In June of 2005, the 3rd Generation Partnership Project (3GPP) completed Release 6 of its technical specifications for the continued evolution of 3rd generation (3G) cellular networks based on the GSM infrastructure. Included in 3GPP Release 6 are the specifications for the Multimedia Broadcast/Multicast Service (MBMS), an IP-based technology designed to more efficiently deliver multimedia (video, audio, and text) content over 3G radio and network resources.
MBMS represents a way for 3G network operators to offer multimedia content over their GPRS/EDGE or W-CDMA 3G networks without unnecessarily consuming capacity for voice communications. Today, multimedia content must be delivered as IP packets via unicast transmission, where each individual user consumes network resources to download content such as music or ring tones that are unique to that individual.
With MBMS, however, content is broadcast ("IP datacasting") so that network resources are shared among many users, thereby minimizing the impact on voice communications and reducing costs for network operators.
But MBMS is not just a technology to preserve capacity or reduce costs - by providing an efficient means to reliably distribute multimedia content over 3G networks, MBMS provides an opportunity for 3G network operators to deliver new and innovative revenue-generating services to their subscribers.
Figure 1 -- Without MBMS, unicast transmissions consume more network resources as usage grows
Figure 2 -- With MBMS, broadcast transmissions efficiently use network resources at all usage levels
MBMS Broadcast and Multicast Modes
MBMS delivers multimedia content via a 1-way point-to-multipoint transmission in two forms, either as a stream that is played back at the receiver immediately or as one or more files that are downloaded to the device for later playback. Streaming services are suitable for near-real-time content, while download services support multimedia content that are not so time-sensitive as to warrant streaming.
Data distributed via MBMS is either broadcast to all users or multicast to subscribers of particular services. In broadcast services, all receivers within range of the MBMS signal have access to the content; in multicast services, only those receivers within range who have subscribed to the particular service are authorized to join the multicast group and receive the content.
The MBMS user service discovery and announcement processes provide each user with a menu of available MBMS services. Authentication, key distribution, and data protection are then handled transparently by MBMS. Although MBMS content is delivered as a 1-way transmission, 2-way communications over the EDGE/GPRS or W-CDMA network are used as part of the MBMS protocols to allow individualized user functions, including joining or leaving multicast groups, reporting the quality of reception, and the post-delivery repair of data that may not have been successfully downloaded during the 1-way MBMS transmission.
Innovative User Services via MBMS
From the 3G network operator's point of view, MBMS enables the creation of new revenue-generating services that augment and extend the value of the basic cellular voice network. The services that can be provided via MBMS are wide-ranging, varying in terms of the provided content and the time and place the services are made available.
The variety of multimedia content that can be offered via MBMS as combinations of video, audio, or text is considerable, limited only by the availability of appropriate content. The dimensions of time and place are also under the control of the network operator, allowing the creation of services that are truly available "whenever" and "wherever".
Content that is intrinsically not time-sensitive can be simply provided via file download - so-called "clipcasting". Time-sensitive content can also be supported by file download simply by providing new, updated files to keep the content timely. Service providers can thus use MBMS file download services to "push" content that can be enjoyed by users at their convenience, even in places where the network is inaccessible.
Streaming services, by contrast, support near-real-time content, making it possible to deliver news, sporting events, and other content as it happens. Like a television or radio broadcast, MBMS streaming content must be viewed or heard as it is transmitted, although specific content can be repeatedly streamed in order to extend its availability.
While MBMS services can be made generally available wherever the user has network connectivity, MBMS streaming and download services can also be restricted to specific cell sites, allowing services to be localized to limited geographic areas. For example, stadiums, convention centers, downtown locations, primary roads, major shopping areas, and other appropriate locales can all be targeted with different content at different times.
MBMS services can be readily combined with 2-way communications over the 3G network to allow interactivity to be associated with the MBMS content - users can vote their preferences, purchase advertised merchandise, bet on particular outcomes, or otherwise respond to the content that has been delivered via MBMS.
Billing for MBMS services can then be based on a monthly subscription to specific MBMS multicast groups, the actual usage in terms of downloaded bytes, or the particular content that is accessed. Alternatively, 2-way interactive transactions can be used as another means to charge for MBMS services, thus encouraging impulse purchases, or certain MBMS services can be sponsored by advertising and offered at no charge to the user.
Other Mobile Broadcast Technologies
MBMS is not the only mobile broadcast technology now being advanced, but, because its specifications were only finalized in June 2005, it is the newest. Other standards and technologies that support multimedia broadcasting to mobile devices include:
* BCMCS (BroadCast MultiCast Services) -- a service comparable to MBMS that is currently being standardized by 3GPP2, the 3rd Generation Partnership Project 2, as part of its ongoing specifications for the evolution of worldwide cdma2000-based 3G networks
* DVB-H (Digital Video Broadcasting - Handheld) - an ETSI standard adapted from the DVB-T (Digital Video Broadcasting - Terrestrial) standard to support IP datacasting to mobile devices
* ISDB-T (Integrated Service Digital Broadcasting - Terrestrial) - a standard developed by the Japanese Association of Radio Industries and Business (ARIB) that encompasses digital TV and digital audio broadcasting as well as mobile IP datacasting
* T-DMB (Terrestrial Digital Multimedia Broadcasting) - a Korean standard adapted from the Eureka 147 DAB (Digital Audio Broadcasting) standard to deliver video, audio, and data services via MPEG-2 Transport Streams to mobile devices
* MediaFLO (Media Forward Link Only) - a proprietary Qualcomm multimedia broadcast system targeted for deployment in the US
MBMS is one of a number of current and future mobile multimedia broadcast technologies
Of all these various technologies, BCMCS is the most like MBMS: it, too, is a service provided by an existing cellular network as opposed to a distinct and separate multimedia broadcast network. This fundamental difference between MBMS (or BCMCS) and the other mobile broadcast technologies implies that new networks and new frequency allocations do not need to be deployed to support its rollout. Moreover, MBMS (or BCMCS) has access to 2-way communications capabilities, allowing the services to be combined with user interactivity and simplifying the process of subscribing to multicast groups. For DVB-H, ISDB-T, MediaFLO, or T-DMB, there is no capability of interactivity unless they are combined with another technology and network. Consequently, many of these technologies plan to be hosted by devices that can also communicate with a cellular network, complicating both the commercial and technical aspects of service rollout.
It may seem that MBMS, as a latecomer, is disadvantaged in its competition with these other mobile broadcast technologies. In fact, it may be more correct to say that those other technologies are the ones competing at a disadvantage. The 3G networks that will support MBMS are already deployed, under construction, or planned, and the frequencies required have already been allocated. As a complement to basic voice communications and an alternative to multimedia services delivered using unicast transmission, MBMS will likely be quickly adopted by 3G network operators to boost revenue through new multimedia services while reducing the costs of such services. In the same way that phones equipped with cameras or MMS (Multimedia Messaging Service) became almost effortlessly available to consumers with the fast pace of handset innovation and declining prices, the transition to MBMS-enabled handsets and infrastructure will likely follow a similar transparent path. Once in place, the innovative services offered by network operators over MBMS will then drive its use.
Conclusion - It's Not Just "Mobile TV"
MBMS and other mobile broadcast technologies are often termed "mobile TV". That label, however, suggests that MBMS will simply provide scheduled streaming content to allow users to watch their favorite television programs with their mobile phones. While such services are possible, MBMS and cell phones in general are poor vehicles for long-duration or scheduled entertainment. Streaming video may turn out to be a small part of the services provided by MBMS -- instead, download services may prove to be more valuable as a way to deliver content that can be viewed at the user's convenience.
Multimedia streaming and download services are today provided via unicast transmission, where the network bandwidth requirements are only manageable because demand is not yet that high. As MBMS is deployed, download and streaming services will be delivered more efficiently without impinging on voice capacity, representing a cost savings to the network operator. At the same time, new high-quality multimedia services will help increase revenue and reduce subscriber churn, making MBMS a clear winner for 3G network operators around the world.
About the Author
Alan Jacobsen is Director of Marketing at Digital Fountain, developers of advanced FEC (forward error correction) technology to enhance the quality of communications over data networks. Prior to joining Digital Fountain, Mr. Jacobsen was an independent consultant working with various clients in support of UWB, WiMAX, 802.11a/b/g, VoIP, Bluetooth, and other products. Past corporate positions include VP of Strategic Development at AdSpace Networks, developers of multimedia networks for advertising in public spaces, and VP of Marketing at Diva Communications, wireless local loop equipment manufacturers. Mr. Jacobsen holds a Master of Business Administration degree in Finance from The Wharton School of the University of Pennsylvania as well as a Master of Engineering degree in Electrical Engineering and a Bachelor of Science degree in Physics, both from McGill University.