The Integrated Wireless HD Camera
Wireless HD cameras give a unique freedom in television productions. They can move quickly from place to place – along the touchline of a rugby or football match, for example – or they can allow the camera to reach places where cables would be very awkward – into the audience in an entertainment show, or following sports stars from the dressing room out into the arena.
A number of manufacturers offer wireless kits to add on to existing cameras, and many of these are fine products. Camera manufacturers work in close co-operation with the creators of these products, to ensure that their wireless add-ons fit well, both mechanically and electrically.
Grass Valley, though, is unique in the camera world in offering its own, integrated wireless camera solution. This is possible because of the way they build their cameras: the interface is a separate module, so it is practical to take a standard camera and, instead of fitting a triax or fibre adaptor, fit a wireless transmitter instead.
This seemingly simple point is probably one of the most important benefits of an integration solution rather than an add-on. It does not distort the physical design of the camera, which makes it much easier to use.
A one-piece camera is designed to be balanced. A wireless transmitter will weigh something around 1.5kg, with the battery adding as much as another 1kg. This weight is all at the back of the camera, making it hard to balance on a steady mount and virtually impossible to use on the shoulder, typical uses for a wireless camera.
An integrated solution virtually eliminates this problem. A battery is still needed which is extra weight, but it is not so far off the point of balance so the effect is much less.
As well as being physically almost identical to a fibre or triax adaptor, the wireless adaptor can be largely electronically identical, too. This means that the camera control data can be embedded within the two-way communication.
It also means that the same operational control panel, which is used for a cabled camera can also be used for the wireless cameras. With a very small latency apart, the vision engineer will see no difference between cabled and wireless cameras as they are shaded and controlled. Outside broadcast trucks are major users of wireless cameras: space is at a premium so eliminating the need to have separate control panels for the wireless and the camera part of the system is a benefit.
This commonality between cabled and wireless cameras should extend to quality. In the modular design, the wireless section has to be pin compatible with the triax and fibre adaptors, so it receives the highest possible quality signals, immediately following the camera’s on-board processing, and saving one or more stages of digital signal processing.
A good match between cabled and wireless cameras depends on taking this high quality signal and transporting it to the receiver with as little degradation as possible. There are considerable challenges in this though: the compression scheme has to be high quality, of course, but it also has to be low latency if the camera is to be of any use in action sports, and it cannot be too demanding in terms of processing power – the battery pack has to last at least the 45 minutes of a football half.
Long GOP MPEG-2 can deliver good perceived quality, but at the cost of high latency because the group of pictures has to be coded at the camera and decoded at the receiver. JPEG2000 is more processor intensive, but its intraframe coding, ability to handle 10 bit 4:2:2 and the absence of macroblocks thanks to its wavelet compression mean that it is a better trade-off overall.
Finally, there is the question of the wireless connectivity. Much of this is standard to all wireless camera systems. Local RF licensing requirements determines frequency bands, in the range above 2GHz. All professional wireless camera systems use COFDM transmitter modulation because of its stability in less than perfect reception conditions.
The very short wavelengths used for transmission mean that they are largely dependent on line of sight reception. The receiving antenna has to be located relatively close to where the camera is likely to be used, and certainly not obstructed from it, for instance by walls.
The integrated approach has strength here, too. Because the wireless link is so closely aligned with the camera, it carries all the other signals, which would normally be sent to and from the CCU: intercom, tallies, audio feeds, control data. and so on. Apart from the absence of return video to the camera (which would be too much of an overhead) the wireless link acts exactly like a triax cable.
The benefit here is that the antenna unit, which needs to be out in the stadium, becomes in effect a wireless to triax adaptor. The signal is converted and carried on the cable to the truck where it can be split into its component parts in exactly the same way as any other camera cable. At the antenna unit is a three times diversity reception system to assure an extremely reliable and stable transmission. For very demanding applications where for instance two different areas need to be covered from the same wireless camera - for example out on the pitch and inside the changing rooms; two antenna units can be connected by separate triax cables to the same CCU. There is a fully automated seamless roaming between the two antenna units.
Power for the antenna and interface can be delivered down the triax, so only one cable needs be rigged. With most sports venues now boasting permanently installed cables, setting up a wireless camera can be as simple as carrying small box into position and plugging it in.
For add-on wireless systems, the position is a little more complicated. The pitch-side receiver is the point at which the wireless system provider’s involvement in the process ends, so all of the signals are broken out at this point. So as well as a video cable there needs to be audio cables for the on-camera microphones and reverse audio feeds; cables for camera control and wireless control; intercom and so on. The box may well need a separate power feed too. The situation is more time-consuming to rig, and leaves more types of cables which need protection.
Wireless cameras are used inside studios, too, and many of the same benefits apply there. A studio complex might have a small number of wireless camera kits, which are shared between different studios as productions require them. Because of the commonality between cabled and wireless cameras, all you need do to set up a wireless camera is to plug the antenna unit into the wall box on the appropriate camera cable.
In summary, there are many solutions to the challenges of wireless cameras for today’s HD productions. The advantages of choosing an integrated solution rather than an add-on are image quality; speed of rigging; ease of operation; and perhaps most important comfort for the operator, who still has a nicely balanced camera with which to get those great, up close shots.
This article first appeared in the February 1, 2010 issue of Digital Studio Magazine