The show must go on − securing a future for PMSE

It is a well-documented preoccupation of spectrum managers to seek ever more spectrum to support the established and projected growth in demand for wireless connections to smart phones and tablets. This brings big challenges and big consequences. We have written about this in several previous editions of the newsletter (in January 2011, February 2012, August 2013 Special Edition). Of course much of our attention focuses on changes to broadcasting as a source of new spectrum: it has offered major improvements in spectrum efficiency over the last 10 years – through digitisation and improved coding efficiency - and this is still ongoing, complemented by evolution in the consumption of media. It also occupies a large part of the so-called 'sweet spot' of frequencies with good propagation and other characteristics. But the need for frequencies that support the making of programmes, as well as a much wider range of cultural, social and economic activity, are also a major element in this subject.

Two years ago, this Newsletter set out the background and described some of the challenges facing the programme making and special events (PMSE) sector. This centres on the developing use of the key UHF band, firstly with transition from analogue TV to digital, and more particularly with the transfer of part of that band in Europe now to mobile broadband. This transfer is already decided and underway for 800 MHz, and the current discussion about whether also to tackle the greater challenge to do a similar thing in the 700 MHz band on a harmonised basis is top of the agenda of many. In this previous article, we described three elements to be looked at. The outcomes of this are clear, but indicative of a dynamic rather than a static environment.

  1. The ECC would review the usability of the mobile broadband centre gaps at 1800 MHz. This has proved a very interesting exercise, with analysis now also made for the 800 MHz centre gaps.
  2. The ECC's project team FM 50 looked at the 1452 to 1492 MHz range, including as a potential new space for PMSE. However this is now allocated by ECC Decision (13)03 to mobile supplemental downlink – a potentially important element in the support of the mobile data requirement, focusing particularly on traffic asymmetry. This may appear to be at the expense of PMSE, but there may be more to this story yet (see below).
  3. We also looked at the role of cognitive approaches; more as a means of protecting PMSE from cognitive 'white space devices' than as a vehicle for PMSE itself. Interest in white space remains but is somewhat stagnant for now with the uncertain environment now created in the UHF TV band.

Looking at centre gaps

Lately, most attention has focused on the opportunities in centre gaps at 1800 and 800 MHz. Apart from any other consideration, these are opportunities which are unlikely to be caught up in the changing dynamics of the UHF band, having only recently been established in the new wireless broadband band plans. The first step of the work was to evaluate the constraints which would be needed on wireless microphones to limit interference to mobile devices. But although the wireless microphones are in international frequency law the 'secondary service', the public doesn’t care about that. For example, what is more important at the concert: that a member of the audience receives or can send an SMS, or that a singer’s big moment – and the audience’s enjoyment - is not blighted by the receipt of that unwanted call?

So the next part of the work was to make some evaluation of what use could be made of these centre gaps in the presence of interference from the public mobile service – either from, say, pico cell base stations in a theatre, or from mobile devices inside it. These studies highlighted the need for an appropriate setup procedure to ensure the required Quality of Service for PMSE. They are documented in ECC Report 191 and an addendum to CEPT Report 50 developed in response to a European Commission mandate which will serve as a technical basis for the Commission's next steps in policy-making towards PMSE.

Challenges and opportunities

Although the centre gaps are useful for PMSE as a whole, they certainly do not provide enough capacity for the complete solution, nor enough security against the adjacent channel interference. Even if you take the 700 MHz range away from PMSE there is still a significant potential in interleaved spectrum in the remaining TV bands, although this may well be insufficient for some larger events. But long term confidence in that resource depends on long-term stability in the whole 470-790 MHz band, and that is some way off.

A further factor less often considered is how more widespread pressures on spectrum reduce the opportunity for borrowing spectrum on a short-term basis for large scale events; these are typically too much of a 'one-off' to be subject to European harmonisation, but it adds to the pressure on the PMSE sector.

One strategic problem PMSE faces is that it has secondary status in international frequency regulations. However at a national level, and also if there are sufficiently strong binding agreements between neighbouring countries, PMSE can have whatever status the regulators may determine. In addition, the rather short range required for PMSE communications makes it quite efficient to plan as a secondary service, namely plan the long-running services like broadcasting and mobile first, and then planners establish the framework for PMSE on a compatible basis. So an order of planning which is (rightly) based on technical efficiency doesn’t always reflect the social and economic importance of the service itself.

The ECC’s Project Team FM 51 has now produced a key ECC deliverable, ECC Report 204, which reveals important technical studies and recommended ways forward, to try and establish some greater stability, innovation and opportunity in this key sector. It covers a wide range of PMSE issues, including the wireless microphones which are at the heart of nearly all TV and theatre productions, and which are facing the biggest challenges with diminishing availability of UHF spectrum.

A major area of possibility for wireless microphones is in the L-Band. The band 1492-1518 MHz has recently been identified by CEPT for indoor operation of wireless microphones and the band 1518-1525 MHz is currently under study. This frequency range had already been investigated for professional microphones wireless systems back in 2006-2007 (see ETSI SRDoc ETSI TR 102 546) but the latest developments make it now more attractive.

The conclusion of these ECC deliverables marks a big step forward, but as with all of our work, it doesn't stop there. There are other developments which could play a big part in giving PMSE the secure future which we want for it. The ECC is always trying to optimise the efficiency of use of the spectrum, and sharing possibilities are at the heart of our policies, to maximise opportunities for all spectrum users. So it is with PMSE.

Share spectrum with mobile downlinks?

One very interesting avenue to explore is the possibility for spectrum sharing between PMSE and the downlink frequency ranges of mobile systems. In principle, this is not so different an idea from sharing with TV bands, TV transmissions being, of course, all 'downlinks'.

CEPT's review of the potential uses of the 1452 to 1492 MHz band opted to use it for mobile supplemental down links (SDL); PMSE had been one of several competing applications in the ECC's review. At the strategic level this brought with it a prioritisation and what was assumed to be a mutually exclusive decision not to include PMSE. However, with the right conditions to deconflict the services − given a channelling plan and specific base station siting − the potential for wireless microphones to share these frequencies without compromising their utility is very appealing.

This is particularly so given that the spatial environment of downlink frequencies is much more predictable than for uplinks with their mobile terminals eventually being placed anywhere... even in the back pocket of the young singer who has just won the 2013 Eurovision Song contest, has messaged her friends to share her delight, and is now back on stage for a reprise!

New technologies for wireless microphones – and around them

Looking ahead, technical development for PMSE is crucially important. ECC Report 204 identified that a range of new technologies have been or are currently being developed that may increase spectrum efficiency. However, the Report anticipates that these are for long term rather than short term relevance. We look at these possibilities below.

In the short and medium term wireless microphones will remain largely analogue devices. However, the move to digitisation could provide for greater security of quality in environments of light to moderate interference; on the other hand it also brings with it a similarly demanding requirement for spacial availability: in other words the performer’s microphone may not get an irritating buzzing sound from interference as (s)he moves around the stage, but interference could lead to on-stage hotspots where the voice disappears altogether!

Whilst being currently under study, the use of cognitive techniques for individual microphones is rather to be considered as a long-term option. On the other hand a local theatre/outside broadcast system managed by a cognitive or semi-cognitive local controller/management system, sensing the RF environment, may provide some ability to squeeze more services into a shrinking space.


Mark Thomas
Director of the ECO

Bruno Espinosa
Deputy Director of the ECO

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