Link Research's LinkXP wireless TV camera system

It has been a major challenge to build a digital wireless camera system that can stand up to the demands of live broadcast, but systems coming on the market now are reliable enough to film live sports and news. These will soon bring new kinds of action pictures to our TV screens. Here, we take a look at this new technology for news and sports broadcast, which will free cameramen from trailing cables and will allow them to explore beyond the limits of OB vehicles.

The LinkXP, a digital wireless camera system from Link Research, attaches to TV cameras to make a reliable television link from the camera to an OB vehicle or fixed installation.

Early analog cameras required a second man who would follow the cameraman with a directional antenna. These had limited coverage and required additional operators. Movement causes difficulties in reception, and early systems were vulnerable to sudden picture break-up as they roamed around. This restricted their use in live TV broadcast.

Other issues such as wind-loading and drag on the aerial needed to be addressed, and, of course, with no power cables, the wireless system had to be designed to rely entirely on batteries, which are expensive and add to the weight of the kit.

The first digital cameras using COFDM overcame many of these problems but added new problems such as signal delay and high-power consumption.

With professional DVB MPEG becoming increasingly important, British manufacturer Link Research has built a digital wireless camera system that delivers reliable, professional-quality 4:2:2 TV footage. The system, the LinkXP, has everything needed to make a reliable television link from the camera to an OB vehicle or fixed installation.

At the camera end, the wireless camera system, which weighs 1.1kg, attaches to the back of the camera. This uses 18W of power and provides 100mW RF in the range of 1.95GHz to 2.7GHz. The heart of the system is the encoder, which is based upon the company’s low-delay encoder, and at the receive end, the receiver provides a full decoded output plus ASI.

FPGA technology has been used to reduce the power consumption of the encoder/modulator, including the up-converter, to just 18W. It gives a DVB-T, 4:2:2, 2k carrier COFDM output, which is suitable for all kinds of professional broadcast work. Its inputs include composite video, SDI and component video, with a frame lock input at the receiver.

The S-band output connects directly to an aerial. The downconverter, which provides the UHF output, is mounted beneath the aerial and can be installed some distance away from the receiver. The UHF signal from the downconverter feeds one input of the receiver.

The manufacturer has used a diversity reception technique in the demodulator to increase signal integrity. The diversity principle takes two or more inputs with the same single-channel content and builds one output with valid content, regardless of which input it came from. Thus, if the inputs were derived from different RF pathways, then when a packet from one input is corrupted, the system uses the other input to recover the packet. Like this, it is only if all inputs are corrupted that the packet is lost.

In a wireless camera system, the benefits are obvious. Using two or more aerials will significantly improve signal integrity. It also is possible to increase coverage almost without limit. The same system is just as useful for other applications, such as seamless redundancy switching.

A wireless camera with a diversity antenna will give a more reliable picture. In addition, the receiver is designed to prevent interruptions in transmission and reduce the effect of transmission errors, ensuring that no picture will go black.

The tuner/demodulator in the encoder processes the two signals to produce one valid transport stream. In fact, similar improvements are achieved with widely spaced aerials, and it is possible to work with four aerials simultaneously, which will improve signal integrity even more and allow a broadcaster to cover a much wider area. Another important requirement for any wireless camera system was low signal delay. The manufacturer has achieved this with a DVB receiver that gives 40-millisecond end-to-end signal delay, without compromise in signal quality.

Link Research has been trialing the prototype wireless camera system at some of the world’s large international stadiums and racetracks. It does not take long to set it up. Engineers just put the downcoverters and the decoder in place and then use coax cable to fix the two small dipoles to a suitable support.

Distances in excess of one mile have been achieved line-of-sight, and the system is easily capable of covering a large sports stadium, including the sheltered areas. The camera was used for an extended period in trials, confirming that only 18W of power is required. Battery costs will be less of an issue with these systems.

The LinkXP gives cameramen freedom to move around as they work. It delivers the key requirements of low power, small physical size and low signal delay. It is flexible enough to offer multiple channels and operate over a wide area of coverage. While the current system is ideal for news-gathering and similar applications, a two-way unit is in development.

Wireless cameras like this one will bring broadcasters new ways to capture fast-moving sports and news. Producers will be able to get new kinds of pictures by sending cameramen much further away from OB vehicles, into crowds and into tunnels or even up in planes.