DISHING IT UP -- DIGITALLY...

INTRO

If you’ve just got used to the idea of television programmes beaming into your home from orbiting satellites 36,000 kilometres above the earth then hold on to your hats, digital satellite broadcasting is about to start, and you ‘aint seen nothing yet!

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In keeping with tradition we’ll begin with the bad news. That shiny new, state-of-the-art satellite system you’ve just had installed is now technically obsolete. The good news? Don’t panic you’ve got two, possibly three years to save up for the new equipment, that has consigned your system to an early trip to the scrap heap. More good news, you won’t have to replace your present dish and LNB, probably...

So what’s going on, and why didn’t anyone warn you that this was going to happen? Satellite TV is going digital in 1997, though it could be 1998, no-one is really certain because they’ve only just figured out how it’s all going to work, and there’s a still lot of important details to be settled. But who are ‘they’ and what’s this digital business all about? They are the usual mix of national and international government organisations, broadcasters and commercial interests. To cut a very long story short, they have a cunning plan, to overcome overcrowding  on the airwaves, that was threatening to develop in a major problem for international telecommunications and broadcasting early in the next century.

At the moment pretty well all TV and radio transmissions, whether from land-based terrestrial transmitters, satellites or via cable networks, rely on analogue broadcasting technologies, that use up large chunks of the radio-frequency spectrum. Digital transmission techniques make far more economical use of this finite resource, by sending information as streams of data, lots of little blips that take up comparatively little space, as opposed to big, noisy analogue signals that wobble about all over the place. The trick has been to cram in the vast amount of information required to create a video image, and high-quality stereo sound, into the narrow confines of a digital data stream. Making the data stream run at a faster rate has helped but there are limits as to how quickly these systems can operate. The core development, that has made digital video broadcasting (DVB) viable, is data compression.

COLD COMPRESS

You’re going to be hearing a lot about something called MPEG-2 from now on. MPEG or the Motion Picture experts group, is a body set up by the International Standards Organisation (ISO) to develop the encoding systems and algorithms that are needed to convert video information into a compressed digital form. The MPEG-1 compression system is widely used by the PC and multi-media industry to handle video information within computers and computer software, however picture quality is not so hot, certainly not good enough for serious broadcast applications, which is where MPEG-2 comes in. MPEG-2 is now the agreed standard for DVB in Europe and quite a few other places, including Australia. The USA have adopted their own home-grown system called DSS (digital satellite system) which uses the DigiCipher II compression system.

Confused? Well, for once you needn’t be because it looks as though we’re going to be spared yet another formats and standards battle. As both systems operate within the digital domain they are not totally incompatible, in any case there’s unlikely to be any significant overlap in services, at least as far as consumers are concerned. There was talk of a major US broadcaster attempting to start up a proprietary digital STV service in Europe but that story has gone quiet lately and the threat seems to be receding. Don’t get complacent though, there’s still plenty of if’s, but’s and maybe’s that promise to muddy the already murky waters.

We’ll get to those in a moment but first it’s worth briefly touching on how digital compression systems work, and what effect they will have on picture and sound quality. The central premise in video compression is that there is comparatively little difference between adjacent frames in a TV (or movie) picture, so rather than convert each individual frame into digital data for transmission, the system concentrates on processing the parts of the picture that change, from one frame to the next.

All kinds of clever tricks have been devised to do this job, and the end result is that video compression systems like MPEG-2 and DigiCipher II can reduce the amount of information in a television picture by a factor of four or five, with little or no noticeable effect on picture quality. To put some numbers on that, an uncompressed colour TV pictures contain up to 30 megabytes of information per second; after it’s been through an MPEG 2 processor the same picture has been reduced to just 6 megabytes/sec. The really clever feature of this system is that the compression rate can be continuously varied, according to the content and complexity of the image, so it’s possible to get a good picture with data rates as low as 2 Mb/sec. Of course, none of this need concern the viewer, digital satellite receivers will still be bland-looking black boxes, and in the early days at least picture quality will be about the same as it is today, so why bother?

DIGITAL BENEFITS

There are a number of good reasons for going down the DVB route, the most important one for the viewer will be a dramatic -- and we mean dramatic -- increase in the number of available channels, from the dozens we have at the moment, to hundreds, possibly more than a thousand channels within a few years. That’s because digitally encoded and compressed TV signals take up much less space than analogue signals. For example, each of the current Astra satellites have 16 transponders, one for each analogue channel; theoretically it is possible to transmit up to 18 digital TV channels from each transponders, though in practice there’s likely to be a lot less than that, additional room or ‘bandwidth’ will also be required for multiple audio channels, digital radio and other forms of digital data, which we’ll look at later on. Nevertheless, it’s conceivable that the next generation of Astra satellites will carry in excess of 100 TV channels each, add that to the three or four new TV satellites being launched each year and a thousand TV channels by the turn of the century is not impossible.

DVB signals won’t necessarily produce better pictures, at least not in the short term, though they do provide a speedy route for broadcasters into widescreen and high definition TV. The technology exists, it’s more a question of whether or not we’ll be willing to pay for it. The more immediate benefit is that DVB signals will have a greater immunity to fading and interference, and we should at last see an end to the dreaded ‘sparklies’ on satellite TV pictures, every time it rains. It should also be possible to use smaller antennas, no-one is committing themselves to actual sizes just yet but it’s possible that DVB dishes could be less than half the size of the ones we use today, for analogue STV broadcasts. There should be a big improvement in sound quality too,  most experts agree it will be comparable with CD, and there’s enough flexibility in the system to have half a dozen or more soundtracks per channel, so we could have multi-channel surround-sound movies, without the need for additional decoders.

A little further over the horizon is the prospect of using digital satellite channels to carry computer software, which can be downloaded into personal computers and video games consoles. Plans are already afoot to develop a Sega Channel in the US, that will be carried on their DSS system. Users will be able to load games software from the satellite channel, using a modified cartridge connected to a satellite receiver. Microsoft and chip makers Intel have been collaborating with General Instrument in the US to develop a range of interactive multimedia services that can be delivered by digital satellite systems. The LinX platform will allow subscribers with PCs connected to their digital satellite receivers (and a telephone line), to access detailed programme listings, choose from a menu of games, shop from video catalogues, order movies or TV shows from video-on-demand services, carry out personal banking transactions, call up telephone directories, even compete in television game shows, the possibilities are almost endless. Similar systems are under development in Europe and both Nokia and Thomson have demonstrated satellite receivers that have a high-level of interactivity built in, with the promise of full PC multi-media connectivity in the near future.

WHAT’S THE CATCH?

It all sounds too good to be true, so what’s the catch? There’s several, not least the cost, and who’s going to pay for all this wonderful technology. More fundamentally the question that still has to be resolved is how are they going to get us to pay for what we’re about to receive? This comes under the general heading of conditional access, that’s the scrambling and encryption side of things, that controls who sees what. At the moment is seems that we could be in for a repeat performance of the situation that has arisen on Astra, where different broadcasters have adopted a variety of encryption systems. No one really wants to end up with stacks of plug-in decoder boxes and armfuls of smart cards, but that’s the way it could go if there’s no agreements soon. The most optimistic observers reckon that the first system used by a major broadcaster will become the de-facto standard, but if, as many suspect that’s going to be BSKYB, then broadcasters that are unwilling to fall into line and pay Rupert Murdoch for the privilege of using his subscription system, may well go their own route.

That’s a real possibility because the spin-off from this vastly increased channel capacity could be an ‘explosion’ in narrowcasting in the next few years, as Tim Fern, Engineering Manager at Pace puts it. ‘As the cost of leasing satellites transponders falls from a couple of million pounds a year, as they are at the moment, to just a few tens of thousands of pounds for a digital channel, then there’s going to be a massive increase in the number of special interest channels, from fishing to caving’. Rikard Negler of Nokia agrees but he sees other new services quickly soaking up the new channels. ‘Video on demand is an obvious front-runner, where the same movie will be shown across several channels, with the start time staggered so that you’re never more than a few minutes from the beginning’. However, Negler is a little more cautious about when all this is going to happen; ‘There’s no need to throw away your Astra system yet, even if broadcasters like BSKYB do go digital they’ll still be running their analogue channels for many years to come, after all they’re not about to risk loosing millions of subscribers by going exclusively digital overnight’. 

NUTS AND BOLTS

What does this all mean in terms of nuts and bolts, pounds and pence? Hardware manufacturers are all being tight-lipped about the probable cost of DVB hardware, with good reason. There are a lot of unknowns, not least the outcome of the conditional access debate, and the hoped-for economies of scale that will accrue if and when services begin and the system gains consumer acceptance. The only point manufacturers we’ve spoken to will agree upon is that it’s very unlikely digital satellite equipment will ever be as cheap as analogue systems are today.

Will you need to buy a new receiver box, or can existing designs be modified? Again there is widespread agreement throughout the industry and the simple answer is yes, you will have to buy a new receiver, and no, analogue receivers can’t be modified.  Moreover, the chances of anyone developing a ‘dual-standard’ analogue/digital receiver seems remote, considering the costs involved.  Amstrad have optimistically fitted a ‘digital output’ socket to the back of one of their latest receivers, but there’s nothing to connect it to at the moment, or likely to be within the lifespan of that receiver, according to industry insiders. Existing dishes and LNBs are likely to be okay for digital transmissions, though much will depend on what satellites are used, and where they’re located.

Finally, assuming you had a DVB MPEG-2 receiver, what would there be to watch now, and in the foreseeable future. Not a lot is the simple answer, at least not if you live in Europe. There are a handful of test transmissions coming from various satellites, and BSKYB are widely expected to start trial broadcasts from Astra 1D later this year, but it will be some time before scheduled transmissions begin in earnest, at least not until the question of conditional access has been settled. However, that may not be too far off, it’s in no-one’s interest to loose the momentum and delay these services too long. We only need to look back and see how far the technology has progressed to date. Three years ago MPEG-2 and DVB were little more than ideas on paper and rough technical specifications, now look at it!

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DIGITAL ON CABLE

At the moment most of the attention surrounding DVB is centred on satellite TV services and terrestrial broadcasting, but there’s no reason why digitally compressed TV signals cannot be squirted down cable TV networks. Technically it’s a fairly simple matter, though older ‘narrow-band’ systems may not have the capacity to handle more than a few dozen channels. However, the real fly in the ointment is the proven reluctance of cable operators to invest in costly new technologies. This is understandable to a degree, due to the economics of updating and maintaining the thousands of consumer set-top units used in  fixed-link networks. The fact is comparatively few cable networks offer more than a small handful of channels with stereo soundtracks, let alone openly discuss the prospect of advanced multi-channel digital services. Ironically cable TV systems are better placed to take advantage of proposed interactive services as there already exists a fixed hard-wire link that can carry two-way traffic between the broadcaster and the viewer. Satellite interactivity depends on a separate connection by telephone, between the two ends of the transmission chain.

If and when cable operators do decide to go digital,  at some point in the future there shouldn’t be a problem developing suitable consumer hardware, indeed Pace in collaboration with NTL have designed an MPEG-2 set-top decoder for cable operation, called the DVC200. This is going into production shortly, for the Australian market where three digital pay-TV services are due to begin later in the year.

Away from the traditional cable networks there are a host of new possibilities, including the much-publicised Video On Demand and Video Nearly On Demand (VOD and VNOD) systems proposed by BT, which send compressed digital video information down ordinary telephone lines. Similar proposals have been under consideration by the electricity generating companies and the former National Grid, to use mains power lines to distribute television services.

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FIRST VIEWS

With so much uncertainty surrounding the final structure of the proposed European DVB services, and the current scarcity of transmissions, it’s hardly surprising that hardware is a little thin on the ground. At the recent Cable and Satellite trade show held in London, several manufacturers had prototype DVB MPEG-2 receivers on display. These were mostly engineering samples with open-ended specifications, that the companies were quick to assert would bear little resemblance to any production receivers. The exceptions were Pace-NTL and  Nokia.

Pace have collaborated with NTL (National Transcommunications Ltd) to develop a range of four DVB units for satellite and cable applications. The DVB500 is the closest one in design and operation to the kind of  consumer product we can expect to see in the next couple of years. It’s an integrated receiver decoder, fully compliant with the DVB MPEG-2 specification. It is compatible with a variety of conditional access software and has the ability to handle a wide range of data transmission speeds and protocols. It’s fitted with a PC interface that will enable it to receive and process software transmitted in the MPEG data stream. It will also have a multiple PIP (picture in picture) display, for scanning through channels, or acting as a ‘video wall’ , showing multiple camera angles from sports events, for example. Pace-NTL have been quick off the mark because they’ve won a major contract to supply digital receivers for the world’s first commercial MPEG-2 pay TV service, due to come on stream in Australia later this year. The three service providers plan to eventually reach most of the continent’s six million households by the turn of the century.

Nokia have also sought to avoid the spectre of premature obsolescence by giving their first DVB MPEG-2 receiver, called the DVB9500S, a high level of operating flexibility, including a patented system that automatically adjusts itself to changes in data rate. Nokia have also devised an upgradable operating and control software system that can be quickly updated to accommodate changes in transmission format and conditional access, using software downloaded by telephone, smart-card, computer or even over the air, by the satellite broadcasters. Another feature of this receiver is an interactive Electronic Programme Guide or EPG. This is an advanced on-screen display system -- Nokia call it a ‘magazine’ -- that gives the user access to a wide range of programme information that hopefully will be provided by the broadcasters. It’s a kind of supercharged teletext, but with the information presented in a more friendly and useful manner. It has been deliberately designed to resemble the kind of ‘Windows’ graphical interfaces used on computers. Features include a high level of interactivity, with information carefully organised and categorised, to make it more accessible, moreover users will be able to mark programmes they wish to watch, the receiver will then remind the viewer to change channel, or set the VCR.

Neither Pace-NTL or Nokia will commit themselves to showroom prices, other than to say they will cost significantly more than analogue receivers, what a surprise...

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Ó R. Maybury 1995 1104