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Cutting Edge - Latest broadcasting technologies and solutions

April 15, 2009



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Even as revenues from traditional voice markets are declining, emerging technologies have created new opportunities for telecom operators. While most operators are currently focusing on internet protocol TV (IPTV), mobile TV is also set to witness rapid growth in the next 12-18 months as 3G deployments increase globally. Both these services have complex technologies and solutions.

IPTV

IPTV involves the distribution of TV signals over an IP-based data network.Content streams are acquired, demodulated and decrypted if necessary, and reencoded digitally for IP transport, at times with additional compression and new encryption.

IPTV is a transmission and control technique to deliver broadcast and videoon-demand (VoD) streams to a set-top box (STB). It makes use of IP signalling to change channels and control other functions, and a point-to-point networking infrastructure that supports broadcast video using multicasting techniques.

The access network is still a bottleneck and telecom operators can either improve the copper infrastructure or deploy fibre-to-the-home. While most operators have upgraded the copper infrastructure, in the US, telecom major Verizon has been aggressively deploying a fibre-to-the-premises overlay network. The company plans to eventually abandon copper wires completely.

Regardless of the access network, the IPTV network architecture consists of the national head-end, regional head-end and customer premises equipment (CPE).While the centralisation of back-office functions and content with a countrywide audience will reduce the number of tiers, providing one-on-one content or content with a small group of viewers increases the number of tiers. Very large operators use two national head-ends to provide redundancy and avoid long hauling video feeds.

Network components
The primary IPTV components are video encoders, video servers, middleware, conditional access system/digital rights management (CAS/DRM) and STBs.

Video encoders: These transform an input stream, which can be of various formats, into a digital compressed stream. The video output is either in MPEG2, MPEG4 AVC or WM VC1 format. Video encoders can also encapsulate the video streams into a transport format that can be an asynchronous transfer mode (ATM) adaptation layer or IP packets. Though most video encoders for live TV are in the national head-end, they may also be present in regional headends for local programming.

Video servers: These are computerbased devices connected to large storage systems. Video content, previously encoded, is stored either on a disk or in large banks of random access memory (RAM). The servers stream video and audio content via unicast or multicast to STBs. These are mostly used for VoD. The key technical attributes of video servers are scalability in storage, number of streams, management software and variety of interfaces.

Middleware: Middleware is the software and hardware infrastructure that connects the components of an IPTV network. It is a distributed operating system that runs both on servers at the telecom operator's premises and on STBs. The middleware performs end-to-end configuration, provisions the video servers, links the electronic programme guide (EPG) with the content, acts as a boot server for the STB and ensures that all STBs run compatible software.

CAS/DRM: CAS allows for the protection of content. As IPTV becomes a mainstream service, content providers are mandating CAS and DRM, which not only controls real-time viewing but also what happens to the content after it has been viewed once. Most CAS/DRM systems are a combination of scrambling and encryption. The video feed is scrambled using a control word. The control word is sent over an encrypted message to the decoding device. The CAS/DRM module on the decoding device decrypts the control word that is fed to the descrambler.

STB/Terminal: The STB is the CPE responsible for the interface between the user, the TV and the network. It hosts the middleware. For live TV and VoD, the STB supports an EPG that allows users to navigate through content. The STB transforms a scrambled digital compressed signal into a signal that is sent to the TV. The cost of the STB is potentially the most important factor for any IPTV operator.

Key technologies
Broadcast video is implemented using multicasting. Internet group management protocol (IGMP) is the control protocol of choice.

IGMP/Channel change: Most applications on IP networks are unicast, which means that a data connection is set up between two hosts. However, for IPTV, data must be multicast from a source (called the root) to a number of end devices (called leaves). IP multicast allows a host to send packets to a virtual address that is not directed at a particular host. The multicast address is used as a logical identifier for the content. To support this mechanism, most IPTV deployments use the Internet Engineering Task Force's IGMP. IGMP allows for the creation of multicasting trees built from the leaves onwards. When a subscriber wishes to view a specific video content, an IGMP "join" message is generated from the STB to the network. The message travels upstream until it reaches a multicast node. The "join" request is detected by the multicast node, upon which the required content is replicated and a copy forwarded tothe STB. Similarly, when a user wishes to change the channel, it first sends an IGMP "leave" message to the multicasting node. Only after it has effectively left a multicasting group can a user join another group.

However, switching and/or routing multicast groups can take time (from 100 milliseconds to seconds). Making this happen fast enough for channel-hopping is a major IPTV design challenge.

Video codec: The IPTV video encoding techniques include MPEG2, MPEG4 AVC and WM VC1. MPEG2 is the encoding of choice for digital cable and digital satellite systems. However, the compression efficiency of MPEG2, while sufficient for hybrid fibre coaxial (HFC) or pure fibre networks, is not sufficient for copper wire.

As a result, MPEG4 AVC or WM VC1 is mostly needed. The superiority of MPEG4 AVC over MPEG2 is largely due to a substantial improvement in motioncompensated prediction. MPEG4 also extends the adaptive field or frame encoding mechanisms. MPEG2 uses pictureadaptive field or frame coding. MPEG4 AVC adds the tools to allow the field or frame coding to be adapted on a macroblock basis.

As the technology of most IPTV components is now mature and the cost of equipment has reduced, IPTV presents a successful business model.

Mobile TV

While the mobile TV market has grown slowly so far due to the huge investments involved, the service is now poised to become the next great mobile accessory with analysts projecting that 50 million digital TV-ready mobile handsets will be shipped in 2009.

There are currently around seven standards for mobile TV. Digital multimedia broadcasting (DMB) is widely used in South Korea, while Qualcomm in the US relies on the MediaFLO standard that it developed itself. In the UK, Virgin Mobile is offering TV services based on digital audio broadcasting (DAB), a technology generally associated with digital radio. The European Union uses the digital video broadcasting-handheld (DVB-H) standard.

DVB-H
DVB-H is one of several technologies that are competing to become the global standard for mobile TV. DVB-H is an open industry standard that was developed by the DVB Project, an industry consortium, and is supported by companies such as Nokia. DVB-H works in the same way as existing digital TV services. Signals are directly broadcast from towers to compatible handsets, bypassing the mobile phone networks altogether.

Proponents of DVB-H say that the system is best because it is not constrained by the capacity of the networks. So, for example, if thousands of people want to watch a sporting event at the same time, the system can still deliver good quality video and sound.

The technology offers a channel changing time of 1.5 seconds with MPeFEC (multi-protocol encapsulation forward error correction) and short synchronisation time, and provides 9 to 18 channels of content in 6 MHz of spectrum, depending on the resolution of content. However, according to industry experts, while DVB-H's quality of service (QoS) is improving, it is yet to broadcast digital content at the claimed speed of 25 frames per second.

DVB-H uses time slicing to enhance the battery life by leaving the radio frequency front-end off 90 per cent of the time. This means that with an 850Ahr battery, DVB-H can deliver a viewing time of at least three and a half hours. Most of the battery is consumed by the phone's display.

However, the service requires dedicated spectrum as well as installation of new broadcast equipment.

MediaFLO
Qualcomm has designed from the ground up a multicast technology called Forward Link Only (FLO). FLO is essentially a broadcast service used in case of mobile TV applications.

MediaFLO uses 700 MHz spectrum to support up to 20 streaming channels, 10 audio channels and numerous IP datacasting channels. It has been successfully deployed in the US by Verizon and AT&T, and trials are under way or have been completed in the UK, Japan, Hong Kong, Taiwan and Malaysia.

The transmission modulation scheme is based on orthogonal frequency division multiplexing (OFDM) and is designed to transmit video at more than 15 frames per second to a QVGA screens. This technology allows for four hours of continuous viewing on a single battery charge.

According to the supporters of this technology, it provides twice the coverage or twice the number of channels on the same spectrum. According to Qualcomm's technical white papers, FLO can provide 20 channels over a 6 MHz channel while DVB-H can provide only nine. Enhanced time and frequency diversity, statistical multiplexing and variable bit rates result in extra capacity for additional programming options. The channel switching time is about two seconds.

However, being developed as a proprietary technology, MediaFLO is an isolated standard. A widely adopted technology, on the other hand, promises more handsets, more chipsets, more network equipment and presumably more content to distribute –­ all of which can achieve the economies of scale that a proprietary technology cannot.

Advanced-vestigial sideband (A-VSB)
A new mobile TV standard that has come up in the past one year is A-VSB. This technology is a backward-compatible enhancement to the US broadcasting industry's existing digital TV transmission systems. The platform takes broadcast streams that any local TV affiliate uses over the airwaves, transcodes them into a smaller hand-held screen format and transmits them side by side with normal programming. Thus, all the prohibitive investments that have limited mobile TV are not needed for this technology as broadcasters can use their existing airwaves, content and broadcast gear.

The technology has emerged from the Open Mobile Alliance, but it was developed by Samsung, which, not surprisingly, is its leading proponent. Putting the mobile version of broadcast content back on the broadcasters' airwaves would free up the much more expensive multicast and unicast networks to offer premium content.

Clearly, with so many standards to choose from, mobile TV operators are faced with the task of implementing the technology that will fit their business model best.



 
 

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