Terrestrial transmission

Released by the DVB Project in March throughput is achieved by employing a network of 100 or so transmitters using a and to be made publicly available in the enhanced forward error correction (FEC) single frequency and so it's potentially much middle of the year, the simple goal of DVB- schemes, such as LDPC schemes, as more efficient that the current network." T2 is to improve on a ten-year old standard opposed to just BCH convolution used in Despite the benefits on offer, Mike and put terrestrial broadcasters in the 21st DVB-T. It is essentially the same LDPC that Brooks, head of R&D at Arqiva, sounds a century. It is the second generation digital DVB-S2 introduced to improve DVB-S. This note of caution. "Nothing comes for free; terrestrial transmission (DTT) standard, suggests around a 2dB improvement, which you can't get something for nothing and if succeeding DVB-T, which was developed in can be converted to capacity either through we're changing parameters we need to 1995 and is used by most of the DTT using less error correction or moving to a understand what those impacts are. There implementations around the world. higher order constellation, such as are consequences for doing that which The common consensus is that mass- 256QAM (DVB-T allows up to a 64-QAM mean that, in the same way as DVB-T, you market DVB-T2 products will be available constellation per carrier). have to pick and mix from the suite of A look inside DVB-T2

The new standard will empower DTT broadcasters and help them fight back against competing platforms, but many compromises are involved, says Goran Nastic

by mid-to-late 2010, although prototypes As Darren Fawcett, chief technologist at options that will be available within the T2 are expected to emerge in 2009. Chip Pace Micro, points out, FEC schemes spec. The big thing about the DVB vendors are said to be working on it ultimately improve the robustness of the standards is that they allow flexibility - they already, and simulating the options in their signal, but it's down to the broadcaster how are a toolkit of options that enable you to programmable arrays. they choose to use LDPC. "They can use it trade robustness, and hence the number of The headline figure is that DVB-T2 to improve the resilience but not choose to transmitters, against the data throughput. promises at least a 30% improvement in exercise higher order modulation. Given the And that philosophy is continuing with T2." capacity. According to Peter MacAvock, drive is to increase the efficiency and executive director of the DVB Project Office, capacity of the network, it's likely they'll A competitive platform? simulations have shown that up to 60% move to higher order modulation." DTT HD services are the main driver behind capacity improvement is attainable, although Significantly, there is a 32k carrier mode, the specification, and it is likely that the exact performance gains depend on the in addition to 2k and 8k for DVB-T. transition to DVB-T2 will be linked to roll- parameters that are chosen. Significant According to Simon Gauntlett, technology out of these services. This makes innovations of the new specification director of the Group commercial sense. As Mathias Leutiger, compared to DVB-T include new forward (DTG), the benefits this option brings is the head of product marketing of broadcasting error protection, high-order modulation ability to use single frequency networks T&M products at Rohde & Schwarz, points modes, variable modulation and coding of (SFN) and increased robustness to impulse out, one of the biggest challenges for a services and increase in the number of interference. "This makes the 32k mode successful introduction of new technologies OFDM carriers. extremely important as part of the DVB-T2 is adding value for and being accepted by Principally, the increase in data spec. The UK could in theory be covered by TV viewers. "Only when they perceive a page sixteen www.csimagazine.com Cable & Satellite International march-april 2008 Terrestrial transmission

To MIMO or not to MIMO? “Simulations have shown that up to Whenever a MIMO (multiple input 60% capacity improvement is multiple output) approach is used, it is attainable, although exact reasonable to expect an improvement in robustness and a reduction in performance gains depend on the destructive interference in SFN. parameters that are chosen.” Arqiva has, in fact, been working with the BBC and National Grid Wireless clear advantage will viewers be willing to average bit rate for HD in H.264 in a (NGW) on a trial in Guildford looking at accept the added expenditure." statmuxed environment by 2010, you are the benefits of MIMO and says there will So while DVB-T2 doesn't mandate looking at maybe five or six HD services in undoubtedly be capacity increases; in MPEG-4, there are good reasons for a multiplex. For some countries, that might some cases it effectively doubles the combining the two to ease transition. be enough. capacity of a single channel. “What’s being considered for the delivery of “You can also pack many more SD The technology, however, falls foul HDTV is an MPEG-4 box so you may as channels through with T2 and H.264. If of one of the commercial requirements well add DVB-T2 to make that jump as far your proposition is payTV, such as Malta, of T2, which stipulates that the T2 as possible and avoid lots of mini Netherlands and Sweden, then it will broadcast will be compatible with switchovers. That’s why the tie between definitely be a technology that you will want existing DVB-T (and by implication DVB-T2 and MPEG-4 is made. It makes it to use. For example, we see a very clear analogue TV) domestic installations, more attractive to the consumer, as you split in the countries that want to do payTV ie single antenna, single downlead. can’t really sell technology for technology’s in terrestrial in that most are using MPEG-4 The general consensus, driven sake,” says DTG’s Gauntlett. even though the STB costs are currently a by the commercial module, is that For this reason, it is likely that all T2 little higher. In the public service broadcast existing antenna system in peoples’ boxes will be H.264 based. It’s a matter of model, which is more prevalent in DTT, the homes shouldn’t be disrupted, bundling new technologies together at a majority are MPEG-2 and less aggressive in and these legacy issues preclude convenient point, with a new consumer the amount of channels they are trying to a MIMO type implementation. device that has enough of a value pack into a multiplex. Ultimately, it is the There is an option to deal with proposition for them to change business model that drives the technology MISO (multiple input single output), and The question is whether DVB-T2, even choices, but MPEG-2 and MPEG-4 AVC there are techniques such as Alamouti hand in hand with H.264 encoding, will be remain critical in terrestrial,” he adds. schemes which could allow that to enough to make DTT a viable competitor to In the UK, a splinter group from the DTG happen so those are incorporated, cable and satellite, particularly with just one proposes to use the spectrum efficiency of according to Arqiva. multiplex as proposed by Ofcom in the UK? SFNs, claiming Ofcom’s proposals could There is work to enable future According to Tim Sheppard, senior seriously compromise DTT’s long term development of a MIMO technology to business development manager of viability They see eight HD channels as the be allowed, but MIMO will not be broadcast at Cisco, how many HD channels minimum level to keep DTT competitive, incorporated from Day 1. are possible varies hugely by country, but a and argue that up to 40 HD channels are realistic target would be at least four HD possible on DTT using this approach. In IPR issues channels in a terrestrial multiplex. Of addition, it would also free up spectrum for Given the problems the DVB had with course, MPEG-4 encoders continue to get other uses, such as portable TV, as can MHP, any potential property rights better as well, he notes. “Also if you put already be found in SFN areas like Germany. issues have to be considered upfront. four into a multiplex you can take advantage It is worth pointing out here that DVB-T2 Indeed, MHP kicked off a whole of statistical multiplexing between the is not exclusively about HD. The debate in reinvestigation of DVB’s IPR policy. encoders, meaning that one can go as high the UK is mainly HD-driven, and As a part of the DVB-T2 work, a new as five or six HD channels in a mux leading significantly, that is where most of the approach to the existing rules was to a position where you have as many urgency seems to be coming from the UK. suggested in that an early formation of H.264 HD channels as you used to have in Elsewhere, interest is in ultra mobile the patent pool was being encouraged MPEG-2 SD.” (portable TV in trains, cars etc), as well as so that any IPR issues would come to A similar argument is made by Simon SD capacity, according to DVB’s MacAvock. light well in a advance of anybody Frost, business development director at deploying a network. Tandberg. “The 30% increase in bandwidth The aim is to avoid licensing issues gives you around 30Mbps to play within an down the line. 8MHz RF channel. Taking 5-6Mbps as the page eighteen www.csimagazine.com Cable & Satellite International march-april 2008 Terrestrial transmission

encapsulation overheads. One of the Time frequency slicing evaluation areas was to look at a native IP TFS is a technique that allows services to transport layer that could exist inside T2, so be spread over more than one multiplex, that you may be able to handle IP data maximising the benefits of statistically As some sort of guide to the level of more efficiently and easily within the overall multiplexing more services, a harder issue interest, MacAvock points to the fact that transport. It may apply to even transport when moving from SD to HD. As with while some 30 companies formed a subset layers of interactive applications perhaps MIMO, the concept of TFS is extremely of actively involved members in DVB-S2, that have previously been carouselled. compelling, but it looks like it has not made this number is closer to 60 with T2, with There is, however, no shift in concept that its ways into the original specification given Russia, China, the US, and Korea to name the MPEG TS is dead and everything will be its broader complexity from a chipset point but a few all involved. streamed in IP,” says Frost. of view. The compromise decision in the Although DVB-T2 does have the tools to This brings into question whether DVB-T2 committee is to have the TFS as an enable ‘mobile’ TV better than DVB-T, T2’s terrestrial broadcasting will eventually adopt optional part of the spec. commercial requirements are aimed an all-IP approach that includes Tandberg’s Frost believes because the primarily at rooftop aerials, and the work transmission. Arqiva’s Brooks acknowledges availability of silicon in the tuner and the that supports handheld mobile phone type that IP does provide a common layer across commoditisation of the pricing are critical TV is outside the scope of the T2 work, all sorts of platforms and makes distribution factors, TFS is unlikely to feature in according to Arqiva’s Brooks. “There is an and contribution circuits easier to commercial products, at least for the time initiative within the DVB called Next- implement. “So I can foresee a situation being. “If it hasn’t made it in as a Generation Handheld (NGH), which will be where we may see an IP infrastructure mandatory profile there isn’t going to be a looking at this aspect,” he says. being deployed in the future. That said, I lot of interest in adding that.” Tandberg’s Frost notes that T2 had the have not heard of any specific plans to For Luc Ottavj, chief scientist officer and option of a mobile focus, but there was make everything IP-based.” co-founder of UDcast, typical questions to general lobby against confusing it with an Even Sheppard’s Cisco agrees that an all- be checked are what the exact overhead is emerging DVB-H market. “Having said that, IP approach isn’t necessary, despite some for TFS compared to the statmux gain, and a DVB-H and T2 mix could be interesting.” inherent benefits. “I’m not sure it’s - due to the network plannings - how many necessary to remove the TS from the core UHF channels having exactly the same The road to IP video. But you can imagine services like footprint can be TFS-grouped in a network. DVB-T2 further cements the arrival of IP in push VoD and interactivity besides the core These are mere semantics, however. In the broadcast industry by including GSE video and audio, which would logically reality, it requires having more than one (Generic Stream Encapsulation), an make sense to go over IP because that’s DVB-T2 multiplex, which doesn’t fit with the evolution from the traditional method of the format that’s now contributed in, current Ofcom proposal. putting IP over the MPEG Transport Stream distributed in and browsed in.” CSI understands that while a number of (TS) over physical layer. The use of GSE - Cisco commissioned an independent companies were known to be pushing for while not mandatory - contributes to the study that forecast that 65%+ of spend in this technology to solve their transmitter 30%+ gain in capacity, especially when three years time on video networks will be problem, TFS has been dropped due to the applied to IP-based services. IP-based, and Sheppard is confident that ambitious timescale of the Ofcom proposal “IP over MPEG TS has never been that some of that convergence story will leak and that the BBC, the standard’s champion, efficient; it’s a little clunky in terms of over into the end transmission side. CSI feared that including this method would delay deployment. DVB-T DVB-T2 These developments have led to Error correction BCH LDPC accusations that DVB-T2 has been modified Modulation QPSK, 16-QAM, 64 QAM Addition of 256-QAM to suit UK interests. Because parts of the FFT sizes 2k and 8k Addition of 32k mode Uk are already concerned and nervous that Physical/link MPEG- 2 TS MPEG-2 TS or IP Baseband frames DVB-T2 might impact the DSO, it arguably layer interface would have been better to implement the Bandwidth 5, 6, 7, 8Mhz 5, 6, 7, 8Mhz technology following DSO’s completion. Multiplexing Single TS per Multiplex Potential for bonded UHF channels With this in mind, despite its many Transport ~24Mbps ~32.4Mbps (44Mbps+ with MIMO) advancements, it is in some ways hard to rate/RF escape the conclusion that DVB-T2 could Codecs MPEG-2, MPEG-4 AVC, VC-1 MPEG-2, MPEG-4 AVC, VC-1 have been much more than the sum of its Source: Various; CSI parts, at least in its first incarnation.CSI

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