Max # of wifi access spots in one area?

[chorb]

Theoretical question:

How many wifi access points / routers do you think could work without failure (interference from one another) in the same room?


What we know:

802.11 standard has 11 'channels' that can be switched to, so I'm going on the assumption that at least 1 router on each channel, probably more.

Living in densely populated apartment buildings in the past I've seen many wireless routers all on the same channels in close proximity (different rooms obviously) that worked without issue.



Does anyone have any knowledge of what to expect in a real life scenario should lets say 50 routers were all in the same room, spaced evenly across the available channels?

What if the wireless power output was de-rated?

 

[Tarrant64]

How big of a room?

802.11n?

 

[spidey07]

There are 3 non-overlapping channels. That's all you have to work with, not 11. Even in the highest density deployments you're looking at only 5-10,000 sq ft per AP. 3 in one room is the max unless you start using different antenna patterns other than omnis. Co-channel interference (another AP on the same channel near by) is a really bad thing. Anything more than 3, at any power will hurt performance.

5 Ghz is much better with 12 non-overlapping channels so 12 aps. If you want to learn more google "pico cell" which is very high density deployments.

 

[imagoon]

What spidey says. Enterprise level you could pack more in there but that is because there is a back end controller syncing timing / power / making them all play nice with each other.

 

[spidey07]

What spidey says. Enterprise level you could pack more in there but that is because there is a back end controller syncing timing / power / making them all play nice with each other.

True, but you can't overcome the laws of physics. I'm getting big into location/RFID stuff and even at that density there are severe challenges with co-channel interference that can really screw things up. An apartment complex? Forget about it. Use 5 Ghz.

 

[imagoon]

True, but you can't overcome the laws of physics. I'm getting big into location/RFID stuff and even at that density there are severe challenges with co-channel interference that can really screw things up. An apartment complex? Forget about it. Use 5 Ghz.

Well yeah but the systems I am talking about and I am sure you are thinking of for Enterprise can do some neat power control / time sync etc but most home people won't drop 20k on the controller let alone several $500 APs....

 

[RadiclDreamer]

Well yeah but the systems I am talking about and I am sure you are thinking of for Enterprise can do some neat power control / time sync etc but most home people won't drop 20k on the controller let alone several $500 APs....

True, but they will also live with reduced reliability and performance. Businesses wont so they will pay for the controller and access point.

 

[imagoon]

True, but they will also live with reduced reliability and performance. Businesses wont so they will pay for the controller and access point.

Exactly. That is what I really was inferring. When you ask "how many APs" the answer really tends to be "how much do you want to spend." Like above the simple base like is 3 non-overlapping channels gives you a good "3 can be in range and not interfere with each other." Once you add controller backed power, sync, interference management it gets more murky because the AP's are now aware of each other and change power levels / switch channels to not mess with the neighbor APs allowing for a higher density of APs. You see these style of setups in high density people areas like airports and business centers where one ap would be quickly overwhelmed. You group several AP's running reduced power outputs (to reduce their signal throw) together to break up the load. Add in some antenna work and you can have a decent density without massive interference issues.

 

[ScottMac]

Cisco has a white paper on their support website that describes a technique to use a four AP rotation; there's "just a little" interference at the band edges, but the signal is down so far at that level you "probably" won't see a performance difference.

 

[chorb]

thanks for the replies

what kind of degradation are we talking about?
total failure (unusable) of 2 APs on the same channel?
Or reduced transmissions speeds?
Or is it unknown and is a case by case basis?

b, g and n are all allowable, would one of them work better than the others?

 

[spidey07]

Co-channel interference straight noise and severely hampers performance. It can cause you to drop down to less than 11 Mbs data rates on 802.11g even if you're very close to the AP. It can get so bad that everything drops to 1 Mbit.

Think about it - you have two people yelling at you at the top of their lungs so you can't understand anything they're saying.

As far as best, that would be 802.11n in the 5 Ghz range.

 

[RadiclDreamer]

This is pretty much an academic question because the number of AP is purely down to what you consider to be an acceptable level of service. At some point its going to get so noisy you wont be able to use it all, but it comes down to what you are willing to deal with, is 1mbps acceptable? 11? etc

 

[imagoon]

Co-channel interference straight noise and severely hampers performance. It can cause you to drop down to less than 11 Mbs data rates on 802.11g even if you're very close to the AP. It can get so bad that everything drops to 1 Mbit.

Think about it - you have two people yelling at you at the top of their lungs so you can't understand anything they're saying.

As far as best, that would be 802.11n in the 5 Ghz range.

Not sure who you are replying to but that is why the controllered AP's start talking in softer voices.

 

[chorb]

This is pretty much an academic question because the number of AP is purely down to what you consider to be an acceptable level of service. At some point its going to get so noisy you wont be able to use it all, but it comes down to what you are willing to deal with, is 1mbps acceptable? 11? etc

I'm researching this topic for a possible product development. Just spoke with our lead engineer and he's estimating a VERY low data rate for the application we need, 10Kbit/s.

Just purchased 15 wireless routers to try out a few experiments... If anyone is still interested I'll let you know how it turns out.

 

[seepy83]

I'm researching this topic for a possible product development. Just spoke with our lead engineer and he's estimating a VERY low data rate for the application we need, 10Kbit/s.

Just purchased 15 wireless routers to try out a few experiments... If anyone is still interested I'll let you know how it turns out.

Honestly, putting 15 SOHO wireless routers in 1 room sounds like it has fail written all over it. I hope you save your receipt and can return them when it doesn't work, because I'm guessing you're out at least $1000 right now...

 

[chorb]

Honestly, putting 15 SOHO wireless routers in 1 room sounds like it has fail written all over it. I hope you save your receipt and can return them when it doesn't work, because I'm guessing you're out at least $1000 right now...

$254 with shipping :thumbsup:
Link

 

[ScottMac]

$254 with shipping :thumbsup:
Link

Well, I'm sure you're in for an interesting effort. The less expensive APs tend to have lower (poorer) sensitivity and selectivity, as well as a tendency for higher spurious radiation that adds that much more interference to the local RF environment.

I think I'm glad I don't have to live or work on the other side of that wall ... on the positive side, your hot food and beverage will stay hotter longer (maybe even self-heat!) on your desk.