Wireless visualisers and wireless network

[CyberNerd]

School want to get wireless tablet visualisers with bundled "slate tablet" things

"Bundle Elmo L-12 Visualiser & CRA-1 Slate Bundle"

According to the spec sheet they need to run over a 2.4GHz network

http://www.chooseav.co.uk/prod_media/319711_1.pdf

 

What are your thoughts about this if we have a central wifi network?

[plexer]

Shouldn't be a problem to be honest.

 

It doesn't say how it connects to the host laptop though does it use an ad-hoc wireless connection or it's own dongle?

 

Ben

[CyberNerd]

Instinct says it uses an ad-hoc wireless.

[plexer]

Nope has a dongle:

 

http://www.elmousa.com/sites/default/files/Manual_CRA-1_Eng.pdf

 

Ben

[CyberNerd]

Thanks.

 

The link says

Do not use near the following:

■ Microwave ovens, industrial, scientific or medical equipment, such as pacemakers

■ In-factory radio stations for mobile unit identification systems (radio stations that require a license) used in production lines of factories.

■ Specified low power radio stations (radio stations that do not require a license)

■ IEEE802.11g/b wireless LAN units

When this unit is used near any of the equipment mentioned above, it is possible that electric wave interference could occur.

 

so presumably, dongle or no it is going to interfere with the school wireless.

[dhicks]

What are your thoughts about this if we have a central wifi network?

 

I'd go for an iPod touch or iPad Mini instead and mirror the output to the classroom PC. Use a retort stand if they need something to mount it on.

[plexer]

Interference is going to occur a lot in your environment anyway and equipment is designed to deal with interference to a certain degree I guess they are just covering their own backs.

 

Ben

[SYNACK]

2.4 does not mean wireless, it is probably some cheap implementation that does not require patents or standards. Should be fine if you have decent gear with 5Ghz radio to work around the pollution. I do agree with the others that maybe something a little less 'educationally focused' like a gopro with wireless which will give you way more possibilities and probably way better quality for less than the visualizer or selling your soul to apple. Edited October 1, 2013 by SYNACK

[CyberNerd]

Could someone explain this to me in a bit more detail please.

My wifi works on 2.4GHz 802.11g (and on 5Ghz at 802.11a)

If these devices are running on the same frequency, how are they not going to interfere with the operation of the wireless network? and how is the wireless network not going to overpower the devices>?

[SYNACK]

Could someone explain this to me in a bit more detail please.

My wifi works on 2.4GHz 802.11g (and on 5Ghz at 802.11a)

If these devices are running on the same frequency, how are they not going to interfere with the operation of the wireless network? and how is the wireless network not going to overpower the devices>?

2.4 is not going to interfere with 5 unless the hardware is illegally bad. Given the device is probably not WiFi but just a digital radio that uses 2.4 it will scream out at whatever power level it sees fit that is still legal and will probably not be adaptive at all, this could easily scream over the top of what the WiFi is putting out. Stuff like Bluetooth and WiFi also have methods to cohabitate with each other, steering away from each other. Some random 2.4GHz device may just chuck out a continuous stream on whatever channel(s) it sees fit. If you force stuff around it to only use 5Ghz and no Bluetooth it should not cause issues, if not it will depend on how smart and how loud it is.

[neilmac]

From a purely technical perspective, when a device is preparing to transmit a frame, it first checks to see if there is any energy in the air. This is known as the Clear Channel Assessment.

 

If it detects energy, here is how it is handled:

 

Signal below -82 dbm, ignore and proceed. (Too Cold)

Signal above -62 dvm, STOP

Signal between -62 dbm and -82 dbm, attempt to read PHY header, look for FRAME_LENGTH and DURATION_VALUE fields to work out how long to wait before possibility to transmit.

 

Predictably, I like to call this the "Goldilocks Zone", not to hot and not too cold.

 

The main point here is that any wifi device that detects the signal from this Elmo device can be affected. The Elmo will probably have an FCC or ETSI power rating, probably similar to WiFi so will transmit from 14dbm to 20dbm.

 

If a nearby station detects the Elmo transmission stronger than -62dbm, will effectively stop working until the signal drops. If it doesn't drop, the device is jammed. Here is where it MAY be OK -

 

1) Elmo doesn't continuously transmit - when it does, it's above -62dbm, so any in air frame is corrupted, all other devices stop until Elmo is silent.

 

2) Elmo transmits in the Goldilocks zone or below, WiFi devices continue to function, however may be interfered with by Elmo transmissions, causing retries, lower data rates and roaming attempts.

 

By the way, -62dbm = 6.31×10-7 mw, or 0.000000631 milliwatts, it's not a lot of power.

 

NM

Edited October 1, 2013 by neilmac

[CyberNerd]

That is a pretty awesome explanation.

So I'm guessing the real answer if I was being hardline about it is to steer clear and go for something like @dhicks suggests.

The slacker answer being that they will probably 'work' but could cause longer term issues.

[neilmac]

Well, it depends on what type of access points and clients you have now. As has been suggested, if you are using 5GHz it won't be a problem, but if you have a lot of stuff in 2.4 Ghz I would really look for a WiFi based solution - a lot of commenters seem to know products that would fit that category.

 

WiFi devices all speak the same language and co-exist very well, and you can take positive tuning steps to increase performance. Non WiFi is like a road drill outside the classroom, just does its thing, squashed everyone when it's active and leaves you to do what you need to do between the gaps. I would say avoid, as I speak from a purely technical perspective, but there are a lot of switched on people here who may have experiences that can guide you to a proper solution.

 

NM