Delivering Regional DVB-T2 Services
Laurent ROUL, ENENSYS Technologies, Product Marketing, Broadcast Network Equipment
DVB-T2 has already achieved incredible success for delivering digital terrestrial television. More than 30 countries around the world have selected it for their DTT standard. The first deployment was in the United Kingdom in December 2009. 2010 and 2011 saw the launch of DVB-T2 services in Sweden, Finland and Italy. Several new rollouts and trials are planned for the rest of 2011 in Europe, Africa and Southeast Asia. DVB-T2 is the world’s most advanced DTT system offering higher efficiency, robustness and flexibility. It greatly increases the channel transmission capacity to meet HD and 3D bandwidth demands and offers flexibility through a range of business models using Multiple Physical Layer Pipe (MPLP) technology, which provides services-specific robustness.
Multiple PLP allows operators to transmit HD services with low robustness at the same time as SD services with high robustness. Also, a single DVB-T2 multiplex can address fixed TV antennas as well as nomadic and mobile devices. Additionally, Multiple PLP technology is also a fantastic tool to enable regional business models where regional/local TV content is inserted into a nationwide multiplex/frequency.
Regionalization aims at offering, in addition to national or common TV services, regional or local-specific content into a region that could be a city, a county or a country. Today, out of the over 1700 TV channels that are broadcast terrestrially throughout the EU, 50% are local channels. Offering regional programming in DTT services is now considered mandatory.
Therefore, each region has to broadcast its own DVB-T2 multiplex composed of national and regional/local content. Regionalization can be operated through different kinds of architectures (national, regional, local) that vary depending on where the regional or local content is inserted.
In the case of a national transmission network architecture, the national TV content is aggregated with regional TV content. Each region provides the content to the central head-end. Each regional DVB-T2 multiplex is created from the national content multiplex and the regional TV services or regional multiplex as described below:
In this case, for example, the T2 gateway creates the different regional DVB-T2 multiplex using MPLP technology. Each T2 gateway has one PLP dedicated to national TV content and one or several other PLPs dedicated to regional content. National TV content is retrieved from the national multiplexer. Regional TV content is provided directly from the regional encoders or regional multiplexers. Then, all regional DVB-T2 multiplexes are carried towards the different regions from the centralized head-end. Although this model is quite straightforward, it is disadvantaged by having to duplicate the national content on the distribution network as many times as there are regions to address, which increases significantly the data rate for the contribution network.
In a regional transmission network architecture, regionalization is performed within regional head-ends. Each of these head-ends receives the national content from the central head-end, adds the regional or local TV content, and then broadcasts the new DVB-T2 regional multiplex consisting of national and regional content to all transmitters in the relevant areas. In this architecture, the regional T2 gateway outputs a T2-MI stream containing the national TV multiplex in one PLP and regional TV content in other PLPs.
The main constraints of this model are the use of 2 distribution channels (from central head-end to regional head-end, and from regional head-end to transmitter sites) and the duplication of the national content in the secondary distribution link for each region.
Finally, in a local transmission network architecture, the national T2 gateway generates national content in a specific PLP and generates other PLPs for content that will be replaced with regional content. The regional content is generated centrally, regionally or locally through a dedicated regional T2 gateway. In each transmitter site, a deterministic local T2 inserter gets from the distribution network the national T2-MI feed from the national T2 gateway and the regional T2-MI feed from the regional T2 gateway. The BaseBand frame data field of every T2-MI packet, with a matching plp_id field (e.g., plp-id of the regional PLP), is then replaced from the national T2-MI feed with the regional T2-MI feed. Employing this deterministic method of replacing PLPs ensures SFN preservation.
This model offers a great deal of advantages:
• Bandwidth saving: reduces the OPEX of the content delivery to the transmitter sites without duplicating the national content delivery
• SFN capable
• Standard-based solution: use of multiple technologies
• Statistical multiplexing capability between regional or local TV services
• Local TV insertion capability
In addition to offering improved robustness and/or improved bandwidth capacity, DVB-T2 provides also high operational flexibility – opening a wide variety of new business models such as regionalization. Several national, regional or local network architectures can be used to enable regional/local content insertion. All of them rely on the multiple PLP technology. By only having to deliver common TV services once, this local network regionalization model offers more flexibility to operators and helps them to save network distribution bandwidth.