Multimedia images, radio and internet are brought to portable devices by using digital radio transmission. Both satellites and terrestrial methods can be used for digital multimedia transmission methods [Wisegeek, 2010]. A handset which is installed in mobile phone s, laptops and other portable devices is used to receive these transmissions. Terrestrial methods of transmission uses VHF and UHF radio frequency. Terrestrial transmission provides the best quality for image output since it uses some of the best audio and video coding. The advantage of using satellite based transmission is that it can cover an entire country [Freepatentsonline, 2006].
The term convergence depicts both, the unification of various industries such as communications, computing, entertainment etc. as well as converging video, voice and data over a universal infrastructure. A factor which plays a major role in convergence is the transformation of a desktop computer to support advanced graphics and multimedia features by using faster processors. Computers today are a collaboration of both media tool and communication. Major factors which lead to convergence is the cost required for maintaining three separate networks for data, voice and video. Using converged networks leads to significant savings for major corporations [Gerami. M, 2010]. Organisations can achieve cost saving by using voice over frame relay, VOIP and voice over ATMs using the same WAN lines for both voice and data transmission [Gerami. M, 2010]. Organisations also want to install WAN and LAN networks for delivering real time audio and video data.
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The aspect of converging network to transmit various data in the same communication format is called as payload converging [Takanashi, H. et. al. 1998] . The network is not prohibited by the payload convergence from carrying data according to the required service. The difference between legacy networks and converged networks is that the former networks are designed to transmit several protocols but one type of data where as converged networks transmit one protocol but depending on the service requirements, different types of data e.g. video, interactive video etc [Gerami. M, 2010].
When payload travels over the same network irrespective of the service requirements, physical convergence occurs. The features of the edge network can be used by both, web and multimedia traffic. This happens even though multimedia has more stringent bandwidth, delay and jitter requirements [Gerami. M, 2010].
If the same network architecture supports various network paradigms in a single system, then it is called as device convergence [Takanashi, H. et. al. 1998] .
The appearance of various applications that integrate former separate functions is represented as application convergence. The plug-in applications used in web browsers to allow audio, video and other graphic features are an example of application convergence [Gerami. M, 2010].
A common network technology which can satisfy both LAN and WAN features is a representation of technology convergence [Gerami. M, 2010]. An ATM which provides both LAN and WAN features is an example of this type of convergence [Takanashi, H. et. al. 1998] .
Integrated interactive video, audio, text and data can be delivered to the real multimedia using digital transmission at the technical level. It can be noted that each type of transmission is designated with a type of communication. For example, point to point communication is linked with telephonic communication and wireless transmission is related to news and entertainment. However, with development with digital transmission can increase the transmission capacity of telephone and cable infrastructure to deliver a range of data that previously required expensive broadband cables [Gerami. M, 2010]. Digital compressions also allow advanced radio transmission to conduct increased point to point communication [Takanashi, H. et. al. 1998] .
Digital communication allows IT companies and telecommunication organisations to offer services on an international scale rather than their usual business sector. Convergence is not just about technology but it is more about the development of the Information Society as a whole [Takanashi, H. et. al. 1998] [Gerami. M, 2010].
Digitisation drives innovation in technology and services. Examples are higher speed broadband and huge diversity in the physical infrastructure, widely distributed connectivity and also the social web [Gerami. M, 2010]. The developments in the broadband speed and the infrastructure are a sign of availability of a wide variety of choices and increase in the bandwidth [Takanashi, H. et. al. 1998] . The advancements in distributed connectivity and the smart radio design have hugely increased the market for wireless radio connectivity over wired access [Gerami. M, 2010].
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This trend is also true for computer networking and IP-multimedia services. But it is most notable for the integration of information processing known as ubiquitous computing [Gerami. M, 2010]. The side effects of digitisation are the increased use of content monitoring technologies and also the need to improve security and identity management.
Convergence at the Marketplace
The technological development has widened the access to communications links allowing distribution of both commercial as well as entertainment materials. It has also lead to great development in the field of telephonic communication. Different types of data representation such as video, audio, text etc. have combined together due to digital technologies. This has lead to the removal of distinction between the various types of information production and distribution [Gerami. M, 2010]. Also various digital platforms are providing a choice of various services to the consumers. Therefore emerging technologies will provide unlimited educational, informational ad entertainment resources to the consumers. It will also redefine the way people communicate with one another [Takanashi, H. et. al. 1998] .
When considered at the market level, convergence is the increase in the mergers, the acquisitions and the strategy based alliance between major corporations in IT telecom and broadcasting industry. Therefore when developing new policies for the digital transmission it must consider the various issues raised by these convergences [Gerami. M, 2010].
Introduction to DMT
Digital multimedia transmission has gained lot of importance recently. Digital transmission has replaced analogue TV transmission. Mobile communication has evolved from being purely telephony to third generation mobile multimedia communication. The combination of broadcast systems such as DAB or DVB with mobile multimedia networks such as UMTS is very important these days [Takanashi, H. et. al. 1998] . Multimedia Broadcast/Multicast Service (MBMS) is an example of point to group, i.e. a person to a group of people in a particular area transmission. As the name depicts it has two modes namely: Broadcast mode and Multicast mode [Gerami. M, 2010].
Broadcast mode is a unidirectional single entity to multi user transmission of multimedia data such as text, video, audio etc. It can reach all the users in the area or areas of broadcast. In this mode data is transmitted over a common radio channel thereby effectively using the radio or network resources. The broadcast area where the data is transmitted is defined by the network [Takanashi, H. et. al. 1998] .
The multicast mode allows a unidirectional transmission to occur from a single entity to a multicast group in a multicast area. Multimedia data such as video, text, audio etc. is transmitted. The data is transmitted in a common radio channel. The multicast area for data transmission is defined by the network. In multicast mode, it is possible for the network to transmit selectively to cells in the multicast area contained by the multicast group [Gerami. M, 2010].
DMB is noted as the future of digital broadcasting services for both interior and outside users. In Korea, current DMB users can enjoy CD quality audio services and real time video streaming even when moving at a speed of up to 125 mph. The DMB audio services support standardised stereo broadcasting at the rate of 48 KHz. This service provides better quality audio than the analogue FM radio. The maximum bit rate for audio is 128 Kbps [Gerami. M, 2010].
The technique used to cover a mass communication in different areas is satellite digital multimedia broadcasting (S-DMB). It can be used in areas where terrestrial coverage is not possible. It can be employed in areas where terrestrial coverage is too expensive to be deployed. It provides high data rate transmission to 3GPP standardised sets. It operates at the IMT-2000 frequency having a dedicated geostationary satellite.
DMB technology introduces its users to features like very clear video, theatre type audio and it also allows the streaming of data in handheld devices. If the analogue technology is used in mobile devices, it produces broken images and other noises. The most important factor of DMB technology is speed which is responsible for providing stabilised services to portable equipments [Takanashi, H. et. al. 1998] . The DAB mechanism is utilised by DMB technology to provide services to its users. The major operation concerns are a full nationwide coverage to increase the number of audiences and delivering content in a cost effective manner and prevention and protection against unauthorised content sharing [Freepatentsonline, 2006]. The operation of S-DMB is as follows:
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A direct satellite distribution link which exploits 3GPP distribution over MBMS is used to convey the multimedia content to the 3G handset.
The 3G mobile network is used to achieve service management and interactivity.
The push service technology along with the local storage is used to control the bandwidth usage and also to maximise the content delivery capability of the satellite broadcast.
The local storage is filled and managed by using predictive cache management techniques.
Only the contents that might be of use to the subscriber are processed at the physical level of the handset.
The 3GPP MBMS streaming by pre emptying the capacity allocated for the purpose of push and store services are used to deliver streaming services [Gerami. M, 2010][Freepatentsonline, 2006].
T-DMB provides audio services using the Digital Audio Broadcasting (DAB) framework. The multimedia services provided by T-DMB have VCD visual and CD audio quality. It can also provide data services which may or may not be dependent on the audio video services. The telecommunication channels are used to recognise the subscriberââ‚¬â„¢s interactions with local and remote surroundings. ITU-T H.264| ISO/IEC 14496-10 MPEG-4 ââ‚¬" AVC (Audio Video Coding) for video and ISO/IEC 14496-3 MPEG-4 BSAC (Bit Sliced Arithmetic Coding) for audio and ISO/IEC 14496-1 MPEG-4 system for interactive multimedia are the major components of the T-DMB system. The BER performance is improved using the Reed Solomon coder and ISO/IEC 13818-1 MPEG-2-TS is used for the purpose of multiplexing the contents [Gerami. M, 2010]. MPEG-4 AVC has twice the compression efficiency of MPEG-4 Part 2 visual. MPEG-4 BSAC has the same compression efficiency as MPEG-4 AAC (Advanced Audio Coding) but has better grain scalability. Another reason for adapting MPEG-4 systems is that it provides interactive services with proper synchronisation between the multimedia objects.
Satellite Digital Multimedia broadcasting is a concept which helps convergence between telecommunication and broadcasting. Among all the frequencies available for the purpose satellite use, the most suitable for mobile environment is the S-DMB frequency. The code division multiplexing (CDM) used by S-DMB is similar to the one used by cellular phone services. It is not only best suited for signal reception in a cell phone but also to protect against multiple channel interference which can reduce the quality of signal reception in a mobile environment [Gerami. M, 2010].
T-DMB vs. S-DMB
CH 12 in band III
1 VHF TV channel
13 channels in 25MHz bandwidth
Available on ground (Underground and gaps not guaranteed)
Possible solution for gaps
National level broadcasting
Source [Gerami. M, 2010].
The technology which aids in a resourceful distribution of the digital signal to mass audiences and cost effectiveness is called as IP data casting. It is a combination of digital broadcasting and IP based services and data. It aids in large scale distribution. It not only works for hand held devices but also for other equipments such as in car entertainment [Wisegeek, 2010]. The transmission cost in IPDC is fixed irrespective of the number of users. But in case of 3G and WLAN networks it depends on the number of users. Broadcast doesnââ‚¬â„¢t depend on the number of user or the bottlenecks to reach its users.
In-built antennas, reduced screen size and battery power are the IPDC differences between mobile devices and digital TVs [Gerami. M, 2010]. Up to 90% of the power can be saved using the DVB-H technology. Digital TVs can send only 3 to 4 channels in the same network but IPDC can send 50 to 80 channels.
IPDC Operation [Gerami. M, 2010]:
The content producer creates the content.
It is the delivered to the content provider who modifies and sells it to the content aggregator.
It is then combined with various services and then passed on to the IPDC service provider.
Here the contents are encrypted and service guide and list of pricing is created.
It is then broadcasted in the air and is received and consumed by the user.
The physical connection is maintained by the interaction channel network operator [Gerami. M, 2010].
Content of DMT
Texts, images and sound that is digitalised and served to the subscribers make up the digital content. Video games, e-learning, mobile are all representatives of digital content. One Source Multi Use (OSMU) is the uniqueness of digital contents. The distribution and availability of wireless handsets and its applications will help increase the value of PC, DTV and other such industries [Gerami. M, 2010].
The most important property of broadcasting product is its content.
Some of the other important factors are: the attention span of the mobile user which is very limited, the display clarity of the equipment, the sound settings, battery life and the standard of living of the user. Constant innovation of new contents is necessary. Combining concepts and approaches that attract new customers and are suitable for the mobile device is very important. Remodelling the existing structure helps cut down costs. This has to be done in a short duration and must be placed within existing parameters [Gerami. M, 2010].
It is an early stage for convergence between telecommunications and broadcasting. It depicts two different trends namely, broadcasting different forms of data o the same line and merging various devices such as TV, phones and computers. Most platforms used today support multi-play and services and this will gradually evolve towards multiservice convergence [Takanashi, H. et. al. 1998]. I this paper I have discussed about the process and properties of convergence and explained its various advantages. I have explained how convergence takes place at various levels. I have provided an introduction into the Digital multimedia Transmission techniques and explained various types of Digital Multimedia Broadcasting technologies. This includes a comparison between Terrestrial and Satellite Digital Multimedia Broadcasting. An overview of the various contents of DMT and its significance has also been provided.