TV white spaces are the unused TV channels in any given market that could be used to deliver broadband access, services, and applications. TV white spaces devices and networks will work in much the same way as conventional Wi-Fi, but because the TV signals travel over longer distances and better penetrate walls and other obstacles, they require fewer access points to cover the same area. These excellent range and obstacle penetration characteristics explain why people increasingly refer to TV white spaces as "Super Wi-Fi."
Regulations in the United States provide for two classes of white space devices:
- Fixed devices are permitted to operate at up to 4 Watts EIRP on second or more adjacent TV channels. They may operate on unused TV channels 2-51, except 3, 4, and 37.
- Personal/portable devices are permitted to operate at up to 40 milliwatts EIRP on adjacent channels and 100 milliwatts EIRP on second or more adjacent TV channels. They may operate on unused TV channels 21-51, except channel 37.
Other governments’ regulators are considering similar power limits.
Distance and Throughput
Operating at the same power levels afforded to current Wi-Fi devices (40 or 100 milliwats), a simple calculation shows about 16X fewer access points are needed in the UHF part of TV white space (600 MHz) to deliver the same coverage as Wi-Fi in 2.4 GHz. With the same number of access points offering four times the range, one can achieve sixteen times the coverage.
Fixed TV white space devices operating at higher power can provide multi-kilometer wide area connectivity akin to current 3G/4G wireless networks. Based on performance testing on current generation devices, TV band white space devices are expected to operate at efficiency levels (as measured by bits per hertz) comparable to other competing wireless technologies, but with the benefit of additional range derived from using available TV band spectrum.
Better throughput was achieved closer to the base station. With non-contiguous and contiguous channel bonding an expected feature of second generation TV white space devices – for example, taking advantage of the emerging 802.11af/ac Wi-Fi standard – even better throughput can be expected.
Another key difference from traditional Wi-Fi is that white spaces devices will gain managed access to unused TV channels by providing their precise locations to a database which in turn provides channel lists along with other operating parameters, such as power, duration, and geographic boundaries. White space devices will only use those channels provided by an authorized white space database.
If no channels are returned, a white spaces device will not transmit on TV band spectrum. With the ability to exchange information on channel utilization, throughput, packet loss, and other measures of quality, white space devices and databases will use this spectrum more intelligently over time.
Microsoft Spectrum Observatory
The Microsoft Spectrum Observatory was created with the purpose of providing an intuitive presentation of the usage of the wireless spectrum. The project is sponsored by Microsoft's Technical Policy Group and the data is made freely available to the public. Data is recorded through monitoring stations and is stored and processed for visualization through the Windows Azure cloud.
Microsoft Research White Space Database
The Microsoft Research White Space database enables users to learn about the available TV white spaces spectrum, i.e., unoccupied TV channels, at a given location. A user can specify a location, and our service returns a list of TV channels that can be used for voice, video, and data communication along with the allowed power levels on each channel.
Networking Over White Spaces (KNOWS) - Through this research, that started in 2005, we invented several protocols, including WhiteFi, which formed the basis of IEEE 802.11af. We designed, prototyped, and demonstrated amongst the world's first radios, databases, and an operational network in October 2009.
Cognac: Cognitive Network Access - The Cognac project tries to re-imagine WiFi in a world where spectrum may be fragmented (e.g., white spaces) and radios are feature-rich (e.g., software-defined).
Decentralized Networking in White Space - There are several design challenges to make a decentralized white space wireless network work, such as signal interference and spectrum fragmentation. The goal of this project is to come up with technological solutions that would overcome the challenges.