Pro-active channel selection during normal operation

Hi Infinet,

How difficult would it be to add another radio channel which can continously scan all available channels whilst the radio is in operation (does not cause link outage) so the radio can immediately jump to a quieter channel without loss of communication (COT and DFS all cause link outage)?

I'm guessing very difficult but it would be a nice feature in a country where the 5GHz spectrum is not licensed and wireless equipment hops all over the place at RADAR events

Thanks

Nick Metcalfe

If I don't get wrong, on non MIMO gears Alvarion, Lancom and others (not sure if Motorola too) does a background scan during their normal operation. This background scan continuously updates the "Available Channel List", which is quickly accessed whenever a Radar is found. This would take link realign to be faster  (even if it'll drop anyway I suppose).  In no case (to answer Nicholas) DFS and COT can be disabled, otherwise you won't comply EN 301 893. What it should be implemented I think, is the "Off-Channel CAC" (Check Availability Channel). see par. 4.7.2.2 of EN 801 893 v 1.5.1
Pls. note that v 1.6.1 is in the early draft stage and should be final draft within may 2011 (http://webapp.etsi.org/workProgram/Report_WorkItem.asp?wki_id=34603)

Now what there's new models with POE on second ethernet port, wouldn't it be viable to have a special piece of equipment just for this purpose ?

Let's say, a tiny appliance with cheap antenna, what could be mounted on a pole along with the main device, powered from the second ethernet port, and can scan available channels independently. It may catch radar events and change settings on the main unit via snmp, for example.

For this setup to be viable, how much this device should cost ?

Nah... Using separate antenna for radar detection is probably against regulations...

Such appliance will be useless for fighting DFS-caused downtime.

EN 301 893

4.7.1.3

NOTE 1: The master device may rely on another device, associated with the master, to implement the Radar
Interference Detection function. In such a case, the combination has to be tested against the requirements
applicable to the master.

Looks like there'a a possibility.

 Infinet equipment does have such feature also.

Please refer to "Dynamic frequency selection" in technichal user manual.

Regards, Vladimir

Yes IW equipment comply with DFS requirements.
A second equipment which just "listen" to the air would be fine, but will raise the total price (equipment + installation). I think it's better to have this feature integrated in the radio itself.
What I think is missing would be Off-Channel CAC.

4.7.2.2.1 Definition (excerpt from EN 301 893 v 1.5.1)
Off-Channel CAC is defined as a mechanism by which a RLAN monitors channel(s), different from the Operating Channel, for the presence of radar signals. The Off-Channel CAC <u>may be used in addition to the Channel Availability Check</u> defined in clause 4.7.2.1, for identifying Available Channels. Off-Channel CAC is performed by a number of non-continuous checks spread over a period in time. This time, which is required to determine the presence of radar signals, is defined as the Off-Channel CAC Time. If no radars have been detected, the channel becomes an Available Channel.

This would "assist" the main CAC algorithm in creating the "available channels list". Whenever a Radar is found, the radio may choose the best channel in the list, avoiding the scan. But I suppose that the it is mandatory to listen for radar for 60secs even in this case. Off-Channel CAC would allow in spare 6sec (default) for each scanned channel, which can be a long time if radio is using small channels (20, 10, 5MHz).