Five 3D Channels Likely per Transponder by 2020

It looks like satellite Pay TV operators are going to lead the roll-out of broadcast 3DTV, with BSkyB already committed to a launch later this year and DirecTV tipped to announce 3D plans soon. Based on a technical study undertaken by technology consultancy ZetaCast on behalf of the UK regulator Ofcom, any satellite operators providing this service can expect to dedicate around 10 Mb/s of bandwidth to each broadcast 3D channel by 2020, assuming the most likely of several technology development scenarios.

The ZetaCast authored document, Beyond HDTV: Implications for Digital Delivery, suggests the most probable scenario for satellite 3D providers in 2020 is that a DVB-S3 standard will have provided a 15% efficiency improvement over DVB-S2 to achieve a 52.9 Mb/s bit-rate from a 36MHz satellite transponder. By then, broadcast 3DTV will be possible in 11.7 Mb/s bit-rates for CBR (Constant Bit Rate) services and operators can expect to fit five channels onto a transponder after statistical multiplexing gains.

Besides the most likely technology scenario, ZetaCast offered Ofcom optimistic and pessimistic projections as well. In a worst case scenario as few as two 3D channels would be possible on a 36MHz transponder but it could also be as many as eight by 2020.

Applying the same methodology to digital terrestrial TV, ZetaCast predicted four 3DTV services per 8MHz ‘channel’ of frequency as the most likely outcome by 2020. This is based on the same bit-rate of 11.7 Mb/s (for CBR). It assumes that a DVB-T3 modulation standard has been bought to market but without using MIMO (multiple input multiple output) technology, so achieving a 20% bandwidth efficiency improvement over DVB-T2. Thus the expected bit-rate from an 8MHz terrestrial channel is 43.1 Mb/s.

The optimistic forecast for digital terrestrial is 11 channels of 3DTV in 8MHz of spectrum by 2020. This would go some way to making up for the general scarcity of DTT bandwidth and is based upon a future where a DVB-T3 standard uses MIMO techniques to potentially double bit-rate capacity over-the-air to 71.8Mb/s in 8MHz. There would then be what ZetaCast calls a “virtuous circle” effect of statistical multiplexing, whereby the larger the number of channels, the less bit-rate is required per channel.

ZetaCast explains that MIMO uses two antennas for both transmission and reception, but would require changes to the transmission infrastructure and the home installation, “which would be both very disruptive and expensive to implement”.

For the report, ZetaCast uses its optimistic forecast to mean there is only a 10% probability of this projection being bettered. Its pessimistic or worst case scenarios have a 90% chance of being exceeded. “The year 2020 was chosen for the scenarios since by then stereoscopic [3D] TV is likely to have either matured to become a mainstream service or else been relegated to a niche market that is of little interest to broadcasters,” states ZetaCast.

And we should all be warned. Based on the Gartner Hype Cycle, ZetaCast says 3DTV today displays all the characteristics of a classic ‘Peak of Inflated Expectations’. What follows, according to Gartner’s theory, is the 'Trough of Disillusionment'.

“There is current consumer interest in stereoscopic or ‘3D’ TV in the home, but whether this interest would actually translate into real consumer demand is not yet proven,” the report authors state. “One of the key barriers to delivering “3D” TV services to the home is finding display technology that provides effective stereoscopic rendition in a manner that the consumer would find acceptable for long-term use. In the immediate future, the only viable technologies require the use of some form of glasses, either passive polarised or active shutter glasses. There remains some doubt over how acceptable this will be to the user.”

ZetaCast says that until this demand is confirmed, broadcasters are unlikely to be willing to invest large sums of money in installing infrastructure or replacing existing set-top boxes. “In the short to medium term, there is therefore likely to be a range of different interim solutions deployed by different broadcasters around the world to enable them to test the market. For example, a major constraint on BSkyB at the moment is the need for their initial “3D” offering to be supported by currently deployed HDTV set top boxes. The consequence of this is that each eye receives video with half the resolution of 720p/50 or 1080i/25.”

According to ZetaCast, medium-term implementation of stereoscopic TV is likely to be characterised by a proliferation of different broadcasting approaches whilst broadcasters and consumer equipment suppliers test the market. “During this period, it is likely that the ability for an already deployed population of set-top boxes to decode the stereoscopic signal will be important to many broadcasters, even if that requires a reduction in the video resolution.

“By the year 2020, it is assumed that the consumer demand for stereoscopic TV will be either proved or disproved. If there is confirmed consumer demand, it is assumed that both the broadcaster and the consumer would be willing to invest in the infrastructure and equipment necessary to deliver full 1080p/50 HDTV resolution video to each eye.” The report outlines six ways this might be achieved, leading to bandwidth demands of between 120% and 220% of 2D television.

ZetaCast says the most probable solution for stereoscopic broadcasting in 2020 is to use what is called 2D plus Difference. This is a form of 2D television plus stereoscopic metadata, where either the left or the right eye view is chosen as the 2D video, which is encoded conventionally. The ‘difference’ signal is used to modify the 2D video to re-create the view from the other eye. If delivered correctly, viewers with a 2D decoder should be able to view the 2D video normally using this part of the signal. The difference signal can be compressed using a standard video encoder or some other form of data compression, the authors explain.

2D plus Difference uses 1080p/50 HDTV plus metadata and the required bit-rate is forecast to be 140 – 180% that of 2DTV.

ZetaCast reckons that we should expect the ‘Plateau of Productivity’ - the final stage on the Gartner Hype Cycle - in 2020 for 3DTV. And with commercial broadcast 3DTV services due on air this year, and FIFA and Sony promising to film up to 25 of the 2010 FIFA World Cup South Africa matches in 3D, it is hard to imagine that the 'Trough of Disillusionment' is coming for a while yet.

By John Moulding , Videonet