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Amid the flurry of activity and hype surrounding mobile TV, STAY CONNECTED steps back and takes a look at the various network models and technology platforms that have emerged as contenders. It is generally well accepted that UMTS-based mobile TV has limitations. The service is here and available now, but the unicast (one-to-one) nature of UMTS means that as the viewer base grows, mobile TV will not be sustainable on this approximately -12 to -16 dB (depending on frequency band) compared with the average rooftop antenna. Additionally, consumers have also come to expect their handsets to work indoors and in using the terrestrial broadcast model, should be capable of providing coverage of a large city using 20 to 50 repeater sites. Qualcomm in the USA is using this model for its commercial MediaFLO service (using the FLO platform), platform—even as UMTS heads towards moving vehicles, each reported to incur but, as other trials have shown, it is also ideal for ‘3G long term evolution’ (3G LTE) or in-band another -8 to -12 dB (or more) signal impact. deploying DVB-H. cellular broadcast techniques such as The provision of indoor coverage is considered The UHF band is also suitable for networks multimedia broadcast/multicast service one of the main challenges of mobile deployed using the cellular overlay model, since (MBMS). Recent reports have suggested TV networks. UHF frequencies are just below conventional that it makes more sense to use the spectrum A third infrastructure model, incorporating global standard for mobile communications for wireless data services that can be charged satellite blanket coverage supported by (GSM) or US ‘Cellular’ code division multiple at a higher rate than can television. low-power terrestrial repeaters, has been access (CDMA) frequencies. This type of network Mobile carriers are therefore turning to proposed. The repeaters would be co-located at is being trialed in many countries across Europe. There is presently a great deal of industry hype broadcast models for mobile TV. Their quest mobile base stations to supplement urban and One of the main challenges associated with surrounding ‘mobile television’. Said by some to to utilize existing base station sites has provide indoor coverage. the UHF band is the limited availability be the next ‘killer app’ of the mobile sector, and led to the ‘cellular overlay’ model for mobile A unifying element in all three network models of spectrum in most parts of the world, but dismissed by others as having no sustainable TV, where broadcast infrastructure is deployed is the convergence of industries that have been especially Europe. Some governments are business model, mobile TV is a conjure of at mobile base stations to provide mobile TV hitherto quite separate. Mobile carriers will considering assigning two or three UHF possibilities. It lies at the eye of a maelstrom of coverage in a similar way to a cell-based mobile need to embrace broadcast technology and frequencies for DVB-H mobile TV services, technologies, network models and frequency network. content; broadcasters (or infrastructure/service which can be deployed as single frequency bands, waiting for many trials to end and the manifestation of a clue as to the most practical Coverage adjustments providers) will need to team up with carriers, who already have the subscriber base. In fact, it networks (SFN). Although it makes network configuration more complex, an SFN is a and commercially viable direction. The broadcast industry approaches mobile seems logical for mobile TV systems to be intrin- highly efficient use of spectrum, and a TV coverage from the other direction. sically linked with mobile phone services, which network of two or three overlapping SFNs 6 COVER STORY Conventional free-to-air TV is typically broadcast from centralized high-power transmission sites, supported by supplementary repeater or ‘gap can provide a one-to-one back-channel for interactivity. This could even prove to be a driver for consumer take-up. could be a promising option. The VHF Band III has even better RF propagation characteristics than UHF. It is not suitable for the 7 The notion of delivering television signals to a important difference is that DVB-H transmits It starts with delivery filling’ stations. It is relatively straightforward to deploy a mobile TV service in the same manner; The band debate cellular overlay model, since the antennas would be too large for existing base stations; moving receiver is not an entirely new concept. the signal in bursts in order to conserve handset The choice of technology platform is just one however, there do need to be adjustments From a technical—and practical—standpoint, but it is an ideal candidate for the terrestrial A number of countries have for years enjoyed battery life. It also incorporates greater element of delivery—and delivery just one to coverage planning. the other major delivery option pertains broadcast model, where city coverage could be live digital television in buses and trains, forward error correction, essential for boosting consideration—in the riddle that is mobile TV. Research indicates that the ‘high-power to frequency band, of which several are achieved with just a handful of repeaters. From courtesy of digital video broadcast terrestrial handheld reception. Commercial imperatives drive all, and are also terrestrial broadcast’ model for mobile TV being considered: VHF (170 to 240 MHz), a network deployment perspective, VHF would (DVB-T) technology. Utilizing coded orthogonal Another significant difference is the data dependent on such aspects as consumer will require more repeater sites than for UHF (470 to 860 MHz), L Band (variable appear to offer the lowest roll-out costs coupled frequency division multiplexing (COFDM) encapsulation technique. The DVB-H stream viewing habits, handset development, conventional television. One reason is because, depending on region, but generally falls with the best indoor coverage. modulation, DVB-T was originally designed with mobile applications in mind. The signal can is an IP datacast at 200 to 500 kbps/program, yielding up to 50 programs in an 8-MHz channel. content licensing and government regulatory environment. Yet it is with delivery that the owing to an increase in reflections at ground level, the forward error correction applied to somewhere between UHF and S Band) and S Band (2170 to 2200 MHz). Factoring in availability accommodate variations in signal strength, field This resolution is sufficient for the tiny handset whole mobile TV enterprise gets moving, and the signal is increased, resulting in a trade-off Most popular globally for digital terrestrial Korea and China are both deploying commercial strength and multiple reflections that typically screen. In contrast, standard-definition DVB-T delivery infrastructure that represents a in signal-strength that needs to be addressed. television is the UHF band, which has also seen T-DMB mobile TV services in VHF Band III, as per reach a receiver in motion. uses MPEG-2 (or MPEG-4) encoding at significant proportion of capital outlay. It has been reported that a receiver at ground the most mobile TV activity to-date. It has good DAB services. To-date, there has been no move However, despite this foresight in its 4 to 5 Mbps/program, yielding up to five Consequently, the question of which delivery level incurs a signal-strength penalty of propagation characteristics and, if deployed to deploy DVB-H in VHF Band III; however, since development, DVB-T as it stands is not ‘standard resolution’ programs per channel. model proves best—and most cost-effective— appropriate for broadcasting to handheld DVB-H is not the only mobile TV platform is one of high interest. devices. Nor is its US counterpart, the advanced television systems committee (ATSC) standard, finding favor. Korea and China are the first to embrace terrestrial digital multimedia broadcast Speculation is compounded by the existence of several different industry players. On the one hand, there Network models for mobile TV utilizing 8 Vestigial Side Band (8VSB) (T-DMB), derived from the Eureka 147 digital are the mobile communications carriers. These have modulation, which was never designed for audio broadcast (DAB) standard. Moreover, the an existing subscriber base and perceive mobile TV mobile applications. USA’s Qualcomm has developed the forward as a means of extending and differentiating their Experiencing TV on handheld devices raises link only (FLO) technology for the delivery of service. Many have introduced third-generation a whole new set of issues that have spawned multimedia content. T-DMB, FLO and DVB-H (3G) mobile TV services based on universal mobile several new broadcast technology platforms. have each addressed the same handset-related telecommunications service (UMTS) in recent Attracting the most attention globally is the issues—battery life, reception and screen months, while at the same time partnering broad- digital video broadcast to handhelds (DVB-H) resolution—albeit in different ways. cast-based mobile TV trials. standard, which is derived from DVB-T. The Cellular overlay model High-power terrestrial broadcast model Hybrid satellite / terrestrial model
DVB-T services operate in VHF Band III, there seems little reason why DVB-H would not as well. The main obstacle is again one of spectrum availability—of the four considered bands it has the most limited availability in most countries— coupled perhaps with convention. The other two bands—L Band and the satellite S Band—are emerging as contenders. Both provide reduced terrestrial propagation and in-building coverage compared with the lower frequency bands, but have the advantage of being more readily available. L Band looks set to support a commercial deployment of DVB-H mobile TV services in the USA; S Band is that proposed to support a DVB-H based hybrid satellite/terrestrial repeater model. Irrespective of which frequency band is selected, the signal polarization is also under examination. The FLO systems being deployed use circular polarization (CP), which is a combination of vertical (VP) and horizontal (HP) components. It has been speculated that a CP signal may facilitate reception at the mobile handset regardless of orientation. 8 COVER STORY This may, however, be a moot point, since the multiple reflections experienced by HP and VP signals can alter the polarization, effectively producing a mixture of polarization components by the time the signal reaches the handset. Vertical polarization is favored at present by both DVB-H trials and T-DMB deployments. In the latter case, this probably harks back to the DAB convention, since radio signals are often VP to enhance reception by car antennas. Use of VP also enhances isolation from HP television signals at similar frequencies. Most DVB-H trials are using VP, although at least one utilizes a HP signal. Ultimately, the selection of polarization will depend upon the receiver performance when faced with multiple signals from reflections, plus the indoor penetration of the signal. Which way forward? The future of mobile TV depends on many factors; but if it is proved that consumers want mobile TV—and are prepared to pay for it— then half the battle is won. The network model will then be determined by how cost-effectively networks can be deployed and the availability of frequencies and licenses. This is likely to differ on a case-by-case basis. Utilizing existing infrastructure will be a key element. It is not difficult to incorporate mobile TV services into existing broadband terrestrial broadcast systems—particularly if the systems were initially designed to accommodate additional services or channels. The most significant capital outlay would come with the deployment of additional repeater stations. If, on the other hand, a mobile TV network is deployed as a cellular overlay, this will involve a significant shift in broadcast infrastructure philosophy. The quest to deploy television antennas at existing mobile base stations (hundreds, perhaps thousands, of sites) will encounter the same challenges as experienced by mobile phone carriers—the demand for low-profile, environmentally friendly antennas; Mobile TV at a glance Major technology platforms include: • DVB-H—derived from DVB-T • T-DMB—derived from DAB • FLO—developed by Qualcomm Network models: • Cellular overlay—broadcast network overlaid at mobile communications base stations • High-power terrestrial broadcast— based on terrestrial broadcast models with an increased number of repeater stations • Hybrid satellite/terrestrial—uses satellite for blanket coverage, supported by terrestrial repeaters the mandate for low emissions; site-by-site negotiations; and the trade-off between capex and opex. It could also promote utilization of the higher-frequency L Band and its inherently more compact infrastructure. Co-location interference issues also need to be considered when overlaying mobile TV and wireless communications services. With UHF frequencies so close to the GSM 900-MHz receive band (usually 890 to 915 MHz) and the CDMA 800-MHz receive band (usually 824 to 849 MHz), careful frequency planning and coordination will be required. Moreover, if the broadcast signal is too high in power, it could cause ‘blocking’ in the sensitive GSM or CDMA receivers, unless RF filtering is deployed. Similar situations arise with both the L Band and S Band frequencies, which are all in the vicinity of high-band GSM, CDMA and UMTS services. In addition, it is likely that all mobile TV network topologies will ultimately need to incorporate dedicated wireless indoor solutions (WINS) to provide coverage inside multi-level buildings, large campuses (such as airports and shopping malls) and underground road tunnels and metro systems. These could be integrated with existing broadband WINS systems for mobile wireless communications. True convergence Clearly, for mobile TV to succeed as a commercial venture, it will involve many players in the wireless sector: mobile phone carriers, broadcasters, handset manufacturers, content Frequency bands: • VHF Band III (170 to 240 MHz)—Best propagation, including indoor coverage, but limited availability • UHF television band (470 to 860 MHz)— Good propagation with moderate indoor coverage, but limited availability • L Band terrestrial/satellite (between UHF and S Band, depending on region)—Lower terrestrial propagation and poor indoor penetration, and availability dependent on country • Satellite S Band (2170 to 2200 MHz)— Low terrestrial propagation and indoor penetration, but very good availability. providers, infrastructure groups, base station OEMs, government and licensing bodies. These parties will need to collaborate and form partnerships in order to make mobile TV work—both technically and commercially. The quest to maximize the bottom line will ultimately reveal which network model, technology platform and frequency band combine to form the most viable option for a specific country or market. And it will be dependent on which provides the most attractive and accessible model for consumer uptake. Whatever the outcome, it will represent a true convergence of multiple technologies. From this will materialize the true meaning of mobile TV. China mobilizes for mobile TV A complete VHF antenna solution from Radio Frequency Systems allows Guangdong Mobile Television Media Co. Ltd to deliver one of China’s first mobile television services. In early 2006, one of China’s newest mobile media companies, Guangdong Mobile Television Media Co. Ltd (GMTM), embarked on a three-stage broadcast initiative, delivering dual-channel mobile television service to China’s southern province of Guangdong. The Guangdong mobile TV project is the largest commercial mobile television network in the world to date, and represents a broadcast engineering accomplishment of the highest order. One of China’s first mobile television services, the Guangdong mobile TV network employs digital multimedia broadcasting (DMB) technology, making GMTM one of the first service providers outside of South Korea to adopt the digital transmission system. With the Chinese government yet to establish a national digital transmission system standard, the success of the Guangdong mobile TV network is sure to provide a valuable reference point. Implemented in three stages and scheduled for completion in mid-2007, the Guangdong mobile TV project incorporates 42 separate antenna systems. With transmission sites located in Guangdong province cities of Guangzhou, Foshan, Zhongshan, Dongguan, Shenzhen and Zhuhai, the country’s latest broadcast installation is predicted to attract over three million viewers. A series of combined broadcast systems designed and manufactured by Radio Frequency Systems, allows the transmission of two Band III VHF channels, delivering mobile TV to the handsets of urban and rural citizens of Guangdong. Putting the signal on the ground With extensive global experience in providing broadband RF solutions, RFS joined the Guangdong mobile TV project in the early stages of design, and collaborated with GMTM in order to produce a fully engineered broadcast system, tailored to the various local broadcast environments. According to Kimbo Zeng, RFS Broadcast Product Manager China, providing digital mobile television coverage to handheld devices differs greatly from the provision of standard terrestrial TV coverage, and involves a unique set of engineering challenges. “When planning coverage for broadcast signals to fixed television antennas, the receive antenna height is assumed to be approximately ten meters (30 feet) off the ground,” says Zeng. “However, to ensure optimum mobile TV reception, greater coverage saturation is required. Mobile TV coverage planning should be carried out assuming that the signal must be supplied only one meter (3.3 ft) off the ground or ‘put on the ground’. This means that existing planning tools used to design traditional fixed TV coverage need to be modified. RFS’s broadcast experience and knowhow has enabled us to adapt to the unique technical requirements of mobile TV.” The 42 combined broadcast systems used to achieve this saturated coverage comprise a range of the latest RFS technologies. RFS’s 618 series side-mount dipole antennas or RFS’s 659 series panel arrays were used to provide a precise broadcast signal to suit each site’s individual broadcast environment. A RFS CA6PX180DAB balanced combiner system enables the RF combining of the two mobile TV channels broadcast from each site. The RF link between the transmitter and the antenna is achieved using 1-5/8-inch diameter HELIFLEX or CELLFLEX coaxial transmission line. Zeng explains the need for using two different antenna types: “The 659 series panel array allows a more tailored pattern coverage, like that required in the built-up environment of Shenzhen,” he says. “The 618 series side-mount dipole antennas are used in the other Guangdong cities where a standard 270 or 360 degrees horizontal radiation pattern (HRP) was required.” TV in the hands of the people Stage one of the Guangdong mobile TV project was completed in May, 2006, with eight antenna BROADCAST 9 systems installed across the major city centers. These support uninterrupted broadcasts of a range of information, sports and entertainment programs. “Stage one of the mobile TV network is already providing the citizens of Guangdong province with unprecedented flexibility in their television viewing,” says Zeng. “Broadcast technology from RFS has placed television in the hands of the Chinese people.” Stage two is due for completion by the end of 2006 and includes the provision of an additional 13 antenna systems, with 21 antenna systems to follow in the third and final project stage in mid-2007. With the 2008 Beijing Summer Olympic Games approaching and the 2006 World Cup contested earlier this year, the implementation of the mobile TV technology could not have come at a better time. “The first-stage network provided die-hard football fans with around-the-clock World Cup coverage, while the completed Guangdong mobile TV network will be fully operational in time for the 2008 Olympics,” says Zeng. “RFS’s ability to provide GMTM with a tailored end-to-end broadcast solution means millions of Chinese sports fans won’t miss a thing.”
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