Yep, we all must live in a yellow submarine … or a white space wifi submarine. It’ll be quite the shootout between the hype and those trying to give some reality checks to the situation. If the only tool you have is a hammer, everything starts looking like a nail. Here goes current opinion:
First of all if White Space Wireless (who the hell even said you could call something WiFi already before it exists? WiFi Devices must be certified by the WiFi Alliance! Everyone knows that!) – If it has such a long range – It is not going to be a consumer end-user device or service. It’s going to be a commercial or public system offered (free or pay?) to end users. Can you imagine everyone having a 1 or 2 mile access point in their house? That’s just crazy. Well with small antennas they’d not get near that – but they might get 4 or 6 city blocks though.
Second of all Crowded 2.4 Ghz band – If everyone goes to a new band then it gets crowded too. Now if *everyone* gets on a new UHF band but one with a much more range … then everyone sees everyone else’s signal and everyone interferes with everyone else for an easy mile or two circle. If you want to hear and interfere even further then just get yourself a nice UHF Yagi Antenna. That shouldn’t be hard to build especially with Surplus TV UHF Yagi antennas available. There might even be one in the local trash dump. Or one someones roof that they’d give you. There will also no doubt be UHF omni-directional “all around” gain antennas similar to how such antennas are now available for the 2.4Ghz and other bands. Put one of those up in the air and you get some more miles per gallon, right?
* So here’s another blogs take on this thing: http://wifinetnews.com/archives/2010/09/dubious_about_white-space_overhyped_potential.html
I don’t see how what’s postulated is possible. The TV channels in question are 6 MHz wide. Shannon’s Theorem always wins. Channel capacity is a function of bandwidth mitigated by the level and ratio of signal to noise.
Wi-Fi can use 20 to 40 MHz channels in 2.4 and 5 GHz, and likely 80 MHz or more in future 5 GHz iterations. Without multiple radio receivers, encoding improvements in 802.11n over 802.11g bumped the raw rate from 54 Mbps to about 65 Mbps. Take two radios and 40 MHz, and your raw rate approaches 300 Mbps. Three and four radios and 450 Mbps to 600 Mbps.
White-space spectrum can only be used in 6 MHz blocks. Even with an extremely efficient encoding, I don’t see how one can get more than 15 to 20 Mbps out of a channel. I’ve seen several statements that white-space networks will hit 400 to 800 Mbps.
The high power that’s allowed–4 watts EIRP, the effective power after antennas–is pretty remarkable. Wi-Fi is limited to 1w EIRP, and in the nature of radio waves a 4fold increase in EIRP means more than 4fold improvement in distant reception. Correction: Wi-Fi is limited to 1W of transmitter power, but 4W of EIRP. The greater range of white-space devices will come from much, much lower frequencies, which carry further and penetrate better.
However, my understanding is that by the same token, MIMO is ineffective because MIMO doesn’t work over long distances. It requires reflection over short spaces to provide the multiple spatial paths that boost speed. So by going long, you lose MIMO, and encode with a single radio.
Also by going high power, you lose the advantage of cellular infrastructure, whether for Wi-Fi or 2G/3G/4G mobile networking. The greater area you cover, the more your shared medium is split among users, even in a contention-free scheduled environment, which will likely not be what happens. As an unlicensed band technology, you could be contending with interferers of all kinds the higher power you use and greater area you cover.
(More at the link above.)
* Anyway with all of that having been said … History and People have a way of repeating themselves. But sometimes on a good note. Back in the Telephone Modem days there were “theoretical” limitiations on how fast you could go on a pair of copper phone wires. Both modem technologies with compression and such feats and DSL playing nice tricks with the “above voice audio frequencies” – seemed to somehow prove the (even technical) naysayers wrong by pulling it off. So maybe some companies will pull off the supposedly impossible once again. I’d like to see this all under the “Umbrella Corporation” (ha! ha! ha! Like in the movie Resident Evil?) – well I mean under the auspices of a nice standards body like the IEEE, which does the Eight Oh Two Dot … stuff. It would be nice if whatever comes out was freely available to both the Close Source and Open Source communities. A lot of amazing things do come out of open source … including operating systems and parts thereof that create jobs and small business opportunities for the likes of ME and many many others.
* See: Modem: http://en.wikipedia.org/wiki/Modem
* See: DSL: http://en.wikipedia.org/wiki/DSL
* There’s a boat in Fort Lauderdale called Never-Say-Never. So Alan Spicer, although I may nit pick at White Spaces, is never going to say NEVER about it.
* There’s an interesting blog post on this White Space stuff here: http://blogs.broughturner.com/2010/01/wi-fi-in-the-tv-white-spaces—80211af-task-group-underway.html
Alan Spicer Marine Telecom
communications @ marinetelecom.net