Building strong foundations for TVWS

9th January 2018

Dr Alistair Braden
Lead Engineer

The Dynamic Spectrum Alliance (DSA) has published new Model Rules for TV White Spaces. This is a template set of rules and regulations to ease the adoption of TV White Space by countries around the world.

These new rules combine and refine the best parts of existing regulations. They can be customised for any country’s specific needs, and they harmonise with existing models to facilitate international market development.

Nominet are proud to have been a major contributor to the new Model Rules. We believe the internet is a force for good, and we see tremendous potential in using TVWS to bring the internet to unconnected citizens all over the world. Our contribution draws on our years of experience with the operational, regulatory, and mathematical aspects of TVWS, and we are excited about what can be built upon this foundation.

Why Are Model Rules Needed?

TVWS is commonly used to provide broadband connectivity to rural not-spots lacking a fibre network; in the UK about 5% of the population lives in not-spots. Bringing the social and economic benefits of broadband to these places is valuable in developed countries, but there are vastly bigger potential gains in using TVWS to connect the 65% of people with no access to broadband in developing countries.

Any country wishing to introduce TVWS regulation must establish complex technical regulations to dictate how devices behave, and coexistence calculations to prevent harmful interference to incumbent users. This is a high barrier to entry, but the regulatory model need not be created from scratch. TVWS regulations are currently in force in five countries: UK, USA, Canada, Singapore, and Colombia. Each of these countries invested considerable effort in clearing that barrier to entry, and a great deal of that work is more generally applicable. However, some assumptions are only true in the specific country they apply to, and some models are underpinned by proprietary data. Each model presents its own advantages and disadvantages, and practical experience has highlighted areas for improvement.

The DSA identified that developing a template regulatory model would help to accelerate the uptake of TVWS around the world. By using the best aspects of the existing models – and refining the less successful aspects – the DSA has created a generic template for regulations, significantly lowering the barrier to entry for a country to adopt TVWS.

How is TVWS Regulated?

A significant part of a country’s economy relies on effective use of the radio spectrum. A role of Telecoms regulators, such as Ofcom in the UK, is to enable and ensure effective use of that spectrum. Anyone wishing to transmit radio signals must adhere to the regulator’s rules.

Radio spectrum regulation typically takes one of two approaches: licensed or unlicensed. Licensed regulation is a user (e.g. a mobile phone operator) paying for generally exclusive usage of certain frequencies, locations, and times. Unlicensed regulation allows anyone to use parts of the spectrum for a certain purpose on a free-for-all basis (e.g. Wi-Fi).

TV White Space uses a third approach to regulation, known as Dynamic Spectrum Management. A TVWS radio device must contact a White Space Database (WSDB) over the internet to report its location and capabilities, and to request permission to transmit. The WSDB will grant that device a dynamic licence to transmit at certain frequencies, at certain maximum power levels, for a specified period (e.g. 24 hours).

The exact frequencies and power limits in a dynamic licence are computed by complex coexistence calculations set by the regulator, using data describing incumbent users (e.g. television broadcast towers and domestic receivers). By simulating other users of the spectrum – and what effect that device’s transmissions may have upon them – the WSDB calculates power limits at each frequency to avoid causing harmful interference. Nominet provides such a dynamic licensing service in the UK.

This dynamic approach is well-suited to television frequencies (i.e. UHF and VHF), as about half of these are unused at any given location. However, these gaps (or ‘white spaces’) are in different frequencies in different places. Neither of the traditional regulatory approaches facilitates widespread general-purpose use of these gaps, making Dynamic Spectrum Management attractive to regulators wishing to maximise the benefit to their citizens through efficient use of their spectrum.

Access to the internet is increasingly seen as a basic human right, a right which is denied to many millions of people by a lack of infrastructure. TVWS is a proven technology for bringing broadband internet to under-served areas. The DSA’s new Model Rules provide a solid foundation for the ongoing growth of TVWS around the world, and help to promote a more dynamic approach to spectrum that will prove a valuable, sustainable connectivity solution in our ever-evolving digital world. Learn more about the technical detail of these new rules in Long Read: Enabling TVWS and Protecting Incumbents.