Wednesday, May 23, 2012

Cambridge white space technology trial conclusions


Some interesting findings from the recent trial of white space technologies in Cambridge. From the backgrounder to the trial:
"Governments create rules designating how radio frequencies can be used and, over the years, have assigned radio and television stations to certain blocks or “channels” of frequency in the spectrum. Limitations in transmission technology and the high costs to cover rural populations have led to gaps in the TV broadcasting bands. For decades, the hiss of “white noise” was familiar to anyone tuning a television from one channel to another — traversing the empty “white spaces” between TV broadcast frequencies. This situation remains today. While some white spaces in the TV band are dedicated for uses such as radio-frequency telescopes, other spaces lie vacant. On the other hand, the radio spectrum used by mobile phones and other wireless communications devices is becoming overpopulated. Growth in demand for applications, such as TV streaming, internet access, voice calling, music services and video downloads, are overloading the spectrum used by wireless communications devices."
Which is where the opportunity resides - making use of the spectrum between broadcast frequencies for a range of applications in a managed way so as not to interfere with TV reception. From the same background document:
"TV white spaces networks — wireless networks built to use TV frequencies — work in much the same way as conventional Wi-Fi, but because the signals travel over longer distances and better penetrate walls and other obstacles than those in the current Wi-Fi frequencies, they require fewer access points to serve multiple square kilometres with a strong, reliable signal. The use of TV white spaces has the potential to help close the broadband performance gap between cities and the countryside...It helps in more densely populated areas too. TV white spaces spectrum is less impacted by obstructions such as masonry and concrete walls. This greatly improves the flexibility, range and effectiveness of wireless networks, allowing TV white spaces networks to serve users across a wider area."
The report of the trial includes the following key findings:
  • TV white spaces spectrum can be used for a range of applications, from improving rural broadband connections to machine-to-machine applications.
  • There is significant TV white space capacity, depending on the power requirements and regional variations, which could be shared with new broadband devices.
  • Geolocation databases potentially provide a reliable and responsive way to control frequency use by the TV white spaces radio devices.
  • The basestations were carefully commissioned by Arqiva to prevent interference and no complaints arose from activities in the Trial. Houses in the areas around the basestations were provided with contact details in case they encountered any reception problems and none were reported.
The report makes a number of recommendations, including that administrations should:
  • Recognise the potential contribution which TV white spaces and database enabled spectrum access can make to improving spectrum efficiency and to mitigating the spectrum shortage.
  • Within the EU, implement the recommendations of the RadioSpectrum Policy Program (RSPP), especially those regarding white spaces, without undue delay. The Trial has demonstrated that TV white space devices can co-exist with established services. Given the use of a correctly designed geolocation database (or databases) to enable TV white space spectrum access, any changes arising from the evolution of market requirements and technology advances can also be accommodated.
The technology's characteristics enable flexibility in terms of coverage and throughput; white space networks can:
"...trade off coverage for increased throughput. For example, in remote rural areas where user density is low, it might be desirable to enhance coverage at the expense of throughput...The key attraction of TV white spaces in this application is the enhanced range which lower frequencies enable (compared to the higher frequency bands traditionally used for wireless broadband access). This extended range translates into fewer basestations being required to cover a given area and, hence, lower coverage costs. An additional advantage of licence-exempt access, which can be enabled through the use of geolocation databases, is that rural communities would be free to provide their own wireless networks."
Geolocation is "the key to securing flexible, dynamic and cost-effective spectrum access":
"Protection of existing licensed services is a prerequisite for the use of the white spaces. Essentially, TV white space devices need to know which frequencies are available for them to use and at what power levels. This information is provided through a geolocation database. The database provides a list of white space channels with corresponding transmission power limits for a device at a given antenna location, height and configuration. It may also indicate the duration for which the frequencies can be used and, hence, when the database would need to be consulted again. This dynamic approach to spectrum access allows it to be shared effectively and enables the framework to evolve with changing technologies and market requirements. By preventing disruption to the licensed services, the database facilitates use of the spectrum on a licence exempt basis, lowering the barriers to the introduction of new technologies and applications."
A summary of the technical findings from the trial is also available.

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