Dynamic broadcast bridges the gap on the spectrum level, dynamically attracting spectrum to TV stations and cellular WiFi.
Pressure on broadcast spectrum is rapidly growing in many parts of the world. In Europe, many countries have already allocated 72MHz of broadcast spectrum in the 800MHz band to mobile network operators. Further allocation of broadcast spectrum away from its traditional purpose is already being discussed. In light of this, DVB has created a Study Mission to look at Cooperative Spectrum Use. One of the approaches discussed in the Study Mission is Dynamic Broadcast.
The technology for consumer TVs has developed rapidly over recent years. Today's TV sets and set-top boxes are connected devices that are not only equipped with broadcast tuners but also provide broadband connection interfaces (Ethernet or WiFi) as well as built-in storage devices such as hard disks or solid state disks. Taking advantage of these innovations, additional TV related functionalities are provided, such as personal video recording, accessing electronic programme information or video on demand. Currently, a number of receiver manufacturers use this connectivity for offering their own, individual web portals, whereas television networks make use of it by offering additional data services synchronised to their TV programme. Middleware standards, such as HbbTV, allow the delivery of additional TV-related content via a broadband network that is combined with the broadcast content in the receiver. However, up until now the enhanced connectivity does not support real interworking between the two delivery means - broadcast and broadband. This is where Dynamic Broadcast comes into play. The focus of the concept is on cost optimised and spectrum efficient content delivery. An overview of the system architecture can be seen in the accompanying diagram. The key components of the system are the Decision Logic, which is responsible for the network management, and the User Terminal, which is a Dynamic Broadcast receiver.
In Dynamic Broadcast, TV content can be transmitted equally well via a broadcast or a broadband network, so that broadcast and broadband complement each other in terms of content delivery depending on the popularity of the TV content to be transmitted. For instance, delivery via broadcast is optimal if there is a large number of viewers watching a TV programme, whereas for a small audience broadband is more appropriate. As a result, Dynamic Broadcast no longer uses static assignments of TV services to predetermined distribution channels but decides dynamically over which of the networks, broadcast or broadband, a certain piece of content corresponding to a certain TV programme will be delivered. The User Terminal then composes linear TV services out of single content items received from different sources and thus becomes an active network component that switches between different delivery networks in response to comprehensive signalling delivered via broadcast or broadband.
In addition to broadcast and broadband network connections, a local storage device, built-in or connected to the User Terminal, provides the basis for non-real time delivery of TV content. The advantages can be explained as follows: Nowadays, TV content is broadcasted in realtime - this holds true for live events as well as for pre-produced programmes and even repeats. In contrast, these three types of programmes are handled differently in Dynamic Broadcast, consequently providing another degree of freedom for the content delivery. The system distinguishes the delivery schedule (the order in which content items are transmitted to the User Terminals) from the programme schedule (the order in which content items are presented to the user) and avoids retransmission of TV programmes. For instance, one episode of a TV series, which appears during the afternoon in the programme schedule, could be pre-transmitted to the User Terminals the night before. If so, the number of User Terminals that will have to receive the corresponding TV content live will then be reduced, as most User Terminals are able to play back the content from the local storage device. The few remaining User Terminals that didn't store the episode may then receive a live stream via broadband. Usually, an episode is repeated at least once, e.g., in the morning of the next day. The repeat will not be broadcast and the number of required broadband live streams will even decrease compared to the previous day as the total number of viewers is much lower during the morning than in the afternoon. It has to be emphasised, that from the point of view of the TV audience, the traditional broadcast experience remains unchanged as switching between broadcast transmission and broadband delivery as well as between live reception and playback from the storage device happens seamlessly. Consequently, capacity can be freed on the broadcast network at times when live broadcasting of TV content is replaced by broadband delivery and/or playback of pre-stored content. Parts of the TV spectrum can thus be used for purposes other than broadcasting. So, in addition to conventional static TV white spaces (locally underutilised parts of the TV spectrum), secondary users can make use of temporarily available spectrum, referred to as dynamic TV white spaces. Providers of public WiFi hotspots can benefit from dynamically freed spectrum resources by offering higher data transfer rates to their customers during high traffic hours. The diagram illustrates an interface for dynamically offering this spectrum to secondary users via a Dynamic White Space Database. Thus, Dynamic Broadcast can also be seen as an approach based on cooperation at the spectrum level, allowing for flexible spectrum management and, therefore, more efficient use of TV spectrum.
By Jan Zöllner, chair of the DVB Technical Module study mission on Cooperative Spectrum Use and Peter Neumann, both of Braunschweig Technical University, Institute for Communications Technology.