Satellite uplinks have endured the most adverse environments, war zones and regions hit by natural disasters, where there is no infrastructure at all. They need to be compact, lightweight and close to indestructible, yet easy for a small crew to operate in an environment where there is no support. To address broadcasters' needs, the manufacture and design of satellite uplinks are changing.
Light, portable antenna systems
We have come a long way since the earliest satellite uplinks. They were made with aluminum reflectors, and the cases were made of aluminum honeycomb. Nowadays, most antennas are made from carbon fiber, the same material that is commonly used in the aircraft industry and in the construction of Formula One racing cars. The carbon fiber manufacturing process is intensive and expensive, but the material is unique because it combines ultra-lightness and strength. This same material is generally used to manufacture the antenna's reflector, although frequently other parts are made with the same material to maintain overall lightness. One of the lightest 1m antennas on the market weighs 22kg. This lightness is achieved by making almost every component out of carbon fiber.
The fastest route to a breaking news story overseas may involve transportation through commercial airlines, which means that the biggest constraint on the manufacture of satellite uplinks is the airline's IATA baggage restrictions. The weight limit remains at 32kg, and the maximum dimensions of any baggage should be less than 158cm (length, width and height). These limits are being enforced more strictly, and airlines, which might previously have been more flexible on baggage limits, are now requiring equipment to be repacked in order to comply with the guidelines.
Often, it is the smaller flyaway — which arrives first at a news location — that gets the first video pictures. Here, the advantage of being able to get on the next available flight with the equipment is imperative. If there is to be a continuing news story, broadcasters will normally follow the initial flyaway with a larger, more permanent installation.
Although the packaging of the antenna is crucial, the rest of the system, including the electronics, must also be considered. Traditionally, systems have been built around 1U high, 19in rack-based equipment. Some manufacturers, recognizing that this may not be the easiest form to transport, have introduced smaller, modular units in robust environmental packaging.
Ka-band and multiband equipment
Currently, manufacturers produce several products to cover the range of frequencies that broadcasters require. For satellite uplinks, the common frequencies range from C band (6GHz), X band (8GHz), Ku band (14GHz), DBS band (18GHz), Ka band (30GHz) and the new Q band (47GHz).
Traditionally, satellite uplinks for video broadcast use C band and Ku band. C band is predominantly used in high rainfall regions, although the latest generation of satellites does offer high-power Ku band operation. The Ku band in Europe still has a reasonable amount of capacity available, although in North America and parts of Asia, bandwidth is in demand.
New satellites operating the Ka band have been launched, and as a result, there are more inquiries for equipment in this relatively new band. Initially used for military applications, the capacity available in the Ka band is now destined to be the answer for the increased requirements for HDTV, especially in the USA.
By 2007, satellite providers plan to implement MPEG-4 AVC via Ka-band satellite in three orbital slots to offer more than 1500 local HD channels and more than 150 national HD channels and other advanced programming services.
Another way for manufacturers to meet broadcasters' demanding requirement for equipment that can use all the available frequencies is to offer multiband equipment. This is particularly important for flyaway systems, which need to have the flexibility to work well in all corners of the world. They require the ability to adapt to local climate conditions and to be able to use whatever satellite coverage is available.
Today's antenna systems have to be easily configured for the different operational frequency bands available. The concept of a cartridge feed system provides the operator with multiband capability, and C-, X-, Ku- and Ka-band systems have been introduced. Vehicle-based antennas also have to offer this multiband capability.
Besides changes in how the antennas are designed and made, there are important developments in the features and capabilities of the newer uplinks that will really benefit broadcasters.
Satellite identification and acquisition
Manufacturers are working hard to develop more accurate satellite identification. With satellites positioned at every two degrees in the sky over the USA, there is a risk of a rogue transmission causing interference. In fact, interference caused by misdirected satellite signals is a major problem for broadcasters in certain parts of the world. This is difficult to regulate because often the sender of the signal cannot be identified. Encoder manufacturers are further addressing this issue by inserting identifiers into the encoded data stream. The identifiers will indicate where the signal is coming from.
Traditionally, this process required a skilled operator to find the right satellite with a spectrum analyzer, align the antenna correctly and peak the azimuth and elevation. This highly skilled process, which can be quite daunting to the untrained operator, has forced manufacturers to consider working on ways to automatically find satellites.
The majority of satellites have unique beacons that assist the operator to identify the satellite. These can be used by motorized antenna systems for automatic satellite location. Where there are no beacons available, relative adjustments can be made from known beacons, with final confirmation by decoding the relevant channels.
Satellite network IDs, an identifier in the encoded data stream, also can be extracted and used to confirm the correct antenna positioning.
New signal processing technology
Until recently, the way to transmit broadcast-quality SD contribution over satellite uplinks was to use an MPEG-2 encoder, modulate the encoded signal using DVB-S, upconvert and transmit. An uncompressed SD signal is about 270Mb/s. The current MPEG-2 compression for broadcast-quality for contribution would deliver a data rate of about 5Mb/s. The data rate is one of the major factors in determining the cost of the satellite uplink operation.
As everyone knows, HD is here. It is in regular use in the USA, Australia and parts of Asia. HD brings new challenges, mainly because of the increased required bandwidth. The industry has responded with a technological leap both in the encoding standard — by moving to H.264 (MPEG-4) — and with a more efficient form of modulation — DVB-S2. Both these standards are highly processor-intensive and have only really been realized in their present compact form through advances in semiconductor technology.
Typically, an HD signal has about six times the data of an existing SD signal. Uncompressed, an HD signal is about 1.5Gb/s. MPEG-2 encoding reduces this to about 25Mb/s. Using MPEG-4 encoding can half the rate to about 12Mb/s.
DVB-S2 modulation is the latest satellite transmission technique for DVB. The improvements made to optimize the way in which the forward error correction is estimated appear to be so near the optimum that it is unlikely that there will be a need for further developments. It is estimated that using DVB-S2 broadcast services can benefit from its introduction with a bandwidth saving of at least 20 percent to 30 percent or, of course, a comparable increase in picture quality. This means that our 12Mb/s MPEG-4 compressed data stream can be reduced to 9Mb/s — not too different from the existing SD rates.
Both MPEG-4 and DVB-S2 units are available and will be more pervasive over the next couple of years. Satellite uplinks will undoubtedly embrace this technology.
Sending video over Internet Protocol (IP) using modems is also a longer-term option. The bandwidths required will be similar because the information transfer will have the same data content. The requirement to guarantee that the picture gets through still means much of the current and foreseeable infrastructure will be based on a point-to-point connection using the current technology. Undoubtedly, IP operation will expand and improve as the bandwidths get wider and more reliable.
Getting news in minutes
Today, setup time is paramount; customers want to know how long it will take to set up their link so that their news report can begin. With the latest equipment, this might be as little time as 15 to 20 minutes to assemble and align to the right satellite.
The important features to look for on new uplinks will be motorization, multiband operation, intelligent lightweight packaging, automatic identification of satellites, encoding and modulation options. It is feasible to combine multiple components, such as the encoder, modulators and upconverters, into one unit with a high-power amplifier (HPA), and this might all be controlled by a single unit.
The use of a wireless camera system with a satellite uplink adds another degree of freedom for the cameraman to capture those live action moments. Wireless cameras give that initial short hop, of anywhere between 1km to 5km, to the satellite uplink, which then beams the signal back to the central production area. Although presented live, there are, of course, transmission delays due to the length transmission path and encoding electronics. However, these can be reduced by the use of low-delay encoding techniques. Recent coverage of the war in Iraq has seen interviews and events conducted on the move, live on-air, with true broadcast picture quality. This is something that would have been a nightmare to produce a couple of years ago.
There are different ways to get the picture back. Telephone modems, using the DVB-H standard for handheld devices, all currently provide live but sometimes lower-quality coverage. Undoubtedly, these technologies will improve.
However, broadcast-quality terrestrial wireless coverage — such as cellular diversity systems, whereby live TV coverage from a wireless camera can be captured over a small metropolitan area — gives the operator another option and is becoming more popular. These systems preclude the use of satellite uplinks; however, they would only be viable in areas of major interest and would only work when there is a suitable fiber communications infrastructure, which is not always the case.
But when it comes to the crunch, when there is no network, no electricity, no infrastructure, no fixed communications and no order, the only way you can still guarantee to get your picture out is with your satellite uplink.
Roger Davies is the engineering manager of Advent Communications, a division of Vislink Communications.
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