Original URL: http://www.theregister.co.uk/2009/03/09/pmse_ofcom/

Ofcom plots out wireless mic future

Redefine and reduce, then turn digital

By Bill Ray

Posted in Broadband, 9th March 2009 03:26 GMT

Last month, ITV sold off its 70 per cent share of JFMG, the organisation that manages spectrum used for programme making and special events. But at the same time, Ofcom published research into the future of PMSE, concerned largely with how to get rid of it.

PMSE users currently lurk between the analogue TV channels, supplying connectivity for wireless microphones used in everything from West End shows to the Big Brother house, but with analogue TV about to be switched off, Ofcom is under pressure to find somewhere else for the wireless mics to go, though the regulator would much prefer to wield the magic wand of technical progress and simply make the problem disappear.

Ofcom has already said that after the digital switch off, there will be a band-manager for 854-865MHz, able to sub-let the spectrum to theatre-sound companies and businesses, and it's likely that Arqiva (who now own 100 per cent of JFMG) will be wanting to fill that role. But the band manager will have to pay the market rate, calculated using AIP, and pass on those costs to the spectrum users. Considering that a touring show might already be paying £900 a week for radio licences, any increase is being eyed suspiciously by the industry.

And that is less spectrum than the industry is using now, which is what prompts Ofcom's latest analysis of the future of PMSE. The report (pdf), carried out by Cambridge Strategic Management Group, examines all the technologies, techniques. and processes that might make the PMSE requirements less onerous: to Ofcom at least.

The first thing the report does is split PMSE requirements between professional and amateur or casual users, with everyone except the professionals being pushed into unlicensed spectrum such as 2.4GHz or higher. That leaves the professionals, who can't afford a millisecond of interference or signal degradation.

While Ofcom is clearly hoping that magic technology will make the problem vanish, the report is slightly less optimistic. Technologies such as Ultra Wideband and Cognitive Radios are put into a 10-year timescale. An optimistic estimate. But that's only to be expected given that it was supplied by the equipment manufacturers.

Digital microphones offer one path to squeezing more use into the available bandwidth, but those have generally rejected by the theatre community for three reasons: they are too expensive, the latency involved in compressing and uncompressing the audio is unacceptable, and the signal drops out suddenly rather than gracefully failing as an analogue rig will.

But this is one area where technology is progressing, and Orbital Sound are already using 32 digital microphones in the production of Carousel currently playing at the Savoy Theatre in London's West End. These microphones have a latency of 1.9ms, which sneaks under the 2ms considered acceptable (engineers generally muck about with the latency anyway, to allow for "imaging", but 2ms gives them enough room to play with the sound). Orbital reckon they can2 fit around twice as many radio mics into the same spectrum by going digital, which is a start.

Belfast-based APT reckon they can get 4 or 8 microphones into the same space as one analogue one, with the same 1.9ms latency and no observable loss of quality. That's a step too far for the industry right now - though with licensees including Shure, the technology will no-doubt be more widely adopted.

But squeezing a few more microphones into a reduced space isn't going to solve the PMSE problems, and neither is redefining a proportion as non-critical users who can shift in to more error-prone technologies or frequencies. Charging AIP fits with Ofcom's ideal that those who pay most will make greatest use of spectrum. But it doesn't address the luvvies problem that much of the money they generate isn't going in to their pockets, and while the new report tries to find ways around the problem ultimately it's just a list of technologies that might deal with the problem in a decade or two, when what's needed is a solution for the next year or two. ®