Last July, the DVB Steering Board approved a new specification profile targeted at mobile broadcast services. Known as DVB-T2-Lite, this new specification brings together a subset of the very efficient existing DVB terrestrial television standard DVB-T2 with some extensions specifically aimed at addressing receivers that are incorporated in portable or handheld devices.
Already, the specification has attracted much attention. It has been tested by the BBC and showcased successfully on the DVB stand at IBC 2011. However, questions remain regarding the commercial prospects for any mobile broadcasting standard given the limited success of similar standards in the past.
DVB-T2-Lite technology
The DVB-T2 standard is a highly flexible system that allows network planners to select the appropriate modes to use based on the needs of their terrestrial broadcast network. Because many of the features of DVB-T2 allow it to be suitable for mobile and handheld usage, it was possible to develop a new specification, DVB-T2-Lite, from a selection of its features.
DVB-T2-Lite is based on the same core technologies as the DVB-T2 standard but uses only a limited number of available modes that are best suited for mobile reception. By avoiding modes that require more complexity and larger amounts of storage memory, receivers can be designed that are less power consuming and with a smaller silicon size.
Features of the DVB-T2-Lite specification include:
- A maximum bitrate of 4 Mbits/sec for each service
- Limitations on the FFT size to exclude the 1K and 32K carrier modes
- Prohibition of the use of rotated constellations in 256-QAM
- Possibility for only short FEC frames (Nldpc = 16200)
- Limitation of the size of the time interleaver memory (approximately half the size of normal DVB-T2).
As a result of these requirements, the silicon chip size in a DVB-T2-Lite demodulator is 50% smaller than that in a DVB-T2 demodulator and considerable power savings are possible. In addition, two new LDPC error control code rates, 1/3 and 2/5, have been added to the DVB-T2-Lite profile that were not in the normal DVB-T2 standard to offer additional robustness necessary with mobile reception.
Services using the DVB-T2-Lite profile can be transmitted within the same radio frequency channel as normal DVB-T2 services. Mixing of parameter sets for different parts of the signal had already been possible because of the Physical Layer Pipes (PLPs) feature of the DVB-T2 standard, but it is now possible to make use of a different FFT size and guard interval. The DVB-T2-Lite profile makes use of the Future Extension Frame (FEF) feature of the DVB-T2 standard.
FEFs had been incorporated into the DVB-T2 standard to allow for the inclusion of future improvements in modulation technology. They allow the signal to transmit something other than normal DVB-T2 for certain periods of time. The DVB-T2-Lite signal that is constructed as a FEF of the DVB-T2 signal is ignored by the normal DVB-T2 receiver while the normal part of the DVB-T2 signal that is time multiplexed in another FEF is ignored by the DVB-T2-Lite receiver.
During the live, over-the-air transmission of DVB-T2 and DVB-T2-Lite signals from a single multiplex, the following technical parameters were used:
This allowed for reception of the one of each of the two streams as appropriate onto an HDTV receiver and a small screen handheld receiver.
Commercial prospects for DVB-T2-Lite
DVB-T2-Lite allows service providers to offer broadcast television services to mobile and portable devices. Should video consumption on mobile devices continue to increase at its current rate, the use of a broadcast network can help to reduce congestion on mobile broadband networks. However, much of its success will depend on the business model adopted, consumer demand and the availability of receivers, and the regulatory regime put in place.
In the past several mobile broadcast standards have been developed. Few, however, have been able to successfully secure a foothold in the market and have instead created market lassitude. Apart from Asia where free-to-air mobile television services are available, service launches in Europe and North America have yet to succeed. In the United States, Qualcomm launched a paid service using its MediaFLO standard but shut it down in late 2010 due to a lack of subscribers. In Europe, several countries launched paid mobile television services using the T-DMB standard and/or the DVB-H standard but many of the services have since been closed due to a lack of subscribers.
The question remains how DVB-T2-Lite can succeed when other standards enabling similar services have failed. Three key differentiators should be noted. First, the demand for mobile video content is likely to increase, especially given the emergence of the market for tablet computers, although it is not clear that a broadcast standard is necessary to provide such content. Second, it is expected that all DVB-T2 chipsets will support DVB-T2-Lite. This means that DVB-T2-Lite chipsets will be widely available, at a low price, and large numbers of receivers will be in the market, albeit mostly fixed receivers. Finally, DVB-T2-Lite only requires a small initial investment since it can be combined into an existing DVB-T2 network. Unlike other standards, it would not be necessary, at least initially, to build a separate network, and this may encourage service operates to launch services gradually based on the demand of the local market.
