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TV Technologies: Key options to deliver television services

April 15, 2010

With internet protocol television (IPTV) and mobile TV deployments taking off around the globe with digital video broadcast transmission to handheld (DVB-H) and other technologies, operators are now looking at different methods of optimising the transmission networks. This is vital both from a technical as well as a business viewpoint as it will lead to lower operational costs and higher margins.

With IPTV emerging as a key revenue generator for telecom operators and proving to be a viable alternative for the delivery of video by telecommunications and cable companies, wireless options for last mile access are increasingly being considered by operators. Simultaneously, telecom operators across the globe are leveraging their existing networks and experimenting with different broadcast technologies for delivering mobile TV services in order to tap the huge revenue potential offered by these services.

IPTV

IPTV or television distributed over an IP network such as the internet or a local area network (LAN) is different from television, which is normally distributed through traditional broadcast methods or cable. In the case of internet TV, streamed TV, video and radio are transmitted via broadband access.

There are four basic types of IPTV: internet IPTV, telecommunications IPTV, broadcast IPTV and local or building IPTV. Internet IPTV is delivered over the public internet to all parts of the world.However, since content is delivered over the public internet, there is no effort to optimise either bandwidth or content delivery. Therefore, there are delays in transmission and the quality of content is low.

Telecommunications IPTV is delivered through a wired service. In this case, operators can implement quality of service (QoS) mechanisms that ensure reliable delivery of live and on-demand content. In the case of broadcast IPTV, television broadcasters transmit their programming via the internet for public consumption. However, the broadcast suppliers have no control over the bandwidth or QoS.

Local or building IPTV is designed to distribute television and video across buildings and campus networks over a closed network or LAN. Content is distributed directly into the network, giving users access to high quality television and video.Building IPTV offers many advantages, including access to the almost unlimited bandwidth available from a LAN, the control of and ability to charge for content, and no costly internet bandwidth use.

IPTV network architecture

The IP network over which IPTV is delivered is controlled by the operator and several types of networks are used for delivering triple-play services including wired and wireless networks.

Wired IPTV networks

IPTV networks are built by wireline carriers using either hybrid fiber coax, digital subscriber line (DSL), Ethernet or passive optical networks (PONs).

While coax cables support a higher bandwidth than the twisted pair, these may require upgradation to support high definition television services. In the case of DSL, which delivers services across a copper connection, there are multiple variants, with the asymmetric DSL family being the most prevalent. Being distance sensitive, DSL cannot reach every subscriber on its own, and fibre must be deployed to connect to a DSL access multiplexer (AM) located in an outside plant cabinet.

PON technology is used to deliver the service using end-to-end fibre. A single fibre leaves the central office, and a passive splitter in the outside plant splits the signal to support multiple subscribers. Broadband PON supports up to 32 subscribers per port, while gigabit PON supports up to 128 subscribers per port. Ethernet, sometimes known as active Ethernet to differentiate it from PON, is used for point-to-point connection to subscribers.

These technologies can also be used in combination. Ethernet is commonly used to deliver the signal to a DSLAM located in the outside plant.

Wireless IPTV networks

Apart from wireline operators, fixed wireless and mobile service providers are also looking to offer triple-play services. In these cases, the satellite is an option for delivering television services to a large customer base cost effectively, as major telecom operators have entered into partnerships with satellite providers. However, the 120 millisecond delay introduced by the satellite makes it a poor choice for real-time or bi-directional traffic. Therefore, telephone services are not provided and data services are typically viable only for customers in remote areas that cannot be serviced by cable modems, DSL or PON.

Fixed wireless technologies such as Wi-Max are also being evaluated for IPTV delivery since they provide high bandwidth and greater scalability. However, analysts at consultancy firm Research Rethink Associates state that the technology, in its current flavour (the mobile version), delivers 288 Mbps in both directions within a single cell. While this may be sufficient, it is not viable for fixed TV as it is unable to meet the capacity requirements.Also, contention ratios are much lower for broadcast TV, and in practice 288 Mbps might only be able to serve 100 or so consumers per cell for high density services requiring 8 Mbps per channel with advanced H.264 compression. In contrast, most IPTV multicasts use 600 Mbps to 1 Gbps. Yet, some major TV distribution vendors, such as Motorola, are backing Wi-Max for IPTV in the longer term, arguing that the bandwidth constraint will only be temporary. The forthcoming WiMax 802.16m standard will increase the bandwidth per cell by almost four times to 1 Gbps, making TV delivery feasible.

Mobile TV

For telecom operators, mobile TV services have the real potential to boost top line revenue growth, increase market share and improve customer satisfaction and retention, and offer a huge business opportunity.However, the growth of digital TV subscriptions has not taken place at the originally anticipated pace despite impressive service offerings in the market.

While existing mobile video offerings have suffered from a number of technical issues such as irregular image streaming, buffering and low image quality, the challenge has been compounded by the various mobile TV technologies and networks under consideration across the world.Mobile TV is currently delivered via broadcast, unicast and multicast technologies.

Unicast

Most mobile operators currently deliver mobile TV over their networks using a unicast platform. Unicast can deliver scheduled (and live) streaming (TV/multimedia) services as well as video-on-demand. This platform can be used to efficiently deliver a large number of niche TV channels to individual end-users, to deliver on-demand TV and time-shift the delivery of linear TV, and to provide interactivity for and facilitate the personalisation of TV services.

However, this technology is not optimal for a large number of subscribers located in the same geographical area –­ a situation where many users are watching the same channels at the same time. With increasing mass audience uptake of mobile TV, the most-watched TV programmes will need to be broadcast by an overlay infrastructure, and enablers to maintain QoS will need to be built into the network.

Broadcast

An alternative approach is to use a broadcast network to offer mobile TV services.Broadcast mobile TV delivery platforms offer a number of advantages over unicast.One of these is the utilisation of dedicated spectrum for broadcast services, which eliminates any impact on finite capacity 3G services. The dedicated spectrum also means that mobile TV services can be broadcast using more ideal spectrum. For instance, ultra high frequencies (460 MHz to 860 MHz) and very high frequency band III (170 MHz to 240 MHz) offer the best balance of coverage penetration, handset design, infrastructure costs and practicality. There are a number of technology platforms for delivering broadcast content to mobile terminals: in-band cellular broadcast technologies such as the multimedia broadcast/multicast service (MBMS); terrestrial digital broadcast networks and their extensions such as DVB-H terminals, based on DVB-T standards; Media Forward Link Only (MediaFLO), a Qualcomm proprietary solution improving DVB-H, etc.; and hybrid satellite/terrestrial systems such as S-DMB from SKT in Korea, and MobaHO! from MBCO in Japan (both projects use the same MBSAT satellite).

Multicast

Multicast services within UMTS networks are based on MBMS. The multicast service optimises the delivery of services dedicated to a large number of users as it reduces overall bandwidth consumption and the load on network elements. The service is also scalable. With MBMS, the greater the number of users in a particular area, the more compelling the service, since revenue is received a number of times while data is sent only once over the radio.

Around end-2009, an emerging broadcast technology –­ integrated mobile broadcast (IMB) –­ a complement to the existing MBMS standard, became more than a blip on the industry's radar with the GSM Association and operators including Orange, SingTel, Softbank, Telstra, T-Mobile and Vodafone backing the technology.

IMB will enable better mobile TV picture quality since the technology makes it possible to use more bandwidth per channel and more channels. It will also enable operators to take advantage of the previously unused time-division duplex spectrum, which most operators in Europe received when they were awarded 3G licences. Spectrum is also available across Asia and most parts of Latin America and North America.

Network topology

The choice of network topology for broadcast mobile TV is largely driven by the ability to leverage the existing infrastructure. There are currently two architecture models that can be deployed. While the existing mobile base station infrastructure is employed in the mobile network overlay, a broadcast network overlay utilises the existing broadcast transmission infrastructure.According to industry experts, a broadcast overlay network is more economical as mobile TV multiplex/services are deployed at a city's main television broadcast transmission site to provide blanket coverage.Supplementary in-fill repeater stations support the main transmitter. This architecture requires lesser transmission sites than those associated with a mobile network overlay.However, service providers need to compare both options, as local issues may have an impact on the final decision.

While different technologies and architectures are available for both mobile TV and IPTV, operators will need to determine the right combination of technologies and the most suitable network topology to maximise revenues from these services.

 
 

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