The migration of satellite news gathering to IP, combined increasing HD content, is driving demand for bandwidth and solutions that make best use of the available spectrum. There is some overhead in the process of encapsulating MPEG 2 or MPEG 4 video over IP, but the main cause of additional bandwidth is growing use of HD and the simultaneous transmission of IP and ASI as some broadcasters are doing.
“We didn’t think news gathering would be important because we didn’t realize it used so much bandwidth,” said David Furstenberg, chairman of Israeli satellite transmission vendor Novelsat, whose NS3 technology increases the spectral efficiency of DVB-S2 communication by 20 percent.
But, news gathering organizations have been deploying NS3 partly in order to transmit simultaneously in IP and ASI during the transition phase. At the same time, the rate of migration to IP has been gathering pace, according to Furstenberg.
“During the recent Libyan campaign, close to 80 percent of the transmissions back to the UK (which played a major role in the NATO action against Gaddafi’s regime) were done over IP rather than ASI,” said Furstenberg.
The move to IP is occurring right along the whole broadcast chain, bringing advantages such as a return path in distribution, ability to store and forward content more easily, and general economies of scale in components and technologies. For SNG, IP’s two-way communication also brings benefits, making it possible to conduct real-time interviews in the field, for example, without any terrestrial links, share files and add comments or other non-video content to interviews. IP-based SNG equipment also tends to be lighter and faster to set up, using Ethernet rather than coaxial cables, for example, and this is a big advantage for locations such as warzones where equipment often has to be set up and taken short at very short notice. Another technical advantage is that IP brings a range of traffic acceleration tools that help cater for the inherent delay of satellite communication. This all adds up to competitive edge at the news gathering coal face, particularly for live coverage of major breaking events. IP contribution also allows studios and head ends to become totally IP-file based, reducing capital and maintenance costs, while increasing flexibility and reliability.
But, there are migration challenges, which is why most broadcasters will need a transition period during which ASI and IP co-exist. During this time, they can perform the conversion across their contribution/distribution chain all the way to digital archiving and only turn ASI off when that is complete. There are products that support such migration, such as DualFlow from Newtec, which enables SNG IP migration to be performed in stages, and makes use of the DVB-S2 Multistream feature enabling simultaneous transmission of different signal types, especially ASI and IP, without external multiplexing.
The NovelSat NS3 technology can then play its part by increasing video throughput by 28 percent to 78 percent, depending on specific conditions. This builds on the raw 20-percent improvement in spectral efficiency, achieved by reducing roll-off, which is the guard band at each end of a channel to protect interference. In DVB-S2, this guard band is 20 percent of the channel spectral width, which itself was an improvement over the 35 percent of the first generation DVB-S. But, Novelsat says that by exploiting the greater processing power available now, compared with the time over a decade ago when DVB-S2 was developed, it has been able to reduce the roll off band to just five percent at each end of a channel. This accounts for much of the throughput improvement.
But, further techniques developed by NovelSat have built on the spectral improvements, with the bigger video capacity gains closer to the 78 percent being achieved when broadcasters use the wider spectrum 72MHz transponders, where there is greater scope for statistical multiplexing to cut the average bit rate of each channel. This may be less relevant for SNG, but even a 28-percent improvement in capacity is significant.
At the same time, NovelSat has made much greater progress on raw data rates.
“Three weeks ago, one of our customers in California measured our data rate at 357Mb/s on a 72MHz transponder,” said Furstenberg. “When we asked them what the best was they could measure using vendors, they told us the best was 168Mb/s under similar conditions.”
Furstenberg added that NovelSat was aiming to boost data rates a further three times, and deliver 1Gb/s over 72MHz transponders by the end of 2012.
“We believe this will be very important for satellite based Internet services for rural customers,” he said.
