A Report On Vterrestrial HDTV Communications Essay

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HDTV (High definition Television) dates as far back as the 1960's, where it all began from Japan. Since then, a lot of development has been made to make HDTV a reality. A couple of years back, it would have been said that “HDTV is the next thing in television revolution”. This cannot be said now, as individuals currently use this technology in their homes. Even at that, many questions are still being asked, like what are the different formats? What are the different displays? These are just to mention a few. We shall try to discuss some of these in this paper, as well as the use of standards in Terrestrial HDTV, the UK and international roll-out of terrestrial HDTV and the various set-up boxes and their functionality.

HISTORY

The history of television dates back to 1925[1]. This was invented by John Logie Bird who introduced the 30 line mechanical system. In 1936, the 405 line systems were started and broadcasts were carried out on those systems. Further down the years in 1960, the development of HDTV started in Japan, and colour televisions were also introduced in the 1960's. In 1966, the 625 line system was started and begun broadcasting. Later in 1985, the 405 line system was fully terminated. As far back as 1985, HDTV development was started in Europe. In 1989, broadcasting began by satellite transmission. Much later on in 1998, digital broadcasting began and in 2006, HDTV broadcasting finally kicked off. Although brief, this is the basic history of the television in relation to out topic of discussion.

Digital Terrestrial television was launched in the UK on the 15th of November, 1998, soon after the digital satellite television was launched in 1st October 1998. This technology (digital Terrestrial television) required that the British government license broadcasting of channels in groups of six, known as ‘multiplexes'

STANDARDS IN TERRESTRIAL HDTV

Various standards for broadcasting are used all over the world. Europe and America have different standards which are called PAL and NTSC respectively. This is because; Europe maintains a 50Hz main supply, while America maintains a 60Hz main supply. Similarly, Japan and Asia also have different standards.

As it is known, MPEG (Motion picture experts group) is the name given to the family of standards for encoding video formats. There are various standards in use, to mention few, MPEG-1, MPEG-2, MPEG-3, MPEG-4, MPEG-7, MPEG-21, MPEG-A, MPEG-B, MPEG-C, MPEG-D, MPEG-E. MPEG-3 was intended for HDTV, but it was found to be redundant and as such was merged with MPEG-2. Formats like MPEG-V, MPEG-M, and MPEG-U are currently under development.[2]HDTV requires four times as much bandwidth as a standard definition television to transmit its signals. MPEG-2 was used to transmit HDTV signals, but MPEG-4 could also be used. This came at a cost, because MPEG-4 isn't compatible without the use of special hardware. Currently, HDTV is transmitted H.264 standard. The H.264 standard is mostly used for HD transmission and blu-ray discs.

Currently in the UK, the analogue and digital systems run on the 625/50 transmission system. This means, the basic 625 lines per frame and 50 frames per second. As stated earlier, 50Hz is the standard main supply in Europe. Hence, the HDTV system runs on 1250/50 transmission system, which is double the line per frame of the earlier systems.

The table below gives a summary and comparison of the standards between standard television and high definition television.

STANDARDS

SDTV (Analog)

HDTV(Digital)

Total Lines

625

1250

Active Lines

480-486(Maximum visible on screen)

1080(Maximum visible on screen)

Sound

2-Channels (Stereo Sound)

5.1 Channels (Surround sound)

Maximum Resolution

720 X 486

1920 X 1080

Table 1. Retrieved from world television standards and DTV/HDTV, http://www.cybercollege.com/tvp009.htm

As image quality increases, the memory that is taken up by the images also increases. Video and images are similar in this respect. This is raises an issue in transmission, because of the memory usage. “HDTV source signals generally have a bandwidth around four times that of conventional TV signals.”[3] HDTV uses a 16:9 aspect ratio as compared to the conventional 4:3 aspect ratio used on standard televisions.

There are various HDTV modes for broadcast; these include 720p, 1080i and 1080p. These numbers refer to the number of horizontal scan or the pixels of vertical resolution. The ‘p' and ‘i' stand for progressively scanned and interlaced respectively. When the 720p is broadcast at 60 frames per second (60 Fps), it significantly reduces the amount of flickering. It is mainly used with the ATSC broadcast standard. It operates on the standard screen size of 16:9 and its resolution is 1280 X 720. This means 1280 horizontal pixel lines and 720 vertical pixel lines. This format is always progressive scan and never interlaced. The frame rates commonly used with the 1280 X 720 resolution are 23.976, 25, 30, 50 and 59.94 frames per second. PAL countries use mainly the 25 and 50 frames per second, while NTSC countries use the 23.596 and 59.94 frames per second. All these variations of 720p are compatible with both the DVB and ATSC standard. On the other hand, the 1080p standard is referred to as Full High Definition. Its resolution is 1920 X 1080. In the past, the ATSC standard in the United States, supported only frame rates of 23.98, 24, 25, 29.97, 30 frames per second. Soon after, amendments were made to the ATSC standard to incorporate MPEG-4 AVC/ H.264 compression and frame rate of 50, 59.94 and 60 frames per second. Since two streams (MPEG-2 and MPEG-4) cannot be broadcast over the same channel due to network restrictions, the wide-spread availability of the latter is not expected soon. In the UK, the DVB standards support the 1080p with 25 frames per second. The 50 frames per second are in development, but this requires more bandwidth and more efficient codec.[4] Although, in September 2009, the maintainers on the DVB standards added support for the 1080p with 50 frames per second signal code with MPEG-4 AVC. The DVB standard also supports the 1080p encoded in the ATSC standards. These include at the ATSC various frame rates.

TERRESTRIAL HDTV IN THE UK

There are different methods for transmitting digital signal. These digital signals include the video and voice. These methods could be by satellite, by cable or terrestrial. It is a fact that the bandwidth available for transmission in satellites is greater than that of terrestrial transmission, even with this; video still needs to be compressed.[5] If the bandwidth in satellite is increased, it will be better, but this comes at a cost. HDTV satellites have a bandwidth of 12GHZ, but the 22GHZ is currently in development.[6] Terrestrial broadcasting is the means by which analogue television signals are transmitted. The difference with terrestrial and satellite transmission is that since terrestrial is used for transmission of analogue signals, when a digital signal is transmitted terrestrially, a special hardware is required to decode the received signals and transmit then to the screen. Terrestrial bandwidth is only 6MHZ.

In the UK, the various displays for viewing in HD are the CRT (Cathode ray tube), the plasma and the LCD. The CRT, is rarely used and is less suitable for HDTV because of its ‘flickering'. This occurs because of the 50Hz frequency, but it can be stopped if the frequency is enhanced to 100Hz.[7] United Kingdom is in the premature stages of adoption. Most of the viewing is done in standard definition, although High definition broadcasts are currently available over digital satellite. These are both by subscription and free-to-air, as well as digital cable. These broadcasts are available on the sky-HD satellite service and on the virgin media cable service.

The broadcasting technology used in the UK is the DVB-T (digital video broadcasting-terrestrial), which carries compressed video, audio and data in a transport stream, using COFDM modulation. The six ‘multiplexes' that are broadcast in the UK that carry the free public channels are operated by BBC, ITV, Channel 4 and channel 5. As at the 3rd of December, 2009, a report published stated that free-view HDTV had just been broadcasted in the UK, propelling UK into the fore front of digital television. It was switched on at ‘crystal place' and ‘winter hills' transmitters. This service is broadcasted using DVB-T2 standard for the first time. This service may not be available for all consumers till the spring of 2010.[8] The current trend of migrating from analogue terrestrial broadcasting to digital terrestrial broadcasting will be done from region to region in the UK on the freeview service. One of the advantages of digital terrestrial HDTV is in the fact that it provides for many channels. Moreover, newer teletext feature are available and as earlier mention, it is broadcasted in a 16:9 anamorphic widescreen. Digital terrestrial television is received by a compatible ‘set-top box' or an ‘integrated Digital television' (IDTV), which is normally connected to an analogue receiving antenna normally located externally. These antennas are similar to those used to receive analogue signals for analogue televisions. Set-up boxes will be discussed further on in this paper. Transmissions received via set-up boxes can be recorded on to a compatible disc, using a PVR (personal video recorder). PVRs are capable of recording digital video onto a medium; the medium here can be a hard drive or a disc. The recorder will have to be directly connected to the set-top box.

SET-TOP BOX

Set-top boxes (STB), also known as set-up units (STU) are devices that connect to the television and to an external source. They receive signals from the external source and with some algorithm, convert the received signals into contents that can be view on a television screen. Set-top boxes are used for receiving digital television signals on televisions sets that do not have an in-built tuner. Specifically in the UK, they are used in receiving digital terrestrial broadcasts. This is through a series of ‘Freeview' mentioned earlier in this paper. STB can be used to access television, audio and interactive services. The current Set-top boxes available are not able to able to decode DVB-T2 signals required for the terrestrial HDTV. Hence special HD receiver will be required for this.

On the 9th of December, an article stated that the DVB-T2 Set-top box had been unveiled. “A firm, 3-view, has unwrapped what it has labelled the "world's first web-connected set-top box" able to receive free-to-air terrestrial HD telly channels.”[9] The drawback with this is that the device will not be available to purchase until March 2010. As earlier stated, Freeview kicked off on the 3rd of December, 2009, in parts of the UK. This development requires special new tuners (Set-top box) to receive the DVB-T2 signal. The new 3view STB that has just been unveiled, is unique in the sense that it allows you to watch one live HD broadcast and record another simultaneously. The 3view STB has either a 320GB or 500GB hard disc which allows recording to be paused and rewound in real time. This set-top box has USB ports which allows user to connect devices to watch personal videos and photos on an HD screen. It supports MPEG-4 video formats. Finally, the STB has an Ethernet connection which allows a variety of web based widget to be used, there is an option of purchasing a keyboard and mouse so as to use the device's Opera-based based browser to surf the internet. The table below summarizes the STB options available for different transmission sources, and the type of TV sets. The STB's are categorized according to the transmission signal source.[10]

SIGNAL SOURCE

ANALOG TV

HD-READY TV

HDTV with INTEGRATED TUNER

CABLE

Digital cable box with internal digital TV converter (DTC)

Digital cable box with internal tuner OR

Digital “cable-ready” HDTV tuner

If digital “cable ready” DTV, no box OR

Digital cable box (for additional advanced functions or if DTV not “cable-ready”)

SATELLITE

Satellite receiver with internal DTC

Satellite receiver with internal HDTV tuner

Satellite receiver

BROADCAST(TERRESTRIAL)

DTC

HDTV tuner

No box needed

Table 2: Retrieved from Jennifer Thorne Amann, Set-top Boxes: Opportunities and issues in setting efficiency standards, American council for energy-efficient economy, (Report A041), p.6

CONCLUSION

HDTV is currently being viewed in homes internationally. Users desire the ultimate viewing experience, hence the HDTV. This technology still has room for growth. It has started affecting our everyday lives, with users being unsatisfied with any view that is not in high definition.

The terrestrial HDTV transmission, has begun in the UK, and is yet to cover the Whole of the UK, region by region. This will be completed by 2010. A complete phase out of analogue broadcasting is in the process and will be replaced by digital terrestrial broadcast completely.

Currently, Terrestrial broadcast of HDTV is free, in the near future, there will be a subscription charge, but for now, it is important that most consumers get a feel of the broadcast and appreciate its technology.

REFERENCES & BIBLIOGRAPHY

[1] Ellis R.J.G.(1996), The Historical Development of Television Systems, IEE Colloquium Advanced widescreen and High definition television systems-where are they now?, IEEE London, pp. 1/1-1/5

[2] Moving Picture Experts Group,(2009) retrieved from Wikipedia online encyclopaedia, http://en.wikipedia.org/wiki/Moving_Picture_Experts_Group on 4th December, 2009.

[3] Thomas G.A.,(1996) High Definition TV Broadcast Formats, IEE Colloquium Advanced widescreen and High definition television systems-where are they now?, IEE pp. 2/1-2/5

[4] EBU-UER (May 2005), Future High definition television systems, The need to develop television production equipment for a progressively scanned image format of 1920 horizontal by 1080 vertical resolution at 50 and 60Hz frame rates, EBU statement-Geneva, Retrieved from http://www.ebu.ch/CMSimages/en/tec_text_r115-2005_tcm6-37869.pdf on 11th December, 2009.

[5] Charik S.I.,(1990) HDTV Via Satellite, IEE colloquium Transmission of HDTV by Satellite, IEE (Digest No.092), pp. 1/1-1/3

[6] Dobbie W.H.,(1990) Satellite Transmission of HDTV at 22GHz, IEE Colloquium on `Transmission of HDTV by Satellite' (Digest No.092), 1990, pp. 3/1-3/3

[7] Parker D.W.(1989), Receivers and Displays for HDTV, IEE Colloquium on `Progress Towards HDTV (Digest No.40), pp. 4/1-4/4

[8] Nigel Whitfield, (December 2009), FreeView HD goes live, Reg-Hardware: from the lab to the living room, Retrieved from http://www.reghardware.co.uk/2009/12/03/freeview_hd_launch_report/ on 10th December, 2009.

[9] James Sherwood, (December 2009), DVB-T2 Set-top box unveiled, Reg-Hardware: from the lab to the living room, Retrieved from http://www.reghardware.co.uk/2009/12/09/3view_stb/ on 11th December, 2009.

[10] Jennifer Thorne Amann, Set-top Boxes: Opportunities and issues in setting efficiency standards, American council for energy-efficient economy, (Report A041), pp.1-20

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