The distribution of live video programs for reception on mobile devices was announced with the deployment of third generation or “3G” wireless networks. But quite early on, it became clear that the technical limitations of the 3G networks would not allow for the delivery of multiple video services to many end-users. Simply put, traditional cellular technologies aren’t well suited for “broadcasting” content simultaneously to many users. Existing cellular technologies (2G/3G) are best suited for a peer-to-peer type of communication.
A better technical solution consists of using digital broadcast technologies and adapting them for reception on mobile devices. Using the best of both architectures, a complete video delivery solution to mobile subscribers can be comprised of a broadcast path (based on DVB-H, for example) and a bi-directional mobile/cellular interactivity path (based on 2G/3G cellular technologies).
Broadcasting video via DVB-H provides the delivery of a large amount of popular content to a large group of users at a relatively low cost. But this service is very limited with respect to interactivity and content personalization. It can be characterized by the following points:
- Suitable transport mechanisms include streaming, carousels and download.
- Large quantities of data are transferred.
- Possible push of contents to terminals.
- Contents are simultaneously broadcasted to a large audience.
- Subscription-free or subscription-based services.
Cellular telecommunications systems are not designed to provide a low-cost delivery mechanism when a large group of users simultaneously downloads a large amount of data. They do allow a high level of interactivity and advanced content personalization. The 2G/3G cellular systems are therefore perfect for enabling the delivery of additional and personalized content and services. This mode of content delivery can be characterized by the following points:
- Suitable transport mechanisms include streaming and download.
- A suitable bi-directional transport mechanism including full IP connectivity as well as messaging services, allowing various types of individual interactions.
- Support of “one-to-one” relationship.
- Possible personalized delivery.
- May contain a charging and billing infrastructure.
- Allows interaction with broadcast services.
End-user terminals range from mobile telephones, PDA and mobile vehicle-mounted receivers to laptops. These types of end-user terminals can be used by pedestrians, as well as in cars, trains and buses. And the characteristics of these devices affect the way content is transmitted to subscribers, hence the standard that has been developed.
TECHNOLOGIES & STANDARDS
DVB defined the standards that can be used to deliver a full range of video and interactive services to mobile devices: DVB-H and DVB-CBMS. These new standards offer the opportunity to broadcast and manage audio-visual content services directly to mobile and handheld terminals over digital terrestrial networks such as UHF channels.
Thales Broadcast & Multimedia is strongly involved in the design of DVB-H systems and more generally in convergence projects between broadcast and broadband technologies.
As DVB-H is perfectly adapted to the distribution of content in broadcast mode, 2G/3G standards such as UMTS can be used to provide a return channel for interactivity, thus allowing broadcasters and telecommunication service providers to offer combined value-added services.
Based on DVB-T transmission, DVB-H (H for Handheld) provides for additional features to cope with delivering signals reliably to handheld terminals. These terminals are defined as lightweight, battery-powered apparatus with a low bit rate, limited processing power and memory size, which are equipped with a small screen. DVB-H addresses the following issues:
On the transmission system link layer (implemented on the IP over DVB gateway):
- Time-slicing: this reduces average power consumption by sending the data in burst mode towards the terminals. Time-slicing essentially allows the receiver to be switched off, extending device usage time. It also enables smooth and seamless frequency handover to ease access to the DVB-H services when receivers leave a given transmission cell and enter a new one.
- MPE-FEC (Multi-Protocol Encapsulation - Forward Error Correction): This feature gives additional robustness and mobility by improving C/N performance and Doppler performance in mobile channels, and also by improving tolerance to impulse interference. This feature is especially important on handheld devices that typically have antenna size and gain limitations.
On the transmission system physical layer (implemented on the DVB-H modulator):
- DVB-H signaling in the TPS-bits to enhance and speed up service discovery.
- 4K mode, which is a tradeoff for mobility and SFN cell size, allowing single antenna reception in medium SFNs at very high speed, thus adding flexibility in the network design.
- In-depth symbol interleaver for the 2K and 4K modes to improve their robustness in the mobile environment and impulse noise conditions.
While probably not an important feature for the U.S. since ATSC is the standard for DTV, DVB-T and DVB-H services can be multiplexed together in the same channel. DVB-H can also be used in 6, 7 and 8 MHz channel allocations for broadcast applications and a 5 MHz channel for non-broadcast systems.
2G / 3G
UMTS is the third generation (3G) cellular mobile system designed to provide mobile terminals with multimedia services. Based on a cellular network like GSM, UMTS enhances 2G standards by offering the capability to deliver content at a higher bit rate (up to 2 Mbps). 3G can therefore be used to transfer low-resolution video services to mobile devices. However, UMTS is not suited for the simultaneous delivery of a same content to multiple users, in terms of bandwidth capacity usage. Broadcasting is much more adapted to these types of applications.
However, pairing UMTS for the return channel will allow the set up of mixed video/interactive services such as votes, games shows and quizzes during broadcasted programs. In a basic scenario, the broadcaster can provide a data carousel on a multiplex using DVB-H. The data carousel enables hyperlinks that can be accessed by the end-user through the UMTS connection.
The DVB-H standard is designed to transmit IP-based services towards handheld terminals. IP Datacast (IPDC) is an end-to-end broadcast system for the delivery of any type of digital content and services using IP-based services. The DVB Technical Module CBMS (Convergence of Broadcast and Mobile Services) intends to define specifications for the delivery of IP-based services over DVB-H networks.
In particular, IPDC is designed to allow end-user terminals (PDA, laptop) that do not have the possibility of connecting to the cellular network to receive IPDC services.
DVB-CBMS has defined different workgroups to resolve and define suitable technical solutions on the following topics:
- Video and audio coding format and rate recommendation according to receiver screen size and computation power (resolution / compression).
- Electronic Service Guide, which must be delivered “in-band” through the broadcast network. This ESG will be used by receivers to display the available services and to display additional information regarding these services.
- Content delivery: how to deliver a file in broadcast mode to a large number of users; the protocols that will be used to deliver the ESG, ESG (event)-related vignettes, but also bitmaps, texts, etc. for the interactive services.
- Digital Rights Management for service purchase and selection, implying the protection of content over an IP broadcast system and user rights.
- QoS and network performance.
The deployment model for broadcasting to mobile terminals will incorporate multiple transmitter sites broadcasting on an RF channel(s) to blanket a given coverage area. For large-scale deployments, a satellite contribution system will provide content distribution from a central Network Operations Center (NOC) to each of the DVB-H transmitter sites. The NOC will contain functions defined in DVB-CBMS including content encoding, DRM, IP encapsulation, and interface to the cellular network. Individual transmitter sites will incorporate a satellite receiver, DVB-H exciter/modulator and RF transmission, which are optimized for the allocated channel.
Several factors will determine the actual coverage of a given DVB-H transmitter site including channel frequency, effective radiated power (ERP) and terrain. However, since the DVB-H service does not have user capacity issues vs. RF channel allocations that are associated with cellular network designs, far less DVB-H transmitter sites will be needed to blanket a market.
DVB-H is an open standard and there are multiple vendors already supplying equipment to the market. Several trial announcements have been publicized including locations in the U.S., Germany, France, England, Finland and Australia. In the U.S., Modeo (formerly Crown Castle Mobile Media) successfully completed a DVB-H trial in Pittsburgh, PA using 1.65 GHz band. At CES, Modeo announced that it plans to deliver live mobile TV to the top 30 markets.
Richard Lhermitte is a Product Line Manager, and Joe Turbolski is the Director of Marketing & Sales Operations for Thales Broadcast & Multimedia. For additional information, contact firstname.lastname@example.org.
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