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Two New Developments Emerge Under The “White Spaces” Heading
Microsoft enters the fray; and is a new "post white spaces" wireless company entering the market?
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Two interesting developments have emerged recently under the heading of “white spaces”.

First, if you recall, the FCC authorized the development and eventual marketing of “white space devices” that have now come to be known as TVBDs (TV Band Devices).

However, the technical requirements for these devices are quite stringent; specifically, that they must sense other signals and take a lower priority in any given location than existing TV broadcasts and wireless microphones.

Microsoft, working with researchers at Harvard University, has announced that it has set forth protocols for networks that will use this “unlicensed spectrum”.

Wireless microphones pose a significant challenge to such devices and networks because they’re very low power, and also, are only on when they’re being used.

To deal with this, Microsoft’s approach includes an algorithm that detects available frequencies and switches to a backup channel if interference is detected.

In tests, the device has detected interference from a wireless microphone and moved to another frequency within three seconds.

Three seconds? That can be an eternity if you are experiencing a wireless system dropout, but it depends on the situation as to whether or not it would be a problem.

For instance, what if you turn on all the wireless transmitters for a particular scene in a stage production?

In that scenario, the TVBD or local network would recognize these transmissions and avoid them with plenty of time before the wireless mics would actually be used.

On the other hand, imagine there’s a person in the lobby of a theater, uploading a file to a network from his TVBD. Then, he walks into the theater in the middle of an ongoing performance, where his TVBD starts to interfere with a wireless mic channel being used for the show.

In this case, there might actually be a wireless mic dropout that would last a full three seconds.

Of course, this assumes that the signals did not interfere with each other from the lobby, but would do so the instant they were in the house together.


Comment (1)
Posted by Henry Cohen  on  08/26/09  at  08:44 PM
"Microsoft, working with researchers at Harvard University, has announced that it has set forth protocols for networks that will use this “unlicensed spectrum”."

In the paper "White Space Networking with Wi-Fi like Connectivity" I presume you're referencing (and can be found at http://ccr.sigcomm.org/online/files/p27.pdf), the described "WhiteFi" networking protocol developed by the two is merely an R&D project (see pg. 27 paragraph labeled "Abstract") which is far from being anything concrete, though it stands to reason if it's robust and meets FCC Part 15 Subpart H requirements, something like it may be the architecture for TVBDs.

"In tests, the device has detected interference from a wireless microphone and moved to another frequency within three seconds.

Three seconds? That can be an eternity if you are experiencing a wireless system dropout, but it depends on the situation as to whether or not it would be a problem."

What you're not understanding is that this is the time it took for the TVBD and AP to stop transmitting on the channel suddenly occupied by the wireless mics, re-negotiate, and begin operating on the new channel (pg 35, Sec 5.3). The re-negotiation is the most time consuming portion of the event, meaning the TVBD detected the wireless mic and stopped transmitting in far less time. Besides, who fires up a mic and has talent speaking on it in three seconds? That's not nearly enough time for LO to come up to temperature and stabilize or even to do a "one, two, three, test".

Further to this point, the authors state that "in this paper, we do not address the problem of accurate incumbent detection, which remains an active research area" (pg 30, Sec 3), so any inferred potential interference to wireless mics, and mitigation of, should be taken lightly.

"For instance, what if you turn on all the wireless transmitters for a particular scene in a stage production?

In that scenario, the TVBD or local network would recognize these transmissions and avoid them with plenty of time before the wireless mics would actually be used.

On the other hand, imagine there’s a person in the lobby of a theater, uploading a file to a network from his TVBD. Then, he walks into the theater in the middle of an ongoing performance, where his TVBD starts to interfere with a wireless mic channel being used for the show.

In this case, there might actually be a wireless mic dropout that would last a full three seconds."

Again, three seconds is the full re-negotiation time, not the time it takes for the TVBD to sense and stop transmitting.

"Of course, this assumes that the signals did not interfere with each other from the lobby, but would do so the instant they were in the house together.

It seems that there is still major room for improvement before these devices are ready for prime time."

And it is precisely this scenario that the FCC is requiring the White Spaces Database in which all the TV channels occupied by the event's wireless will be registered that morning, the day before or months before if an ongoing daily performance. In fact, as it stands now, there'll be a 1km protection zone around the coordinates given for the venue, which will surely encompass the lobby.

"Second, a company called RF Venue has emerged, promising to “Refine Wireless Microphone Performance in the White Space Era”.

It’s not clear if this company offers hardware, software, system management or some combination of these elements. What is clear is that this may be the first new company to enter the market, post-white spaces."

This is Robert Crowley, formally of Crowley & Tripp microphones. It's not clear however from which of his current companies (Ambit or Soundwave Research) this technology will be offered.

On an unrelated note, you seem to be the only one of the bloggers and opinion writers on this site who uses an alias, and by my estimation provides the most incorrect or incomplete information. Are the two related?

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