designing wireless for a building

hi all,

i have to design a wireless network for a building with ten floors. i am pretty confused however of certain points:

1. the area of each floor is 530 sq m. initially i thought of placing a cisco 1200 access point on each floor, but then can we use one access point to cater for two floors? there are approx. 30 users each floor.

2. if the idea of putting an access point on each floor is ok, then how will i be able to do the channel settings since 1,6,11 are the only non interfering channels.
please help

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Ten9t6

feline78 wrote:

hi all,

i have to design a wireless network for a building with ten floors. i am pretty confused however of certain points:

1. the area of each floor is 530 sq m. initially i thought of placing a cisco 1200 access point on each floor, but then can we use one access point to cater for two floors? there are approx. 30 users each floor.

2. if the idea of putting an access point on each floor is ok, then how will i be able to do the channel settings since 1,6,11 are the only non interfering channels.
please help

That is true for DSSS devices check out FHSS devices..You can colocate more devices with FHSS. But there is quite a bit more to look at.....Like..Cost and throughput...Hope this gives you some more ideas..

seek

Interesting question..Im not sure really as I never got the chance to plan something like this out.

Wonder if 1,6,11,1,6,11,1,6,11,1 would be far enough apart. Three floors of concrete should be enough to block signal.

If so, 1 AP per floor set to only allow that floor PCs..seems like a good plan.

I guess a lot depends on what kinda throughput and apps you using.

This not really exact science either..from what I read lot of "first" designs for wireless centers require changes and upgrades..but maybee someone here with hands on be better to answer

My 5 cents.

Seek

jbetts

You can paint the ceiling with Wi-Fi Proof Paint (They do make it, and it does work).

The best idea I can think of is to only use 2 AP's.

Yes, 2.

Use signal repeaters throughtout the building to propogate an AP on floor 7, and an AP on floor 3. Have them both use Channel 6, and encrypt them - giving access to the floors designated. There really is no way to do it easily, and that seems like the easiest and best way to me.

My 5.1 cents.

Gawd

They tested out that WiFi Blocking Paint on The Screen Savers yesterday and it only did about a 30% decrease in signal strength.

Gawd

mike adejoh

why dont u try using the 5ghz UNNI BAND it has more chanells to reuse

mford

Here's what I've done in similar scenarios. If you are looking to place 1 AP per floor then try to off-set the location of the AP.
I.E. 1st floor NE side, 2nd floor SW side and flip flop as you go up. Also, I've stopped using the 2.2dbi rubber duck antennas for most all of my designs and installations and have moved to the 5.2 dbi omni-directinal antenna. This produces less bleeding between the floors and also provides better latteral coverage. Another adjustment you might wish to consider is to lower the transmit power setting down to 20-30 mw, again less bleeding between floors and with the 5.2dbi gain ant will give you what you need.

hope this helps... mike

TheWarrior520

Hi, can you guys correct me if I am wrong on this one, because I have been studying for my CWNA and I would like to know if I am grasping this right. In mford's last suggestion he suggested lowering the transmit power to have less bleeding between floors, now I agree that the higher gain omnis will produce a flatter "doughnut" coverage area, but when you lower the power don't you not flatten this doughnut but actually stretch it out, therefore causing more bleeding. I believe this is how the book illustrates it, and I will check when I wake up.

strauchr

TheWarrior520 wrote:

I believe this is how the book illustrates it, and I will check when I wake up.

You type on forums in your sleep?!? Impressive

sprkymrk

Lot of good ideas posted so far. I would just add a reminder to do a good site survey, followed by a check from the parking lot and nearby high rise buildings for any signal leakage. If possible, place the AP's in the center of each floor.

JDMurray

The typical solution is to use highly directional antennas which will spread the signal out across the floor in a flat plane and not bleed over to the adjacent floors. Use the 1/6/11 channel spacing and perform a site survey to see where the bleeding occurs. With any luck, there will be enough grounded metal in the plenum between floors to limit the signal without needing to reduce the signal strength. Also, if you are having receiving problems because of dead spots or far-ranging nodes, try using more sensitive and directional receivers before increasing the transmitter's power.

keatron

Hi,

A proper site survey is going to be key. You can start by getting a feel for the RF in the environment. You need to identify if there are other WLAN's in the area leaking into your building. This could have an impact on whether or not you use UNII or ISM bands. There are many software packages and devices you can buy to assist in this (most of them are not cheap), however a cheap way to do it is to use something free like netstumbler to see what is in use in the area. After you decide on the least used bands, you can go to the manual technique of placing an access point/points, then moving around the building to see where your coverage wont be sufficient. As already pointed out, with 802.11a for example, you have 12 non-overlapping channels maximum instead of three with 802.11b. Keep in mind that though G and A boast maximum speeds of 54mbps, you will never see it, as for one, 802.11 is half duplex and also because of CSMA/CA. Most vendors or resellers will usually try to push you to 802.11g, but you should always take a serious look at 802.11a as well. If you take a look at most areas with a spectrum analyzer or even something like stumbler, you will notice that the ISM band is kinda crowded with 802.11b and G devices.

certmagnet

What's a good number of users to be on each access point, though, optimally?

keatron

certmagnet wrote:

What's a good number of users to be on each access point, though, optimally?

This will depend in part on what these users will using it for. My general rule of thumb is no more than 25 users per access point, but it can drop below that real fast if they're going to be using bandwith hogging applications or if they're going to be working with large files often. It's important to understand the architecture of 802.11 standard. Only one client can communicate with the AP at a time (although the switching between clients happens at lightning speed). I wont go into the management frames and why there is this limitation right now, but a good place to start understanding it is to read the 802.11 standards and drafts, and amendments.

Also, I'd like to add that if you do choose to go with G, be aware of something known as "protection". G uses ERP-OFDM. This in part is how you get the higher signaling rates. However, if a G access point detects a B access point for example (via beacon frames), it will go into protection mode by setting a frame value know as Nonerp_present to a bit value of 1 which in turn sets the use_protection bit to 1 and that of course means it's now in protection mode. Not only that, every AP within RF hearing distance of that AP will also go into protection mode as well.(regardless of SSID and Security implementations). What does this mean? That 54Mbps signaling rate is out the door. Your AP will be forced to modify it's coding techniques and will be knocked down to signaling rates of 1, 2, 5.5, and 11. It's important to understand that this process has nothing to do with association. Most people understand that using 802.11G allows for backwards compatibility to B, but to what expense is the question. To get all the details of this, read Devin Akin's 802.11 protection ripple white paper.

In the end you have to consider things like is there going to be access granted to the public, or non-company individuals? If so, then G might be your only option. If you have complete control over what wlan client cards will be used, then a might not be a bad choice after all. And also, don't forget you can use both A and G, to service different requirements.