Mobile TV Television Technology
Published on July 25, 2016
Mobile TV is the wireless transmission and reception of television content - video and voice - to platforms that are either moving or capable of moving. Mobile TV allows viewers to enjoy personalized, interactive television with content specifically adapted to the mobile medium. The features of mobility and personalized consumption distinguish mobile TV from traditional television services.
The experience of viewing TV over mobile platforms differs in a variety of ways from traditional television viewing, most notably in the size of the viewing screen.
The technologies used to provide mobile TV services are digitally based,the terms unicast and multicast are used in the same way they are used for IPTV. That is, unicasting is transmission to a single subscriber, while multicasting sends content to multiple users. These definitions also correspond to those given for similar Internet-based applications. For network operators, the challenge has become: 'How can large-scale delivery of high-quality multimedia to wireless devices be implemented profitably?' Although delivery of this type of content is technically feasible over today's existing unicast networks such as 3G, these networks cannot support the volume and type of traffic required for a fully realized multimedia delivery service (many channels delivered on a mass market scale). Offloading multicast (one-to-many) multimedia traffic to a dedicated broadcast network is more efficient and less costly than deploying similar services over 3G networks
Introduction of Mobile TV
There are currently two main ways of delivering mobile TV. The first is via a two-way cellular network, and the second is through a one-way, dedicated broadcast network. Each approach has its own advantages and disadvantages. Delivery over an existing cellular network has the advantage of using an established infrastructure, inherently reducing deployment costs. At the same time, the operator has ready-made market access to current cellular subscribers, who can be induced to add mobile TV to the services they buy.
The main disadvantage of using cellular networks (2G or 3G) is that mobile TV competes with voice and data services for bandwidth, which can decrease the overall quality of the mobile operator's services. The high data rates that mobile TV demands can severely tax an already capacity-limited cellular system. Also, one cannot assume that existing mobile handsets can receive mobile TV applications without major redesign and replacement. Issues such as screen size, received signal strength, battery power, and processing capability may well drive the mobile TV market to design hand-held receivers that provide a higher quality of voice and video than is available on most current cellular handsets.
Many 2G mobile service operators and most 3G mobile service providers are providing VOD or streaming video. These services are mainly unicast, with limited transmission capacity. They are built upon the underlying technologies used in the mobile cellular system itself - GSM, WCDMA, or CDMA2000. An example of a technology designed to work on a 3G network is Multimedia Broadcast Multicast Service (MBMS), a multicast distribution system that can operate in a unicast or multicast mode. Mobile TV services over existing GSM and WCDMA cellular networks operates in the 5 MHz WCDMA bandwidth, and it supports six parallel, real-time broadcast streaming services of 128 kbit/s each, per 5 MHz radio channel
DVB-H is a broadcast/multicast technology that is a derivative of the existing DVH-T (digital terrestrial) standard, but designed for use with mobile devices.Digital Video Broadcasting-Handheld (DVB-H) is based on Digital Video Broadcasting-Terrestrial (DVB-T) specification and provides a solution to lower receiver power consumption and improves mobile receiving performance. The common routes with DVB-T offer a major advantage as where there are existing DVB-T implementations adding DVB-H is cheaper than implementing a system from scratch.
DVB-H is officially endorsed by the European Union as the "preferred technology for terrestrial mobile broadcasting or digital terrestrial television with additional features to meet the specific requirements of handheld, battery-powered receivers. In 2002 four main requirements of the DVB-H system were agreed: broadcast services for portable and mobile usage with 'acceptable quality'; a typical user environment, and so geographical coverage, as mobile radio; access to service while moving in a vehicle at high speed (as well as imperceptible handover when moving from one cell to another); and as much compatibility with existing digital terrestrial television (DVB-T), to allow sharing of network and transmission equipment.
This system is implemented in two major parts: a front-end buffer control mechanism and a parallel DVB-H TV signal decoding model.When receiving a DVB-H TV program signal from a base station, signal is demodulated to generate video and audio data. As video bit rate, quality, and resolution are directly related to content complexity, running too many buffers will consume power, while too few buffers will cause the program to fail to be played successfully.The parallel DVB-H TV signal decoding model uses a data partition processing method to run parallel DSP decoding of DVB-H videos on a heterogeneous multi-core platform. It also schedules videos according to the DVB-H video features, in order to reduce data dependency among the frames on a multicore platform.(refer to figure1).
Figure 2 shows the outline of the DVB-H/T system specifications for common TV broadcasting programs using the DVBT signal transfer mode. Senders can use an A/D converter to convert the analog video and audio signals to a digital signal, respectively, and use a Moving Picture Experts Group 2 (MPEG-2) codec technique to convert TV program data into MPEG-2 format. DVB-H service data are compressed
and encapsulated into an IP packet then encapsulated into the transmission stream through a Multiprotocol Encapsulation (MPE) mechanism.
Meanwhile, the time slicing data stream is added. Along with other DVB-T TV services, the multiplexer multiplexes it into a larger transmission stream (or multiple program transmission stream) before sending the data in a DVB wireless network. At the receiver, if a client wants to receive certain services, the receiver front-end circuit must run continuously in order to obtain the complete transmission stream. Then, the demultiplexer extracts the video, audio, and data information streams of the selected programs and delivers this information to the video decoder, audio decoder, and other applications for processing.
The sender Multi-Protocol Encapsulation-Forward Error Correction (MPE-FEC) and time slicing mechanisms are collectively called the DVB-H IP-Encapsulator, while the receiver reverse recovery portion is called the DVB-H IPDecapsulator. The IP data container format for each layer of DVB-H has an IP packet in the MPE section and redundant data in the FEC section. After Section format encapsulation, the MPE and FEC sections are connected end to end according to the encapsulating sequence to form a section data string. Then, it begins to slice the first and all of the other 184 bytes of each section data string.
A 4-byte transmission stream header is added to the front of the 184-byte data length in order to complete a transmission stream encapsulation or MPEG2 transmission stream packet. Its data length is 188 bytes, with two major parts. The first is a data front-end header that occupies a 4-byte length with the available information, including a Sync. Byte = 47 hex for synchronizing the emitter and receiver, error indications, and stream packet recognition. The second part is the data transfer payload, which length is 184 bytes.
MEDIA FLO :
The MediaFLO system is an end-to-end mobile broadcasting technology that can deliver high-quality video to any mobile device. The "FLO" part of the name is an acronym for Forward Link Only. Forward Link is another term for the downlink connection on a mobile phone, meaning that the system only sends data to the mobile devices and does not receive any data back from it. Currently, the only commercially released devices that can receive the MediaFLO signal are mobile phones, but the technology is capable of sending the signal to any device equipped with a MediaFLO receiver.Qualcomm®, an innovator in wireless technologies, has demonstrated the broadcast of a MediaFLO signal on several mobile devices that are NOT tied to any cellular network. In the US, Qualcomm will broadcast its service on what used to be UHF Channel 55, which is roughly the 700MHz frequency band
FLO technology was designed specifically for the efficient and economical distribution of the same multimedia content to millions of wireless subscribers simultaneously. It actually reduces the cost of delivering such content and enhances the user experience, allowing consumers to "surf" channels of content on the same mobile handsets they use for traditional cellular voice and data services, also works in concert with existing cellular data networks, FLO effectively addresses the issues in delivering multimedia content to a mass consumer audience. Unencumbered by legacy terrestrial or satellite delivery formats, this technology offers better performance for mobility and spectral efficiency than other mobile broadcast technologies, offering twice the channel capacity. The FLO service is designed to provide the user with a viewing experience similar to a television viewing experience by providing a familiar type of program -guide user interface. ).
Content Acquisition and Distribution
In a FLO network, content that is representative of a linear real-time channel is received directly from content providers, typically via a C-band satellite in MPEG-21 format (704 or 720 x 480 or 576 pixels), utilizing off-the-shelf infrastructure equipment. This is the most common format utilized by programmers, making it relatively simple for content providers to interface with a FLO System. The use of a standard definition as a source content provides sufficient resolution to allow for efficient transcoding to H.2642 QVGA resolution supported by the FLO network.
Non-real-time content is received by a content server, typically via an IP link, and then reformatted into FLO packet streams and redistributed over a Single Frequency Network (SFN). This distribution of the FLO packet streams is facilitated by the MediaFLO Media Distribution System (MDS). This non-real-time content is delivered according to a pre-arranged schedule.
The transport mechanism for the distribution of this content to the FLO transmitter may be via satellite, fiber, etc. At one or more locations in the target market, the content is received and the FLO packets are converted to FLO waveforms and radiated out to the devices in the market via FLO Transmitters. If any local content is provided, it will be combined with the wide area content and radiated out to the target market.
Only those devices that have subscribed to the service may receive the content, which in turn can be stored on the mobile device for future viewing, in accordance with a service program guide, or as a linear feed of content, delivered in real-time to the device. This content may consist of high-quality video (QVGA) and audio (MPEG-4 HE-AAC3) as well as IP data streams. A 3G cellular network is required to provide control functions to support interactivity and facilitate user authorization to the service. Equally important, the 3G network provides a basis for interactivity, including purchase and download transactions
Power Consumption Optimization
FLO technology simultaneously optimizes power consumption, frequency diversity4, and time diversity5. Other similar, but less efficient, systems optimize one or two of these parameters but ultimately compromise the others. FLO has a unique capability that allows it to access a small fraction of the total signal transmitted without compromising either frequency or time diversity. As a result of these considerations, it is expected that a FLO-enabled mobile device can achieve comparable battery life to a conventional cellular phone; that is, a few hours of viewing and talk time and a few days of stand-by time per battery charge.
The FLO air interface employs Time Division Multiplexing (TDM) to transmit each content stream at specific intervals within the FLO waveform. The mobile device accesses overhead information to determine at which time intervals a desired content stream is transmitted. The mobile device receiver circuitry only powers up during the time periods in which the desired content stream is transmitted; at all other times it is powered down. The receiver ON/OFF duty cycle is expected to be relatively low or immaterial, depending on the media content size and data rate used
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