Following the recent announcement that Nominet has has been awarded the first qualification to operate a TV white space (TVWS) database in the UK, we have received quite a few questions about this new and exciting technology. We therefore thought it would be useful to write a short primer to explain the basics of TVWS. If you are interested in learning more then please read on…
What is TV White Space?
Between 2008 and 2012 the UK’s terrestrial television system switched from analogue to digital broadcasting. The TV transmission system is arranged regionally and so to avoid interference between neighbouring regional signals there needs to be space between the channels used in each region. Devices used for program making and special events (known as PMSE), such as wireless microphones, occasionally use some of these spare channels, but the remaining channels can be shared for other uses. TVWS technology makes use of these available channels (known as white spaces) using an online geo-location database that tells the wireless device which frequency it can use without causing interference to TV broadcasters and PMSE operators.
TVWS Physical Characteristics
Depending on the availability of channels in an area, TVWS can offer tens of Mbps per channel over several kilometres. There is potential to increase the bandwidth to offer up to 100 Mbps by combining multiple channels. One of the attractive features of TVWS is that it uses lower frequencies compared to Wi-Fi and mobile networks, thus allowing the signal to travel much greater distances and penetrate permanent obstacles such as buildings and trees, as well as travel around terrain allowing non-line of sight connections.
A TVWS radio and aerial
The availability of TVWS channels does vary depending on where in the country you are and also what time of the day it is. The speed and availability of the service cannot be guaranteed, as within this spectrum range TV broadcasters and PMSE operators take priority. In addition, TVWS users share the available channels with any other users in that particular area, which may have an impact on the performance of the connection. TVWS therefore performs best in rural areas where the spectrum is generally less congested than in urban areas.
Uses Cases for TVWS
Given the appealing characteristics of the TVWS frequencies, a number of potential use cases have been identified for TVWS such as rural broadband, campus networks (also referred to as “Super Wi-Fi”), and connecting IoT devices.
Regulation and Operation
Following extensive consultation and trials over a number of years, in February 2015 Ofcom decided to move ahead and enable access to unused parts of the radio spectrum in the 470 to 790 MHz frequency band through dynamic sharing controlled by a spectrum database. Ofcom is currently preparing the regulatory changes that will permit public usage of TVWS in the UK, which is expected to come into force in January 2016. Ofcom’s eventual aim is for TVWS to be like Wi-Fi, where anyone is free to use the technology without the need to pay a licence fee. However in the near-term, TVWS users will need to obtain an operational licence (expected to be £1500 per year per operator for unlimited devices). Once devices that are able to autonomously report their location become available (expected in the next 12-18 months), there will be no longer be a requirement to have an operational licence.
In order to transmit on TVWS channels, devices are required to contact an Ofcom approved TVWS database to check the availability of channels in their area, as illustrated in the diagram below. Devices send their location to the database, and in return they receive a list of available channels and the power at which they are permitted to transmit on each. Devices are required to check in with the database every 15 minutes to ensure they remain clear of TV broadcasts and wireless microphone users. Nominet has built such a database (the first to have been approved by Ofcom) that will be available when TVWS launches in the UK in early 2016.
Image source: Ofcom
Outside of the UK, TVWS use has been approved in a number of countries, including the USA, Canada Philippines, Singapore, and a number of countries in Africa. The regulatory framework of each country varies slightly but all are based around the dynamic spectrum management paradigm.
Equipment Availability and Cost
A small number of specialist manufacturers currently offer radio equipment that operates in TVWS.
The main vendors are Adaptrum, 6Harmonics, and Carlson Wireless. The prices for the devices currently range between £1200 and £4500. These are 1st generation devices and the prices expected to drop significantly when volumes build and the technology becomes more mature.