BANGALORE, INDIA: Television has always been confined to the living room. But it's now set to change dramatically thanks to the Mobile Technology. Bringing TV in a newer form today is much more than just bringing the video and audio to the user.

In the digital world, there is much more to it, by way of adding the difference of the additional quality while using lesser bandwidth for the same effect. Also in the digital transmission we talk of additional data being sent which bring added value to the user, in the form of guide and more importantly from a commercial angle the payment for a service, all controlled using software.

TV in its newer avatar has become more complicated. Thanks to convergence and rapid advancement of technology in the world of consumer electronics. Television has indeed come a long way. Devices like the mobile phone, IP networks and broadcast TV are converging.

Both IPTV and mobile TV are great examples. In both these, there are forms that deal with TV from a streaming perspective, where the TV is more on-demand option with pre-recorded content and not a TV in true broadcasting sense.

Here, it will mean live TV as it happens from the source or as intended by the broadcaster, where the user can switch channels and watch his preferred program, live. In addition he should also be able to get information about the programs on offer.

The reality
Mobile TV is becoming a reality as a use-case; from the way mobile phones have evolved. Maturity in LCD screens and low production cost has fuelled their adoption in a host of consumer devices. The mobile phones of today have ceased to be what they were intended to be. They have grown up-to be intelligent devices with calling as "one" of their features.

Though digital broadcasting has been around for sometime now, it would not address the requirements for the new form of mobile TV for the following reasons

a) The size video format planned earlier will not address the new scenario as the screen is small.
b) Does not address effective use of bandwidth.
c) Content protection for paid services cannot be applied from the traditional setup with card
d) The key requirement is for a mobile environment where the user is expected to move at good speeds and the video is not expected to break.
e) Extreme power constraints, which is not the case with Conventional TV.

Technology has to address the above problems if TV has to work on mobile devices. Fundamentally all technologies around the world addressing mobile TV have, as implementation, MPEG4 or H.264 for video format and the size is CIF mostly. And additionally some if not all have good definition for guide. As format is different from the traditional TV, new setups are required to create these and subsequently decode.

Before we get into the details of the system that implement mobile TV, we need to understand how it is laid out. The technology that addresses this new use-case can be divided into two broad parts:

a) One is the bearer technology, which defines the underlying platform for providing all the necessary features to achieve the constraints mentioned above. This is very important as this forms the fundamental block for building the logical layers.
b) Second is the technology for the logical layers or called service layers, which defines how the content is described and the methods for decoding at the end device and usecases for the user to use the system. This mentions what is coming in the stream, how to receive and use it.

The following diagram shows the layout of some of these technologies:

DVB-H system
The DVB-H system is defined based on the existing DVB-T standard for fixed and mobile reception of digital TV. The main additional elements in the link layer (i.e., the layer above the physical layer) are time slicing and additional forward error correction (FEC) coding. Time slicing reduces the average power in the receiver front-end significantly—up to about 90%–95%—and also enables smooth and seamless frequency handover when the user leaves one service area to enter a new cell. Use of time slicing is mandatory in DVB-H.

FEC for MultiProtocol Encapsulated data (MPE-FEC) gives an improvement in carrier-to-noise (C/N) performance and Doppler performance in mobile channels and, moreover, also improves tolerance to impulse interference. Use of MPE-FEC is optional for DVB-H.

CBMS: Convergence Of Broadcast and Mobile Services
* Technical specification and guidelines by CBMS group of DVB Project, for Media and Data Services that utilizes co-operation between broadcast and mobile telecom platforms also referred to as the IPDC.
* Set of systems layer specifications originally designed for use with the DVB-H physical layer.
* Used as a higher layer for all DVB mobile TV system including DVB-SH.
* Could be used as a higher layer for any IP capable system.
Specifications define
a. "What" is delivered
b. "How" it is delivered
c. "How" it is described
d. "How" it is protected
* Focused on functionality, enabling delivery of IP-based services to small, personal, mobile handheld and portable terminals like cellular phones and PDA

The adjoining figure shows the layout from the CBMS/IPDC perspective, showing what the core technology achieves and what it stands on.

OMA-BCAST
* OMA Mobile Broadcast Services.
* By Open Mobile Alliance.
* Create Mobile Delivery system which is bearer agnostic.
* Define the requirements for the enabler for Mobile Broadcast Services.
* Specify the set of functions needed to enable the
a. Mobile broadcast
b. Service guide
c. Service/content protection

The similar view from OMA-BCAST shows the way it is defined for multiple bearer technologies supporting also many services being defined.

Protocol Stack in DVB-CBMS or OMA-BCAST
* Transport of A/V data using RTP/RTCP over IP
* Complete TV guide (ESG) is broadcasted with high compression using Gzip/Bim. ESG is in XML form
* FLUTE (File Delivery Over Unidirectional Transport) protocol/ALC, is used for file delivery over IP
* ESG (Electronic Service Guide)
* Images, Alerts
* Video clips
* PSI/SI data used for service selection (ESG, A/V)
* Interactive network is used for service subscription

End-to-end Architecture in a DVB-H system with IPDC or OMA-BCAST
The end-to-end architecture comprises of how the raw content is got into the system, encoded/transcoded as the case may be (If the content is in MPEG2 then it is transcoded to H.264, a very likely case as the regular digital world uses MPEG2), encrypted using the CAS (Conditional Access System), creating meta data for the ESG (Electronic service guide) and ESG server encoding the ESG data stream and finally passing all this to the IP encapsulator to create the TS (transport stream) which is then modulated and broadcasted.

Multiple A/V sources represent multiple TV Service feeds. These feeds are then routed by the SDI routers to A/V encoders/ transcoders, where the Media data is customized for Mobile TV scenario. ESG Server handles creation and maintenance of ESG. File Server is responsible for file data casting, which includes delivery of ESG CAS module, will interact with Encoders and ESG server for encryption of content and creating information for the terminal to access the protected content.

IP encapsulator handles creation of MPE stream from IP stream and also time slicing. The DVB-H Network manager is manages the entire head-end set up and provides options for configuration of the system.

On the receiver side counter layers are present to handle what encoded at the head-end.  First in the chain is the tuner, which tunes to the frequency of transmission, then the demodulator extracts the TS and gives it to the layers which handle the MPE/FEC (this is what was created using the IP encapsulator).

This layer also handles the time slicing, it is a coordinated effort with the tuner and demodulator as these have to be powered off during the bursts of data and hence saving of power. All these processing are collectively done in silicon and are know as the baseband processing.

The remaining of the processing is done in the software layers running on a host processor of a mobile phone. First of the activities done at the protocol layer by the middleware is, the location and extraction of the right ESG. Then it is decoded and presented to the user. The ESG is the basis for discovering the layout of the stream with respect the channels that are available and how to handle them. The ESG also contains detail information on programs that are available on each channel.

Once the user selects a channel to watch, the SDP file (Session description protocol) pertaining to the channel is extracted and passed to the player. This lets the player know the stream format and how to receive it. The actual video/audio data is pumped into the TCP-IP layer in the registered ports.

The player configures its H.264 and HE-AAC (incase of audio) codecs based on the SDP file data and reads the audio/video packets packaged in the form of RTP /RTCP decodes them using the depacketiser proceeds them to the decoders. In case the data protected, the middleware interacts with the CAS or the security protection module check on the rights of the user to be able to watch the program. This is done using data available on the mobile device in the SIM card or could be done fully in software.

Once the rights are established, the right keys are obtained for the de-scrambler module to process the scrambled data. This is then processed in the same way as in the case of free-to-air channel.

On the receiver side the two clear applications that interact with the user are the TV browser and the TV guide. The browser is the application that lets the user use the TV in the conventional form, i.e. change channels, maybe interact with the program if interactivity is enabled, possibly switch on subtitle and also change volume.

The TV guide is the application that presents the ESG to the user and lets him browse the data of the channels and the programs. It contains data like description apart from the basic information. It would also tell the user about which channel is free-to-air and which is paid and give information about cost, which could also include different payment options.

Variants
Mobile TV as mentioned above can be enabled on a host of devices other than just the mobile phones. Any device that has good LCD, audio, sufficient processing power and is battery powered can enable mobile TV. So we are looking at PDAs, laptops, portable DVD players, gaming consoles, car navigation devices and possibly pure handheld TVs.

These devices would be collectively known as unconnected devices as they do not have the return channel like the mobile phones. Only complication is that the user on the fly cannot contact the operator to purchase the channel, this has to be done offline. Also in these kinds of devices interactivity is not possible in the right sense.

As it is quite clear, technology has addressed all the right issues for making Mobile TV successful in the broadcasting scenario, though the setup and use-case may vary based on regional preferences. One of the biggest issues in the success of mobile TV today, is the complicated business model that has to be accepted, and there is no universal formula. Country specific business model based on the regulatory authority and the lobby have to fall in place.

The author is System Architect, Multimedia Solutions, Tata Elxsi Ltd