City WLAN Mesh Deployment

[cbento]

Dear All,

I am just another wireless passionate eager to deploy a open WLAN in my current city of residence.
To begin with we are interested in covering a 4 square Kms area.

I have some rookie questions that I would like to answer. I am sure you guys with your experience can help me to answer these questions and point me in the right direction.

1. Imagining I would deploy a 12dBi Omni antenna on top of a 7 store building, would people inside that building be able to connect to my antenna using their laptops PDAs or smartphones? How can I get inside buildings into peoples apartments?

2. What can be the average range of a 12dBi Omni antenna? I know it depends a lot on the scenario... but can you please give-me a minimum amount? Will it be able to cover a radius of 1Km with good signal? lets say a signal strength for at least 5Mbps.

3. Would a sectorial antenna have more range than a Omni when talking about of a single section?

3. Do I need to install any kind of hardware in the users laptops, PDAs or smartphones? I mean, If my AP is 1Km away and they receive the signal, do they need also to be able to have transmiting power to transmit over 1Km?

4. Does anyone of you have experience in deploying a WLAN in a city environment or any other kind of environemnt? I would appreciate your help...

Cant wait for your answers,

Thank you all very much for your time,

Cheers!

Cristovao Bento

[tog]

A high-gain 12dBi antenna on top of the building will not reach the people in the building it is mounted on very well. A high-gain antenna does not have very good coverage directly above and below it.

Your best bet to provide access to that building would probably be to have antennas mounted elsewhere close enough to the building that the people inside the building could use them.

Keep in mind that 802.11g wifi clients themselves have a non-adjustable distance limit (ACK timeout) of about 600 meters. Even if you can send and receive a decent radio signal to and from the clients beyond 600 meters, you will start to run into problems with their ACK timeout setting which you cannot adjust.

So, you will have to setup your network so that there is an access point within at least 600 meters of every point.

Given this limitation, it may not make sense for you to use 12dBi antennas since you will want to reduce the size of your radio footprint so you can re-use the same frequencies more often. A lower-gain antenna will also provide you more coverage above and below the antenna as well as being smaller and less of an eyesore.

[rafamous]

To have that type of coverage you will want several sectors to penetrate the buildings. It's not an easy task but you could start with one area at a time and work your way around.

[cbento]

Thanks guys!

So this means that 600 meters is the minimum distance between last mile APs for people with normal wifi equipment. Didnt knew about that!

But being people inside the building and my antenna outside, lets say a sectorial antenna at 500 meters. Will their normal 802.11g or b clients be able to transmmit through the walls and cover that distance? do they have power enought? We are talking about normal hardware that is shipped today with laptops or PDAs.

[tog]

Depends upon what the walls are made of and how many there are between the AP and client. It's more feasible to receive the client signals through some walls if the AP side is using directional sector antennas so the AP has a better "ear" for hearing these otherwise faint signals.

[David L. Vrablic]

Cbento,
You asked a direct question and you deserve a direct answer.
All of our AP's are Hot Spots..
You will be greatly dissapointed at the coverage of laptops that are in the hands of the general population.
I am convinced they are designed to work across an open room and that is about it.
All my sites are multi sectored with only a few omni execptions that are down at ground level.
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If you are transmitting from a building high above street level most of the signal will pass right over the potential customers.
I try to use 4 PAC wireless 90* sectors at each site mounted out on the edge of the building with enough down tilt to get the signal on the ground.
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Like Tog and Rafamous said,
Building penetration is going to depend on so many things.
I was in a HIVAC penthouse last week and the backhaul antenna was not more than 1000 yards away at the same height.
I could not get a wiff of any signals on my laptop. The penthouse was surrounded with steel corragated siding. (A big Faraday cage as it were)
A lot of the new buildings have steel 2 x 4's , in place of wood and the new windows have a tendancy to stop rf like a screen would.
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You are asking the right questions but I fear you will not like the answers.
The key is lots and lots of pop.s.
Good luck!

[rbolduc]

You will be greatly dissapointed at the coverage of laptops that are in the hands of the general population.
I am convinced they are designed to work across an open room and that is about it.


Hmmmm For some reason my Laptop with a WLM54G card always seem to see wireless signals that other people cant ;)

Reed

[David L. Vrablic]

I'll bet it works better than most Reed,
You ought to see the trouble I get into with certian Apple laptops that only see for about 300 ft.
My boss has one. In the office he can see 3 units on the same floor.
I use a Ubiquity PCMCIA SCR card and I pick up and can connect to 11 stations.

[tog]

The 15 inch Macbook Pro seems to have an odd problem with poor signal. My initial 10-second guess without any real investigation was that the antenna was trapped behind/inside some metallic structure that was messing it up.

It is using an otherwise really good sensitive atheros card.

That particular laptop is just about the ultimate test for working with other crappy signal laptops. If you can get a link to the Macbook Pro 15 inch you can probably get a link to somebody using a horrible PCMCIA card antenna.