Special Report
which builds upon DVB-T and improves its cameras that captured the full 24 hours from
robustness in highly mobile wireless camera each car, including the new transmitters (Link
systems. LMS-T uses fewer carriers; 399 XPu) for the in-car cameras.
rather than 1705 for DVB-T. This gives
improved Doppler and fading performance for Getting different views of the race
high speed vehicles and reduces sensitivity to
phase noise making a more robust link. Each car was equipped with three cameras,
one forward-facing to get the driver’s view,
Dealing with Doppler one rear-facing to capture cars overtaking
and one pointing at the driver. They used
Typically 10MHz is allocated by regulatory software on a PC to switch from one camera
bodies for wireless camera operation. to another over a UHF control link.
Nominally DVB-T uses 8MHz, and the Visual used two UHF transmitters at
remaining 2MHz is not used. LMS-T uses different frequencies, transmitting the same
9.4MHz bandwidth and this alone gives up to data and camera control. They were able to
25% additional throughput. The linearity and switch between the three cameras in each car
performance of Link’s output RF stages still and they gen-locked each of the cameras so
ensures that systems can be run in adjacent that there would not be any break-up on the
frequency slots. switching camera.
LMS-T has deeper interleaving than DVB- The on-board pictures were a major part of
T, spreading the data over a greater time the final production. They were reliable and
period. It also has a much more powerful the pictures were always there.
error correction system, LDPC. These make it "The course at Le Mans runs through a lot
much more resistant to the burst interference of trees," said Chris Moore, principal RF
and short duration fades that are typical of engineer at Link Research, "and rain would
mobile use. make the course more difficult for the drivers,
Overall LMS-T has a throughput that is engineering and is very experienced in the TV crews and the RF engineers. It’s also
65% higher than DVB-T at the same level of wireless digital video for sports and challenging to manage all the frequencies that
robustness, which is a major advantage for newsgathering. are in use, solve the Doppler shift and
wireless camera systems transmitting high bit Seven cars, the Audi, Peugeot and one channel fading of cars travelling at up to
rate signals. A further option available with Corvette were fitted with in-car cameras and 350km/h. The crews and equipment arrived
LMS-T is support for dual-channel operation five handheld cameras covered the pit lanes. on Monday and the cars came out on
to double the throughput where additional One more wireless camera was used, Wednesday, so we only had Tuesday for the
channels are available for licensing or the sometimes on a quad bike, to pick up events set-up. But everything went according to
channel allocations are 20MHz or wider. In its around the track. plan. On Saturday the pictures were clean for
dual-channel mode LMS-T can support bit Antennas and fibre optic cables were the warm up and it was close to perfect. We
rates as high as 36Mbps (16QAM, rate 2/3) installed around the course to provide full RF had one very minor problem, someone
whilst retaining highly reliable link coverage of the entire race area. With these in accidentally unplugged one of the fibre
performance. place and tested, a live transport stream from connections, but this was easily fixed."
each car is relayed instantly to the OB truck. Yves Le Moing, technical specialist of
How Visual TV managed the event Comat’s solution included the wireless Comat Metracom, said: "Link has focused its
development on making it easier to get a
The French production company, Visual reliable picture, in spite of weather, trees and
TV, provided the coverage of the entire race, structures in the environment. One of the
working right through the night, using pit reasons why we got such good results is
lane cameras and in-car cameras fitted with Link’s COFDM-based modulation system
transmitters from Link Research. LMS-T. It resists interference and fades and
Visual TV is no stranger to large RF reduces sensitivity to noise and vibrations so
projects; it has invested heavily in wireless it gives us a more robust link."
camera equipment and has already covered Stéphane Alessandri of Visual TV said:
many important news and sports events such "Everyone was really ecstatic. The race went
as the Rugby World Cup and the French Route extremely well for us. We got the amount of
du Rhum sailing boat race. coverage we set out to get - and we achieved
The RF equipment, the wireless what we intended to do. We were able to
transmitters, receivers and antennas were cover 100% of the circuit with only a couple
provided by Comat Metracom, the French of minor glitches. The RF links worked for the
distributor for Link Research, based in Paris. full 24 hours with no problems. It was
Comat Metracom specialises in RF and amazing. The feedback from everybody was
communications solutions for broadcast immense."
80 IBE SEPTEMBER/OCTOBER 2008
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