OVERVIEW OF TECHNOLOGIES FOR MOBILE TV
Everything should be made as simple as possible but not simpler.
—Albert Einstein
5.1 WHY NEW TECHNOLOGIES FOR MOBILE TV?
In October 2003, Vodafone KK of Japan introduced a mobile phone with an analog TV tuner, the V601N from NEC (Fig. 5-1). The mobile phone could be used to receive analog NTSC broadcasts from local stations. In 2004 Vodafone KK extended the range of phones with the announcement of Sharp mobile phones V402SH and V602 SH. The V402SH has a QVGA LCD display with 320 × 260 pixels capable of displaying 30 frames per second, i.e., the normal telecast frame rate. The tuner in these phones is designed for NTSC reception. The phone also has an FM tuner to receive FM broadcasts. The V602SH is a 3G phone. The phones are capable of receiving analog TV broadcasts from the local station. Similar handsets are available for receiving PAL broadcasts. Pocket PCs are available with Windows Mobile OS and SDIO tuner for PAL and NTSC. If mobile phones can receive analog terrestrial broadcast stations, just as they do FM stations, why do we need new technologies for mobile TV?
FIGURE 5-1 Mobile Phones with Analog Tuners
Television transmission via terrestrial networks is a well-established technology with dozens of channels being broadcast in major cities. Analog TV broadcasts continue to date in various countries in PAL, NTSC, and SECAM formats alongside digital TV and are not expected to be phased out immediately (e.g., not in Europe before 2012). If we can receive TV transmissions using a mobile handset, it is natural to seek an answer to the need for new technologies, chip sets, etc. The answer lies in the way the mobile phones function and receive TV broadcasts.
The analog tuner-based mobile TV handsets have an antenna, which needs to be designed for the VHF band (channels 2–13) and the UHF band (channels 14–83) and thus needs to cater to wavelengths of 35cm to 5.5 m. This implies the use of the handset earphone leads (wires) as de facto antennas for the FM/VHF band. In general a strong signal is required for broadcast reception of analog broadcasts. The reception can vary based on location. Inside buildings, the phone must be connected to an RF socket connected to an external antenna. The quality of reception may also depend on the orientation of the mobile phone and whether user is moving. The transmissions are essentially designed for stationary reception rather than mobile reception. The effects of fading due to transmission are also prominent.
5.1.1 TV Transcoding to Mobile Screens
The transmissions being in standard analog formats, the decoders (which follow the tuner in the phone) generate the decoded signal in 720 × 480 (NTSC) or 720 × 576 (PAL) resolution, which needs to be converted to QCIF (176 × 144) or QVGA (320 × 240) formats. The transcoding needs processing power within the cellular chips and creates a drain on the battery.
5.1.2 Mobile Handset Battery Life
The technologies of a normal TV transmission are designed for a wall-socket-connected receiver for which limitation of power is not a major issue. Using conventional tuners and decoders as in analog sets limits the use of the phone to around 1 to 2 hours even with the new advanced batteries. This is due to current tuner technologies. For example, in 2006, the Sony BTF-ZJ401 tuner still needed around 800mW, which would likely go down to 200 mW with advancements. Also the frame rate of NTSC transmissions is 30 fps, which due to the display characteristics leaves streaking trace on the screen of the mobile phones, for which the desirable refresh rate is 50 fps.
5.1.3 Mobile vs Stationary Environment
Mobile phones are meant to be used on the move, which means use in cars or trains traveling at anywhere up to 200 km/hour or more. Even with advanced internal antennas, mobility means ghost images due to the Doppler effect and fading due to transmission for analog TV reception.
The fact remains that terrestrial TV transmissions, whether analog or digital, use transmissions that are meant for large screens and are inherently inefficient if displayed on mobile devices that have limitations on display size, refresh rates, and power consumption. There is also a need for the handsets to be usable in mobile environments the speeds of which can reach 200 km/hour and above. Further, a mobile user may leave the local TV transmitter station reception area. The technology of mobile TV should support reception across large regions.
5.2 WHAT DOES A MOBILE TV SERVICE REQUIRE?
The requirements of any technology that can support transmission of mobile TV are thus:
• transmission in formats ideally suited to mobile TV devices, e.g., QCIF, CIF, or QVGA resolution with high efficiency coding;
• low power consumption technology;
• stable reception with mobility;
• clear picture quality despite severe loss of signals due to fading and multipath effects;
• mobility at speeds of up to 250 km/hour or more; and
• ability to receive over large areas while traveling.
None of the technologies that have been in use, such as analog TV or digital TV (Digital Video Broadcast for Television (DVB-T) or ATSC), are capable of providing these features without certain enhancements in terms of robust error correction, better compression, advanced power-saving technologies, and features to support mobility and roaming. This has led to the evolution of technologies designed specifically for mobile TV.
The evolution of technologies has also been dependent on the service providers and operators in the individual fields of mobile services, broadcast services, and broadband wireless, each of whom has moved toward extending the scope of its existing networks to include mobile TV as an additional service. For example the mobile operators launched mobile TV based on the 3G networks, while the broadcasters launched handheld TV trials based on the technologies for handhelds derived from DVB-T terrestrial broadcast TV networks. Other operators used digital audio broadcasting (DAB) and moved in with extensions of the DAB services to an evolved standard of DMB (digital multimedia broadcast) based on both satellite and terrestrial transmission variants. The DAB-IP is another extension of the DAB technology to provide TV broadcasting over DAB.
5.3 MOBILE TV SERVICES ON CELLULAR NETWORKS
Mobile operators have been attempting to provide TV video streaming and downloading as well as audio downloading since the inception of 2.5G technologies, which permitted data transmission. The aim was to provide video and audio download services similar to what could be used over the net using IP streaming and file downloading. The video clips that could be transferred were generally short (on the order of a few seconds). Where streaming services were available these generally offered jerky video (due to the low frame rates) and occasional freezes due to the network and transmission conditions.
As the networks migrated to 3G the data rates increased and protocols were defined for video and audio delivery. This led to the offering of live video channels by the 3G carriers at speeds of 128 kbps or more, which when coupled with efficient coding under MPEG-4, could provide a workable video service. The need to provide video services uniformly across networks and receivable on a wide range of handsets led to a standardization effort under the 3G partnership fora to standardize the file formats that could be transferred (i.e., how the audio and video will be coded) and the compression algorithms that could be used (MPEG-2, MPEG-4, or MPEG-4-AVC/H.264).
The success of mobile TV and video/audio streaming and download led the operators to opt for new models of multicast delivery, leading to the development of the multicast-based delivery services, i.e., Multimedia Broadcast and Multicast Service (MBMS) or higher bandwidth channels such as HSUPA. The wide geographical coverage of 3G networks, particularly in the United States and Europe, empowered the operators to roll out the services throughout the coverage area and in particular where the 3G nodes and capacities have been available.
5.4 DIGITAL TV BROADCAST NETWORKS
In the meantime the TV broadcasters, who had been left out of the quest by mobile operators to provide mobile TV services, looked at the extension of their own networks for the rollout of the mobile TV. The obvious choices were the terrestrial broadcasting networks. These networks broadcast in the VHF and UHF bands. Most of these networks in Europe, the United States, Japan, and other countries are migrating to digital TV broadcast stations, which helps in reducing bandwidth demand by packing seven to eight standard definition TV programs into the same frequency slot that was occupied by only one analog carrier.
The concept of mobile TV using terrestrial broadcasting networks is somewhat similar to that of the FM radio receivers built into the mobile handsets. Here the radio reception is from the FM channels and does not use the capacity of the 2G or 3G networks on which the handset may be working. The handsets have a separate built-in tuner and demodulator for the FM signals. Even if there is no 2G or 3G mobile coverage the FM radio continues to work. Mobile TV using terrestrial broadcast technologies follows the same concept and uses the VHF or UHF spectrum for carriage.
For the purpose of carrying mobile TV, the TV broadcasting community found it expedient to modify the DVB-T standard used for digital TV broadcasting in Europe, Asia, and the Middle East (and many other countries except the United States, Canada, Taiwan, and Korea, which used the ATSC standard, or Japan, using Integrated Services Digital Broadcasting (ISDB-T)). The DVB-T standards were enhanced with additional features suitable for carrying television signals to a handheld, and the new modified standards were renamed DVB–Handheld (DVB-H) standards. This they did by modifying the transmission so that the data is transmitted in bursts for a particular channel to conserve battery power of the mobile, adding additional forward error correction (FEC) and modulation techniques to take care of the handheld environment. The new standard of DVB-H was put to trials at over 30 locations by the middle of 2006 to prove the concept of delivering the mobile TV service. In most cases the trials involved the use of the same transmitters that had been installed for terrestrial digital TV. The DVB-H standard also identified the coding and compression standards for video and audio signals, which can be carried through the DVB-T networks, as well as the IP datacasting standard, so that all mobiles can work across the various DVB-H stations in a uniform manner. A single DVB-H carrier of 8 MHz can carry between 20 and 40 video and audio services (depending on the bit rates) in a typical operating environment. The concept, which has proved successful in the trials, demonstrated that mobile TV services could be provided in a broadcast manner by using existing (or new) infrastructure for DVB-T, modified for DVB-H. Commercial deployments based on DVB-H are rolling out based on the positive results of the trials conducted. The spectrum for DVB-H still remains an issue in many countries, as the regulators allocate the available spectrum to pave the way for digitalization of the terrestrial broadcast services.
FIGURE 5-2 Typical Coverage of Mobile and Digital Terrestrial Transmissions
DVB-H services are potentially quite attractive owing to the broadcast mode of transmission, which thereby saves valuable 3G spectrum and associated costs for the users as well as the service operators. However, the terrestrial transmitting networks cannot reach everywhere and are limited by the line of sight of the main transmitters (and repeaters if any). This places the DVB-H service squarely in the category of TV broadcasts. 3G networks on the other hand traverse the length and breadth of most countries and can provide uninterrupted viewing for individuals traveling anywhere in the coverage area (Fig. 5-2).
5.5 DIGITAL AUDIO BROADCASTING AND DIGITAL MULTIMEDIA BROADCASTING
Digital audio broadcasting, which is delivered through satellites as well as terrestrial media, has been used in Europe, Canada, Korea, and other countries and is popularly known as the Eureka-147 standard. Digital audio broadcasting is a replacement of the traditional analog FM transmissions. DAB has the capability (including protocols) to deliver high-quality stereo audio and data through direct broadcasts from the satellite or terrestrial transmitters to DAB receivers, including those installed in cars and moving vehicles. As the DAB services have been allocated spectrum in many countries, this was seen as an expedient way to introduce multimedia broadcasting services, including mobile TV. The digital multimedia broadcasting standard was an extension of the DAB standards to incorporate the necessary features to enable the transmission of mobile TV services. The DMB developments were led by Korea and have seen implementations in Europe recently.
5.6 MOBILE TV BROADCAST USING DIGITAL MULTIMEDIA BROADCAST TERRESTRIAL TECHNOLOGIES (T-DMB)
The DMB technologies developed as a result of modification of the DAB standard were introduced using terrestrial broadcast by Korea. The Korean T-DMB system was deployed in VHF band III. The service is currently running in Korea with handsets provided by various manufacturers such as LG and Samsung. The Korean implementation of the T-DMB service divides the 6-MHz VHF slot into three carriers of 1.54 MHz each, similar to the carrier sizes in the DAB network. Each of these carriers then can carry two to four video channels and additional audio channels. This gave an opportunity to smaller broadcasters with potentially one or two channels to launch their service for this niche market.
5.7 BROADCAST AND UNICAST TECHNOLOGIES FOR MOBILE TV
There are two approaches to delivering content to a mobile TV. These are the broadcast mode and the unicast mode. In the broadcast mode the same content is made available to an unlimited number of users via the network used. The broadcast mode is thus ideal for the delivery of broadcast TV channels with universal demand (Fig. 5-3).
The unicast mode on the other hand is designed to deliver user-selected video or other audio/video services. The virtual connection is different for each user, with the user selecting the content to be delivered as well as the other interactivity services. Unicast obviously has limitations on the number of users that can be supported within given resources. For example, streaming video for a sports event may be selected by hundreds of thousands of users, resulting in the exhaustion of resources for delivery of such services. The scalability of the unicast model is thus limited; at the same time the degree of user-specific services that can be provided is very high.
FIGURE 5-3 Broadcast and Unicast Transmission for Mobile TV
The older generation mobile networks provided the streaming and downloading modes for video, with limited capacity owing to the use of the limited bandwidth of the 2G/2.5G networks. As the mobile networks have evolved from 2G to 2.5G and now to 3G, they have preceded, in terms of time frame, the mobile TV networks, which are now being rolled out. The new technologies that have now emerged are focused on the need to provide broadcast TV as well unicast services to a large number of users, potentially unlimited. The 3G (or Universal Mobile Telephone System (UMTS) as well as CDMA) networks are designed to cater to much higher data rates. However, even the 3G technologies have limitations in terms of the unicast traffic in a given cell area. The industry has been furiously working on the technologies and spectrum resources that can help extend the speed, user density, and range of services that can be provided on the 3G networks. New technologies such as HSDPA and MBMS, EV-DO and MCBCS, are the results of such developments. MBMS was devised as a bearer mode point to multipoint service, with the transmission being characterized by the transmission of datagrams that are received by all the intended recipients.
As the name indicates, the Multimedia Broadcast and Multicast Services have two modes of providing services to a large number of customers. 3GPP release 6, which has defined MBMS, has specified the following modes for operation of the services:
1. The multicast mode involves the transmission from the source to all the devices in a multicast group. These devices can lie in different cell areas or be mobile. Hence the multicast transmissions are not delivered to all recipients in a given area; rather, delivery is selective.
2. The broadcast mode involves the transmission of multimedia data as packets through the bearer service to all recipients in a given area.
5.8 BROADCAST MOBILE TV AND INTERACTIVITY
The receivers for mobile TV are handsets that are connected to 2G or 3G networks. The handsets can therefore be used for voice and data communications in addition to serving as receivers for mobile TV. These handsets use an underlying 3G or 2.5G mobile network, which may be a CDMAor a GSM network based on the country of operation as well as the operator.
Multimedia services offered on 3G networks have traditionally been focused on the bidirectional nature of the mobile networks and include services such as video calling, video conferencing, instant chats, sharing of pictures, and downloading of music. They also include interactive applications such as video on demand, mobile commerce applications, betting, auction and trading services, and exchange of user-generated content. In some cases alternative back channels such as WiMAX, WiBro, and wireless LANs have also been planned as back channels.
When mobile TV services are offered using broadcast mode networks, they are much more focused on the provision of unidirectional broadcast mode TV to very large audiences. Nevertheless, the operators of such broadcast networks (traditionally broadcasters) have recognized that there is an underlying communication capability in the mobile receiver, which can help provide interactive applications.
This has led to many of the technologies being developed to have multiple implementation modes involving the interactive return channel. As an example the DVB-H service, which is a broadcast service, can be implemented as a one-way service (with limited interactivity based on the data carousal concept) as DVB-H (CBMS). However, the applications for DVB-H CBMS are designed in such a manner so as to use the mobile network for interactivity. DVB-H can also be engineered as a two way service with DVB-H OMA BCAST.
Similarly, the DMB-S services offered via satellite in Korea have provision for a return channel and the content providers on the DVB-T services use the CDMA network in Korea. Mobile TV offered over 3G networks is always interactive owing to the omnipresent 3G data network.
There are a number of technologies that are being used for providing mobile TV services today. This is in part due to various operator groups such as mobile operators, traditional TV broadcasters, and wireless broadband operators seeking to leverage their networks to deliver mobile TV as well as multimedia services. Mobile operators have networks that span the length and breadth of virtually all inhabited parts of the world. It is natural for them to leverage their networks to provide mobile TV services. At the same time, the TV broadcasters who have traditionally been in the business of broadcast TV view it as an extension of their terrestrial broadcast networks, which are equally extensive. Consequently we have a slew of mobile TV offerings based on terrestrial broadcast leveraging existing networks, such as DVB-H or ISDB-T. There are, of course, some operators who have chosen to lay out entirely new terrestrial or satellite networks only for mobile TV. The broadband operators have also steadily increased the offerings of IP TV-based services and have the networks and technologies to deliver broadband Internet and, along with it, mobile TV as well. We therefore see mobile TV being offered using a number of technologies. It is useful to classify these multifarious services into broad categories as depicted in Fig. 5-4.
Briefly we can summarize the mobile TV services under three broad streams of 3G networks, terrestrial and satellite broadcast networks and broadband wireless networks. Under the 3G umbrella in particular, the services fall into the classification of broadcast and unicast modes. All of these technologies are in a continuous state of development due to the evolution of mobile TV services, which indeed are in an early phase of their service lives.
FIGURE 5-4 Mobile TV Technologies
5.9.1 Mobile TV Services Using 3G Platforms
Mobile TV using 3G platforms and 3G+ extensions can be further considered to fall into the categories of unicast services and multicast and broadcast services. The 3G networks also comprise two streams—the 3G-GSM-evolved networks, which have been standardized under the 3GPP, and the 3G-CDMA-evolved networks, standardized under the 3GPP2 fora.
A. 3G (UMTS) Networks, 3GPP Standardization
The 3G (UMTS) and evolved networks can provide video streaming, download, or progressive download services for video clips and live TV. The networks can also provide a range of other multimedia services. Some examples are:
• 3G UMTS (wideband CDMA (WCDMA))—video streaming or download,
• WCDMA HSPDA (high-speed packet download access technology).
B. CDMA 3G-Evolved Networks under 3GPP2 Standardization CDMA2000 networks can provide high-speed data for unicast or multicast TV. Most operators have also upgraded their networks to a data overlay mode, i.e., 1×EV-DO, which can provide a separate channel for transmission of multimedia, including mobile TV. Some examples are:
• CDMA 1× to CDMA 3×-based mobile TV,
• CDMA 1×EV-DO-based mobile TV.
The TV can be in streaming format or use a fixed-rate bearer to provide live TV. The TV can be in streaming format or use a fixed-rate bearer to provide live TV.
2. Multicast and Broadcast Services
Live TV can be provided by a network in broadcast mode in which all routers at the edge of the network repeat the transmission to the connected terminals. Alternatively, it can be provided in a multicast mode in which only selected terminals receive the transmissions. Both the 3G-GSM-evolved networks and the CDMA-evolved networks support the broadcasting and multicasting of content to be delivered as mobile TV.
A. 3G (UMTS-WCDMA) Networks under 3GPP: MBMS
B. CDMA and 3G-Evolved Networks under 3GPP2: BCMCS (Broadcast and Multicast Service).
5.9.2 Mobile TV Using Terrestrial Broadcasting Networks
Mobile TV services using terrestrial broadcasting form a very important class of services. This is because the spectrum used does not need to be allocated from the 3G pool, which is highly priced and scarce. This is not to say, however, that the spectrum is available very easily in the VHF and UHF bands used for terrestrial broadcasting; this is not the case due to the transition to digital TV. However, even one channel slot (8 MHz) can provide 20–40 channels of mobile TV and many countries are now focused on providing such resources.
In the area of terrestrial broadcast mobile TV, also, there are three broad streams of technologies that have evolved:
• Mobile TV broadcasting using modified terrestrial broadcasting standards: DVB-T, which is widely being implemented for the digitalization of broadcast networks in Europe, Asia, and other parts of the world, can be used with certain modifications such as DVB for handhelds or DVB-H. This is a major standard based on which many commercial networks have started offering services. ISDB-T used in Japan is a similar case.
• Mobile TV broadcasting using modified Digital Audio Broadcasting standards: The DAB standards provide a robust medium of terrestrial broadcasting of multimedia signals including data, audio, and music and have been used in many parts of the world. These standards have been modified as DMB standards. The advantage is that the technologies have been well tested and spectrum has been allocated by the ITU for DAB services. The Terrestrial Digital Multimedia Broadcast (T-DMB) is such a broadcast standard.
• Terrestrial broadcasting using new technologies: In countries such as the United States, where ATSC is the digital TV transmission standard, there is no easy way for terrestrial broadcast mobile TV. Even the digital audio broadcasting services are in the 2.3 GHz band using proprietary technology or use standard FM band (IBOC) for digital radio services. Hence terrestrial transmission networks for mobile TV need to be developed from scratch. FLO is a new technology using CDMA as interface, which can be used for broadcasting and multicasting by adding capabilities to the CDMA networks.
Following is a summary of the terrestrial broadcast mobile TV technologies:
• DVB-H
• T-DMB
• ISDB-T
• MediaFLO
5.9.3 Mobile TV Services Using Satellite Broadcasting
Some operators such as TuMedia in Korea have launched a satellite with a very high powered focused beam over Korea and Japan (MBSAT) to provide direct delivery of mobile TV to handsets. The standards developed for this service are based on the DMB technology and the services are denoted by DMB-S or SDMB. Such services are also planned for Europe and other countries.
5.9.4 Mobile TV Using Other Technologies such as WiMAX or WiBro
WiBro (Wireless Broadband) is a high-speed Internet wireless access service. It uses the WiMAX frequency bands (e.g., 2.3 GHz in Korea). It can provide Internet access while the receiver is in motion at speeds up to 60km/hour. In a typical implementation WiBro can provide 512K to 3 Mbps downlink speeds and 128 K to 1 Mbps uplink speeds with a channel bandwidth of 10MHz. Typical applications for WiBro are audio and video on demand, ring tone downloads, and electronic commerce.
In Korea the government issued three licenses in 2006 for WiBro services. These included Korea Telecom, SK Telecom, and Hanro Telecom for launching services over WiMAX. Of these only two networks are operational.
Figure 5-5 provides a summary of this section.
5.10 MOBILE TV USING 3G PLATFORMS
5.10.1 MobiTV MobiTV MobiTV MobiTV MobiTV MobiTV MobiTV MobiTV MobiTV MobiTV MobiTV MobiTV MobiTV
MobiTV is perhaps the single best example of a mobile TV service over the 3G networks (Fig. 5-6).
MobiTV provides over 50 popular channels live from broadcasters, including CNN, CNBC, ABC News, Fox News, ESPN, The Weather Channel, and Discovery, with many others being continually added to the list. It provides its services through a number of operators in many countries with 3G networks. These include:
FIGURE 5-5 Technology Overview—Mobile TV
FIGURE 5-6 Example of 3G Mobile TV
• United States—Sprint, Cingular, Midwest Wireless, Alltel, Cellular South, Verizon;
• Mexico—Telcel;
• Peru—Moviestar;
• Canada—Bell, Rogers, TELUS;
• UK—Orange, Three.
The service had over 1 million users within a year of its launch.
The concept of providing mobile TV services with diverse content has proved to be very popular. An exercise that began as streaming of short clips or recorded programs has become a video streaming service provided by mobile telecom operators using their UMTS networks or third generation networks.
The ITU has approved 3G networks under its IMT-2000 framework revolving around two core technologies—UMTS and CDMA2000. The UMTS (WCDMA) technology line was specifically developed for countries with GSM networks, and the 3G frequencies in UMTS are allocated separately in the UMTS spectrum. The CDMA2000 framework on the other hand was designed to be backward compatible with cdmaOne. The 3G networks are based on use of a large frequency band (e.g., 5MHz in WCDMA-3G) using a WCDMA carrier. The code division multiple access with large bandwidth enables the delivery of video, audio, and data services over the network. The 3G platforms are being used for mobile TV applications owing to the large bandwidth available for 3G or UMTS services. 3G platforms are currently operational in Europe, the United States, Korea, and Japan and the maximum implementations of 3G services as well as trials have been observed from these regions. However, the 3G or UMTS networks are not optimized for voluminous video-type data delivery to a large number of simultaneous users. Using “in-band” transmission the number of simultaneous unicast sessions is generally limited to around six 256 K streams and also limited to number of users per cell site for unicast video.
2.5G platform usage is characterized by short clips, news, headlines, or local content, which are viewed on 3G-based handsets. This is distinct from live TV channels, which are provided on satellite or terrestrial broadcast networks. This is because the 3G networks use the same bandwidth as voice for video delivery as well in 3G delivery technologies such as MBMS. MBMS is an in-band cellular broadcast technique.
Other technologies make use of spectrum outside the UMTS band. Owing to the limited spectrum the bandwidth on 3G tends to be expensive. The capacity is being increased with the introduction of new techniques such as HSDPA and long-term evolution 3G LTE technologies under the 3G partnership project. Using this technology and using the coding of video signals as per 3GPP standards it is possible for 10–12 channels to be multicast in a 5-MHz band.
5.10.2 More Examples of 3G Mobile Services and Networks
Another example of content aggregator for mobile TV is the GoTV network. It offers content from ABC, Univision, and Fox Sports, as well as original programming produced specifically for mobile phones. Its services are available on the Sprint Nextel, Cingular, and Boost Mobile wireless networks. The delivery networks include Wi-Fi and WiMAX networks. Channels specifically launched for mobile networks include GoTV, SportsTracker, Hip Hop Official, and Univision. The Univision mobile channel is the largest Spanish mobile TV network in the United States (www.1ktv.com).
Verizon VCAST is a video clip streaming service from Verizon available on its CDMA2000 network and has proved quite popular for downloads of songs, music, news, and cartoons.
Sprint TV Live! offers Sprint PCS Vision subscribers over 20 channels of continuously streamed content.
In the United Kingdom, British Sky Broadcasting Group PLC’s mobile television service tie-up with Vodafone Group PLC has supplied more than 5 million live TV transmissions since its November 2005 launch. BskyB has over 8 million customers on its satellite TV platform (Fig. 5-7).
FIGURE 5-7 Live Mobile TV in the United Kingdom
5.10.3 Broadcasters with Mobile TV-Specific Channels
Both broadcasters and mobile operators have started providing mobile TV services. The effort of broadcasters is focused around providing special content that is best suited to small screens and short attention times. Broadcasters also specialize in generating content. The candidates for such content are the headlines, sports events, music, weather, fashion, and even full-length serials, as the HBO offerings have demonstrated.
Some of the broadcasters with 3G-specific channels are:
• Discovery Mobile: featuring its premium show MTV with content prepared especially for either mobile sets.
• HBO also offers premium content in packages of 90 min especially for mobile markets.
• CNBC prepares bulletins and headlines especially for mobile TV.
• Eurosport and ESPN content is also available for display on mobile sets.
The list of such broadcasters is quite large and it is certain that almost all major broadcasters will either offer their content directly on mobile platforms or prepare content especially for mobile TV.
FIGURE 5-8 Cingular 3G Mobile TV (June 2006)
Cingular Wireless in the United States has launched a countrywide commercial service for live TV as well as streaming video on-demand services tailored for the mobiles (Fig. 5-8).
Customers need to sign up for Cingular’s MEdia Net Unlimited package to receive the video services. The use of video is simple with a click of the CV icon (Cingular Video). Cingular video was available in over 20 cities by the middle of 2006.
5.10.4 3G+ Networks for Mobile TV
3G networks offer streamed video and TV content. However, this type of delivery generates significant network traffic and can quickly overload the network. The realization that the mobile TV will be used much more intensively than envisaged at the time the 3G standards were finalized is leading the operators to request extensions to the 3G standard including MBMS (in-band spectrum for data) and HSDPA(extra spectrum for data).
The MBMS envisages the use of one broadcast channel in each cell rather than a point-to-point dedicated connection for each handset.
The MBMS technology is meant to address some of the issues that arise with respect to the frequencies and spectrum resources of 3G against the technology of HSPDA. Examples of MBMS services are:
• O2 trials in the UHF band (independent of 3G) and
• TDtv services of IPWireless, which use part of the 3G spectrum (WCDMA) set aside for data transmission.
5.10.5 Mobile TV Using 3G HSDPA
HSDPA is an evolution of 3G technology for the carriage of higher data rates in a quest to support video services. HSDPA can extend the bit rates to 10 Mbps or even greater (downlink) on 5-MHz 3G networks. This is achieved using new physical layer techniques such as adaptive modulation and coding, fast packet scheduling, and fast cell selection. On average a user can expect 550–1000 kbps download speeds even in a loaded environment. This makes possible the delivery of DVD-quality video for the small screens of mobile TV.
By mid-2006 52 HSDPA networks were already in operation in 35 countries and over 120 were in the advanced stages of planning. Cingular Wireless in the United States planned to deploy HSDPA in most U.S. cities by end of 2006.
The technologies such as HSDPA are not static but constantly evolving. Operators who have HSDPA networks or plans include:
1. Europe
• Orange (France, UK)
• T-Mobile
• Mobilkom Austria
• Hutchison 3G
• O2
• Vodafone
• SFR
• Bouygues
• Telenor
• Telfort
• TEM
• TIM
• NTT DoCoMo
• Vodafone KK
• KTF
• SKT
• Telstra
3. United States
• Cingular Wireless
Work is already on for even higher data rate throughputs through 3GPP initiatives such as UMTS Terrestrial Radio Access Node Long Term Evolution.
5.10.6 Mobile TV Using MBMS
Multimedia Broadcast and Multicast Services is a new technology designed to overcome the limitations of 3G networks, particularly for carrying live channels to be delivered to live audiences. MBMS networks use multicast users to broadcast content rather than using one-to-one unicast sessions, which are inherently limited by the capacity of the mobile network frequency resources. Such multicast is especially useful for special events such as sports or music concerts, when millions of users may want to access the event simultaneously. MBMS were successfully demonstrated in Stockholm by Ericsson.
5.10.7 TDtv Mobile TV Services
IPWireless has brought out a new form of multicast TV that does not use the common bandwidth of 3G networks for unicast TV transmission. The TDtv technology is based on the UMTS TD-CDMA technology and uses spectrum assigned for TD-CDMA-based air interface. The signals are telecast in a multicast mode, which enables an unlimited number of users to view live TV without clogging the voice and data bandwidth. It is possible to deliver 50 channels of TV at 128 kbps or 15 channels at high speed (384 kbps) over 5 MHz of unpaired spectrum. Sprint Nextel, which owns spectrum in the 2.5-GHz band, is currently using the IPWireless technology for TDtv to offer live TV services.
5.11 MOBILE TV SERVICES USING TERRESTRIAL TRANSMISSION
Mobile TV services using terrestrial transmission are an important class. This is because of the high power terrestrial transmitters can provide and thus reach mobile phones, even with small built-in antennas, and indoor areas.
There are four broadly different technologies for mobile TV services using terrestrial transmission:
• mobile TV using DVB-H,
• mobile TV using T-DMB, and
• mobile TV services using ISDB-T (used in Japan).
• mobile TV services using MediaFLO.
5.11.1 Terrestrial TV Technology Overview
Before going to mobile terrestrial TV it is helpful to understand the terrestrial TV broadcast environment. Terrestrial television was the earliest form of broadcast TV. PAL- or NTSC-based terrestrial broadcasts have been in vogue for over 50 years. Terrestrial broadcast transmitters use high-power transmission (in kilowatts) and are designed to reach receivers in the areas extending around a 30-km radius. The high powers transmitted make them ideal for direct indoor reception as opposed to satellite-based transmission for which a line of sight is required. The analog broadcasts have been giving way to digital terrestrial broadcasts in most countries in a progressive manner with the objective that the analog broadcasts can be phased out over a period. In Europe the target of the phase-out of terrestrial analog television is the year 2012.
Terrestrial broadcasting uses the UHF and VHF bands, which give a total capacity of around 450 MHz in the two bands, permitting up to around 60 channels of analog TV. DVB-T, which is the DVB standard for digital TV, uses MPEG-2 multiplexed video and audio carriers. Each channel on the UHF and VHF bands, which can carry one PAL or NTSC program, can carry, using the DVB-T MPEG-2 multiplex, three to five digital channels, thus enhancing the capacity in the existing spectrum.
5.11.2 DVB-T: Digital Terrestrial Broadcast Television
The digitalization of television is primarily happening via the DVB-T and ATSC terrestrial broadcast technologies. The ATSC standard is used in the United States, Canada, South Korea, etc., which have the NTSC transmission standard and follow the 6 MHz channel plan (Table 5-1). DVB-T is used in Europe, Asia, etc., where the digital carriers need to coexist with the analog PAL carriers. DVB-T uses the same spectrum as is used for analog TV, i.e., in the UHF and VHF bands in the frequency ranges of 174–230 MHz (VHF band III) and 470–862 MHz (UHF band). Each channel slot, which can be used for the carriage of analog TV (one channel), can be alternatively used by a digital carrier (DVB-T carrier) to carry three to five digital channels (Fig. 5-9).
TV and Radio Standards
DVB-T uses COFDM modulation, which is designed to be very rugged for terrestrial transmission. Whereas an analog signal suffers degradation in quality due to multipath transmission and reflected signals, which can cause ghost images, digital transmission is immune to the reflected signals, echoes, and cochannel interference. This is achieved by spreading the data across a large number of closely spaced either 2K or 8K subcarriers (for example, 1705 subcarriers in the 2K mode and 6817 subcarriers in the 8K mode). A typical DVB-T carrier can have a flexible bit rate of 4.98 to 31.67 Mbps. An example would be a carrier rate of 19.35 Mbps with Reed Solomon (RS) coding 188/204 and IF bandwidth of 6.67 MHz. DVB-T also uses frequency interleaving in addition to a large number of carriers to overcome the multipath fading. The carrier modulation is QPSK, 16QAM, or 64QAM. DVB-T can also be used for transmission to mobile devices with appropriate tuners, but the use of 64QAM with 8K subcarriers is limited to moving speeds of less than 50km/hour. This is because the small symbol duration limits the maximum delay of accepted echoes due to reflection and Doppler effects.
5.11.3 ATSC Standard for Terrestrial Broadcast
The ATSC standard uses a different modulation scheme called 8-level vestigial sideband (8VSB). Typically a data rate of 19.39 Mbps can be accommodated in a bandwidth of 5.38 MHz including a RS coding of 187/207. ATSC is an “umbrella standard,” which specifies all components of the broadcast stream (Fig. 5-10):
• audio coding—Dolby AC-3 audio compression (proprietary standard used under license ATSC A/53);
• video—MPEG-2 video compression (ITU H222);
• MPEG transport stream (ETSI TR 101 890);
• program service and information protocol PSIP (ATSC A/65);
• Base data applications software environment (ATSC A/100), Java (JVM), and HTML standards;
• data broadcast standard—TCP-IP (ATSC A/90) and MPEG (ETSI TR 101 890) standards.
The 8VSB networks are not well suited to single-frequency networks as well as high-speed reception. In fact the ATSC limit for reception in vehicles is motion can be as low as 50 km/hour.
FIGURE 5-10 ATSC Transport Stream
Owing to the unsuitability of the ATSC standard for modification for mobile TV transmissions, countries using this standard have been inclined toward the use of alternative technologies. One example is the MediaFLO technology (promoted by Qualcomm), which is based on a CDMA air interface operating in the 6-MHz bandwidth slot. The system uses a frequency of 700 MHz in the United States with radiating towers being provided source signals via satellite. Korea, which also uses ATSC, has moved toward DMB technologies and Japan toward DMB-S and ISDB-T. One of the advantages of DVB-T is that DVB-H carriers can share the same transmission infrastructure. However, despite the fact that the advantage of adding the mobile multimedia broadcast onto existing terrestrial transmission networks is not possible for ATSC, companies are still going ahead with new DVB-H installations, such as Crown Castle in the United States. The new network for DVB-H is based on the use of the L-band and is independent of the ATSC transmission network in the country.
5.11.4 DVB-T for Mobile Applications
The digital video broadcast standard for terrestrial television (DVB-T) has proven effective in meeting more than purely stationary digital TV requirements. For example, DVB-T has been used to provide television services in public transportation, as is the case in Singapore and Taiwan, and recent receiver developments make its use possible in cars and highspeed trains. DVB-T has been adopted in Australia to provide HDTV and in Europe and Asia to provide multichannel standard definition television. DVB-T-based receivers have been tested at speeds up to 200 km/hour in Germany (Fig. 5-11). However, it has many drawbacks, which limit its use in mobile phones, including high power consumption, transcoding requirements from standard definition TV to the QVGA screen, and poor signal reception due to its antenna limitations. These have been modified in the mobile terrestrial TV technologies under the DVB-H standards.
FIGURE 5-11 DVB-T Reception in Vehicles (Picture Courtesy of DiBcom)
5.12 TERRESTRIAL BROADCASTING TECHNOLOGIES FOR MOBILE TV
The main alternatives to terrestrial TV for providing live television services on a handheld device currently available are T-DMB, ISDB-T, MediaFLO, and DVB-H.
DVB-H is a technology developed as an extension of DVB-T with certain additional features that make it suitable for delivery to mobile devices. Mobile devices such as phones and PDAs are battery-operated sets with the need to conserve power, small antennas with low gain, and the need to keep the complexity of the receiver low. DVB-H provides for time slicing to save mobile handset power, providing Doppler effect compensation, better FEC using multiprotocol FEC, and an optimized mode for modulation (4 K mode). It also has a provision for video coding as per MPEG-4/AAC and uses IP as the underlying medium. DVB-H technology is seen as very promising as it can effectively use the DVB-T infrastructure and spectrum already available and provide broadcast-quality TV services to an unlimited number of users.
DMB delivers mobile television services using the Eureka-147 DAB standard with additional error correction. The new standard for DMB was formalized by ETSI under ETSI TS 102 428. The DMB has a satellite delivery option (DMB-S) or a terrestrial delivery option (T-DMB).
T-DMB uses the terrestrial network in VHF band III and/or band L, while S-DMB uses the satellite network in band L or band S. The most successful S-DMB and T-DMB implementations have been in Korea with the satellite MBSAT at 145.5E being used for S-band transmissions.
Integrated Services Digital Broadcasting, developed by Japan as its digital terrestrial television standard, provides some modes that are suitable for broadcasting for handheld reception. As part of its original digital television strategy, the government has allocated 1/13 of the digital television transmission network for mobile broadcasting to portable and handheld devices. The ISDB-T standard provides audio, video, and multimedia services for the terrestrial television network including mobile reception and HDTV. The bandwidth size in ISDB-T (one segment) is 433 kHz.
MediaFLO is a proprietary system developed by Qualcomm to deliver broadcast services to handheld receivers using OFDM. Qualcomm intends to roll out these services in the 700-MHz frequency band in the United States, since it holds a license in this part of the spectrum. Table 5-2 summarizes the terrestrial broadcast-based mobile TV technologies.
5.13 OVERVIEW OF DVB-H SERVICES
Building upon the portable and mobile capabilities of DVB-T, the DVB Project developed the DVB-H standard for the delivery of audio and video content to mobile handheld devices. DVB-H overcomes two key limitations of the DVB-T standard when used for handheld devices—it lowers battery power consumption and improves robustness in the very difficult reception environments of indoor and outdoor portable use in devices with built-in antennas. DVB-H can be used alongside mobile telephone technology and thus benefit from access to a mobile telecom network as well as a broadcast network (Fig. 5-12).
Comparison of Terrestrial Broadcast-Based Mobile TV Technologies
FIGURE 5-12 DVB-H Transmission System
The fact that the DVB-H platforms can be collocated and share the infrastructure with DVB-T makes it imperative to take cognizance of DVB-H standards, potential service scenarios, and licensing processes.
The first trial of DVB-H service was in 2005 with Finnish Mobile TV running the first pilot for DVB-H for 500 users with Nokia 7710 receivers. The initial package included three television and three radio channels. In the United Kingdom a pilot project was conducted by NTL Broadcast and O2 (a mobile operator). In The Netherlands as well, the trials were successful using the network operator Nozema. Trials have also been conducted in France, Spain, and other European countries. Crown Castle in the United States is launching the Modeo DVB-H service. Commercial DVB-H services have also been launched in Europe where Operator 3 in Italy launched its DVB-H network coinciding with the FIFA World Cup 2006, with services being offered in Rome and Milan. Commercial DVB-H license has also been granted in Finland to Digita, by which commercial trials have also been completed. A number of countries are expected to come out with DVB-H commercial networks soon.
However, the growth of DVB-H in individual countries is dependent on the release of spectrum from the DVB-T and analog bands when the analog transmissions are stopped. This could take as long as until 2012.
5.14 MOBILE TV USING DMB TECHNOLOGIES
The DMB technology is being led by Korea and Japan. China has also opted for use of DMB technologies in its networks. Mobile vendors such as Samsung, LG, and the Korean government have also lent their weight to the technology. The standards for DMB services and DAB services have been adapted by the ETSI and are now considered global standards (ETSI Standards TS 102 427 and TS 102 428). The adaptation of the standards is paving the way for the use of the technologies providing mobile TV services in Europe, 80% of which are already covered by DAB services.
5.14.1 Digital Audio Broadcasting Services
The DAB standard for digital audio broadcasting was set by the ETSI in 1995 and was primarily meant as a replacement of analog FM and AM radio transmissions. The Eureka-147 standard for DAB has been in use for terrestrial as well as satellite broadcasting and involves the use of a digital multiplex, which is program-based multiplexing (Fig. 5-13). The multiplex, or ensemble, carries a number of programs at different bit rates.
FIGURE 5-13 DAB Eureka 147 System
The DAB uses OFDM modulation with DQPSK. It also uses robust error correction via 1/4-rate convolution code and bit interleaving. The total bandwidth of the transmitted carrier is 1.5 MHz. The WARC ‘92 has allocated satellite digital audio broadcasting spectrum in the L-band at 1452–1492 MHz. For terrestrial transmission the VHF band (300 MHz) is used. Spectrum has also been allocated in the S-band (2.6 GHz) for DAB services.
The DAB has four transmission modes based on the band used for the transmission of the signals, with each mode using a different number of carriers as per Table 5-3.
In the L-band the DAB uses mode III with 192 carriers of 16 kHz each and with 8-kHz spacing. Mode III can be used up to 3 GHz.
DAB Transmission Modes
Each DAB frame in this mode has a duration of 24 ms and can carry 144 symbols of main service channel data or payload data (154 symbols including overheads, synchronization, and service information). The main service channel can have a number of subchannels. One symbol carries 384 bits (using the underlying multicarrier structure).
One symbol per frame thus implies 384 bits every 24 ms or 16,000 bits per second (16 kbps) of capacity. To carry an audio service coded at 128 kbps with 1/2 FEC gives a total bit rate of 256 kbps. This can be carried using 16 symbols per frame as each symbol gives a bit rate of 16 kbps.
The frame, which carries 144 symbols per frame, can thus be used for 144/16 = 9 services. The total available bit rate for various services is 128 kbps × 9 = 1.152 Mbps per 1.537 MHz of spectrum slot using 1/2 FEC.
DAB is used in around 35 countries around the globe. Countries with DAB broadcast include Canada, Australia, South Africa, and those in Europe and Asia, including China. DAB broadcasts can be received by using a wide range of portable as well as stationary receivers (Fig. 5-14).
As the original DAB standards provide for the use of MPEG-2 Layer 2 coding, which is not very efficient, there is a move toward using DAB standards with AAC+ or WMA9 codecs and DAB-IP, which uses WMA9 and WMV9 codecs for audio and video, respectively (DAB version 2). Ofcom in the United Kingdom has urged broadcasters to work with receiver manufacturers to have receivers available for the new DAB version. Sweden has stopped expansion of the DAB network, while France has decided not to use it at all (Table 5-4).
FIGURE 5-14 A Portable DAB Receiver
Audio and Video Codecs for DAB and DMB Technologies
5.14.2 DMB Services
One of the advantages of the DMB services is the availability of the spectrum (for DAB) in Europe and Asia, which makes the rollout less dependent on spectrum allocations. DMB services are a modification of the DAB standard that adds an additional layer of error correction to handle multimedia services. The DMB services make use of the same 1.537 MHz carriers and spectrum allocated for DAB services.
DMB uses MPEG-4 Part 10 (H.264) for the video and MPEG-4 Part 3 BSAC (Bit Sliced Arithmetic Coding) or HE-AAC V2 for the audio. The audio and video are encapsulated in MPEG-2 TS. The stream is RS encoding. There is convolution interleaving made on this stream and the stream is broadcast in data-stream mode on DAB.
5.14.3 Korean T-DMB Services
T-DMB services were launched in Korea as a result of six operators being licensed by the government, each with approximately 1.54MHz of bandwidth. This enables 1.15 Mbps per carrier and can carry VCD-quality (352 × 288 pixel) video at 30 fps (for the NTSC standard). The video is coded using the H.264 compression protocol. It also carries CD-quality audio (DAB MUSICAM). The terrestrial DMB standards also have provision for carriage of interactive data or presentations. The T-DMB services are free in Korea (Fig. 5-15).
FIGURE 5-15 T-DMB Transmission Systems
Samsung chip sets such as SPH B-4100 provide the capability of dual satellite and terrestrial reception on the same phone.
More than seven broadcasters in Korea are taking part in this service, with sharing of transmitters and providing free-to-air services. Commercial services using the T-DMB technology have been launched in Europe as well. Mobile operator Debitel has launched T-DMB services in Germany (Berlin, Cologne, Munich, Stuttgart, and Frankfurt) in cooperation with the broadcaster MFD. These services are expected to be expanded rapidly.
DMB services can be provided via satellite or terrestrial transmission.
5.14.4 Satellite-Based DMB Services
S-DMB is based on the broadcast of mobile multimedia (including mobile TV) signals via satellite in the designated frequency bands for direct reception by handhelds. As the handsets have very small antennas compared to the satellite dishes normally used for satellite reception, the satellites have to be specially designed to deliver very high effective isotropic-radiated power (EIRP). Typically these satellites are in the geostationary orbit, with large (12 m) antennas to provide highly focused beams over the desired area of coverage. For example, the beams can be of 1° width delivering 76 dBw to the coverage area. In addition, for within-building and covered areas, terrestrial “gap fillers” are required to deliver the signals with adequate signal strength. The forward error correction mechanisms are also very robust to compensate for the low signal strength directly received by the mobiles.
Use of the S-band with high-powered satellite transponders enables direct reception by handheld mobiles without the use of a special antenna. The DMB technology is a development of the DAB standards, which were earlier designed to carry only audio services.
5.14.5 The Korean S-DMB Digital Multimedia Broadcast System
S-DMB services were launched in Korea and Japan by Tu-Media. The mobile TV services delivered directly via satellite are receivable in the areas of the footprint of the satellite when the users are in an open area. The satellite (MBSAT at 144E) is a high-powered satellite with transmission in the S-band of 2.630 to 2.655 GHz, which is reserved for high-power satellite DAB services. Inside buildings use is made of S-band repeaters by which the signals are rebroadcast terrestrially to enable reception. The S-DMB services are pay-TV services with monthly charges of around 13,000 KWN/month (approx. $10 per month). The service bouquet comprises up to 14 video channels, 24 audio channels, and electronic program guide (EPG). Briefly, the services comprise an MPEG-2 TS (transmit stream structure) containing a number of video and audio channels. The video channels are coded in MPEG-4/H.264.
The satellite transmissions occupy a bandwidth of 25 MHz and make use of CDMA technology to deliver the multimedia streams. The Korean DMB system with 25-MHz bandwidth can carry 11 video channels, 25 audio channels, and 3 data channels (the mix of channels can vary).
The use of ITU-designated spectrum makes it easier to plan, compared to the other services such as DVB-H and 3G-based services, where the spectrum availability is very constrained. On the negative side is the use of the high-powered dedicated satellite, which is not easy to deploy for every country in a short time frame.
The digital mobile broadcasting services are based on the use of the S-band spectrum. The system configuration is as given in Fig. 5-16.
The satellite DMB transmission is in the S-band with frequencies of 2310–2360 and 2535–2655 MHz. This band is assigned for use in India, Korea, Japan, Pakistan, and Thailand as per ITU radio regulations (WARC, RSAC 5/2005).
5.14.6 S-DMB in Europe
The S-DMB services in Europe differ somewhat from those launched in Korea by virtue of the fact that the S-DMB service is designed to use the MSS spectrum earmarked under IMTS 2000. The frequency band is 2170–2200 MHz and is adjacent to the European allocations for terrestrial 3G services in Europe (2110–2170 MHz). This implies that 3G handsets can receive the satellite (or gap-filler) transmissions using the same antenna and other circuitry as the 3G. The 3G networks also provide a return path for interactivity (Fig. 5-17).
FIGURE 5-16 S-DMB Services in Korea
The satellite transmissions are designed to use the 3GPP UTRA FDD WCDMA technology, which is the same as that used by handsets for the terrestrial 3G services.
The satellite is designed to provide high power over up to six beams, each of which can be up to 600 km in width and thus cover significant urban agglomeration. This requires 72–76 dBw of EIRP in order to meet the service objectives of 15 dB of margin. The European project is being implemented under the “Mastreo” project, which involves a bandwidth of 5 MHz per beam. Each beam can provide up to 768 kbps of data capacity. The mobile handsets are expected to be used with a multimedia 128- to 512-Mbyte memory card, which would provide storage of broadcast data.
5.14.7 DMB—India
India’s Indian Space Research Organization is providing satellite transponders of 8 MHz bandwidth with C-band uplink and Ku band downlink. Insat4E will contain six transponders. The EIRP will be 56dBw. The frequencies assigned are as per WARC allocations for India for DAB/DMB.
5.14.8 DMB—United States
The United States has not yet approved any standard for DMB or S-DMB services. Technologies based on MediaFLO and DVB-H are the ones that have found favor so far. One of the reasons for this is the large geographical area of the country and the difficulty in providing high-power focused beams for significant coverage. However, there are plans to introduce T-DMB via satellite radio systems such as Sirius.
5.14.9 Mobile TV Services in China Using DMB Technology
Guangdong Mobile Television Media Co. Ltd. is moving ahead to provide mobile TV services based on terrestrial DMB technology. In Beijing Jolon’s DMB services will witness the growth of DMB-based services. The handsets for these services will be provided by Samsung. Shanghai will also get a terrestrial DMB television service this year. China Shanghai Oriental Pearl (Group) Co. Ltd., in partnership with its sister company Shanghai Media Group, plans to introduce a terrestrial DMB service during the second half of 2006.
5.15 MediaFLO MOBILE TV SERVICE
MediaFLO is a subsidiary of Qualcomm that has been set up to provide 3G-based mobile services (FLO stands for forward link only).
The MediaFLO system is a proprietary technology of Qualcomm and is designed to provide high-quality streaming multimedia (video and audio) services to its wireless subscribers. In the United States MediaFLO mobile services will be provided using the Qualcomm band of 700MHz (UHF channel 55). The services will be launched by Verizon Wireless and Qualcomm. Qualcomm’s MediaFLO is specifically designed to provide mobile TV services and streaming video and audio. The MediaFLO technology will be provided by Qualcomm as a shared resource to CDMA2000 and WCDMA operators (Fig. 5-18).
The MediaFLO network is based on:
• multiple types of encoding schemes, including H.264, MPEG-4, Windows Media, and RealVideo;
• flexible radio distribution networks, including 1×EV-DO, 1×EV-DO Gold Multicast, and other multicast networks; and
• a flexible layered source coding and modulation scheme.
The layered modulation scheme has been designed to provide a high-quality service (QVGA (352 × 240)) at 30 fps (or 25 fps for PAL), which degrades gracefully to 15 fps in the case of degradation of the signal-to-noise ratio (S/N) due to higher distance to user, adverse propagation conditions, or noisy environment. This means that the picture that would have otherwise frozen due to the higher bit rates not being supported by the receiver S/N ratio can still be received, but at lower bit rates.
FIGURE 5-18 The MediaFLO Network
The MediaFLO network is designed with an air interface (FLO interface) that has multiple-level error correction and efficient coding built in, which permits efficiencies of 2 bps per Hz (or 2 Mbps per MHz). This allows a slot of 6 MHz to carry up to 12 Mbps of data. This can provide over 30 live TV channels (QVGA at 30 fps),10 audio channels coded in HE AAC+, and, in addition, video on-demand channels and multimedia data.
FLO technology has also taken into account the need to conserve power in mobile handsets and the receiver can access only that part of the signal which contains the channel being viewed. It also allows the users to switch channels in switching times of less than 2 sec.
FLO radio transmitters can be designed to be installed up to 50km apart (depending on the power transmitted) and thus cover a metropolitan area with three or four transmitters. This is against thousands of gap fillers needed in technologies, such as S-DMB, that are power limited. FLO uses a single-frequency network with timing synchronization between transmitters.
FIGURE 5-19 Conceptual Diagram of the MediaFLO Network in the United States
5.15.1 Connectivity for MediaFLO
The MediaFLO network will use the 700-MHz spectrum in the United States, which was already owned by Qualcomm through the 2003/2004 spectrum auctions. The transmission will be via towers and masts, which are being installed. MediaFLO will also integrate content from various operators (satellite and cable) and also the TV stations in the United States. The local towers will receive the signals via satellite. With this aggregation the MediaFLO system is expected to support up to 100 national and international channels and the system will use Intelsat Americas 8 (IA-8 satellite) for connectivity (Fig. 5-19).
MediaFLO is not restricted to the use of the 700-MHz band. It can operate at any frequency between 300 MHz and 1.5 GHz. However, it is optimized for use in the UHF band 300–700 MHz. As other countries begin services, we should see the networks roll out in other frequencies.
5.15.2 Technologies Underlying MediaFLO Services
Essentially the FLO technology innovates the process of multicast to increase the capacity of the system and reduce the cost to a large number of simultaneous users.
EV-DO Platinum multicast is an evolution of 1×EV-DO. It uses CDMA to transmit data packets to a single user (unicast) or simultaneously to multiple users (multicast) during different time slots; this is known as time division multiplexing (TDM). The users can thus select from video on-demand type services or TV, radio, or short form content that is multicast. Each data packet is provided with the full forward link power from one cell sector during its time slot.
A further improvement in the multicast is achieved by having all the adjacent cells use the same time slot in the TDM to multicast content. The common video/audio-carrying packets are then transmitted in the reserved multicast slots to all the users in the region. The mobile handsets receive the same packet from multiple cells and then combine the energy to improve reception.
5.15.3 Transmission in MediaFLO
The transmission in MediaFLO uses the OFDM, which simplifies reception from multiple cells. The use of the 700-MHz spectrum, which is in the terrestrial television VHF band, permits high-powered transmission. The FLO technology is thus ideally suited to such countries or operators that have access to the dedicated high-power spectrum.
5.15.4 Multimedia Quality in MediaFLO
The MediaFLO technology will offer QVGA video at 30 fps and stereo audio. This will be an improvement on the existing multimedia systems over 3G, which use lower resolution and frame rates.
5.15.5 Receivers for MediaFLO services
Mobile handsets will be required to have an additional tuner/receiver for 700 MHz in addition to the 850- and 900-MHz bands in order to receive the FLO media casts. BskyB in the United Kingdom has also announced its plans for MediaFLO trials for the UK market.
5.16 DAB-IP SERVICES FOR MOBILE TV
The DAB standard has seen another extension for providing mobile services through the DAB-IP standard. The standard for providing mobile TV services via DAB-IP was approved by ETSI in July 2006.
Using this standard it is possible to provide mobile TV services with 1.5-MHz spectrum slots available for DAB. Virgin Mobile of the United Kingdom was the first mobile operator to sign up with BT Movio to offer services based on the DAB-IP standard. DAB-IP is important owing to the spectrum-related issues that are preventing the rollout of services based on DVB-H.
The DAB-IP standard is based on the use of an IP layer that carries all the data streams of audio, video, and IP. The content is delivered by IP multicast. The standard has flexibility in the use of the types of audio and video codecs. These can be H.264 or Windows Media 9 for vide and AAC+ or BSAC, as an example. The IP layer can be carried over any type of broadcast or unicast network such as DAB, DVB-H, or 3G (UMTS) (Fig. 5-20).
The DAB-IP offering from BT Movio includes the DAB-based radio channels in addition to mobile TV channels.
5.17 MOBILE TV USING ISDB-T SERVICES
Mobile TV using ISDB-T terrestrial broadcast are being provided in Japan. ISDB-T stands for Integrated Services Digital Broadcasting and is a proprietary standard.
The ISDB-T network uses a fraction of the digital terrestrial bandwidth (1/13), which is called one segment. At present such services are being provided under the name OneSeg, reflecting the use of a segment of the terrestrial bandwidth.
FIGURE 5-20 DAB-IP for Mobile TV
Digital terrestrial broadcasting (DTTB) began in Japan in December 2003 and has since been progressively replacing the analog transmissions in the NTSC format. The broadcast spectrum consists of 6MHz channels and as these are vacated by analog carriers, they are used for DTTB services. A majority of broadcasts on DTTB are now in HDTV.
Mobile TV services using ISDB-T began in Japan in 2006 using 1 segment of the 13 in a 5.6-MHz channel. The video and audio coding parameters for ISDB-T are:
• video—coded using H.264 MPEG-4/AVC base line profile L1.2 at 15 fps resolution QVGA (320 × 240);
• audio—MPEG-2 AAC with 24.48 kHz sampling.
One segment, which has a bandwidth of 5.6/13 = 0.43 MHz, or 430 kHz, can support a carrier of 312 kbps with QPSK modulation and a code ratio of 1/2 (giving a guard interval of 1/8). This carrier of 312 kbps can typically carry video coded at 180 kbps, audio at 48 kbps, and Internet data and program stream information at 80 kbps. A single segment can thus carry one channel of video and data along with program information (Fig. 5-21).
FIGURE 5-21 ISDB-T Services—Japan
5.18 MOBILE TV USING WiMAX TECHNOLOGIES
Wireless LAN services, in particular Wi-Fi (IEEE 802.11b), have been quite popular for “wireless hot spots,” which allow the use of Internet from thousands of locations across the country. However, it is the WiMAX, with the promise of speeds in excess of 20 Mbps and coverage of entire cities with a few towers, which has been long awaited by the users.
WiMAX can be characterized as fixed WiMAX (IEEE 802.16d) or mobile WiMAX (IEEE 802.16e).
5.18.1 Fixed WiMAX
Sometimes referred to as IEEE 802.16-2004, fixed WiMAX can provide data rates of 70–100 Mbps. IEEE 802.16d is based on the use of OFDM technology with multiple carriers (256 carriers) and OFDMA for multiple access with 2048 carriers. The OFDM technology with multiple carriers protects the receiver from multipath fading and frequency selective effects. Fixed wireless access with WiMAX has been deployed in Europe, the United States, Singapore, Hong Kong, and other countries. The fixed WiMAX service (IEEE 802.16d) is not designed to provide any mobility.
5.18.2 Mobile WiMAX
In the meantime, Korea had assigned the frequency band of 2.3 to 2.4 GHz for WiMAX services, and companies such as LG and Samsung together with the Electronics and Telecommunications Research Institute of Korea developed a standard called WiBro (wireless broadband), which used OFDMA as modulation and provided 0.5 to 1 Mbps per user at moving speeds up to 60km/hour. The WiBro could be used to provide wireless broadband access to terminals in vehicles. Mobile WiMAX standards were developed based on the Korean WiBro standard under IEEE 802.16e. Recognizing the asymmetric nature of the data transmission, the new standards were based on a modulation technique called scalable OFDMA. Standards for mobile WiMAX, finalized in 2006, permit mobility at up to 150 km/hour and have features such as support of an omnidirectional antenna, which is the norm in mobile terminals. The mobile WiMAX (IEEE 802.16e) provides data rates up to 15 Mbps over a range of approximately 10 km.
Mobile WiMAX has opened up a new dimension in the use of mobile multimedia services owing to:
• The majority of technologies for delivery of mobile multimedia are based on the IP unicast or multicast. Examples are the 3G technologies, which use the 3G network; MBMS multicast services; DVB-H with IP data casting; DAB-IP; etc.
• The WiMAX technologies provide an alternate medium for the delivery of IP-based multimedia and are seen as potentially useful in the constrained environment of the 3G and DVB-H spectrum.
• Mobile phones have started providing Wi-Fi (802.16b), WiMAX, or WiBro interfaces (such as Samsung i730 for Wi-Fi and Samsung M800 for WiMAX, Korea).
• Applications are available that can provide mobile TV over WiMAX or wireless broadband with global compatibility.
WiBro- or WiMAX-enabled phones have been tested by multiple operators (e.g., TIM Italy, Sprint Nextel, “3” UK). They are characterized by constant access to the Internet, ability to place video calls to one or multiple recipients, and streaming video and audio services. Multiple handheld terminals, smart phones, and PDAs with WiBro capabilities, including Samsung i730, Samsung M800, and Samsung H1000 have been tested.
5.19 COMPARISON OF MOBILE TV SERVICES
Any comparison of mobile TV services is a difficult task as the services are at present offered based on a number of constraints such as spectrum availability, which has led to a host of approaches in the quest for early delivery. The features of unicast-based services and those based on multicast and broadcast are completely different. Typically the following parameters are important in evaluation of the technologies:
• robustness of transmission and quality of service expected in indoor and outdoor environments;
• power-saving features;
• channel switching times;
• handset features needed to support service;
• efficient spectrum utilization;
• costs of operating services;
• many features, such as the quality, charges, and reception characteristics, dependent on the underlying networks (i.e., 3G);
• the user’s requirements, such as countrywide availability, roaming capability, types of handsets, and services available.
5.20 MOBILE SERVICES USING 3G (UMTS/WCDMA/CDMA2000)
3G-based mobile TV services are able to deliver acceptable quality streaming TV at rates up to 300 kbps. This is equivalent to consuming resources for around 10 voice calls on the network. Hence when a user sets up a streaming session he commences using a data bandwidth that is chargeable. These charges range from $0.10 to $0.20 U.S. per minute. A user watching 15 min of mobile TV per day on the average will end up spending a minimum of $45 per month for 450 min of TV viewing time. It is true that some 3G operators are charging based on the subscription per month rather than the usage, but such efforts are promotional. This is a constraint of 3G services, which may get addressed as the industry moves to MBMS-based services. Broadcast TV is not the best application for 3G networks, particularly when important events that may be watched by millions of users are broadcast.
On the other hand, mobile networks have significant advantages. First, they provide extensive coverage of the countries and geographical regions in the world. Hence, the users are likely to be in a zone covered by the service. Second, the Unicast nature of the services can provide better support to features such as video on demand. The handsets already have the requisite antennas and tuners for the mobile services and need not be encumbered with additional antennas and tuners for various bands. The degree of interoperability and roaming is very high in mobile networks. Interactivity is also high owing to the availability of mobile return path, which is easy to integrate. Multicast mode technologies such as MBMS and MCBCS overcome the limitations in providing unicast services to multiple users.
5.21 MOBILE SERVICES USING DVB-H TECHNOLOGY
DVB-H is well suited to mobile broadcast television as it is a standard, specifically designed video broadcasting solution for handhelds. It is designed to easily integrate into existing DVB-T networks and share the same infrastructure, resulting in lower cost and time to markets. It also provides for power saving by using the time-slicing technique, which saves tuner power. The use of the 4K mode in the modulator can provide better protection against Doppler shifts while the receiver is in motion. Being based on an IP datacast technology, the network architectures can be fully IP and the services can be delivered to transmitters using an IP network core.
Handsets using DVB-H, however, require separate antennas for 3G and DVB-H networks. Also the channel switching time is also higher owing to the time-slice mode, as the tuner is in a sleep mode for 80% of the time and is activated just prior to the anticipated reception of the packets for a particular channel. This, however, implies more time when the channel is to be changed. Using the mobile networks, limited interactivity can also be supported. However, applications involving video on demand or downloads specific to users are less suited to the broadcast nature of the networks.
While digital terrestrial television can be handled across a large city with only one or two towers, the same is not the case for mobile TV. Considerations of acceptable signal strength particularly indoors imply much higher power transmission or, alternatively, multiple repeaters across the city.
The T-DMB services are derived from the standards for digital audio broadcasting and have a robust error correction layer and mobility features. The handsets can be used at vehicular speeds in excess of 250 km/hour in the VHF band. T-DMB does not have any features that are designed specifically for the support of power-saving tuner technologies. However, the relatively lower bandwidth (1.7 MHz compared to 8 MHz for DVB-H) leads to lower power consumption, though higher than DVB-H (Table 5-5).
5.22 OUTLOOK FOR MOBILE TV SERVICES
The field of mobile TV services together with those of mobile multimedia is likely to witness a significant growth in the near future as the 3G networks continue to grow and evolve further and the rapidly growing number of users reaches a critical mass, which will further drive down the prices of handsets and services.
We are also likely to continue to witness a flux in the technologies deployed as various issues such as spectrum allocation, licensing, and standards evolution continue to move toward a globally harmonized set of accepted solutions. The WARC in 2007 and beyond will act as an enabler of mobile TV services by focusing on standardization of mobile TV services.
Comparison of Mobile TV Services
Some of the parameters should be considered only indicative due to evolution of technologies and operator-specific implementations.
The networks being deployed are capable of delivering much more than only mobile TV and we are likely to witness a continued growth in the use of multimedia services as well, enriched by animation and rich content made available by the networks and playable on the growing base of multimedia phones.