Vanishing Spectrum

Haresh Bhana and Stephen Buckland on behalf of WUNZ (Wireless Users New Zealand) explain ‘Where are Radio Frequencies Going?’ and why it matters. Here are some highlights.

Digital TV is set to radically alter the landscape for smaller users of the radio spectrum. As NZ switches to fully digital TV, the band used for radio microphones is being reassigned. Commonly used frequencies for radio mics must change and – before you wonder ‘do I care?’ – think how widely wireless mics are used… From schools to lecture theatres, boardrooms, and gymnasiums through screen and stage to broadcasters, the changes will be profound.

Where are radio frequencies going and what exactly is happening?

The radio spectrum isn’t really vanishing, it is being reassigned. The frequencies themselves aren’t going anywhere, but bands of spectrum will be made unavailable to general users or used with different technology (digital television, and in the future ‘long-term evolution devices’).

How has the use of the radio spectrum worked till now?

All smaller users operate under a General User Licence (GUL): A default state, not an actual licence, for those outside the big fee-paying users (radio, television, and telecommunications). Operating under a GUL has always meant accepting limits on transmitter output and bands of spectrum available. It also means an expectation that you will not interfere with use by fee-paying broadcasters.

Why WUNZ?

Until WUNZ, users of the estimated 100,000 radio mics in New Zealand had no input into the Government planning. WUNZ has sought to inform the ministry and ultimately to alter the declared government position that: radio mic “users operate on the fringes of the spectrum… don’t pay for a licence, [and] therefore their rights are minimal.” WUNZ’s campaign has won recognition, but uncertainty remains as scheduled changes meet with technical delays, and updates arrive on an ad hoc basis.

How does digital TV affect radio mics?

Traditional TV broadcasting leaves gaps – ‘white space’ – where typically radio mics operate. The ‘white space’ is clear (see accompanying figure Analogue TV – UHF Spectrum) between the peaks and troughs of TV channels. Even within the smaller (8 MHz) bands taken up by single TV channels, there’s white space for radio mics. Digital TV provides quite a different picture (see second figure): A digital channel occupies the entire chunk of bandwidth: leaving no white space at all. If your radio mic operates in that band of spectrum you have nowhere to go.

Goodbye 700 MHz

By March 2015 all users – including wireless mics – must clear the 700 MHz band of spectrum: all analogue transmissions will be switched off, digital TV moved to lower bands, and the free space created – the ‘digital dividend’– put up for auction by the government. WUNZ unsuccessfully fought to retain the spectrum for general use. Unfortunately, the ‘digital dividend’ is seen as a valuable commodity (something that remains to be seen, see below), so radio mics operating through 700 MHz will be redundant by early 2015.

Managing the spectrum

In the USA, the 700 MHz band has been closed off since June 2010, though to date it remains unused. So, is the ‘digital dividend’ really a valuable commodity, or has this been misjudged? And, why can’t the band remain available until it’s actually required for other uses?

Other situations require thoughtful management, for example where many radio mics are used simultaneously – how can conflicting use be managed? Currently, there is no means of resolving conflict, as general users share equal rights. WUNZ looks to support models like that applied to the Rugby World Cup, involving active management of spectrum use.

Looking into the crystal ball: predicting future allocation of spectrum.

WUNZ has projected what future spectrum demand might be. The upshot is – because digital channels use twice the spectrum in certain locations – digital looks set to occupy a lion’s share of spectrum: Maori TV and Sky could occupy 96 MHz for six channels, leaving slim pickings, and major challenges for general users.

Short-term silver lining and the unknown future

Until 2013 demand for spectrum will remain unclear. As 700 MHz vacates, availability will actually improve for a while (an Indian summer before post-digital-TV-winter sets in). In the meantime, all users need to keep informed and manage their use carefully.

See the full article at www.nztecho.com. To keep informed and for more information visit www.wunz.co.nz regularly.

Thanks to Haresh Bhana and Stephen Buckland of WUNZ upon whose presentation this article is based, and Grant Cummuskey of NZ Video News who provided a transcription of the presentation.