WiFi over distance - 300 metres

Greetings

I am looking for a WAP bridging solution including recommendations for
suitable, absolutely reliable antenae for communicating as fast as
technically possible (albeit propriatory 108 MB/s) between two buildings
that are approximately 300 metres apart.

I have line of sight between the two buildings.

Each building has it's own LAN and I'm looking to bridge.

TX in advance

Maurice

On Wed, 30 Nov 2005 03:09:09 -0000, "Maurice Bishop"
<(E-Mail Removed)> wrote:

>I am looking for a WAP bridging solution including recommendations for
>suitable, absolutely reliable antenae for communicating as fast as
>technically possible (albeit propriatory 108 MB/s) between two buildings
>that are approximately 300 metres apart.
>I have line of sight between the two buildings.
>Each building has it's own LAN and I'm looking to bridge.

I assume you have lots of money to spend. Nobody gets 108Mbits/sec
thruput from a commodity cheap wireless bridge. That's the connection
speed. The thruput is about half or less of the connection speed.
You'll also find that 108Mbit/sec works just fine out to about 2-3
meters. Any more requires big antennas. At about 20 meters, timing
becomes a problem and the bridge will slow down. Basically, Turbo-G
and Super-G are not suitable for 300 meter links at full speed. They
work just fine for slower speeds, but not at speed.

Methinks you will need to specify a slower thruput speed that is
acceptable. At 300 meters, a pair of cheap bridge radios (Linksys
WAP54G) with 24dBi dish antennas will work at 54Mbits/sec or about
25Mbits/sec thruput. The problem is reliability. NOTHING on 2.4GHz
is considered reliable because of interference issues. All it takes
is one leaky microwave oven, a wireless security camera, a municipal
wireless deployment, or a nearby 802.11g network, and your reliability
is lost. If you truly want reliability, I suggest a licensed wireless
solution, with frequency and location coordination to insure that
there is no interference.

I suggest you revise your specifications to include:
1. Desired thruput (mbits/sec)?
2. Full or half duplex?
3. Total number of MAC addresses that must be passed?
4. Do you have AC power on the rooftops?
5. Distance (300 meters)?
6. Fresnel zone clearance at midpoint?
7. Maximum cost?
8. What country?
9. Any local interference on 2.4 or 5.7Ghz? Consider 24GHz?
10. Exact reliability figure.

The last item is critical as it determines the system fade margin.
Fade Margin Reliability
8dB 0.9
18dB 0.99
28dB 0.999
38dB 0.9999
48dB 0.99999
99% reliability may sound good, but that means your link will be dead
for 1% of the time or you will experience 3.7 days of outage every
year. Tradition and experience says that it will happen at the worst
possible time. Increasing the fade margin by 10dB (one step on the
above table) is not a trivial or cheap exercise as it requires either
a 10 times increase in transmit power, or a 4 times increase in
antenna size at both ends of the link. Pick your numbers carefully.

I you just want to look at possible products, see:
| http://www.winncom.com
| http://www.winncom.com/products/category/WPP/list.html
which is a distributor that carries a wide range of wireless bridges.
If you call them, be sure to complain about them hiding their prices.
Also:
| http://www.redlinecommunications.com
I don't want to make any recommendations until your supply more
detailed requirements and limitations.

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

> I am looking for a WAP bridging solution including recommendations for
> suitable, absolutely reliable antenae for communicating as fast as
> technically possible (albeit propriatory 108 MB/s) between two buildings
> that are approximately 300 metres apart.
>
> I have line of sight between the two buildings.
>
> Each building has it's own LAN and I'm looking to bridge.

How about looking at some of the free space optical stuff?

This is probably overkill for your 300m mind you but you said you wanted
fast, it's faster than 108Mbps

http://www.orthogonsystems.com

David.

On Fri, 02 Dec 2005 11:31:33 GMT, David Taylor <(E-Mail Removed)>
wrote:

>> I am looking for a WAP bridging solution including recommendations for
>> suitable, absolutely reliable antenae for communicating as fast as
>> technically possible (albeit propriatory 108 MB/s) between two buildings
>> that are approximately 300 metres apart.
>>
>> I have line of sight between the two buildings.
>>
>> Each building has it's own LAN and I'm looking to bridge.

>How about looking at some of the free space optical stuff?
>This is probably overkill for your 300m mind you but you said you wanted
>fast, it's faster than 108Mbps
>http://www.orthogonsystems.com
>David.

Good idea, but very expensive. The LED variety is adequate for
rooftop work at 300 meters.
http://www.plaintree.com/products.htm
The problem is that at 100baseT speeds, the prices for WB4100 boxes
are about $8,000 for each end. That's about as cheap as it gets for
100Mbits/sec.

I've only done two FSO systems. One of them works just fine with no
problems except when the fog rolls in. The other was the nightmare
from hell. It was across a freeway at 850ft and an elevation of about
50ft off the freeway surface at one end and 20ft at the other. It
worked just fine most of the time, but would constantly fail in the
mornings. The problem turned out to be that the inversion layer
created by the vehicles heating the air at the freeway surface caused
the beam to be diffracted. I measured a beam shift of about 6" at one
end. Then the inversion layer was finally broken up by the morning
sun, it was replaced by sufficient turbulence to again lose the beam.
I spent about two weeks trying to salvage the sale and eventually gave
up. It was replaced by a 5.6GHz link which worked as expected.

I've also done some troubleshooting work on FSO. One system would
fail consistently when it was hot, but work otherwise. I found that
one end had been mounted so that it shot over the office building HVAC
unit. Every time the air conditioner fired up in the summer, the
heated air turbulence trashed the beam. Moving the FSO box solved
that problem.

Another more serious problems is the stability of applications and
services that fail to appreciate having their network connection
disconnected. I've seen far too many crashes and hangs caused by
ancient database applications that have no tolerance for loss of
connectivity. Drop the LAN connection on one nightmare retail (cash
register) application I have to deal with, and it locks up. That's
because it opens a new socket number on reconnection leaving the old
session hanging.

Moral: Test your application before you bridge.

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

> >How about looking at some of the free space optical stuff?
> >This is probably overkill for your 300m mind you but you said you wanted
> >fast, it's faster than 108Mbps
> >http://www.orthogonsystems.com
> >David.
>
> Good idea, but very expensive. The LED variety is adequate for
> rooftop work at 300 meters.
> http://www.plaintree.com/products.htm
> The problem is that at 100baseT speeds, the prices for WB4100 boxes
> are about $8,000 for each end. That's about as cheap as it gets for
> 100Mbits/sec.

The original poster offered no budgetary constraints, only that it
should go as fast as possible.

David.

On Fri, 02 Dec 2005 19:18:10 GMT, David Taylor <(E-Mail Removed)>
wrote:

>> >How about looking at some of the free space optical stuff?
>> >This is probably overkill for your 300m mind you but you said you wanted
>> >fast, it's faster than 108Mbps
>> >http://www.orthogonsystems.com
>> >David.
>>
>> Good idea, but very expensive. The LED variety is adequate for
>> rooftop work at 300 meters.
>> http://www.plaintree.com/products.htm
>> The problem is that at 100baseT speeds, the prices for WB4100 boxes
>> are about $8,000 for each end. That's about as cheap as it gets for
>> 100Mbits/sec.

>The original poster offered no budgetary constraints, only that it
>should go as fast as possible.
>David.

Well, in that case, bring on the big ticket laser FSO boxes:
| http://www.canon.com/bctv/canobeam/
1.25 GigaBits/sec to 1000 meters. Only $27,000 per end. Don't forget
the RF wireless backup in case of fog. 60Ghz, 480Mbits/sec.
| http://www.bridgewave.com/wireless_p...wireless.shtml
Only $10,000 per end. If it rains, the 60Ghz will go down, but the
FSO will run. If it gets foggy, the FSO will go down, but the 60GHz
will continue to run.

Incidentally, there's always a cost limit. It's most obvious
immediately after the initial sticker shock. I usually ask my
customers "How much do you wanna spend?" and then tell them what they
can get for the price. Saves quite a bit of negotiation wear and
tear, and tends to give a better picture of reality.

I'm a big fan of do it thyself:
http://ronja.twibright.com
but that doesn't offer much reliability.
--
Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
831.336.2558 voice
http://www.LearnByDestroying.com AE6KS
http://802.11junk.com Skype: JeffLiebermann
(E-Mail Removed) (E-Mail Removed)