Aerial engineer

Terrestrial HD broadcasting gets a World Cup boost

World Cup coverage will showcase the terrestrial high-definition broadcast standard DVB-T2, according to E&T.

It's Friday 11 June 2010, 2:59pm in Johannesburg and you could cut the air with a knife. The Jabulani, official ball of the World Cup, is resting on the centre spot of the Soccer City pitch. Hosts South Africa are on one side of the pitch, Mexico on the other. A capacity crowd of 94,700 - to say nothing of the billions more watching the scene on their TVs - knows that in about 60 seconds the peace that the ball has been enjoying will be shattered for the following 30 days.

One month - that's how long fans will have to wait to learn which of the 32 participating nations will lift the football World Cup. Yet one of the competition's winners has already been decided: it's Team Great Britain, from Europe.

Confused? No, it's not the Summer Olympics and yes, England is the only British team to have qualified for South Africa 2010. But the title goes nonetheless to England, Scotland and Wales (unlucky Northern Ireland misses out this time), the only nations where the World Cup will be broadcast in high definition using the DVB-T2 standard.

The brand new technology (and acronym, which stands for Digital Video Broadcasting - Second Generation Terrestrial) was conceived by the DVB Project as the first major upgrade of DVB-T, which is now used in more than 35 countries to transmit digital terrestrial television (DTT).

Just as the 2006 World Cup in Germany was used as the launch pad for the UK debut of HDTV services on cable and satellite networks, South Africa 2010 has been targeted by Freeview as the event to introduce HD to the UK DTT sector.

The fact that a full four years separates the launch of HD on the pay-TV and free-to-air platforms has less to do with the funding model of each platform, and more to do with the physical limitations within which they operate.

Bandwidth, not money, is where the problem lies. Satellite and, to a lesser extent, cable operators have enough bandwidth at their disposal to add multiple HD channels to their bundles without having to worry too much about sacrificing any standard-definition (SD) channels in the process.

Terrestrial operators can't afford such a luxury. In the UK, DTT is currently provided using six multiplexes. Two of them transmit using the 64-way quadrature amplitude modulation (64-QAM) scheme, which enables a capacity of 24Mbit/s on each multiplex. The other four transmit in 16-QAM , at 18Mbit/s per multiplex. So the total capacity available on Freeview is 120Mbit/s.

Considering that each SD channel encoded with MPEG-2 video compression requires a bit rate of between 2 and 4Mbit/s, an average of 40 SD channels could - and have been - packed into the UK's DTT network.

In 2006, when Sky and Virgin Media (then Telewest) launched their first HD services, the minimum bit-rate required to transmit a single HD channel was 18Mbit/s. Had Freeview decided to follow suit and launch HD at the time, the operator would have had to eliminate six existing SD channels for each new HD signal it carried. The maths just didn't add up.

Scoring first

So what has changed? Three things are beginning to make it possible for multiple HDTV streams to coexist with the usual Freeview programming.

The first is the progress of the digital switchover in the UK. The plan, which aims to switch off all analogue terrestrial TV transmissions by 2012, is progressing on schedule. On 31 March 2010 Wales became the first UK nation to go all-digital, and four other E F regions (Border, Granada, West and West Country) having also made the switch now.

At every site where analogue TV transmitters are turned off, Freeview automatically gains an extra 24Mbit/s of bandwidth, because all six multiplexes are converted to the 64-QAM scheme.

The second is due to the DVB-T2 standard, which brings with it an improvement in spectral efficiency of up to 60 per cent compared with DVB-T, according to Peter Siebert, executive director of the DVB Project.

To achieve this, DVB-T2 adds support for 256-QAM. While multiplexes operating on this mode can boost their capacity to 40Mbit/s, the higher-order constellation means transmissions are also more susceptible to interference.

But DVB-T2 compensates for this with a more powerful error-correction scheme. 'While in DVB-T we were using convolutional codes and Reed-Solomon codes, DVB-T2 employs LDPC (low-density parity-check) error-correction codes in combination with BCH codes,' says Siebert. 'These codes are significantly better than those used by DVB-T equipment.'

The third major factor contributing to the advent of HD on Freeview is the relentless progress that has been made in video compression. 'Three years ago when we were starting to introduce HD services on DVB-T in France, an HD channel required twice as much bandwidth as it did six months ago,' says Nicolas Laroche, head of engineering at set-top box manufacturer Pace France.

Worldwide, the preferred compression standard for HDTV is H.264 (or MPEG-4 Part 10). At the moment, a modern MPEG-4 encoder will enable an HDTV channel to be broadcast at 10Mbit/s. 'So you can put four HDTV channels in one multiplex of 40Mbit/s,' says Roland Faivre-Duboz, a Pace France product manager.

Here's how the three elements interact to introduce Freeview HD. First, at each site that has been switched to digital broadcasting, the extra 24Mbit/s of network capacity is used to vacate Multiplex B and move this content into other multiplexes. Then Multiplex B is upgraded to DVB-T2, giving it 40Mbit/s of bandwidth. Finally, using MPEG-4 compression, four HD channels can be broadcast.

At the receiver end

The first DVB-T2 transmissions started in December 2009, carrying three channels: BBC HD, ITV1 HD and 4HD (S4C Clirlun in Wales). A fourth HD signal should be launched in 2011.

With the BBC and ITV showing practically all the World Cup matches, Freeview has promised - and claims to be on track - to have half of UK homes covered with DVB-T2 in time for the start of the tournament. As well as the regions that have already switched over, an 'early rollout' programme will extend coverage to the London, Newcastle and Tyneside, Leeds/Bradford, Birmingham and Glasgow conurbations.

The rest of the UK will have to wait until the London 2012 Olympics or the Brazil 2014 World Cup to experience a major sporting event on Freeview HD.

Of course, existing Freeview users who want to enjoy the World Cup in HD will first need to make sure they've bought either a new DVB-T2 set-top box to go with their HD-ready TVs, or a new HD-ready screen with an embedded T2 decoder.

According to Adam Thomas, media research manager at Informa Telecoms & Media, the very high installed base of first-generation DTT equipment in the UK may pose the greatest challenge to consumer take-up. 'A large segment of the public will be unwilling to make another equipment purchase until it becomes necessary, so restricting short-term penetration of the technology.'

Having said that, Thomas expects interest in the World Cup to act as a catalyst for the first serious wave of early adopters. Set-top box and integrated digital TV manufacturers have been in a frantic race to get their first-generation DVB-T2 products to market before the start of the Cup.

At the time of writing, with just over a month to go before the inaugural match, four receiver brands (Bush, Ferguson, Humax and Metronic), as well as three TV brands (Bush, Panasonic and Sony) had managed to get their kit on to shop shelves.

Other manufacturers have announced they'll be joining the fray. Pace is one of them. The West Yorkshire-based company is launching two Philips-branded DVB-T2 products in May.

Laroche is particularly proud of the very low power consumption he says Pace has achieved on both products: 'The zapper consumes less than 5W (less than 1W in standby), while typical power consumption of the PVR is 12.5W (less than 0.5W in standby).'

Unlike DVB-T receivers, which operate by decoding an entire multiplex of programmes, DVB-T2 transmissions can be tailored so that receivers only decode one programme at a time, saving power.

World cup recordings

With 99 per cent of new TVs sold in the UK now incorporating a DVB-T chip - and the trend starting to be replicated with Freeview HD integrated digital TVs - how sustainable is the market for DVB-T2 set-top boxes?

'Initially, there is a very good opportunity for us,' says Pace's Laroche. 'If you bought a nice LCD or plasma HD-ready TV two years ago, for which you paid £1,000, what would you do if you wanted to watch Freeview HD? Would you spend another £1,000 to replace your screen? Or would you rather invest in a DVB-T2 set-top box?'

He has a point. In the long run, though, Pace admits that Freeview HD-compatible screens will erode the market for standalone T2 receivers. However, Laroche believes TV manufacturers won't compete with Pace when it comes to PVRs: 'Our belief is that HDTV is strongly related to the capacity to record. We've estimated that PVRs for us will be at least 50 per cent of the DVB-T2 market.'

Asked whether he expects the three HDTV channels currently available on Freeview to grow in the future, Laroche is in no doubt: 'For sure, in five to ten years we can imagine all channels being full HD.' He says his prediction is based on the assumption that MPEG-4 coding technology will continue to improve, allowing the same level of picture quality to be transmitted over an ever-reducing amount of bandwidth.

A report commissioned by the BBC Trust and published in 2007 supports this view. The study, titled 'Advice on spectrum usage, HDTV and MPEG-4') predicts that 'in 2012 an HDTV MPEG-4 service will require between 6 and 13Mbit/s depending on both the quality level required and the extent of improvement in MPEG-4'.

By 2017, the report's authors expect this figure to shrink to between 4 and 7.5Mbit/s. Should such predictions prove correct, DVB-T2 technology would make it possible for Freeview to move its entire programming schedule to high definition.

Do Sky and Virgin Media need to worry, then? Not necessarily, thinks Thomas: 'Despite the greater efficiency of DVB-T2, spectrum limitations will still restrict the scope of the content offering that can be provided. This means [Freeview] will not provide anything near to the HD output of pay-TV operators.'

The analyst says that, by the end of this year, about 4 per cent of UK DTT homes will own DVB-T2 receivers. 'Looking further ahead, we expect more than a third of UK DTT households to take it by 2014.'

That would be four million British families ready to watch the Jabulani take another battering over terrestrial HD, this time at the Brazil World Cup.

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