cancel
Showing results for 
Search instead for 
Did you mean: 
cancel
1421
Views
5
Helpful
6
Replies

AP proximity? (How close can your AP be to someone else's AP).

dhurshowy
Level 1
Level 1

Tried doing some searches but cannot find anything...

If you are designing a WiFi system in a building that already has a system (independent to your new system), how much separation between APs should you have? ie. How close can/should you put your AP to an existing AP?

Sometimes because of the building layout you want to go at the same spot, but I know you need some separation. Assume omni, 100mW APs.

Thanks.

6 Replies 6

Nicolas Darchis
Cisco Employee
Cisco Employee

Well, if you are adding a 2.4Ghz wifi to a building already having a 2.4Ghz wifi, my thought is "forget about it", there's just not enough channels for everyone.

If this is your case, anyway your APs will sit on the same channel as the other APs and will need to share their bandwidth.

But as a general guideline for such a situation, 4 meters is a good distance to avoid "burning" each other receivers.

AP's wil be dual band.

Some buildings only have a handful of exisitng APs.

We have beeing looking at using 2m. Even at full power of 100mW and 4dBi antenans, at 2m you only

receive 0.016mW (-18dBm). Again this would only be in the odd case that >2m is not viable.

I can't find numbers back but -18dbm is considered VERY loud and usually is outside of the acceptable range of receiver sensitivity.

I.e. would damage the AP receiver in the long run.

Leo Laohoo
Hall of Fame
Hall of Fame

I agree with Nico's post (+5).  There are many things I'd consider before writting up a shopping list.  Among them are:

1.  As what Nico's pointed out, every-man-and-his-dog has 2.4Ghz wireless AP enabled.  If you are surrounded in a high-density building then 2.4Ghz 802.11b radio is a fool-and-his-money-is-soon-party.

2.  Are you using RFID tracking or not?  (Before you say "no", look to the future and have a hard think about it.)

3.  What will the wireless be used for?  Roaming?  Conference room only?  Here-and-there?

4.  What's your budget?

5.  Describe the physical environment you're going to install the APs in?  Wide open space (like theatres or warehouse or convention rooms) or office space (with cubicles, file compactors, etc).  If you have office spaces then what are the walls made out of?  Bricks (how thick are these walls), concrete, hallow blocks, pre-fabricated, wooden, gypsum, etc.

6.  What is your wired network like?  Ethernet?  FastEthernet?  Gigabit? 

You have some valid points. But every-man-and-his-dog has a 2.4 AP and it still works then it will most likely still work even if it's "every-man-and-his-dog +1".

Most importantly the system has to be designed correctly regardless of the existing networks. The better your system is designed to work solo, the better it will perform in an environment with other APs. Yes existing networks will obviously degrade your performance, but you can't really find anywhere in an modern urban environment without seeing a dozen APs from either inside and/or outside your building. The existing network could be dense but if it is not used all that much, the degradation should not be extreme.

Besides, you have say 100 users in the building, they can use system A (existing) or B (my new one). If they have the option of using both/either, then you have 50 on A and 50 on B. Is that much/any worse than having 100 on A? Contention is contention though the extra beacons will add to it. For the users that can only use "B", then they will at least have an option, even though it will be at a slower performance than if A did not exist, at least they have an wireless option now. If "A" did not exist, you could build your "B" network, and 1 week later, someone could build "A" anyway.

1) Don't worry, it's not my money. Most of the existing "high density" areas are low usage private wlans. (P.S. What's the definition of "high density"?).

2) RFID is not part of our application.

3) & 5) This is being accounted for in our designs.

4) If we use Cisco, then I hope it's significant. ;-)

6) Gigabit.

Good discussions.

But every-man-and-his-dog has a 2.4 AP and it still works then it will most likely still work even if it's "every-man-and-his-dog +1".

Because of the design of the 2.4Ghz radio spectrum you can operate your wireless effectively if you use three non-overlapping channels.  By default they are channels 1, 6 and 11.  If every-man-and-his-dog is using 2.4Ghz around you then there's a safe bet they are using these channels (if not all).  So why bother with 2.4Ghz then.  Thus the reason why Nico and I recommended your design should NOT include 2.4Ghz because it's just a waste of money.  Go to 5.0Ghz because you can use the spectrum better.

Is that much/any worse than having 100 on A?

You have more channels on 5.0 Ghz to use as compared to 2.4 Ghz.  So in a dense environment 5.0 Ghz is a good choice.

1) Don't worry, it's not my money. Most of the existing "high density" areas are low usage private wlans. (P.S. What's the definition of "high density"?).

When I mean "high density" I mean a significant amount of wireless AP that ain't yours.  Best method of detecting this is to use a client or smartphone with a/b/g wireless card and find out how many SSIDs you can pick up.  Anything more than 6 on 2.4Ghz is not good.

4) If we use Cisco, then I hope it's significant. ;-)

Is this in an office space?  IF office space what are the walls made out of?

Review Cisco Networking for a $25 gift card