HD satellite links and backhaul

New high-bandwidth technologies deliver live video from any location to the studio.
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It has always been the intention of SNG manufacturers to make their flyaway equipment as small, light and portable as possible, but HD changed this; now broadcasters need to introduce larger satellite antennas and additional video compression to transport the content.

The trend to HD means bigger antennas and higher power. A pair of 400W amplifiers, or even larger HPAs, gives the added transmit power needed for HD. There is an increasing demand for the larger vehicle-mounted antenna systems, with automatic or manual deployment. To transmit HD means it is getting more complex to operate a truck. More equipment is needed to control the antenna, the amps and the waveguide switches, but these can all be contained in small units and can be controlled by software.

While HD is behind a trend toward larger and more sophisticated equipment, new standards and technologies such as H.264 and DVB-S2 mean that manufacturers can reduce data streams so that broadcasters can do more without necessarily building larger hardware.

This article examines the implications of the new encoding standards, MPEG-4, H.264 and the new, higher order DVB-S2 modulation schemes such as 16 APSK and 32 APSK, all of which will play a role in reducing data and enabling broadcasters to run larger transmissions over limited channels. DVB-S.2 plays a role, helping broadcasters to use satellite bandwidth more effectively by introducing better error correction and allowing more data over the link. Putting H.264 and DVB-S2 together is a powerful combination. It's sufficient enough that, in many cases, broadcasters will not need to invest in bigger dishes and amplifiers to support HD.

At the same time, manufacturers are adding more software into their products. This will enable more efficient working practices and workflows between the truck and the studio. Most of these are IP-related and include facilities such as PC-based software for remote control and editing in the field. The ability to run ASI over IP provides a convenient transport mechanism from the field to the studio, which is useful for file transfers and store-and-forward type applications where there are IP interfaces to the encoders and decoders.

It used to be that the biggest broadcasters set the development agenda. This seems to have changed, and today, the development strategy is up to the manufacturers. Broadcasters are looking to the industry to come up with ideas, and H.264 is high on the wish list of requirements for new equipment.

MPEG-4/H.264?

MPEG-4 is the latest digital video encoding standard for all kinds of video communications from Internet streaming to HDTV broadcast. MPEG-4 and its AVC/H.264 variant delivers big savings in bit rates, likely to be from 30 percent to 50 percent, by using greatly increased compression. Accordingly, it can achieve big improvements in data rates compared with MPEG-2. As H.264 will assure a professional broadcast quality picture, many branches of broadcasting may want to use it in the coming months.

H.264's main appeal lies in its cost-effective use of bandwidth, which makes it desirable for video over wireless, satellite and Internet connections, for HD and SD.

Opinions vary as to whether signal delay will be an issue for live contribution. Satellite transmission already introduces a small delay of half a second or so and another half-second delay might be noticeable in the finished product, but satellite operators know how to work with delays. The perception that H.264 will introduce a delay suggests that it may not be the right choice for live OB transmissions, but manufacturers are working on this, and it's likely that the developments to reduce the delay to manageable levels will be complete in just a few more months.

In a typical current setup, H.264 might be used to transmit in HD, and the playout facility would transcode it back again to MPEG-2, depending upon how modern the TV center is.

While HDTV demands larger satellite antennas, for an operator already owning an antenna, H.264 may provide a way to migrate to HD without needing to invest in a significantly larger antenna, due to the 30 percent saving on bandwidth. If HD can be achieved without a hardware upgrade, this is an attractive proposition in a tough economic period. The cost to upgrade an encoder is much less than the cost of a new flyaway or vehicle-mounted antenna system.

DVB-S2 and its higher order modulations

16APSK and 32APSK promise to reduce bandwidth requirements even further, and the general trend points toward these modulations. 16APSK is beginning to get established in the data market. Both 16APSK and 32APSK are being used in DTH transmission and are getting more common for contribution links.

At the modulator level, higher order modulation is one thing, but other effects may come into play during transmission, such as the linearity of the satellite used, the availability of higher order demodulating receivers and the back-off requirements of the HPA in the uplink terminal.

So while 16APSK and 32APSK may eventually become the norm for HD transmissions, it may not yet be practical to use them over some satellites.

More new developments

IP will be one of the most significant developments in the coming months. Manufacturers are adding new ASI-over-IP input and output interfaces to their broadcast transmission equipment. This will enable broadcasters to connect to IP networks, giving them a different way of working as opposed to the traditional broadcast truck.

The encoder is typically used to compress video-in prior to sending it over an RF link, a satellite link or a terrestrial microwave link. Adding IP functionality and outputs to the encoder on the transmit side means it can become a multipurpose product, which will work for a flyaway or a satellite link, or it can stream live video directly into a network connection in the street such as a fiber network, and operate without a truck. Also, wireless cameras can feed directly into the IP connection, although the speed of the network will dictate whether or not this will be suitable for live broadcast or just store and forward. An ordinary Internet connection will be too variable for live TV, but may serve a useful purpose for recorded news and events.

ASI over IP serves a useful purpose, carrying video from point A to point B although it will not always be suitable for live news or two-way link-ups. The new encoders will work in the wireless newsgathering zones with cellular diversity facilities now operating in around 40 cities, including London, Helsinki, Brussels and Berlin.

Conclusions

At the moment, if MPEG-4 is used in OB and contribution, the signal needs to be converted during another process later in the broadcast chain. Broadcasters are currently equipped with MPEG-2 equipment and are not yet jostling to buy MPEG-4, so although the bandwidth savings are enticing, the migration to MPEG-4 is likely to be gentle.

MPEG-4 will be good for DTH distribution and prerecorded TV. Although some people think that its latency will prevent use in live news, others are starting to think differently. It offers advantages, and there's a trade-off between cost and delay, provided a sensible encode/decode process can be tolerated. Manufacturers will overcome the delay issues, and the cost-savings promised by H.264 will be realized. H.264 may be useful in microwave links too, where it will enable HD transmissions down a narrow microwave link channel, for example, on wireless cameras, which operate on fixed channel bandwidths. This is an example where the trade-off with delay is particularly significant.

As manufacturers add IP outputs to more equipment, encoders will be able to link into cellular diversity sites or microwave links as well as satellite truck operations. And some or all of these transports can be combined together into one operation. So that an end-to-end IP connection from the camera to the satellite dish or the microwave link is achievable, the signal will go by whichever route is provided. It could go from a wireless camera to a receiver. From there it could go to a microwave transmitter on the top of a high building and onward from there to a satellite. Or it might simply transmit directly from a wireless camera into a satellite system.

James Wilcox is marketing director of Vislink's news and entertainment division, which combines Advent Communications, Link Research and Microwave Radio Communications.