Overlapping Wireless access Points

Posted on 2012-08-16
Medium Priority
Last Modified: 2015-03-21
I am working on creating a collection of overlapping wireless access points in my office to allow better coverage for our users.

I have found several well written instructions on how to do so, but they all provide one step that I admidt leaves me confused:

"configure all Access Points to different hopping sequences of the same hopping set"

...I have no Idea what this means!

Is this a setting in a wireless access point?

When they say "Use the same SSID on each" for example, I have done this and know what an SSID is...

Here, I am lost!

Question by:RKoons
LVL 44

Accepted Solution

Darr247 earned 1000 total points
ID: 38302977
Bluetooth and cordless phone handset/base use channel hopping, but WiFi doesn't
(DFS is not channel hopping).

Here's an overlap pattern to use for 2.4GHz that avoids channel-overlap interference, and can be expanded indefinitely, though you would need to set a switch every 90m to keep the ethernet cable doing backhaul within spec.
2.4GHz overlap pattern
LVL 12

Expert Comment

ID: 38304458
Darr247's diagram is excellent.  If you have multiple levels, as in a 2 or 3 story building, remember that the diagram must be imagined as a three-dimensional diagram as well, with overlapping channels vertically, as well as horizontally.  Also keep in mind that you may already have non-wifi devices operating within some of these channels.  For example, I recently did a job where the owner already had both a wireless audio system running, that was already using one of the channels, and an alarm system using a different channel.

In addition, this diagram is the 2.4GHz channels.  If you are running 802.11n in the 5GHz range, the pattern is different, but would also require the same type of planning.
LVL 47

Expert Comment

by:Craig Beck
ID: 38306650
Are your instructions based on FHSS instead of DSSS technology?  Older WiFi kit did use FHSS but that's very uncommon now.

FHSS uses the whole band, one channel at a time (hence the term Frequency Hopping).  If you had multiple APs using FHSS and they all hopped in the same channel-order, on the same channel, at the same time, you would cause massive interference.  The instructions would appear to be telling you to set the APs to use different hopping sequences to avoid this.

Nearly all APs you'll use nowadays will employ DSSS and is set to use one specific channel at any given time, so hopping sequences are not relevant.
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Author Comment

ID: 38332763
Sorry for the delay

We only have one floor, so three dimantional overlapping will not be an issue.

...though you would need to set a switch every 90m to keep the ethernet cable doing backhaul within spec.

Not sure what is ment by this...

As for DSSS and FHSS, I can see that I have alot of reading to do. Granted, I don't do alot of wireless setup with the kind of business we have, so in my mind, I was just going to go to my reseller and purchase a bunch of AP's figure out how far their antennas reach, and hook them up using the same SSID passcode and channel for each.

I will do more research, but so far, it sounds like I would want DSSS. Granted, I don't think I am talking about High end units for AP's -if this makes a difference.

It will probably be another week before I can jump on this again, but I will do more research and look forward to your additional input.
LVL 44

Expert Comment

ID: 38332830
> Not sure what is ment by this...

What I said immediately before that was the pattern shown could be expanded indefinitely... i.e. to provide practically unlimited coverage. The main limit being 100m for cat5e/cat6, and the typical spec is running it only 90m to leave room for up to 10m of patch cables... after that you need to set a switch to extend it another 90/100m (you didn't specify how large the office is).
LVL 47

Assisted Solution

by:Craig Beck
Craig Beck earned 1000 total points
ID: 38333333
99% of WiFi kit is DSSS nowadays.  It just sounded like your instructions are talking about FSSS, so you need to just read about DSSS wireless.

As Darr said, his cell deployment diagram displays how you should configure your channel allocation per AP.  Forget the "configure all Access Points to different hopping sequences of the same hopping set" instructions as this doesn't apply to modern WiFi kit.  Just configure the channels as per Darr's diagram and you will be ok.

Expert Comment

ID: 40680617
Hello craigbeck,

This post is really helping me understand.

I have a questions regarding "If you are running 802.11n in the 5GHz range, the pattern is different, but would also require the same type of planning.".

What would be different with the pattern? Would I still alternate channels (eg. 157 and 161).

Thank you!


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