TV white spaces (TVWS) – the unused portions of spectrum in the TV bands, such as the guard bands between broadcasting channels and channels freed up by the transition from analogue to digital TV broadcasting – are starting to be opened up on a licence-free basis in the USA and the UK, promising numerous possibilities for new services and business models.
There is significant interest in using TVWS for building rural wireless broadband networks, and they also hold considerable promise for machine-to-machine (M2M) applications, including smart meter communications and distribution automation.
How does communications in TVWS work?
Using TVWS for novel applications such as smart metering communications or broadband Internet connectivity is complex. Incumbent users of the TV band, including TV broadcasters, users of public wireless microphones such as theatres and sports venues, and public safety users, have priority over TVWS devices (e.g. USB dongles or smartphones for broadband access applications, M2M communications modules embedded in devices such as smart meters) and must be protected from interference by such devices.
Before operating, TVWS devices must establish which frequency channels are available at that specific time and location. Various cognitive radio techniques for identifying unused spectrum have been studied over the past few years, including beacons, spectrum sensing, and geo-location. Of these, using a geo-location database shows the most promise in the short term, and is the method currently being pursued by regulators in the USA and the UK.
The purpose of a geo-location database is to provide a real-time view of spectrum usage in the TV band by location, and communicate the available frequencies to TVWS devices prior to operation. Master devices, such as a TVWS base station, act as intermediaries in this process, and determine the frequencies to be used by terminal devices (‘slaves’) within its control (see diagram). Master devices are co-ordinated, to avoid interference being caused to devices within the TVWS network.
In the USA, Spectrum Bridge pioneered the development of a geo-location database for TVWS and is now one of ten FCC-approved TVWS database administrators. The UK regulator Ofcom has also been studying how geo-location databases could be used to protect incumbent TV band users, and plans to issue guidelines on geo-location database operating requirements for prospective administrators.
Why is there excitement about TVWS?
What makes TVWS so interesting? Fantastic radio signal propagation, to start with. And using the spectrum is free. Add to that worldwide availability (eventually) and lots of bandwidth, and the hype begins to make sense. Let’s look at these benefits in more detail.
TVWS are found in the VHF and UHF TV broadcasting frequencies, especially between 470−698 MHz in the USA and 470−790 MHz in Europe. At these low frequencies, radio signals have a very long range. This translates into lower costs for building networks compared to using higher frequencies, because fewer base stations are needed to provide the same coverage. Not only does this reduce capital expenditure on network equipment, it also lowers the ongoing costs relating to network maintenance and operation (e.g. power for base stations). These are some of the reasons why the licensed low-frequency spectrum used for public wireless networks (for example, the 700, 800, 850 or 900 MHz bands) is so highly prized.
Because of these range advantages, TVWS can offer superior coverage to many of the licensed and unlicensed bands that are being considered for smart metering, including the unlicensed industrial, scientific and medical (ISM) 915 MHz band used for RF mesh networks in North America.
Long signal range is beneficial especially for providing coverage of smart meters in rural areas, where other solutions may be uneconomical.
Excellent in-building penetration
Covering all smart meters in a deployment can be an issue for wireless networks, especially where meters are located in basements or cupboards within the home, rather than in outdoor cabinets.
The excellent propagation of TVWS radio signals provides deep in-building coverage, allowing ubiquitous (or near-ubiquitous) coverage of a distribution operator’s smart meter deployment.
“The real benefit to TVWS is the low-frequency VHF and UHF spectrum which will go places other spectrum can't. When coverage is an issue, TVWS will likely be the optimal solution,” says Peter Stanforth of Spectrum Bridge.
Free, unlicensed spectrum
TVWS are being opened up for new uses on a free and unlicensed basis. For example, the USA and the UK, which are at the forefront TVWS developments, are proposing a licence-exempt approach to using TVWS, allowing devices to operate in the TV bands provided they do not cause interference to the primary spectrum users (that is, TV broadcasting stations and other licensed users). Other countries, including Canada and Singapore, are also exploring allowing TVWS devices to operate on a similar basis.
Free spectrum (and prime low-frequency spectrum at that) is a huge boon, as it significantly reduces the costs of operating wireless networks.
Globally harmonised spectrum
“TV bands are harmonised worldwide, so white space can be expected to be available globally,” says Professor William Webb, the CTO of UK TVWS network vendor Neul.
This is a key point, as a global marketplace offers the prospect of economies of scale for network equipment and devices. In the short term, this is stimulating the development of technologies, standards, equipment and devices for TVWS. In the longer term, the market should be of sufficient size for vendors to be able to offer their products at low enough unit costs for mass adoption to take place while achieving good business margins.
Regulatory efforts are ongoing to open up TVWS on a worldwide basis. Following the lead taken by the USA and the UK, several national regulators are starting to consult the industry on local arrangements for using TVWS (see table). TVWS will also be a discussion item at next year’s World Radiocommunication Conference, which is the worldwide forum for reviewing international spectrum usage. Country regulatory developments are summarised below.
A huge amount of spectrum is available in TVWS. For example, research by Neul shows that, at any given time, more than 100 MHz of spectrum is available at 80% of UK locations. Spectrum utilisation surveys in the USA tell a similar story, with a study by Spectrum Bridge showing that over 96 MHz of TVWS bandwidth is available in many parts of the country. In emerging markets such as India and South Africa, where fewer TV channels are used, white space spectrum is likely to be even more abundant.
Putting this into context, in many locations TVWS can provide as much bandwidth as the unlicensed 2.4 GHz band and nearly four times as much as the unlicensed ISM 915 MHz band used in the Americas and Australia. This windfall of free spectrum in TVWS will provide enormous scope for innovation in applications and services, including smart metering communications and other M2M uses.
However, while TVWS bandwidth is abundant at many locations, there are constraints in some places. Typically, more TVWS spectrum is free in rural areas compared to cities. For example, some major cities in the USA, including Los Angeles, Miami, New York and San Francisco, have no TVWS available, but more bandwidth is available in other cities. In addition, in land border areas, TVWS can only be used if international co-ordination agreements are in place.
But the TVWS ecosystem is still immature
Can TVWS be used now? Now that’s the catch. While TVWS offers promise for applications such as broadband Internet access and M2M applications, the ecosystem is immature. It’s going to take time for regulation, technologies and products to be fully fledged.
Regulation still at an early stage
In global terms, regulation to allow TVWS to be used for novel uses is at an early stage. The USA and the UK are the furthest ahead, having both determined the conditions for the licence-exempt usage of TVWS, and a handful of other countries are taking steps towards establishing their regulatory frameworks too. In addition, various studies and trials are ongoing in Europe and the Asia-Pacific region, and these are likely to translate into regulation within three years or so.
There is a realistic prospect of TVWS device operation being permitted on a global basis eventually. Spectrum Bridge’s Stanforth sees regulation evolving fairly rapidly. “By 2013, we expect TVWS use to be widespread around the world, with regulations coming into force,” he says.
However, regulation may come more slowly in some parts of the world. In particular, progress towards regulating TVWS usage is constrained by the pace of the transition from analogue to digital TV broadcasting, which varies around the world. While many countries are due to complete this process before 2015, others, including the least developed countries of Africa, Latin America, and Asia, will not switch off analogue TV broadcasting before around 2020. In such countries, we believe regulation allowing TVWS usage could take five to ten years.
Few geo-location databases
So far, geo-location databases are only available in the USA, where the FCC approved ten providers in early 2011 (Comsearch, Frequency Finder, Google, KB Enterprises/LS Telcom, Key Bridge Global, Microsoft, Neustar, Spectrum Bridge, Telcordia Technologies, and WSdb).
The UK is also in the process of determining operating parameters for its geo-location databases. In a recent consultation, six organisations expressed an interest in becoming a TVWS database provider.
Elsewhere, regulation is generally less developed, and decisions on how incumbent TV band users are to be protected have not yet been made.
Several technologies are being proposed for TVWS operation, including modifications of existing standards such as WiFi and WiMAX and new technologies designed specifically for TVWS. There are various differences between these technologies, depending on the applications they aim to address (e.g. broadband access, M2M communications).
IEEE 802.11af (WhiteFi) is a WiFi profile tailored for TVWS. The standard is expected to be finalised in March 2012. While Internet access is the application most often discussed for this technology, Microsoft has proposed an architecture for advanced metering infrastructure (AMI) communications that uses 802.11af for connectivity from the meter to data aggregation points.
IEEE 802.22 is a point-to-multipoint standard for broadband access, which was ratified in July 2011. It is designed for delivering rural broadband service over large areas, and offers ranges of up to 100km from each base station.
Weightless is a technology being developed by Neul as an open standard specifically for M2M applications. The technology uses a QAM or QPSK modulation scheme to control emissions in adjacent channels without impacting data rates. According to the vendor, the standard is around 90% complete and should be finalised by mid-2012. Significantly for the smart grid sector, major meter manufacturers Itron and Landis+Gyr are both backing the standard.
Products not yet commercialised
Network equipment, chipsets, and devices for TVWS applications are in development, but so far few solutions have been announced.
Prototype equipment and devices have been used in trials in the USA over the past few years. Now that the FCC has finalised the regulatory conditions for TVWS device operation, commercial products are beginning to emerge. Spectrum Bridge expects the FCC to certify the first TVWS solutions by the end of 2011, with the first applications during 2012. Spectrum Bridge’s Peter Stanforth anticipates that market activity will pick up during the second half of 2012 “when there will be multiple options available and the cost/performance of the commercial solutions is better understood.”
Among the vendors planning to offer solutions is US-based Carlson Wireless. It is developing a 802.22-compliant radio solution for rural broadband applications, which it expects to be commercially available in 2012.
In the UK, Neul announced its NeulNET wireless radio system based on its open-standard Weightless technology in June 2011. The system comprises base stations, battery powered terminal devices, antennas, and a set of PC-based network management tools. Trials using NeulNET for broadband Internet access are under way in Cambridge, UK, and production systems are expected to be available in 2012.
Neul does not expect to be in mass production with a chipset solution for embedded M2M devices until early 2013, but expects the market to develop rapidly thereafter. The vendor has a roadmap to bring chipset costs down from around USD5 to under USD1 by 2015.