Attempts to make buildings more energy-efficient in terms of heating and cooling could backfire badly on the networking front, if radio expert Daniel Lewing is to be believed.

Lewing is technical director at Innova Wireless, and a specialist in in-building radio frequency (RF) coverage. He says people will end up having to install additional radio hardware of their own - plus additional wired uplink capacity to support it. But he adds that if done right, this could be a good thing rather than a cost-sink.

"Environmental codes - insulation for energy efficiency and so on - mean RF will get worse," he explains. "For instance, K-glass windows can heavily attenuate signals, as can the sticky films that prevent glass from shattering.

"I don't think building owners know yet that by making buildings energy-efficient, your RF coverage is worse. So you need to install in-building coverage and fund that."

"In-building coverage is still something of a mystery - people are afraid of it," he adds. "Typically they'd go in and install a cellular system for the four network operators, then an FM system, then maybe TETRA... So you're seeing a lot of [wireless] traffic going through, and your roof looks like a porcupine."

The next problem is the huge range of wireless frequencies in use and affected. Lewing says it's not quite as bad as in tunnels (another of his specialist areas - he was lead architect on projects for the London DLR and Heathrow Express) where "you can have everything from 200MHz to 1.5GHz," but it's pretty complex, and getting more so.

That's partly because as wireless technologies evolve, they're having to use what spectrum they can get - and while the technologies are typically international standards, the spectrum allocations are not. Instead, a specific technology might be allocated a few MHz here and a few MHz there, with the specific frequencies varying from country to country.

As an example, Lewing highlights the band planning - or lack of it - for US cellular telephony. "It's all over the place!" he exclaims. "PCS is five [separate] blocks, 850MHz is another seven blocks... And now you can have mobile repeaters too, on trains for instance, which means you have to change blocks at a border."

He argues though that in-building coverage doesn't have to be the RF equivalent of spaghetti cabling - and it could even become a commercial advantage.

"Some will fit it because it's essential to their business or because they can charge for it, for example an airport might be able to charge the cellular companies rental on its in-building system because of the potential roaming revenue from overseas travellers," he explains. "That's the same reason Vodafone and O2 wanted 1800MHz allocations, by the way, to pick up US triband [850/1800/1900MHz] phones."

The big thing that's making all this easier is the software-based radio, along with software-controlled RF filtration. It means that a single radio can cover a whole range of services, Lewing says, noting that this is the area that Innova Wireless has chosen to work in.

"People want an all-in-one system in-building, not separate access points and base stations," he says. "It can't be totally future-proof - nothing is - but you want some degree of re-use, such as antenna banks. Modern antennas are broad enough to do cellular and Wi-Fi, so one box can do 900/1800MHz for GSM, plus 2.1GHz for 3G and 2.4GHz for Wi-Fi."

He adds that it's not just networking that uses RF and needs in-building coverage. You can also get GPS repeaters, for example for a fire-station garage, so that the fire-engines don't have to sit outside waiting for a satellite fix before they can find the fire.

Nor is it only inside buildings - valleys on the coast can suffer poor coverage and need repeaters, even as shipping miles off the coast gets a nice strong signal from the main transmitter up on the hill.

So how do you decide what kind of in-building coverage to provide and how to do it? Not too surprisingly, Lewing advises building in room for growth.

"The first question is what do you want to use it for now - and what will you want it for in five years time? For example, do you want DVB-H? Even if people don't watch mobile TV, it's going to be used for mobile content and for downloads such as films and music."

He concludes: "After that it's how long are you going to be around? Some of the tunnel systems I'm working on now will have to be there for the next 25 years. And then it's resilience - some signals will need it, but others don't."