Terrestrial Digital Multimedia Broadcasting (T-DMB) system, is the extended system compatible with Digital Sound Broadcasting System A, which enables video services by using T-DAB networks for handheld receivers in mobile environment. This system uses frequency bands of band III and L-band, which T-DAB networks are in operation.
T-DMB provides multimedia services including video, audio, and interactive data. For audio services
it uses MUSICAM as specified in DSB System A and for video services MPEG-4 standards. ITU-T
H.264 | MPEG-4 AVC standard is used for video, MPEG-4 ER-BSAC or MPEG-4 HE AAC for the associated audio, and MPEG-4 BIFS and MPEG-4 SL for interactive data. Outer channel coding of Reed-Solomon code applies to guarantee the good performance of video reception.
Field test results and the summary of T-DMB specification are included in the Report ITU-R BT.2049. The specification of T-DMB was standardized by ETSI in 2005. ETSI TS 102 427 and ETSI TS 102 428 describe error protection mechanism and the A/V codec of the T-DMB system, respectively. A variety of receivers are in the market: PC (laptop) type, vehicular type, and PDA type as well as mobile phone.
1.9.2 System architecture
The system for the T-DMB video services has the architecture that transmits MPEG-4 contents encapsulated using “MPEG-4 over MPEG-2 TS” specification as illustrated in Fig. 21.
Video service is delivered through the stream mode of DSB System A transmission mechanism. In order to maintain bit error rates extremely low, this service uses the error protection mechanism described in ETSI TS 102 427. This video service is composed of three layers: contents compression layer, synchronization layer, and transport layer. In the contents compression layer in ETSI TS 102 428, ITU-T H.264 | ISO/IEC 14496-10 AVC is employed for video compression, ISO/IEC 14496-3 ER-BSAC/HE-AAC for audio compression, and ISO/IEC 14496-11 BIFS for auxiliary interactive data services.
To synchronize audio-visual contents both temporally and spatially, ISO/IEC 14496-1 SL is employed in the synchronization layer. In the transport layer specified in ETSI TS 102 428, some appropriate restrictions are employed for the multiplexing of compressed audiovisual data.
Conceptual architecture for the video services
1.9.3 Video service transmission architecture
The conceptual transmission architecture for video services is shown in Fig. 23. The video, audio, and auxiliary data information for a video service are multiplexed into an MPEG-2 TS and further outer-coded by the video multiplexer. It is transmitted by using the stream mode specified in DSB System A.
Conceptual transmission architecture for the video services
1.9.4 Video multiplexer architecture
The conceptual architecture of the video multiplexer for a video service is shown in Fig. 24.
Architecture of the video multiplexer
1.9.5 T-DMB specifications
The list of specifications for T-DMB is shown in Table 4.
Encapsulation and protocols for
transmission of content
ETSI EN 300 401
ETSI TS 102 427
ETSI TR 101 497
ETSI TS 101 759
ETSI ES 201 735
ETSI TS 101 499
ETSI TS 101 498-1
ETSI TS 101 498-2
ETSI EN 301 234
MPEG-2 Layer II
MPEG 4 ER BSAC/MPEG 4
ETSI TS 102 428
ITU-T Rec. H.264 / MPEG-4 AVC
ETSI TS 102 428
1.10 LMDS (Local Multipoint Distribution System)
Since the very preliminary applications of digital terrestrial broadcasting, interactive and multimedia applications seemed bound to play an important role in the take-off of the new broadcasting standard. Later on, the availability of MHP standard and of MHP-compatible set-top boxes definitely opened the doors to interactive and multimedia applications.
Interactive and multimedia terrestrial TV became a key part of the service in Finland, where are operational in MHP standard since 2002 and interactivity is currently tested also on the Digital Terrestrial TV networks of Spain, Germany, and Singapore (other countries are invited to send a contribution on this). With the current launch of Digital Terrestrial Television in Italy, multimedia applications are getting a considerable interest, also for what concerns interaction with public administration (T-government) and education.
Some countries have started a field trial of IP over digital TV broadcasting.
LMDS at 42 GHz is now a mature technology in terrestrial digital video broadcasting with the capability to have a great amount of band to offer services to the customers. For example multichannel LMDS and MPEG2 compression coding system - allowing multiple digital time-shifted programs inside the same
33 MHz video channel - permit NVOD (Near Video On Demand) services, without any "return connection" between the customer and the Service Provider.
Services with a low interactivity level like Video on Demand (VOD), Games or Home Shopping applications, can be achieved over LMDS with telephone return channel: most of the commercial DVB Set Top Boxes (decoders) already include internal telephone modem. Also Internet access with telephone return channel is achievable, deserving some LMDS down-link channels to deliver Internet traffic.
(All sub-sections describe the situation in European Union. Other administrations are invited to provide further information on their own scenarios.)
LMDS technology is rapidly evolving and the introduction of higher levels of interactivity, will move applications from pure entertainment to Wireless Local Loop (WLL) services. In-band return channels offer attractive independence from PSTN (Public Switching Telephone Network) for Service Providers. Interactivity is pushing LMDS and WLL applications into a merge whose continuous technology evolution will contribute extending profitable business penetration.
Some WLL services promise profitable commercial businesses for Small Business or HomeBusiness (SOHO) subscribers; in particular high speed Internet surfing seems to be a valuableservice for most of the users.
1.10.2 Some key factors in the technology
The choice of the complete system architecture requires a deep analysis of communication scenarios, network scenarios and traffic characteristics. The required capacity of a network depends on a large number of parameters, including the number of users, the applications they use, the protocol efficiency and the frequency re-use strategy. Access protocols must be able to cope with traffic loading near saturation.
1.10.3 Technological trends and objective constraints
Technology improvements, especially in the millimetre component field, will contribute to extend interactive LMDS services into large commercial business but, on the other hand, millimeterwave Remote Terminal (RT) transceiver architecture must be maintained as simple as possible in order to be cost effective. Available throughput rate per customer must be traded-off with RT architecture complexity, Base Stations content feeding, modulation schemes, RT output power and return path link budget.
The design of application oriented LMDS network services in real environments appears to be an issue to be solved on a case by case basis. Besides automatic design procedures can help in the design producing an optimised network topology and architecture, cost and infrastructure implications must be carefully evaluated for each situation.
The main arguments in favour of the LMDS technology are increased data rates available to the user, the possibility to deliver both general content services and to customise dedicated services within well delimited geographical areas. Moreover it’s considerable the opportunity for the operators to expand their network over a few years in terms of number of customers and services offered.
One of the most important factors affecting the success of Broadband Wireless Access Operators is the initial amount of spectrum licensed per Operator by the Administration. Another important factor is the availability of additional spectrum to meet demand as Broadband Wireless Access systems rollout. In fact, whilst a modest amount spectrum may be available in the short term, it will not be sufficient in a long term perspective where an increasing number of competitors and services will face the market.
Due to the propagation limitation, line of sight users are mandatory. The target market for Broadband Wireless Access systems could be a single or multi-tenant building within the coverage area of the cell with clear line of sight to the base station, and sufficient traffic volume to economically support the cost of the network infrastructure. There is also the need of a wired building in order to allow the distribution of forward and return channel, needed if a high interactivity level is requested, to each user from the RF terminal on the rooftop.
1.11 Forward Link Only (FLO)
Video and other rich multimedia services on a cellular phone have been primarily delivered via existing 3G wireless networks. Until recently this delivery was primarily via unicast wireless networks, although the availability of multicast methods within the existing unicast networks is increasing. The broadcast-multicast mechanisms of these 3G networks are basically added onto the existing unicast physical layer. For simultaneous wide distribution of content, typically beyond a few users per sector, it is generally accepted as economically advantageous to transition to broadcast-multicast delivery.
While the cost reduction that can be achieved by a broadcast mode within a unicast framework can be significant, even greater efficiencies can be achieved by a dedicated broadcast-multicast overlay. This is the underlying philosophy behind the Forward Link Only technology for broadcasting of multimedia data to handheld mobile devices.
1.11.2 Forward Link Only system architecture
A Forward Link Only system is comprised of four sub-systems namely Network Operation Centre (NOC – which consists of a National Operation Centre and one or more Local Operation Centres), Forward Link Only Transmitters, IMT2000 networks, and Forward Link Only-enabled devices. Figure 25 shown below is a schematic diagram of an example of Forward Link Only system architecture.
Forward Link Only system architecture example
1.11.3 Forward Link Only system overview
188.8.131.52 Content acquisition and distribution
In a Forward Link Only network, content that is representative of a linear realtime channel is received directly from content providers, typically in MPEG-2 format, utilizing offtheshelf infrastructure equipment. Non realtime content is received by a content server, typically via an IP link. The content is then reformatted into Forward Link Only packet streams and redistributed over a single or multiple frequency network (SFN or MFN). The transport mechanism for the distribution of this content to the Forward Link Only transmitter may be via satellite, fibre, etc. At one or more locations in the target market, the content is received and the Forward Link Only packets are converted to Forward Link Only waveforms and radiated out to the devices in the market using Forward Link Only transmitters. If any local content is provided, it would have been combined with the wide area content and radiated out as well. Only users of the service may receive the content. The content may be stored on the mobile device for future viewing, in accordance to a service programme guide, or delivered in realtime for live streaming to the user device given a linear feed of content. Content may consist of high quality video (QVGA) and audio (MPEG4 HEAAC)2 as well as IP data streams. An IMT2000 cellular network or reverse communication channel is required to provide interactivity and facilitate user authorization to the service.
A reasonable Forward Link Onlybased programming lineup for 25 framespersecond QVGA video, with stereo audio, in a single 8 MHz bandwidth frequency allocation, includes 25 to 27 realtime streaming video channels of wide area content including some realtime streaming video channels of local market specific content. The allocation between local and wide area content is flexible and can be varied during the course of the programming day, if desired. In addition to wide area and local content, a large number of IP data channels can be included in the service delivery.
The Forward Link Only technology simultaneously optimizes power consumption, frequency diversity, and time diversity. The Forward Link Only air interface employs time division multiplexing (TDM) to transmit each content stream at specific intervals within the Forward Link Only waveform. The mobile device accesses overhead information to determine which time intervals a desired content stream is transmitted. The mobile device receiver circuitry powers up only during the time periods in which the desired content stream is transmitted and is powered down otherwise.
Mobile users can channel surf with the same ease as they would with digital satellite or cable systems at home.
184.108.40.206 Wide and local area content
As shown in Fig. 26, Forward Link Only supports the co-existence of local and wide area coverage within a single Radio Frequency (RF) channel. When utilizing a SFN, it eliminates the need for complex handoffs for coverage areas. The content that is of common interest to all the receivers in a wide area network is synchronously transmitted by all of the transmitters. Content of regional or local interest can be carried in a specific market.
Hierarchy of local and wide area SFNs
220.127.116.11 Layered modulation
To provide the best possible quality of service, Forward Link Only technology supports the use of layered modulation. With layered modulation, the Forward Link Only data stream is divided into a base layer that all users can decode, and an enhancement layer that users with a higher signal to noise ratio (SNR) can also decode. The majority of locations will be able to receive both layers of the signal. The base layer has superior coverage as compared to non-layered mode of similar total capacity. The combined use of layered modulation and source coding allows for graceful degradation of service and the ability to receive in locations or speeds that could not otherwise have reception. For the end user, this efficiency means that a Forward Link Only network can provide a better coverage with good quality services, especially video, which requires significantly more bandwidth than other multimedia services.
1.11.4 FLO Specification
Standardizing of the Forward Link Only technology has been achieved in the Telecommunications Industry Association (TIA) as Standard TIA-1099 and is further coordinated through the FLO Forum, www.floforum.org.
Other informative references related to the Multimedia system “M” performance include:
– TIA-1102: Minimum Performance Specification for Terrestrial Mobile Multimedia Multicast Forward Link Only Devices.
– TIA-1103: Minimum Performance Specification for Terrestrial Mobile Multimedia Multicast Forward Link Only Transmitters.
– TIA-1104: Test Application Protocol for Terrestrial Mobile Multimedia Multicast Forward Link Only Transmitters and Devices.