How to Work DIGITAL TV
By pradip133
HDTV and NTSC
how to work DIGITAL TV
What is DTV?
DTV is a new "over-the-air" digital television system that will be used by the nearly 1600 local broadcast television stations in the United States. The DTV standard is based on the Advanced Television System Committee (ATSC) standard.
The DTV standard is a very flexible television system that will allow broadcasters to provide new and higher quality services. First, DTV will permit transmission of television programming in new wide screen, high resolution formats known as high definition television (HDTV). In addition, the new DTV television system allows transmissions in standard definition television (SDTV) formats that provide picture resolution similar to existing television service. Both the HDTV and SDTV formats will have significantly better color rendition than the existing analog television system. DTV also will provide improved audio quality, similar to that of compact discs.
Additional features and functions such as color, stereo sound, remote control, cable channels and others have been added. The shortcomings of the 50 year old analog technology used by broadcasters are increasingly apparent—due to limited resolution and color rendition. Also “ghosting” and interference from other radio sources are visible. DTV is the most significant development in TV technology since the advent of color TV in 1950s.
TV viewing will be a different and rich experience as it is going to be highly interactive compared the conventional dumb viewing. According to Allied Business Intelligence there would be 242 million TVs will be digital by 2005 from 40 million in 2000. The number of global TV installations as of today is exceeding 1 billion in number.
The salient features of digital TV are, Channel compression (400% compression), Dolby Audio (5.1), High resolution viewing (1080 X 1920), 16:9 aspect ratio (wide picture).
However Digital TV has the following drawbacks: As the existing TVs are analog and do not handle the digital signal, STB (Set Top Box), which converts the digital signal to analog, is required resulting in added cost. The analog TV set with STB will not be able to reproduce HDTV performance due to insufficient pixel density and bandwidth of the amplifiers. However the performance will be better than the analog TV without STB. The cost of the Digital TV supporting HDTV will be expensive to start with as due to finer (small size pixels), the brightness of the TV reduces. However the cost of the Digital TV will be falling when it hits the market with volume.
Considering the merits of Digital TV compared to demerits and also the solutions to overcome the demerits, Digital TV will be a success.
Many governments are passing regulation to make digital TV mandatory. In US all the commercial broadcasting will be digital by 2003. By 2006 there won’t be any along transmission.
Block Diagram of DTV:-
The digital RF signal from satellite or cable goes to the NTSC tuner section, and from that audio and video signals are decoded. If more than one channel is being transmitted then it is multiplexed and selected. The digital TV has its own RAM and memory control. We can also interface other devices with DTV. This interface is established using PCI bridge. Now the selected channel is audio and video decoded. Graphics controller controls the decoded video signal and give better graphics. If we want to view the digital signal on our conventional analog TV then we require Digital Set Top Box which converts the digital signal to analog signal.
Digital Displays
Digital displays or flat panel displays (FPDs) are digital technology-based displays that are used for notebook PCs, handheld devices, and other IAs. Some of the digital TV technologies are plasma display panels (PDPs), liquid crystal displays (LCDs), and digital light processors (DLPs).
Digital TV Vs Analog TV
Analog TV has a resolution of 486 X 720 pixels, two-channel stereo and 4:3 aspect ratio of the screen compressed in a bandwidth of 6 MHz. The Analog signal is susceptible to noise, multi reflections and fading resulting in quality degradation. Analog TV uses Amplitude modulation for video and frequency modulation for audio.
Digital TV has a resolution starting from 486 X 720 to 1080 X 1290 pixels, 5.1 Dolby/AC-3 audio (two-channel stereo, two-channel surrounding, center channel and woofer channel) and 16:9 aspect ratio of screen. HDTV (High definition TV) has the resolution of 1080 X 1290 pixels. The digital TV also uses 6 MHz channel bandwidth and it sends data apart from video and audio.
The features of digital TV are:
v Channel compression (400% compression)
v Dolby Audio (5.1)
v High resolution viewing (1080 X 1920)
v 16:9 aspect ratio (vide picture)
v Clearer and sharper cinema-like pictures
v Multi-channel (up to five channels/program)
v Broadcasters have the ability to simultaneously transmit multiple video programs using a single TV channel.
v Multicasting: DTV signals are carried over a wider bandwidth and can be split into sub-segments of an original channel but of lower resolution programming.
v There are two types of digital TV systems: standard definition television (SDTV) and high definition television (HDTV). Both HDTV and SDTV formats will have significantly better color performance than the existing analog TV system.
These unique features are made possible by:
• Transmitting TV images, sound, and data services digitally rather than as analog signals.
• Using digital compression techniques: Data rate of the DTV signal in the 6 MHz broadcast TV channel is 19.44 Mbps.
The benefits of the Digital TV are:
v Due to channel compression, more channels can be transmitted or utilization of entire channel results in high quality video.
v Theatrical quality of sound due to 5.1 Dolby / AC-3 audio.
v Finer details of the picture with true color.
v Wider viewing due to improved aspect ratio.
However the drawbacks of Digital TV are:
v As the existing TV is analog and does not handle the digital signal, STB (Set Top Box) which converts the digital signal to analog is required resulting in added cost to the consumer.
v The analog TV set with STB will not be able to reproduce HDTV performance due to insufficient pixel density. However the performance will be better than the analog TV without STB.
v The cost of the Digital TV supporting HDTV will be expensive. However the cost of the Digital TV will be falling when it hits the market with volume.
v High costs of equipment associated with transitioning to digital broadcasting.
v Ability of cable wires to carry digital signals.
v Newly introduced DTV sets cost several thousand dollars.
v Live digital broadcasting is a problem. Signals must be transmitted from the event to a broadcast center and across the network and with limited digital equipment available, the process can be very complex.
v Consumers will view decoded digital images on analog TV sets and have them look worst than standard broadcasts.
Considering the merits of Digital TV compared to demerits and also the solutions to overcome the demerits, Digital TV will be a success. US government has passed a regulation to make all the 1600 TV broadcasting to be digital by 2003 and by 2006 the analog broadcasting will be withdrawn from operation.
Change of today's TV system to DTV
Over the years, additional features and functions, such as color, stereo sound, remote control, cable channels, and parental control features were developed. Even with these improvements, TV sets became less expensive and more affordable.
In contrast, the shortcomings of the 50-year-old analogtechnology used by broadcasters such as limited resolution and color rendition as well as problems with "ghosts" and interference from other radio sources have become increasingly apparent as consumer TV sets have become larger and more technologically advanced.
DTV eventually will replace today's analog television service. After a transition period that allows stations to construct DTV transmission facilities and consumers gradually to replace their TV sets, broadcasts using the existing analog television system will cease and all over-the-air broadcast television service will be provided with the new DTV system.
CHAPTER 2. Architecture of Digital TV
The main equipment / devices required to realize Digital TV is the head-end system and the Set Top Boxes at the subscribers. There is one approach to the architectural implementation of Digital TV depending on the nature of the Set Top Box. If the thin set top boxes are used, the head end needs to be powerful & complex enough to support the thin set top boxes and still deliver the same service. However the complexity can be shifted to the set top boxes such that the set top boxes become thick and the complexity of head end can be reduced. Based on the above there could be one approach:
v Set Top Box Centric Architecture
2.1 The Set-Top Box
The set-top box brings to the end-user information, video and music on demand, interactive TV, games.
There are 2 main types of set-top boxes:
1. For digital (terrestrial) TV
2. For digital (cable/satellite) TV
A set-top box is a hardware device with the following features:
v Main processor
v RAM (64 to 128 Mbytes)
v Digital Signal Processor (DSP)
v Network card
v Hard drive (optional)
v DVD player (optional)
v Smart card reader (optional)
Architecture of Digital STB:-
Above fig. shows the digital set top box. According to the medium used for the transmission of digital signal, QPSK, QAM, OFDM decoders are used. The set top box basically converts digital signal to analog form. To display this signal onto screen it requires I/O control, clock generator. For sound decoding MPEG decoder is used. On screen display and Graphics generator decodes the video signal and combines with the decoded audio signal. Finally it goes to the NTSC or PAL encoder whatever is being used, and final output to the TV set.
We can also interface STB with Smart Card Reader, Computer and other digital devices with digital STB. It is less expensive, smaller in size, less noisy, it operates in conjunction with a TV monitor and a remote control, it is easier to use and more stable.
The following is a list of applications that can run on a digital set-top box:
• Video On Demand (VOD)
• DVD player
• Electronic Program Guide (EPG)
• Personal Video Recorder (PVR)
• Interactive TV
Figure 3 depicts the end to end architecture of the Digital TV with interactivity. The content is created using the authoring tools or by converting the existing web contents using appropriate tool. The contents are then stored in a database for easy and fast access. Based on the program the content is accessed from the database and converted to a stream. The stream is then multiplexed with Conditional access information. The multiplexed data is transmitted through appropriate medium (Satellite, cable, DSL or Terrestrial). The signal is received by the Set Top Box / TV usually from the cable. The cable service provider will capture the signal from other mediums like Satellite and Terrestrial. The received data is de- compressed and decrypted to process the conditional access. The set top box will have the inputs either from the Keyboard, remote control or from the smart card to enable the conditional access. On verification with the access rights, the content is played on the TV. The user can respond to the program using the 04 of 09 keyboard or remote control. The data captured is thus sent back to the server either through cable, telephone or wireless medium. Ideally the back channel also is through the Cable/DSL. Cable/DSL will be only medium entering any house, when the convergence is complete. The Cable/DSL will carry all Internet, TV and phone services to every house. Since the digital TV has to co-existed with the existing system and the existing system has been paced out slowly, the back end channel will make use of existing telephone links for back transmission. When the telephone converges to VoIP on Cable/DSL, the back transmission will be through cable/DSL itself. The battle between cable and DSL will decide the one medium entering the house either Cable or DSL.
Transmission Systems of Analog and Digital TV
3.1 Analog Video Transmission System
A typical analog video transmission system may consist of a baseband video to IF modulator, up-converter, transmit antenna, receive antenna, demodulator and baseband output amplifier. A satellite transmission system includes the actual satellite transponder between the two antennas.
Input DC Impedance & Return Loss Line Time Distortion
Input Amplitude Variation Short Time Distortion
Gain Variation 2T Pulse K-Factor Distortion
Continuous Random Noise (SNR) Chrominance to Luminance Intermodulation
Luminance Non-Linearity Chroma-Luma Gain Inequality
Chrominance Gain Non-Linearity Chroma-Luma Delay Inequality
Chrominance Phase Non-Linearity Amplitude Frequency Response
Differential Gain (DG) Group Delay Frequency Response
Differential Phase (DP)
Field Time Distortion
To measure these parameters, a series of video test signals are injected into the video transmission system. Then measure the response from the output of the transmission system with a video waveform monitor and a video chrominance vector scope. Automated video test systems are also available for such measurements.
3.2 Digital Video Transmission System
A pure digital video transmission system is similar to the analog system except that the video input and output is an uncompressed digital video bit stream, such as defined in SMPTE 259M [4] or SMPTE 292M [5]. These transmission systems may include a video compression stage at the transmit end and a video decompression stage at the receive end, to reduce the bandwidth requirement across the transmission path.
Typical video compression systems, such as MPEG-2, DV, DVCPRO, etc., introduce their own impairments on the delivered video image quality. The list of impairments associated with a digital video transmission system includes:
Bit errors Repeated frames (buffer underflows)
Macro-block errors "lip sync" errors
Truncated DCT series Decoder clock recovery variations
Motion vector errors Bit jitter
Dropped frames (buffer overflows)
In an uncompressed video transmission system, single bit error show up as pixel noise in the video image. When video compression is employed, a single bit transmission error will affect several pixels in the image. For this reason, most compressed video transmission systems employ a variety of error correction mechanisms to reduce the effects of a single bit error. If a large number of bits are impaired, then the error correction mechanisms begin to break down, causing the loss of tens, hundreds or even thousands of bits of data. These errors may show up as bright green horizontal lines across the image, bright green rectangles scattered around the screen, representing the affected macro-blocks, or as dropped or repeated frames.
Over-Compression: If the video transmission system uses a standard video compression scheme, such as MPEG-2, the user must balance the requirement to minimize the data rate against over-compression artifacts in the decoded video image. If the video sequence is over-compressed, the image detail is compromised. At the limit, the image starts to develop a “blocky” appearance, where the image breaks up into little rectangles at the macro-block boundaries, especially around the edge of moving objects. Traditional analog video performance measurements are not well suited to measure these compression artifacts because they normally use a static test pattern. This fixed test pattern compresses much more readily, with fewer artifacts, than normal “live” video.
Buffer Overflows & Underflows: A common problem in MPEG-2 compressed transmission systems is the allocation of the transmission bit rate “bandwidth” across each of the components in the MPEG-2 Transport Stream. If the sum of the average bit rates generated by each of the components is too large to fit within the bit rate imposed by the transmission system, the excess data can cause buffer overflows. This causes the decoded image to break up into little rectangles at the macro-block boundaries or frame skips. Alternatively, if the encoding and decoding delays are configured incorrectly, buffer overflows or underflows may also occur. The underflows occur when the decoder is told that it is time to decode the next image frame, but all of the data for that frame have not yet been received. This causes the decoder to “starve”. When the decoder is starved for video data it merely repeats previous decoded frame.
Lip Sync : If the encoding and decoding delays are not configured correctly, the audio delay does not match the video delay, causing the audio - video synchronization to be shifted. This causes viewer fatigue, especially while watching an on screen actor speaking dialogue, or a newscaster speaking on-camera. Several standards, such as ANSI T1.502, define the acceptable limits for audio - video synchronization as +20 msec(audio leads the video) to -40 msec(audio lags the video). Some studio facilities prefer a tighter specification, especially if they pass the video & audio through several concatenated encode/decode stages. Two methods are normally employed to measure the audio - video synchronization. First is a video test pattern generator that bounces between two visually different images and incorporates an audio tone burst or pop that is synchronized to the image bounce point. The other method is to use a prerecorded video sequence with synchronized video flashes and audio pops.
Digital Video Output Bit Jitter: SMPTE 259M and SMPTE 292M both specify the maximum permitted bit clock jitter over a frequency range related to the fundamental clock frequency for each interface. SMPTE RP 184 [6], SMPTE RP 192 [7] and SMPTE EG 33 [8] define serial data jitter and how to measure it in a serial data interface. Serial digital video measurement instruments from several manufacturers include indicators if the serial digital video source under test has excessive jitter. At least one of the serial digital video performance test instruments presently available indicates a compliance error if it measures excessive timing wander below 10 Hz. However, since no standard presently exists for serial digital video timing wander, this compliance error alarm is not necessarily significant.
3.3 The Components of a Digital Video Microwave Link :
Above figure shows the components which make up a digital microwave link. There are five components, not all of which may be required: MPEG II video compression encoder; multiplexer; modulator; microwave transmitter; waveguide / feeder and antenna. The equipment used to receive, demodulate, de-multiplex and decode the video is almost exactly the ‘mirror’ of the transmission end equipment.
MPEG II compression is required if one or more of the video signals to be transmitted is analog or in an uncompressed digital format. For microwave and many other applications, it is advantageous to use compression because the cost of transmitting uncompressed digital video far exceeds the cost of the compression equipment. An uncompressed standard definition DTV signal has a data rate of around 270MBit/s, a high definition DTV signal easily exceeds 1GBit/s. These signals can be successfully compressed and transmitted at data rates 50 times less without any reduction in picture quality. A separate encoder is required for each digital video signal that needs to be compressed. As standard, most encoders digitize 2, 4 or 6 channels of audio and/or data and incorporate them into the digitized video.
MPEG II Multiplexer :
When a system is required to transmit more than one channel of video, all of the encoded video bit streams need to be combined into one ‘composite’ stream before they can be transmitted across the microwave link. If only one channel of video is being transmitted, a multiplexer is not required and the output of the encoder connects directly to the input of the modulator. The transport stream multiplexer can combine many input streams together (typically up to 15); the output bit rate is a little more than the sum of the bit rates of all the inputs. There are two major types of multiplexer; a fixed rate multiplexer and a statistical multiplexer. The fixed rate version is relatively inexpensive and compact. It is configured to support inputs and outputs at a fixed data rate. A fixed rate multiplexer is commonly used when two, three or four video channels are being transmitted. A statistical multiplexer is relatively expensive and large. It is only a worthwhile investment when there are a large number of video channels to be multiplexed. The system constantly adjusts the data rate used to encode each video stream as the contents of the video changes; however, the sum of all the data rates remains constant. The statistical multiplexer ensures that the link is being used to its fullest capacity and that each video signal is transmitted as artifact free as possible.
Modulator :
The modulator takes as its input a baseband digital bit stream and uses it to modulate either the frequency, the phase or a combination of the phase and the amplitude of a carrier. Typically, the carrier is at an IF (intermediate frequency) of 70 or 140MHz. Two increasingly visible digital modulation techniques are 8-VSB (HDTV broadcast scheme) and 64-QAM (digital cable scheme).
There are four types of modulation scheme that are most commonly used for digital microwave links; these are FSK, QPSK, 8PSK and QAM.
Microwave Transmitter :
The heterodyne microwave transmitter will accept the output of a modulator (usually at an IF of 70 or 140MHz); upconvert the signal to the final RF output frequency and then amplify and filter the digital signal. This type of equipment has seen wide exposure in the broadcast industry when used as an IF repeater in analog multi-hop systems. The key attribute that a heterodyne digital microwave transmitter has, that an analog IF repeater will not have, is a linear Power Amplifier. Specifically, the transmission of PSK and QAM digital signal requires reasonably linear amplification; amplitude variations in the signal need to be passed through the RF signal chain without distortion. Analog FM and Digital FSK signals contain no amplitude modulation component and can be passed through saturated amplifiers.
Digital PSK signals contain transient amplitude variations, which if suppressed in a saturated amplifier, will cause in-channel and adjacent channel distortion. This distortion will degrade the performance of the link and interfere with other users of the spectrum. Typically an amplifier backed off from its saturation point by 3dB (i.e. to half power) will pass amplitude components well enough to be suitable for PSK signals. As always, the greatest care must be taken to ensure that the modulator / transmitter combination does not produce out of channel energy.
Waveguide/Feeder and Antennas :
The hardware used to support analog microwave signals is just as capable of supporting digital microwave signals. As the signal is passed between radio and antenna feed, a fraction of the signal energy will be reflected. The reflected signal interferes with the main, wanted signal and causes degradation in the performance of the link. These reflections have a far greater affect on digital links than they do on analog links. Reflections will occur at every transition in the signal path and they will also occur in the transmission line if there are significant changes in the impedance of the line along its length. The key to avoiding reflections is to ensure that the antenna and transmission line equipment is aligned and tuned. Typically, the return loss into the transmission line at the radio flange should be at least 26dB. If the reflections continue to significantly degrade the performance of the link, it may be time to consider swapping existing antennas for new, low reflection (VSWR) models and/or existing line for lower loss types.
:-> There are two digital transmission systems presently available : 8-VSB (8-Vestigial Side Band) and COFDM (Coded Orthogonal Frequency Division Multiplex).
Both COFDM and 8VSB are very robust digital transmission systems with unique advantages and disadvantages. The 8VSB system is more resistant to impulse noise and phase noise, and it has higher spectrum efficiency and requires less power.
COFDM is superior in high level long delay multipath signals, both static and dynamic. COFDM is clearly superior in large Single Frequency Networks that are used in Europe.
Both systems are well developed in theory and have been extensively tested in laboratory environments.
Digital satellite communication is inherently better over analog satellite communication and has following points :
1) Increased capacity in the multiple access mode :
In satellite transponder utilization power efficiency is of prime concern. To increase this efficiency the high power output amplifiers are required to operate close to saturation. Time division multiple access (TDMA) digital satellite systems, each a significantly increased system capacity when compared to analog multiple FM systems.
2) More robust to interference.
3) Compatibility of analog / digital massages and computers.
4) Most flexible and transmission quality almost independent of distance and network topology.
3.4 Do we need a new TV set to receive DTV?
To enjoy the full benefits of DTV such as wide screen, higher resolution pictures we will need to purchase a new DTV set. Existing television sets will not be able to display DTV signals. However, it is expected that less expensive converter boxes will be available that will allow you to watch standard definition DTV on an existing TV set. These boxes will receive DTV signals and convert them to the transmission system used by existing TV sets. The pictures received through these converter boxes should be clear of the "ghosts," and other interference that are characteristic of today's analog TV service in some areas. These converter boxes will also allow any new DTV programs to be displayed on existing TV sets. However, because most existing TV sets were not designed to display high resolution pictures, converter boxes will not be able to provide the higher HDTV picture quality that will be available on new DTV sets.
3.5 Do we need an outside antenna to receive DTV? Is the antenna we use for existing TV reception is good enough?
If we have an outside antenna and it provides acceptable TV reception now on UHF channels, it should also work for DTV. Also, if our indoor antenna is capable of receiving UHF television service now, we may also be able to receive DTV service with that antenna. Indoor DTV reception is affected by a number of factors that vary depending on local conditions. Many retailers carrying DTV equipment have information about local reception conditions.
3.6 Shall we be able to receive existing TV programming on our DTV set?
Yes, digital television sets available during the transition will be fully compatible with traditional analog TV programming. These new digital sets will have the capability to receive new DTV programming and will also be able to receive all the programming we receive today on our traditional set. This means that new DTV sets will be able to display all of the programming available today from broadcasters, cable operators, satellite TV services, other video service providers, and pre-recorded sources. So if we buy a new digital set, we will not lose the ability to get any of the programs we now receive on our current set.
:-> Will cable systems carry local DTV signals?
Some cable operators have indicated that they may carry the DTV programming of local broadcast stations. If these signals are carried in their original DTV format, no additional equipment will be needed to receive them on DTV sets. Some cable systems may, however, convert DTV programming to different digital formats and / or may carry DTV signals at lower resolutions than the original broadcast signal. In such cases, special cable "set-top" boxes may be needed to receive DTV.
CHAPTER 4. Application
The applications in Digital TV are only limited to imagination of the service and content providers. The typical applications are, TV mail (similar to e-mail), TV Chat, TV Commerce, TV interactive Games, Video on Demand (VOD), Personal Video Recorder (PVR), Electronic Program Guide (EPG), TV Education etc. More and more applications will get deployed in due coarse of time.
4.1 Interactive TV (iTV)
Interactive TV is the combination of digital television and Internet technology to deliver a mix of programming, restricted or open Web access, email, on-line shopping and customer service to viewers watching at home. It can be seen as both a channel to the Internet and as a way to synchronize data with broadcast material so that viewers can influence the outcome of a show, chat to other fans, buy products and play games related to the programmes being broadcasted. While the current generation of interactive television systems offers basic Internet browsing functionality, the next generation of technologies available in the coming months promises to give far greater flexibility both to viewers and to content providers.
iTV is domestic television with interactive facilities usually facilitated through a ‘back channel’. Equally important, interactive television is content that users and viewers can interact. Interactive television is also a way of empowering viewers to use television in new ways. The unifying factor is the television that is central to the entertainment, education, information, leisure and social life of millions of homes all over the world.
The contents will have data apart from audio and video. The data consists of two parts information (variables) and execution code. The execution code gets loaded and executed along with the video & audio, which is being played on the TV. Each segment of interactive content will contain a piece of executable and data (information) required for the executable. For example when an advertisement being shown and the corresponding executable required in capturing the requests of the viewer will be loaded and executed.
On selecting the product shown with specification, the request is captured and sent to the backed server. The back end server will process the request and transact the order and finally the product will be delivered to the viewer at his residence. Thus data captured by the TV/STB is sent to the content server. Based on the application and the request the server will respond appropriately.
4.1.1 Architecture of iTV
Fig.7 illustrates the basic head end architecture for providing interactive TV services. With this comprehensive interactive cable/set-top solution, for example, cable operators can send all types of data—Internet data, voice signals, and video—over a single, packet-based infrastructure. Equally important, the interactive cable/set-top solution leverages the cable operator’s existing network infrastructure, further reducing total cost of ownership.
The components of this architecture are described below :-
4.1.2 Backbone
The backbone plays a key role in deploying enhanced cable services to subscribers. It is a high-speed, digital network that carries Internet data, voice, and video between cable company facilities. Cable operators are well positioned to build a converged IP network because of the extensive regional fiber network already in place. This fiber backbone is made of OC-3 (156 Mbps) to OC-192 (2488 Mbps) Synchronous Optical Network (SONET) or Asynchronous Transfer Mode (ATM) rings. These fiber rings scale to accommodate increasing volumes of data traveling over the backbone. The back bone network also incorporates regional MPEG video systems as well as various back-office systems, and connects to other networks, including the Public Switched Telephone Network (PSTN), to other cable system backbones, and to the public Internet interconnection points used by other Internet service providers (ISPs).
4.1.3 The head end
The head end system brings regional, national, and international program content into the cable network and converts it for use by the backbone. This content includes satellite video, off-the-air video, Internet data, and PSTN voice. As in the backbone system, high-speed routers perform a vital role in the head end system. They route interactive traffic between the backbone and Ethernet in the head end internal network. Signaling protocols provide the intelligence needed to route this traffic in an optimal manner, automatically building and maintaining the routing tables to direct traffic and signal failures for rerouting in the network. The head end system also incorporates a series of interactive application, user data, and system management servers. These servers enable cable operators to deliver cost effective, branded, centrally managed services through set-top boxes. Software applications can include TV mail, TV phone, and Web browsing.
An elaborate server set-up is required at the head end to manage and deliver content and user-profiles. The standard Network Operations Centre (NOC) has a seven-server set-up – transaction, application, commerce, web, database, member ship and broadcast servers. The servers are connected to the network via an ultra-fast Ethernet connection ready for access and broadcast as shown in the fig 8.
Some of these are the middleware servers. The functionality of these servers is as follows :-
-> Transaction servers : These servers provide high bandwidth interactive HTTP and Https sessions and act as a secure gateway for the client to obtain access to web pages.
-> Application servers : These are the servers that host interactive TV applications like games etc.
-> Commerce servers : These servers are used for interactive banking and other ecommerce application.
-> Web servers : These are the regular web servers that provide access to the internet web pages.
-> Database servers : The database servers provide access to the common subscriber database.
-> Membership/Personalization servers : These servers store the viewer’s preferences and perform subscriber management functions.
-> Broadcast servers : These servers perform data carousel ling of in-band MPEG for broadcast delivery of enhanced TV content.
CHAPTER 5. Commercial View of DTV
5.1 The major players of DTV
The Digital TV market can be segmented based on the product or service. The segments are content providers, network operators / service providers and Set Top Box / DTV Manufacturers. The important players in STB manufacturers are GI (Motorola), Scientific Atlanta, Sony, Pioneer, Philips, RCA etc. The middle ware providers for the STB are Open TV, Liberate, Microsoft, Canal+ (Media Highway) etc. The Network Operators / Service providers are AOL, Direct TV, ICTV, etc. The content providers are ACTV, HBO, Two Way TV, Sky digital etc.
5.2 Standard
Various standards are being used in different parts of the globe. The standards on Digital TV are the Advanced Television System Committee (ATSC), the Digital Video Broadcasting (DVB) and the Integrated Services Digital Broadcasting (ISDB). DVB has three sub committee / standards namely DVB-T for Terrestrial, DVB-C for Cable and DVB-S for Satellite
World-wide adoptions of standards for Digital TV by 2000
ATSC is used in Northern America, Japan uses ISDB and rest uses DVB. There are few countries like China, which uses all three standards and some countries using ATSC in Asia. DVB has adopted Multimedia Home Platform (MHP) standard and Europe is standardizing on DVB-MHP. Few countries like Singapore and India have also standardized on DVB-MHP.
The ATSC, DVB and ISDB use the Moving Picture Experts Group (MPEG-2) code for the picture. ATSC digital TV uses Dolby Digital (AC-3) for the sound, DVB digital TV uses MPEG Layer II or AC-3 for the sound and ISDB digital TV uses MPEG-2 AAC (Advanced Audio Coding) for the sound. ATSC digital TV uses 8 level Vestigial Side Band (8-VSB) modulation, DVB digital TV uses Coded Orthogonal Frequency Division Multiplexing (COFDM) modulation and ISDB digital TV uses Band Segmented Transmission of Orthogonal Frequency Division Multiplexing (BST-OFDM) modulation for terrestrial broadcasting.
Choosing the standard for a particular country depends on the existing standard in the analog TV, government policies and the existing transmission network.
5.3 Digital TV Business Model
With the current model (hope fully matures in near future), the network operators decide on the specifications of the set top boxes based on the service he/she provides. Then network operator approaches a device manufacturer for manufacturing the devices. The network operator also influences the device manufacturer in deciding on the chip sets, operating system and the middle ware.
As TV signals move from analog to digital and as the broadcast model is gradually replaced by video (and TV) on demand, the software residing on a set-top box (Client) must offer the end user features that allow for the management of both the analog and digital signal.
The Client software must be able to receive digital signals. For the end user, this means DVD-quality content, Dolby 5.1 sound, and the convenience associated with TV on demand.
The Client software must be configurable for either independent set-top boxes or for set-top boxes connected through a central home server (gateway). A gateway is a server that has large storage capacity and that is connected to multiple TVs and sound systems. This configuration allows the end user to access large personal digital libraries from multiple home devices.
Also, since television will be increasingly more interactive, the software on the set-top box must also be easily upgraded and allow the end user to
DTV is a new "over-the-air" digital television system that will be used by the nearly 1600 local broadcast television stations in the United States. The DTV standard is based on the Advanced Television System Committee (ATSC) standard.
The DTV standard is a very flexible television system that will allow broadcasters to provide new and higher quality services. First, DTV will permit transmission of television programming in new wide screen, high resolution formats known as high definition television (HDTV). In addition, the new DTV television system allows transmissions in standard definition television (SDTV) formats that provide picture resolution similar to existing television service. Both the HDTV and SDTV formats will have significantly better color rendition than the existing analog television system. DTV also will provide improved audio quality, similar to that of compact discs.
Additional features and functions such as color, stereo sound, remote control, cable channels and others have been added. The shortcomings of the 50 year old analog technology used by broadcasters are increasingly apparent—due to limited resolution and color rendition. Also “ghosting” and interference from other radio sources are visible. DTV is the most significant development in TV technology since the advent of color TV in 1950s.
TV viewing will be a different and rich experience as it is going to be highly interactive compared the conventional dumb viewing. According to Allied Business Intelligence there would be 242 million TVs will be digital by 2005 from 40 million in 2000. The number of global TV installations as of today is exceeding 1 billion in number.
The salient features of digital TV are, Channel compression (400% compression), Dolby Audio (5.1), High resolution viewing (1080 X 1920), 16:9 aspect ratio (wide picture).
However Digital TV has the following drawbacks: As the existing TVs are analog and do not handle the digital signal, STB (Set Top Box), which converts the digital signal to analog, is required resulting in added cost. The analog TV set with STB will not be able to reproduce HDTV performance due to insufficient pixel density and bandwidth of the amplifiers. However the performance will be better than the analog TV without STB. The cost of the Digital TV supporting HDTV will be expensive to start with as due to finer (small size pixels), the brightness of the TV reduces. However the cost of the Digital TV will be falling when it hits the market with volume.
Considering the merits of Digital TV compared to demerits and also the solutions to overcome the demerits, Digital TV will be a success.
Many governments are passing regulation to make digital TV mandatory. In US all the commercial broadcasting will be digital by 2003. By 2006 there won’t be any along transmission.
Block Diagram of DTV:-
The digital RF signal from satellite or cable goes to the NTSC tuner section, and from that audio and video signals are decoded. If more than one channel is being transmitted then it is multiplexed and selected. The digital TV has its own RAM and memory control. We can also interface other devices with DTV. This interface is established using PCI bridge. Now the selected channel is audio and video decoded. Graphics controller controls the decoded video signal and give better graphics. If we want to view the digital signal on our conventional analog TV then we require Digital Set Top Box which converts the digital signal to analog signal.
Digital Displays
Digital displays or flat panel displays (FPDs) are digital technology-based displays that are used for notebook PCs, handheld devices, and other IAs. Some of the digital TV technologies are plasma display panels (PDPs), liquid crystal displays (LCDs), and digital light processors (DLPs).
Digital TV Vs Analog TV
Analog TV has a resolution of 486 X 720 pixels, two-channel stereo and 4:3 aspect ratio of the screen compressed in a bandwidth of 6 MHz. The Analog signal is susceptible to noise, multi reflections and fading resulting in quality degradation. Analog TV uses Amplitude modulation for video and frequency modulation for audio.
Digital TV has a resolution starting from 486 X 720 to 1080 X 1290 pixels, 5.1 Dolby/AC-3 audio (two-channel stereo, two-channel surrounding, center channel and woofer channel) and 16:9 aspect ratio of screen. HDTV (High definition TV) has the resolution of 1080 X 1290 pixels. The digital TV also uses 6 MHz channel bandwidth and it sends data apart from video and audio.
The features of digital TV are:
v Channel compression (400% compression)
v Dolby Audio (5.1)
v High resolution viewing (1080 X 1920)
v 16:9 aspect ratio (vide picture)
v Clearer and sharper cinema-like pictures
v Multi-channel (up to five channels/program)
v Broadcasters have the ability to simultaneously transmit multiple video programs using a single TV channel.
v Multicasting: DTV signals are carried over a wider bandwidth and can be split into sub-segments of an original channel but of lower resolution programming.
v There are two types of digital TV systems: standard definition television (SDTV) and high definition television (HDTV). Both HDTV and SDTV formats will have significantly better color performance than the existing analog TV system.
These unique features are made possible by:
• Transmitting TV images, sound, and data services digitally rather than as analog signals.
• Using digital compression techniques: Data rate of the DTV signal in the 6 MHz broadcast TV channel is 19.44 Mbps.
The benefits of the Digital TV are:
v Due to channel compression, more channels can be transmitted or utilization of entire channel results in high quality video.
v Theatrical quality of sound due to 5.1 Dolby / AC-3 audio.
v Finer details of the picture with true color.
v Wider viewing due to improved aspect ratio.
However the drawbacks of Digital TV are:
v As the existing TV is analog and does not handle the digital signal, STB (Set Top Box) which converts the digital signal to analog is required resulting in added cost to the consumer.
v The analog TV set with STB will not be able to reproduce HDTV performance due to insufficient pixel density. However the performance will be better than the analog TV without STB.
v The cost of the Digital TV supporting HDTV will be expensive. However the cost of the Digital TV will be falling when it hits the market with volume.
Some of the early difficulties of DTV:
v High costs of equipment associated with transitioning to digital broadcasting.
v Ability of cable wires to carry digital signals.
v Newly introduced DTV sets cost several thousand dollars.
v Live digital broadcasting is a problem. Signals must be transmitted from the event to a broadcast center and across the network and with limited digital equipment available, the process can be very complex.
v Consumers will view decoded digital images on analog TV sets and have them look worst than standard broadcasts.
Considering the merits of Digital TV compared to demerits and also the solutions to overcome the demerits, Digital TV will be a success. US government has passed a regulation to make all the 1600 TV broadcasting to be digital by 2003 and by 2006 the analog broadcasting will be withdrawn from operation.
Change of today's TV system to DTV
Over the years, additional features and functions, such as color, stereo sound, remote control, cable channels, and parental control features were developed. Even with these improvements, TV sets became less expensive and more affordable.
In contrast, the shortcomings of the 50-year-old analogtechnology used by broadcasters such as limited resolution and color rendition as well as problems with "ghosts" and interference from other radio sources have become increasingly apparent as consumer TV sets have become larger and more technologically advanced.
DTV eventually will replace today's analog television service. After a transition period that allows stations to construct DTV transmission facilities and consumers gradually to replace their TV sets, broadcasts using the existing analog television system will cease and all over-the-air broadcast television service will be provided with the new DTV system.
CHAPTER 2. Architecture of Digital TV
The main equipment / devices required to realize Digital TV is the head-end system and the Set Top Boxes at the subscribers. There is one approach to the architectural implementation of Digital TV depending on the nature of the Set Top Box. If the thin set top boxes are used, the head end needs to be powerful & complex enough to support the thin set top boxes and still deliver the same service. However the complexity can be shifted to the set top boxes such that the set top boxes become thick and the complexity of head end can be reduced. Based on the above there could be one approach:
v Set Top Box Centric Architecture
2.1 The Set-Top Box
The set-top box brings to the end-user information, video and music on demand, interactive TV, games.
There are 2 main types of set-top boxes:
1. For digital (terrestrial) TV
2. For digital (cable/satellite) TV
A set-top box is a hardware device with the following features:
v Main processor
v RAM (64 to 128 Mbytes)
v Digital Signal Processor (DSP)
v Network card
v Hard drive (optional)
v DVD player (optional)
v Smart card reader (optional)
Architecture of Digital STB:-
Above fig. shows the digital set top box. According to the medium used for the transmission of digital signal, QPSK, QAM, OFDM decoders are used. The set top box basically converts digital signal to analog form. To display this signal onto screen it requires I/O control, clock generator. For sound decoding MPEG decoder is used. On screen display and Graphics generator decodes the video signal and combines with the decoded audio signal. Finally it goes to the NTSC or PAL encoder whatever is being used, and final output to the TV set.
We can also interface STB with Smart Card Reader, Computer and other digital devices with digital STB. It is less expensive, smaller in size, less noisy, it operates in conjunction with a TV monitor and a remote control, it is easier to use and more stable.
The following is a list of applications that can run on a digital set-top box:
• Video On Demand (VOD)
• DVD player
• Electronic Program Guide (EPG)
• Personal Video Recorder (PVR)
• Interactive TV
Figure 3 depicts the end to end architecture of the Digital TV with interactivity. The content is created using the authoring tools or by converting the existing web contents using appropriate tool. The contents are then stored in a database for easy and fast access. Based on the program the content is accessed from the database and converted to a stream. The stream is then multiplexed with Conditional access information. The multiplexed data is transmitted through appropriate medium (Satellite, cable, DSL or Terrestrial). The signal is received by the Set Top Box / TV usually from the cable. The cable service provider will capture the signal from other mediums like Satellite and Terrestrial. The received data is de- compressed and decrypted to process the conditional access. The set top box will have the inputs either from the Keyboard, remote control or from the smart card to enable the conditional access. On verification with the access rights, the content is played on the TV. The user can respond to the program using the 04 of 09 keyboard or remote control. The data captured is thus sent back to the server either through cable, telephone or wireless medium. Ideally the back channel also is through the Cable/DSL. Cable/DSL will be only medium entering any house, when the convergence is complete. The Cable/DSL will carry all Internet, TV and phone services to every house. Since the digital TV has to co-existed with the existing system and the existing system has been paced out slowly, the back end channel will make use of existing telephone links for back transmission. When the telephone converges to VoIP on Cable/DSL, the back transmission will be through cable/DSL itself. The battle between cable and DSL will decide the one medium entering the house either Cable or DSL.
Transmission Systems of Analog and Digital TV
3.1 Analog Video Transmission System
A typical analog video transmission system may consist of a baseband video to IF modulator, up-converter, transmit antenna, receive antenna, demodulator and baseband output amplifier. A satellite transmission system includes the actual satellite transponder between the two antennas.
Several international standards address the video performance requirements for various types of analog transmission systems, including: ANSI T1.502 [1], EIA-250-C [2] and CCIR 567 [3]. If a transmission system complies with the requirements in these documents, the user knows that the image quality is adequate for a specified level of service. These standards include several performance measurements for an analog composite video signal which are in common use in video production facilities around the world:
Input DC Impedance & Return Loss Line Time Distortion
Input Amplitude Variation Short Time Distortion
Gain Variation 2T Pulse K-Factor Distortion
Continuous Random Noise (SNR) Chrominance to Luminance Intermodulation
Luminance Non-Linearity Chroma-Luma Gain Inequality
Chrominance Gain Non-Linearity Chroma-Luma Delay Inequality
Chrominance Phase Non-Linearity Amplitude Frequency Response
Differential Gain (DG) Group Delay Frequency Response
Differential Phase (DP)
Field Time Distortion
To measure these parameters, a series of video test signals are injected into the video transmission system. Then measure the response from the output of the transmission system with a video waveform monitor and a video chrominance vector scope. Automated video test systems are also available for such measurements.
3.2 Digital Video Transmission System
A pure digital video transmission system is similar to the analog system except that the video input and output is an uncompressed digital video bit stream, such as defined in SMPTE 259M [4] or SMPTE 292M [5]. These transmission systems may include a video compression stage at the transmit end and a video decompression stage at the receive end, to reduce the bandwidth requirement across the transmission path.
Typical video compression systems, such as MPEG-2, DV, DVCPRO, etc., introduce their own impairments on the delivered video image quality. The list of impairments associated with a digital video transmission system includes:
Bit errors Repeated frames (buffer underflows)
Macro-block errors "lip sync" errors
Truncated DCT series Decoder clock recovery variations
Motion vector errors Bit jitter
Dropped frames (buffer overflows)
In an uncompressed video transmission system, single bit error show up as pixel noise in the video image. When video compression is employed, a single bit transmission error will affect several pixels in the image. For this reason, most compressed video transmission systems employ a variety of error correction mechanisms to reduce the effects of a single bit error. If a large number of bits are impaired, then the error correction mechanisms begin to break down, causing the loss of tens, hundreds or even thousands of bits of data. These errors may show up as bright green horizontal lines across the image, bright green rectangles scattered around the screen, representing the affected macro-blocks, or as dropped or repeated frames.
Over-Compression: If the video transmission system uses a standard video compression scheme, such as MPEG-2, the user must balance the requirement to minimize the data rate against over-compression artifacts in the decoded video image. If the video sequence is over-compressed, the image detail is compromised. At the limit, the image starts to develop a “blocky” appearance, where the image breaks up into little rectangles at the macro-block boundaries, especially around the edge of moving objects. Traditional analog video performance measurements are not well suited to measure these compression artifacts because they normally use a static test pattern. This fixed test pattern compresses much more readily, with fewer artifacts, than normal “live” video.
Buffer Overflows & Underflows: A common problem in MPEG-2 compressed transmission systems is the allocation of the transmission bit rate “bandwidth” across each of the components in the MPEG-2 Transport Stream. If the sum of the average bit rates generated by each of the components is too large to fit within the bit rate imposed by the transmission system, the excess data can cause buffer overflows. This causes the decoded image to break up into little rectangles at the macro-block boundaries or frame skips. Alternatively, if the encoding and decoding delays are configured incorrectly, buffer overflows or underflows may also occur. The underflows occur when the decoder is told that it is time to decode the next image frame, but all of the data for that frame have not yet been received. This causes the decoder to “starve”. When the decoder is starved for video data it merely repeats previous decoded frame.
Lip Sync : If the encoding and decoding delays are not configured correctly, the audio delay does not match the video delay, causing the audio - video synchronization to be shifted. This causes viewer fatigue, especially while watching an on screen actor speaking dialogue, or a newscaster speaking on-camera. Several standards, such as ANSI T1.502, define the acceptable limits for audio - video synchronization as +20 msec(audio leads the video) to -40 msec(audio lags the video). Some studio facilities prefer a tighter specification, especially if they pass the video & audio through several concatenated encode/decode stages. Two methods are normally employed to measure the audio - video synchronization. First is a video test pattern generator that bounces between two visually different images and incorporates an audio tone burst or pop that is synchronized to the image bounce point. The other method is to use a prerecorded video sequence with synchronized video flashes and audio pops.
Digital Video Output Bit Jitter: SMPTE 259M and SMPTE 292M both specify the maximum permitted bit clock jitter over a frequency range related to the fundamental clock frequency for each interface. SMPTE RP 184 [6], SMPTE RP 192 [7] and SMPTE EG 33 [8] define serial data jitter and how to measure it in a serial data interface. Serial digital video measurement instruments from several manufacturers include indicators if the serial digital video source under test has excessive jitter. At least one of the serial digital video performance test instruments presently available indicates a compliance error if it measures excessive timing wander below 10 Hz. However, since no standard presently exists for serial digital video timing wander, this compliance error alarm is not necessarily significant.
3.3 The Components of a Digital Video Microwave Link :
Above figure shows the components which make up a digital microwave link. There are five components, not all of which may be required: MPEG II video compression encoder; multiplexer; modulator; microwave transmitter; waveguide / feeder and antenna. The equipment used to receive, demodulate, de-multiplex and decode the video is almost exactly the ‘mirror’ of the transmission end equipment.
MPEG II Video Compression Encoder :
MPEG II compression is required if one or more of the video signals to be transmitted is analog or in an uncompressed digital format. For microwave and many other applications, it is advantageous to use compression because the cost of transmitting uncompressed digital video far exceeds the cost of the compression equipment. An uncompressed standard definition DTV signal has a data rate of around 270MBit/s, a high definition DTV signal easily exceeds 1GBit/s. These signals can be successfully compressed and transmitted at data rates 50 times less without any reduction in picture quality. A separate encoder is required for each digital video signal that needs to be compressed. As standard, most encoders digitize 2, 4 or 6 channels of audio and/or data and incorporate them into the digitized video.
MPEG II Multiplexer :
When a system is required to transmit more than one channel of video, all of the encoded video bit streams need to be combined into one ‘composite’ stream before they can be transmitted across the microwave link. If only one channel of video is being transmitted, a multiplexer is not required and the output of the encoder connects directly to the input of the modulator. The transport stream multiplexer can combine many input streams together (typically up to 15); the output bit rate is a little more than the sum of the bit rates of all the inputs. There are two major types of multiplexer; a fixed rate multiplexer and a statistical multiplexer. The fixed rate version is relatively inexpensive and compact. It is configured to support inputs and outputs at a fixed data rate. A fixed rate multiplexer is commonly used when two, three or four video channels are being transmitted. A statistical multiplexer is relatively expensive and large. It is only a worthwhile investment when there are a large number of video channels to be multiplexed. The system constantly adjusts the data rate used to encode each video stream as the contents of the video changes; however, the sum of all the data rates remains constant. The statistical multiplexer ensures that the link is being used to its fullest capacity and that each video signal is transmitted as artifact free as possible.
Modulator :
The modulator takes as its input a baseband digital bit stream and uses it to modulate either the frequency, the phase or a combination of the phase and the amplitude of a carrier. Typically, the carrier is at an IF (intermediate frequency) of 70 or 140MHz. Two increasingly visible digital modulation techniques are 8-VSB (HDTV broadcast scheme) and 64-QAM (digital cable scheme).
There are four types of modulation scheme that are most commonly used for digital microwave links; these are FSK, QPSK, 8PSK and QAM.
Microwave Transmitter :
The heterodyne microwave transmitter will accept the output of a modulator (usually at an IF of 70 or 140MHz); upconvert the signal to the final RF output frequency and then amplify and filter the digital signal. This type of equipment has seen wide exposure in the broadcast industry when used as an IF repeater in analog multi-hop systems. The key attribute that a heterodyne digital microwave transmitter has, that an analog IF repeater will not have, is a linear Power Amplifier. Specifically, the transmission of PSK and QAM digital signal requires reasonably linear amplification; amplitude variations in the signal need to be passed through the RF signal chain without distortion. Analog FM and Digital FSK signals contain no amplitude modulation component and can be passed through saturated amplifiers.
Digital PSK signals contain transient amplitude variations, which if suppressed in a saturated amplifier, will cause in-channel and adjacent channel distortion. This distortion will degrade the performance of the link and interfere with other users of the spectrum. Typically an amplifier backed off from its saturation point by 3dB (i.e. to half power) will pass amplitude components well enough to be suitable for PSK signals. As always, the greatest care must be taken to ensure that the modulator / transmitter combination does not produce out of channel energy.
Waveguide/Feeder and Antennas :
The hardware used to support analog microwave signals is just as capable of supporting digital microwave signals. As the signal is passed between radio and antenna feed, a fraction of the signal energy will be reflected. The reflected signal interferes with the main, wanted signal and causes degradation in the performance of the link. These reflections have a far greater affect on digital links than they do on analog links. Reflections will occur at every transition in the signal path and they will also occur in the transmission line if there are significant changes in the impedance of the line along its length. The key to avoiding reflections is to ensure that the antenna and transmission line equipment is aligned and tuned. Typically, the return loss into the transmission line at the radio flange should be at least 26dB. If the reflections continue to significantly degrade the performance of the link, it may be time to consider swapping existing antennas for new, low reflection (VSWR) models and/or existing line for lower loss types.
:-> There are two digital transmission systems presently available : 8-VSB (8-Vestigial Side Band) and COFDM (Coded Orthogonal Frequency Division Multiplex).
Both COFDM and 8VSB are very robust digital transmission systems with unique advantages and disadvantages. The 8VSB system is more resistant to impulse noise and phase noise, and it has higher spectrum efficiency and requires less power.
COFDM is superior in high level long delay multipath signals, both static and dynamic. COFDM is clearly superior in large Single Frequency Networks that are used in Europe.
Both systems are well developed in theory and have been extensively tested in laboratory environments.
Digital satellite communication is inherently better over analog satellite communication and has following points :
1) Increased capacity in the multiple access mode :
In satellite transponder utilization power efficiency is of prime concern. To increase this efficiency the high power output amplifiers are required to operate close to saturation. Time division multiple access (TDMA) digital satellite systems, each a significantly increased system capacity when compared to analog multiple FM systems.
2) More robust to interference.
3) Compatibility of analog / digital massages and computers.
4) Most flexible and transmission quality almost independent of distance and network topology.
3.4 Do we need a new TV set to receive DTV?
To enjoy the full benefits of DTV such as wide screen, higher resolution pictures we will need to purchase a new DTV set. Existing television sets will not be able to display DTV signals. However, it is expected that less expensive converter boxes will be available that will allow you to watch standard definition DTV on an existing TV set. These boxes will receive DTV signals and convert them to the transmission system used by existing TV sets. The pictures received through these converter boxes should be clear of the "ghosts," and other interference that are characteristic of today's analog TV service in some areas. These converter boxes will also allow any new DTV programs to be displayed on existing TV sets. However, because most existing TV sets were not designed to display high resolution pictures, converter boxes will not be able to provide the higher HDTV picture quality that will be available on new DTV sets.
3.5 Do we need an outside antenna to receive DTV? Is the antenna we use for existing TV reception is good enough?
If we have an outside antenna and it provides acceptable TV reception now on UHF channels, it should also work for DTV. Also, if our indoor antenna is capable of receiving UHF television service now, we may also be able to receive DTV service with that antenna. Indoor DTV reception is affected by a number of factors that vary depending on local conditions. Many retailers carrying DTV equipment have information about local reception conditions.
3.6 Shall we be able to receive existing TV programming on our DTV set?
Yes, digital television sets available during the transition will be fully compatible with traditional analog TV programming. These new digital sets will have the capability to receive new DTV programming and will also be able to receive all the programming we receive today on our traditional set. This means that new DTV sets will be able to display all of the programming available today from broadcasters, cable operators, satellite TV services, other video service providers, and pre-recorded sources. So if we buy a new digital set, we will not lose the ability to get any of the programs we now receive on our current set.
:-> Will cable systems carry local DTV signals?
Some cable operators have indicated that they may carry the DTV programming of local broadcast stations. If these signals are carried in their original DTV format, no additional equipment will be needed to receive them on DTV sets. Some cable systems may, however, convert DTV programming to different digital formats and / or may carry DTV signals at lower resolutions than the original broadcast signal. In such cases, special cable "set-top" boxes may be needed to receive DTV.
CHAPTER 4. Application
The applications in Digital TV are only limited to imagination of the service and content providers. The typical applications are, TV mail (similar to e-mail), TV Chat, TV Commerce, TV interactive Games, Video on Demand (VOD), Personal Video Recorder (PVR), Electronic Program Guide (EPG), TV Education etc. More and more applications will get deployed in due coarse of time.
4.1 Interactive TV (iTV)
Interactive TV is the combination of digital television and Internet technology to deliver a mix of programming, restricted or open Web access, email, on-line shopping and customer service to viewers watching at home. It can be seen as both a channel to the Internet and as a way to synchronize data with broadcast material so that viewers can influence the outcome of a show, chat to other fans, buy products and play games related to the programmes being broadcasted. While the current generation of interactive television systems offers basic Internet browsing functionality, the next generation of technologies available in the coming months promises to give far greater flexibility both to viewers and to content providers.
iTV is domestic television with interactive facilities usually facilitated through a ‘back channel’. Equally important, interactive television is content that users and viewers can interact. Interactive television is also a way of empowering viewers to use television in new ways. The unifying factor is the television that is central to the entertainment, education, information, leisure and social life of millions of homes all over the world.
The contents will have data apart from audio and video. The data consists of two parts information (variables) and execution code. The execution code gets loaded and executed along with the video & audio, which is being played on the TV. Each segment of interactive content will contain a piece of executable and data (information) required for the executable. For example when an advertisement being shown and the corresponding executable required in capturing the requests of the viewer will be loaded and executed.
On selecting the product shown with specification, the request is captured and sent to the backed server. The back end server will process the request and transact the order and finally the product will be delivered to the viewer at his residence. Thus data captured by the TV/STB is sent to the content server. Based on the application and the request the server will respond appropriately.
4.1.1 Architecture of iTV
Fig.7 illustrates the basic head end architecture for providing interactive TV services. With this comprehensive interactive cable/set-top solution, for example, cable operators can send all types of data—Internet data, voice signals, and video—over a single, packet-based infrastructure. Equally important, the interactive cable/set-top solution leverages the cable operator’s existing network infrastructure, further reducing total cost of ownership.
The components of this architecture are described below :-
4.1.2 Backbone
The backbone plays a key role in deploying enhanced cable services to subscribers. It is a high-speed, digital network that carries Internet data, voice, and video between cable company facilities. Cable operators are well positioned to build a converged IP network because of the extensive regional fiber network already in place. This fiber backbone is made of OC-3 (156 Mbps) to OC-192 (2488 Mbps) Synchronous Optical Network (SONET) or Asynchronous Transfer Mode (ATM) rings. These fiber rings scale to accommodate increasing volumes of data traveling over the backbone. The back bone network also incorporates regional MPEG video systems as well as various back-office systems, and connects to other networks, including the Public Switched Telephone Network (PSTN), to other cable system backbones, and to the public Internet interconnection points used by other Internet service providers (ISPs).
4.1.3 The head end
The head end system brings regional, national, and international program content into the cable network and converts it for use by the backbone. This content includes satellite video, off-the-air video, Internet data, and PSTN voice. As in the backbone system, high-speed routers perform a vital role in the head end system. They route interactive traffic between the backbone and Ethernet in the head end internal network. Signaling protocols provide the intelligence needed to route this traffic in an optimal manner, automatically building and maintaining the routing tables to direct traffic and signal failures for rerouting in the network. The head end system also incorporates a series of interactive application, user data, and system management servers. These servers enable cable operators to deliver cost effective, branded, centrally managed services through set-top boxes. Software applications can include TV mail, TV phone, and Web browsing.
An elaborate server set-up is required at the head end to manage and deliver content and user-profiles. The standard Network Operations Centre (NOC) has a seven-server set-up – transaction, application, commerce, web, database, member ship and broadcast servers. The servers are connected to the network via an ultra-fast Ethernet connection ready for access and broadcast as shown in the fig 8.
Some of these are the middleware servers. The functionality of these servers is as follows :-
-> Transaction servers : These servers provide high bandwidth interactive HTTP and Https sessions and act as a secure gateway for the client to obtain access to web pages.
-> Application servers : These are the servers that host interactive TV applications like games etc.
-> Commerce servers : These servers are used for interactive banking and other ecommerce application.
-> Web servers : These are the regular web servers that provide access to the internet web pages.
-> Database servers : The database servers provide access to the common subscriber database.
-> Membership/Personalization servers : These servers store the viewer’s preferences and perform subscriber management functions.
-> Broadcast servers : These servers perform data carousel ling of in-band MPEG for broadcast delivery of enhanced TV content.
CHAPTER 5. Commercial View of DTV
5.1 The major players of DTV
The Digital TV market can be segmented based on the product or service. The segments are content providers, network operators / service providers and Set Top Box / DTV Manufacturers. The important players in STB manufacturers are GI (Motorola), Scientific Atlanta, Sony, Pioneer, Philips, RCA etc. The middle ware providers for the STB are Open TV, Liberate, Microsoft, Canal+ (Media Highway) etc. The Network Operators / Service providers are AOL, Direct TV, ICTV, etc. The content providers are ACTV, HBO, Two Way TV, Sky digital etc.
5.2 Standard
Various standards are being used in different parts of the globe. The standards on Digital TV are the Advanced Television System Committee (ATSC), the Digital Video Broadcasting (DVB) and the Integrated Services Digital Broadcasting (ISDB). DVB has three sub committee / standards namely DVB-T for Terrestrial, DVB-C for Cable and DVB-S for Satellite
World-wide adoptions of standards for Digital TV by 2000
ATSC is used in Northern America, Japan uses ISDB and rest uses DVB. There are few countries like China, which uses all three standards and some countries using ATSC in Asia. DVB has adopted Multimedia Home Platform (MHP) standard and Europe is standardizing on DVB-MHP. Few countries like Singapore and India have also standardized on DVB-MHP.
The ATSC, DVB and ISDB use the Moving Picture Experts Group (MPEG-2) code for the picture. ATSC digital TV uses Dolby Digital (AC-3) for the sound, DVB digital TV uses MPEG Layer II or AC-3 for the sound and ISDB digital TV uses MPEG-2 AAC (Advanced Audio Coding) for the sound. ATSC digital TV uses 8 level Vestigial Side Band (8-VSB) modulation, DVB digital TV uses Coded Orthogonal Frequency Division Multiplexing (COFDM) modulation and ISDB digital TV uses Band Segmented Transmission of Orthogonal Frequency Division Multiplexing (BST-OFDM) modulation for terrestrial broadcasting.
Choosing the standard for a particular country depends on the existing standard in the analog TV, government policies and the existing transmission network.
5.3 Digital TV Business Model
The Interactive Digital TV market has not matured enough to have a common business model similar to Computer business. Ideal model could be that the user buys the Set Top Box from any retail shop and signs up with any service provider. Instead the current situation is that, the service provider decides on the contents and the set top boxes. The set top boxes are either sold / given free by the service provider to the subscribers.
With the current model (hope fully matures in near future), the network operators decide on the specifications of the set top boxes based on the service he/she provides. Then network operator approaches a device manufacturer for manufacturing the devices. The network operator also influences the device manufacturer in deciding on the chip sets, operating system and the middle ware.
5.4 Opportunities in Digital TV
Still the Digital TV has to go a long way before it is fully implemented worldwide and operational. The scope of Digital TV is wide with numerous applications, resulting in huge opportunity for business. The digital TV needs to be localized to a particular country / community resulting in large opportunities for the product / service providers in this segment. According to Strategy Analytics there would be 625 million Digital TV installations by 2005 from 40 million by end of 2000. Even the governments of US, UK & Japan are pushing the digital convergence especially from the Digital TV angle very aggressively. The CEA (Consumer Electronics Association) and NAB (National Association of Broadcasters) are joining together in pushing the Digital TV aggressively, leading to opportunities from consumer electronics segments.
5.5 Home Networking
As TV signals move from analog to digital and as the broadcast model is gradually replaced by video (and TV) on demand, the software residing on a set-top box (Client) must offer the end user features that allow for the management of both the analog and digital signal.
The Client software must be able to receive digital signals. For the end user, this means DVD-quality content, Dolby 5.1 sound, and the convenience associated with TV on demand.
The Client software must be configurable for either independent set-top boxes or for set-top boxes connected through a central home server (gateway). A gateway is a server that has large storage capacity and that is connected to multiple TVs and sound systems. This configuration allows the end user to access large personal digital libraries from multiple home devices.
Also, since television will be increasingly more interactive, the software on the set-top box must also be easily upgraded and allow the end user to
jimmy 23 months ago
nice........