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September 30, 2010

White-Fi for All?

White-fi The Internet has been lit up with discussions regarding the future fate of the left over radio frequency (known as white space) from the digital television transition.

The leading contender is a new unlicensed frequency to be used primarily by Wi-Fi to deliver Internet access. An interesting concept, the use of “White-Fi” radio spectrum brings with it both good news and bad. At this point, this is a U.S. only thing and here's the spectrum we're talking about.

The main advantage to using white space is the low frequency in which it operates and the low power radios need to access it. Depending on the location, white space is available between 50 and 800 MHz (though not within a contiguous frequency band everywhere) which is far lower and provides much greater range than the standard Wi-Fi frequencies of 2.4 and 5 GHz. Low frequency signals also propagate well and should provide better penetration within buildings, a frequent gripe with Wi-Fi.  Here's an excellent overview.

This makes White-Fi ideal for rural environments where distance and coverage is everything and deploying a macrocell 3G network in these areas is cost prohibitive. Rural customers are the hardest to reach with conventional Wi-Fi due to terrain and distance. If the DTV Wi-Fi equipment can be produced at a reasonable cost it could hold the key to providing broadband Internet to those who will otherwise go without.  That’s a good thing.  But ironically, the biggest use of wireless connectivity is in urban areas where 3G networks are being crushed under a flood of data traffic from new smart phones.

But White-Fi’s biggest problem is capacity. White space is severely limited by its channel width.  Each white space channel is only 6 MHz wide with a maximum theoretical data rate (read theory) of around 40 Mbps (on a good day).  Upstream traffic contention, RF travel time and interference are just a few problems contributing to performance delays with Wi-Fi covering such large areas. Your speeds and mileage will definitely vary, depending on how the protocol, now in the hands of the 802.11af task group, is implemented. 

And each of these White-Fi channels is shared among potentially thousands of users within a large range, given the distance that low frequency signals travel. Compare this to 802.11a/g Wi-Fi that uses 20 MHz channels and new 802.11n Wi-Fi that supports 40 MHz wide channels and multiple spatial streams capable of delivering 450 Mbps or more. The emerging 802.11ac standard is looking to extend this even further to 160 MHz wide channels and gigabit speeds.

Another big concern is the number of white space channels that are actually available.  In rural areas this shouldn’t be problem but in urban areas, where the majority of wireless handsets live, they are extremely limited, often occupied by other things.

So what role will white space play?  Given its reach, white space will be ideal for creating “urban overlays” to higher-speed microcell Wi-Fi and macrocell LTE networks. 

In such a model, the white space spectrum would be perfect for offloading low bit rate “chatter” traffic, such as application notifications (email, presence lists, etc. generated by handheld wireless devices) from high speed cellular or Wi-Fi networks.

Even when not in use, handheld devices are constantly communicating with the network for updates and notifications using precious battery life from the phone and capacity from the network. By automatically directing this traffic to white space, the high-capacity wireless networks, such as Wi-Fi and LTE, could be used for applications more suited for it such as streaming video.  It’s analogous to have having multiple gears in a car, each of which is used at different times for different purposes.

Finally remember that unlicensed spectrum is just that, unlicensed.  This means that anyone can use it anytime for anything.  As a result, interference will remain an issue, especially for white space given that it can cover much greater areas.

New smart antenna arrays with the ability to constantly survey the radio environment to select the best signal path for traffic at any given time, will add significant value to making these wireless networks much more stable and reliable.

Like anything, white space isn’t perfect and won’t change the world anytime soon, but it definitely has the potential to fill in a lot of the missing pieces in today’s wireless puzzle.

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