Future-proofing RF Ops Amid Spectrum Changes

If there is anything we can take away from the recent confirmation of UK regulator, Ofcom's decision to clear the 700MHz band of UHF spectrum by May 2020, it should be that change is inevitable. Some changes are good, other changes, not so good, but change nonetheless should be expected.

We must, of course, continue to campaign in the interest of preserving UHF spectrum for use by PMSE (programme-making and special events) users of wireless microphones. However, it would be foolish for any serious engineer to rest on their laurels when it comes to our ever-changing RF landscape. There is no specified moment in time where the changes affecting wireless microphone operators will end, and so we must continue to assume further changes will come, and that we must act accordingly.

To shed some light on how engineers affected by the changes are reacting, we spoke to some of the industry's leading RF experts about how their working practice has changed with the decline of clean RF spectrum over recent years.

Onwards & Upwards

Both our commentators work on very different productions, each with their own unique challenges. If there's one common thread between each set of examples, it's that demand for wireless channel count is only heading one way, as Ashley Attwood, Technical Manager at Aztec Event Services alludes:

"Since the 800MHz clearance, we have seen a continuous growth in the number of wireless microphone channels requested by our customers. In our line of work, this often means several smaller two to five systems spread across an exhibition hall. It is common for us to be using 40+ systems per exhibition, with multiple exhibitions taking place per venue. Due to growing numbers — and because of increased congestion in Channel 38 — we always assign frequencies through a fixed site licence rather than relying on Channel 38 alone.  These are coordinated in-house and booked as early as possible by the Project Managers, often as soon as the frequencies are released by Ofcom."

As the amount of wireless systems increase and the space in which to operate decreases, production teams look increasingly to new technology to help mitigate risk. For example, many new digital systems feature high-density operating modes, which enable users to fit impressive quantities of wireless in less space. In exhibition spaces (such as those described by Ashley above), high-density mode is invaluable. "We invested in new digital wireless systems, in part because of features like high-density mode," explains Ashley. "The ability to purposefully reduce operating range — allowing higher channel counts and tighter zoning — has transformed the way we handle these productions given the increasingly congesting RF environment."

 

Early Impact from 700MHz

Despite the fact 700MHz clearance is still over two years away, many wireless users are already feeling the impact. Smart operators are already looking beyond May 2020 in their choice of wireless stock, Ashley Attwood gives us the perspective from Aztec. "There's a noticeable increase in bookings for interleaved spectrum in the 600MHz band. This is particularly problematic in some venues where DTV also occupies the 600Mhz band, specifically in Birmingham where only two interleaved bands are available within our K51 tuning range. If you also consider the impact of 700MHz clearance, in that DTV will have also have to move to the remaining lower bands, we're only looking at further competition for space in the future."

On asking how Aztec would summarise their efforts to maintain standards as the RF landscape continues to change, Ashley sees a combination of new wireless tech, and regular training at the forefront. "We've looked to products in other bands, including the GHz ranges, and while these are an excellent alternative for some, we haven't yet found a solution in this space to meet the ongoing demand from our clients for large simulations channel counts at congested venues across the country. We are currently investing further into digital wireless (particularly wide tuning band systems, such as Axient Digital), as they offer us the most flexibility — and simpler inventory — while also making the most of limited available spectrum. Parallel to this, we will continue to invest in education for our frontline staff on spectrum changes to ensure they're up-to-date. Coordination also plays a huge part in our productions these days. For example, our project managers use multi-zone techniques and variable transmission power to ensure we squeeze the most out of limited spectrum."

Spectral Efficiency with Digital Wireless

Ashley's comments on squeezing more performance from less space were echoed by our second contributor, RF Engineer, Steve Caldwell. In particular, Steve explains how digital wireless systems go a long way toward improving the efficiency of wireless systems.

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 Photo by Steve Caldwell[/caption]

"Using the available spectrum as efficiently as possible is key if you want to stay ahead of the game. There are a few ways to improve efficiency, one of which is the use of more efficient transmission methods. I am, of course, referring to Digital modulation schemes. Due to the nature of digital transmission methods that allow many transmitters to be packed side-by-side, we can run larger quantities of wireless is less space.  It is this same principle that helps Digital TV stations run contiguously, with no interstitial spacing in the first place (ironically, one of the key reasons we are losing spectrum). Have you ever noticed that analogue TV stations always have an empty channel between them within a given location? That's interstitial spacing."

"With the advent of digital radio microphones, we can obtain many more usable channels in the same amount of space when compared to analogue counterparts. Not because they consume less space (not yet anyway), but because they do not produce the levels of intermodulation artefacts that consume adjacent spectrum.

Getting Smart with Coordination

Digital wireless systems go a long way to alleviate spectrum challenges. However, it would be inaccurate to say that digital modulation schemes solve the problem entirely.

"Digital wireless systems have taken some heat out of the situation, but they're by no means a silver bullet," Steve explains. "There are still plenty of perfectly good analogue systems out on the market, and we must also get smarter with coordination to ensure we deploy systems efficiently. One of the tricks that I use to obtain more usable analogue frequencies in a given amount of space, is to utilise the already occupied bands of spectrum (such as a TV channel) to my advantage. Of course, you can't use these portions of spectrum for your usable fundamental frequencies, but those occupied TV bands are a great place for all your Intermodulation products. In short, if we calculate our transmitter fundamentals so that the bulk of the IMD (Intermodulation) product falls into one of these occupied TV channels (where it is insignificant in power, relative to the owner of the channel), then less of the usable space will be occupied by useless IMD products."

Smart coordination techniques, such as those described by Steve above, are indispensable when running some of the most demanding major productions in some of our most congested cities across the globe. Coordination is imperative, but the system is only ever as good as the information it receives and the end-user, as Steve demonstrates with further examples.

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 Photo by Steve Caldwell[/caption]

"Quite often, when calculating a solution for large systems, limiting the space available to the calculator can improve the efficiency of your coordination. For instance, let's say you wish to provide frequencies for 30 IEM (In-Ear Monitors). If you allow the frequency calculator to utilise the entire switching bandwidth of your devices, it will do so spreading out your fundamentals across many tens of MHz. It will also 'block out' a good portion of spectrum with IMD product. In the case of a 3rd order calculation, the coverage area of these IMD products is equivalent to three times the bandwidth of your IEM transmitters' current tuning range. If, through this process, you also go about calculating for your radio microphones, the program finds that not only does it have to avoid the IEM transmitter fundamentals, but also the IMD product. However, IMD product does not need to avoid other IMD product; it can quite easily fall right on top of itself. By constraining the available space that your calculator is allowed to populate with gear, you are also constraining your IMD spread by a factor of 3:1 (reduce the IEM transmitter frequency spread by 1MHz, and you reduce the 3rd order IMD spread by 3MHz). Let all the IMD products fall onto other IMD products, who cares! You are effectively producing a 'junk band' of IMD either side of your IEM's. Nothing can use this space except other IMD's, which leaves the remainder of your band clean for wireless microphones."

Closing Words

It's clear from all the comments above that a solid understand of RF principles is paramount. Mobile broadband is here to stay, and while the clearance of 800MHz certainly had a significant impact, the loss of 700MHz will arguably separate the wheat from the chaff. Sound Engineers and production companies have got their work cut out for the foreseeable future, but we cannot take an attitude of complacency if we're to uphold production values.

Unfortunately perhaps, the changes we face come at a time where the UK creative sector is booming. According to recent statistics, the creative sector is now worth £91.8bn to the UK economy, up from £85.4bn in 2015. Within the creative sector, there are countless productions, from TV broadcast to live performance, all of which rely heavily on wireless microphones.

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 Photo by Steve Caldwell[/caption]

Conclusively, demand for wireless microphones will continue to rise at a time when the space available to operate continues to shrink. As an industry, we need to meet the challenge head-on, and that includes manufacturers. By embracing new wireless tech (such as digital), and by continuing to hone our skills in areas such as coordination and frequency management, the industry stands its best chance of continuing to grow in spite of continual disruption. Ultimately, the next generation of events will be led by those with a genuine understanding of how to efficiently deploy and coordinate world-class wireless systems. Change is inevitable; growth is optional — how will you react?

About our contributors:

Steve Caldwell

Steve is a Technical Manager and RF engineer at Norwest Group. He cut his professional RF teeth at the Sydney Olympic Ceremonies in 2000, and has since gone on to serve a plethora of major events across the globe. More recently, Steve worked on what could arguably be described as his most challenging project to date, as the RF Consultant and Coordinator at the 2016 Olympic and Paralympic Ceremonies in Rio.

Ashley Attwood

Ashley is the Technical Manager at Aztec Event Services, a multi-disciplined audio-visual supplier to the exhibitions and events market. He supports all areas of the business with a sharp eye for robust and efficient solutions. In the last 10 years Ashley has managed the technical delivery of events across the UK, Europe and Far East; ranging from the smallest corporate meeting to international expos. Recent highlights include the British Grand Prix and product launches for Sky and Huawei.