The DVB (Digital Video Broadcast) group has recruited MIMO (Multiple Input Multiple Output) technology to boost the performance and robustness of mobile broadcast for its second-generation handheld standard formerly approved on Oct. 31.
DVB hopes this will bring in a new era for mobile broadcasting after the failure of most first generation efforts, including its own DVB-H (handheld) standard introduced in 2004. Alongside MIMO, the second-generation standard, DVB-NGH (Next Generation Handheld), incorporates other technologies to boost data rates and improve resilience against transmission errors, including Time Frequency Slicing (TFS), with a single tuner, non-uniform constellations, extended LDPC codes, more efficient time interleaving and ultra-robust physical layer signalling.
But, these are common to most emerging terrestrial broadcast standards, so the inclusion of MIMO has attracted most interest from other regional and terrestrial broadcast groups, including ATSC. DVB confirmed its decision to run with MIMO a few months ago after conducting trials over the last two years, which appear to have shown that the main benefit lies in improved robustness of services delivered to moving devices in cars or trains, rather than increasing the data rate and potential video resolution.
“NGH covers the latest modulation as well as coding technologies and can be regarded as the most sophisticated terrestrial broadcast air interface. Furthermore, it also offers additional operational flexibility, such as different protection for audio and video streams in one service” said Peter Siebert, DVB’s Executive Director.
While meeting the emerging requirements of mobile broadcast, DVB has also set out with the new NGH standard to lie to rest the ghost of its predecessor, DVB-H. Just as elsewhere, with the exception of Japan, most mobile broadcast initiatives have failed, such as Qualcomm’s MediaFlo in the US, so DVB-H deployments have almost all been abandoned. Yet, in the first few years of its existence in the mid-1990's, there was great optimism in Europe that DVB-H would provide a foundation for rapid growth in mobile broadcast.
At first, DVB-H was quite widely deployed in Europe by several incumbent Telcos, including KPN in the Netherlands and Swisscom in Switzerland, as well as a number of smaller mobile carriers. But, crucially, DVB-H failed to attract widespread support from device makers, and one-by-one the operators dropped out, including KPN, even though its Mobiel mobile TV service had started welland attracted 40,000 customers by the end of its first year of operation in 2008.
The most successful DVB-H deployments were in Italy, which was the first country in the world to roll out the technology commercially and had two DVB-H networks, one owned by carrier 3 Italy and the other by wholesaler Mediaset, which in turn leased capacity to the country’s two other carriers, TIM and Vodafone. But, even these services struggled to be profitable, and in May 2012, the Italian Government finally authorized the operators to convert their DVB-H frequencies to DVB-T, so that they could redeploy them for digital terrestrial broadcast.
Apart from lack of device support, factors contributing to DVB-H’s failure included: coming too soon before there was sufficient mobile bandwidth; lack of a proven business model; and absence of sufficient demand from users. There was a lack of compatible handsets, and, above all, the tablet — with its larger screen more suitable for displaying video — came too late in the day. Furthermore, deploying was expensive, requiring investment in separate parallel infrastructure.
Yet another factor was that content consumption patterns were changing towards a mixture of linear and on-demand. In designing NGH, DVB, therefore, has attempted to cater for the evolving models of consumption, recognizing that it must be capable of delivering a variety of media on top of traditional linear TV (including various video and audio content, images and text messages), as well as push download to local memory in the receiver. DVB argues that it has catered for all this and that NGH incorporates the optimum technology for broadcast content delivery to handheld and mobile devices for the next decade.
There is also a wider subtext, which is to reach out to the other digital terrestrial groups such as ATSC, while also striving for accommodation with mobile services as LTE/4G deployment gains momentum. On the first front, ATSC has failed to articulate as clear a strategy itself, working on its third-generation ATSC 3.0 specifications while the second is only just starting to be deployed. Mobile broadcast seems to be caught between the two, with some speculation that ATSC 3.0 will align with DVB NGH if that turns out to work well. Among reasons this could happen is the fact that DVB-NGH can work over the same 6MHz channels that broadcasters are using for ATSC, as well as ATSC-MH, allowing stations to migrate to the technology without changing either the antennae or the transmitter.
The other issue concerns possible convergence with mobile services. DVB has realized that the game is up for broadcasters in terms of defending their spectrum against further invasion by cellular operators. But, it believes it has a trump card in its mobile broadcast technology.
At the same time, there are signs that mobile operators are realizing that while unicast delivery is the best approach for niche or long tail content, a broadcast or multicast approach of some kind will be required for popular live or linear channels. Otherwise, network bandwidth will be swamped, all the way from the fiber core, out through backhaul or access, and on to the final over-the-air hop in the case of mobile TV. Popular streamed or on-demand content will have to be cached close to the point of consumption.
DVB can point out that NGH is much better suited to broadcast than 4G/LTE for various reasons. Above all, that because it has larger guard intervals to protect against interference between successive transmission units as a result of propagation delays or multipath effects, it can support much larger calls up to about 70 miles across, compared with six miles for LTE. This makes it much more suitable for broadcast using multiple, relatively low-power transmitters synchronized in single-frequency mode.
All this suggests close attention will be paid to early deployments of DVB NGH with its MIMO technology.
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