture halls with being able to provide adequate wireless coverage to handle what the instructors want to do - have everyone connect to some site and do the same thing at the same time. Of course this can be problematic from the server end, but often the server is fine (particularly when it is local), the connectivity to the wireless clients in the bottleneck.
Most of our large auditoriums of this type have concrete floors built on grade
(thus no mounting APs under the floor), are tiered with fixed seating, many
have fixed tables, and most have a ceiling height of 25-30+ feet at the front
and maybe as little 12' at the back.
Ceiling mounting is problematic - too hard to service above the seats and at
the high end, directional antennas are "too ugly" to be acceptable, and
integrated antennas provide too large of a coverage area to keep client
counts/AP reasonable (especially in the 2.4 GHz range where 75% of our usage
currently occurs).
Wall mounted units (which we use now) do not keep client counts/AP down to a
level that we would like (e.g., about 15 users/AP) and coverage in the center
of the room is poor, mostly caused by an unfettered signal going all the way
across the room & spreading out as it goes. Our Cisco WiSM controllers try to
balance the signal strengths, but that then leaves a coverage hole in the
middle of the room. With only three 2.4 GHz channels to use, this is very
messy. The folks using 5 GHz are much happier.
Under table mounting could be very good with an AP placed to cover maybe a 10'
circle. But, current APs are way to thick to be unobtrusive. I had hoped the
Motorola in-wallbox unit would be small enough for this application, but their
100 Mbps uplink and single radio was a showstopper for us. Why can't the WiFi
folks make an AP the size of a cell phone?? Or, even two cell phones?? The cell
phone folks can do it and pack a phone & other goodies into a very small
package along with their WiFi radio. I'm not looking for great range here, just
small with good service attributes.
I have thought about using leaky coax antennas fastened to the bottom of the
table tops and connected to an AP at each end of an aisle (may also need on in
the middle). Small size would not be too intrusive and hopefully not too prone
to mutilation. I could even put multiple cables in parallel under the table
tops.
My Cisco sales rep had some experience with this type of antenna when he did
some work for an underground mine.
My questions to the group are:
(1) Has anyone ever used leaky coax antennas in any application even remotely
similar to this? Was the experience good or bad?
(2) Does anyone have any vendor recommendations for purchasing leaky coax
antennas?
(3) Is this technically viable for both 2.4 & 5 GHz applications?
(4) What am I missing? If this is a viable solution, why can't I find out
anything about it from a Web search?
(5) Does anyone have any very good or very bad experiences with deployments in
this type of venue that they would be willing to share?
Thanks.
-jcw
[cid:[email protected]]
John Watters The University of Alabama
Office of Information Technology
205-348-3992
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