Define specific radio channel for APs through multiple floors

[david.wzj]

Hello

We deployed a wireless lan for customer. There are 3 floors with 4 APs per floor and connections drops happen. Users complain that, when they work in a fixed place sometimes they lose connection and when they change place, there is more chance to lose connection and they are too close to Ap. Is it maybe an issue caused by co-channel interfere?

Radio: 802.11 B/G AP: 1232

I know channel 1,6,11 donot overlap each other, but in this case how to define each AP channel to gain best performance?

I plan to change current setting, Use channel 1 for the first floor, channel 6 for the second, channel 11 for the third, but I am afraid interfere also happen on same channel of same floor. Anyone can help to give some experiences or advise for me? Does interfere happen in same channel, even if Channel 1,6,11?

Another channel model is considered as below:

Floor 1

6 ----- 1

1 ----- 6

--------------------

Floor 2

11 ----- 6

6 ----- 11

--------------------

Floor 3

1 ----- 11

11 ----- 1

--------------------

AP relative location map:

④ <-------> ①

③ <-------> ②

AP1 is located closer to 2 but far from 3 and 4. it is a similar condition with 3 and 4. Is it feasible at your standpoint?

I'd appreciate for any help from you. Merry xmas!

Regards

David

[scottmac]

David:

I believe you have it nailed as well as possible, with the exception that I'd vertically reverse the order shown for floor 3 (11 ---1, then 1 -- 11).

Depending on the construction of the building, you might get a little "leaking" of the channel 11 signal between floor 2 & 3 ... or if they are near windows and there are nearby buildings / structures, some bounce from the external building / structure.

You might also look at a three freq mix per floor, like

1, 6, 11, 1

6, 11, 1, 6,

11, 1, 6, 11

(the duplicates being diagonal / most obscured from each other)

... something like that.

That would reduce the overlap possibility a little more.

As always, your best friend for this would be a good, comprehensive site survey to verify your design.

Merry Christmas to you as well, take care.

Scott

[david.wzj]

Hi Scott,

So thankful for your kindly guidance and advice.

I would accept your idea to make three freq coexist per floor, it looks reasonable and maybe better. Hope it can help to solve current issue soon.

Also one question I have, in my first design you would like to vertically reverse the order for floor 3 (11 ---1, then 1 -- 11), and you mention that a little "leaking" of the channel 11 signal might occur between floor 2 & 3. Could you help to give any explication about this? If the order for floor 3 is planed like that , then channel 11 in Floor 2 & 3 will be on same side of buliding. Does probability increase for interfere in such condition?

Regards

David

[scottmac]

The goal would be to keep APs using the same channels as far apart or isolated from each other as much as possible.

In the event that they can still "see" each other, then you'd need to reduce the power outputof either or both until there is no overlap.

Depending on the construction materials used between floors, and the radiation pattern of the antennas, it's possible that some signal my penetrate to adjacent floors.

That is one of the reasons for doing a very thorough site survey; to determine how much signal can penetrate and adjust the antennas and/or power to accommodate.

When selecting your antennas, and where they are placed within the area, compare the radiation pattern against the area that it must cover: Omni-directional antennas are for central placement ... putting one in a corner wastes pattern (3/4 of the signal is external to the building) ... for corner placement, look for sector-style antennas with a 90 degree coverage .... against a wall or for a hall, use a "patch" antenna that only radiates 180 degrees.

Sector and patch antennas tend to have a flatter pattern (vertically) so they are also less likely to penetrate into the space above and below.

Again, they best way to plan is to have a solid site survey in-hand. It's truely the only way to know for sure.

Good Luck

Scott

[johnruffing]

A couple of additional thoughts:

If your budget allows for it) you might consider a higher number of access points on each floor. This can result in an overall lowering of transmit power of each access point and may result in less floor-to-floor leakage.

Also (if your application allows for it) by disabling the lower data rates (i.e.: 1Mbps and/or 2Mbps), you are effectively lowering the receive sensitivity of the AP radios - which will help "shrink" your coverage zones (assuming that your RF design will tolerate this) and help prevent APs on the same channel from hearing each other.

John