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Live Tools
BBC Technology

Wireless Cameras Go Digital

by David Fox

One of the only genuine breakthroughs at IBC 2001 was the advent of digital wireless camera links, designed to enable more robust transmission of material, more simply, over longer distances than current analogue links.

Besides their ability to work in built up areas or under bridges without being affected by multiple reflections (the presence of large metal structures can actually help boost the digital signal), they also offer broadcasters cost benefits. The systems don't need directional antennae, being omni-directional, so that nobody is needed to aim the antenna at the camcorder to pick up the signal.

LiveTools' system is already in use with broadcasters, Tandberg has sold its first units, and Gigawave is readying its system for shipment in November. The BBC also showed two different experimental systems, which it is using extensively for its own production, while Sony has also developed a prototype, although it wasn't on show at IBC.

There is, however, one problem - at least for live applications. Most of the systems on show experience significant delay (of three to more than 18 frames). The more robust the signal you need, the more delay you will have to suffer. Except for one new system, D-Cam, from Gigawave, which promises delay of less than one frame. Unlike the others, which use MPEG (or even DV) compression, it uses its own.

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Gigawave D-CAM

Gigawave D-CamDelay using D-Cam is measured in lines, and is "considerably less than one frame", promises John Scott. It also recovers almost instantly if there is signal loss, compared to MPEG, which he says would take two seconds to recover.

A further advantage is that instead of pixellating as it starts to lose lock, it gets softer before collapsing. "It fails more gracefully," he says.

It uses its own proprietary line-based compression system, and own multi-channel modulation, with a range of receiver options and antennae. It will transmit up to about 1km with an omni-directional antenna, or further with a directional unit. It can also increase power for distance, but this drains batteries. Typically it lasts more than an hour on a standard battery.

Scott doesn't believe that being proprietary is a problem. Existing radio cameras are stand alone, and there is SDI i/o. "What happens in the middle is not important. Compatibility is not an issue," he says, while admitting that "it may be in the future" if any single standard is agreed. "We will go with whatever our customers want."

The unit weighs 2.85kg, and includes full camera control and tally. Users of its current analogue G-Cam system can simply upgrade their existing control panels. It doesn't have return video at the moment, but might in future.

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Delay need not be a problem, according to Laurent Zwahlen, general manager, LiveTools, if the systems are used appropriately. "We don't try to produce equipment to mix with tri-ax cameras on the same shoot," he says.

It has sold 50 units in Europe (and a further 35 in the US). Users include: Canal+, FR2 and FR3 in France, and SRG Switzerland. SRG has a 3/4 camera fully wireless OB van, which means all the cameras have the same delay. "To try to have no delay for studio cameras at 18Mbps, the quality isn't good enough for high-end production and you lose robustness for ENG," he says.

Its delay is 15 frames for QPSK modulation, which he recommends as giving a reliable signal at 5.5Mbps. It drops to 5 frames at 64QAM, 15Mbps - which gives a much less robust signal, he says. For medium robustness with only slightly more delay, it can be used at 11Mbps with 6 frames delay. It uses MPEG 4:2:0, which he says gives a better result at 15Mbps than 4:2:2.

The LiveTools system can work with any camera. For DV or other small cameras a back-pack version is used. It can also be added to any video source. It uses a 1U decoder/receiver, which includes video interfaces. It costs 50,000 Euros complete for one camera.

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Tandberg's new system costs about the same (at £31,000), but can transmit either MPEG 4:2:2 or 4:2:0. Because it is completely DVB-T compliant standard MPEG, it can use "cheap, readily accessible receivers," says Ian Trow, group manager for mobile contribution, Tandberg. At its maximum bit rate, delay is reduced to 3 frames, using IP mode rather than IBP. The Voyager Lite includes an MPEG-2 encoder using COFDM, covering from 5 to 21Mbps.

At 5 - 10Mbps (QPSK mode) in difficult areas. "It compromises the coding quality a bit, but gives much more certainty of getting through," he says.

It requires a back pack, which weighs 2kg including battery (which lasts more than an hour). It offers full camera control via an analogue return path, but doesn't have return video.

It can also be used for many other applications - on motorbikes or for remote links for specific events. He also sees a big market for it beyond broadcast, especially for security. It has already shipped a number of units in this market, with other shipments due to start early next year. It is the first new product combining the expertise of both Tandberg and its recent acquisition, microwave company, AVS.

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The BBC is enthusiastic about the potential for digital wireless technology. Ideally, it wants to use it not just for outside broadcasts, but also in the studio to get rid of cabling, and to give producers the ability to do a wider range of camera moves. It would also make the studio safer. "Cables are a nuisance," says David Rayers, senior R&D engineer, BBC Technology. "If you want to do something clever with a camera, you've got to have someone to move the cables."

At the moment the BBC's own MPEG system (which is constructed for it by Gigawave) experiences about a second's delay, "but we have a solution" and will get it down to about two frames, he promises.

The BBC has been using the system extensively over the last year or so, and is getting a good reaction from its users. "It's the best radio cam system I've seen," says outside broadcast camera supervisor, Jon Lord. Previously, he couldn't trust them. Now, even in difficult environments, "the pictures are rock solid, always." For events like the boat race (where there is a small camera on each boar) or marathons, which move through built up areas or under metal bridges, where analogue systems break down, he believes the digital system offers a lot of advantages, especially as the omni-directional receivers can be helicopter mounted.

COFDM can not only operate in an environment with lots of metal, glass and concrete," it works better the more metal posts there are because of the reflections," explains Rayers.

Standing in the middle of a football pitch, Lord says "the quality is as if you were working on a wire." the downside, of course, is the delay. "In terms of live, multi-camera production, it is not really usable."

You could cut round it, but he believes it would be too much for an already busy director to think about. A newer version, using DV, has a three frame delay, and the next MPEG version should be almost invisible if it gets down to two frames.

For studio use, it would have to have a full return path for cue lights, camera control and return video.

Besides live use, he believes it will also be useful for getting recorded pictures quickly back from places which don't have wired links in place.

The BBC hopes the system will be taken up by a manufacturer for production. Meanwhile, Ikegami showed new credit-card sized MPEG-2 encoder/decoder modules at IBC with 7 frames delay, which its says are getting a lot of interest from companies interested in making wireless cameras.

FEB 2002

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© 2000 - 2010

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    David Fox