High-definition television got delayed in entering the consumer market, mainly because of multiple standards, according to PanAmSat India project manager Dr R Ramani. Of late, some of the major broadcasters, including Discovery and ESPN, are delivering content in high-definition format.
Making a presentation at the recently-concluded broadcasting conference in the capital, Dr Ramani said, HDTV is gaining momentum all over the world for entertainment, sports and even special events like solar eclipse. Explaining what HDTV is all about, Dr Ramani said, the images are sharper and wider, with digital sound quality. “It is more like watching a movie screen or watching more of a football field. No wonder, that is getting more popular.”
According to Dr Ramani, there are more than 5 million households in the US, which are capable of receiving high definition TV signals. More data: Around 1.5 million out of 70 million cable homes in the US are equipped with HDTV capable set-top boxes. Also, this number is projected to grow to over over 10 million in just two years. As per available estimates, cable operators are already providing HDTV services in 80 per cent of the US market.
Besides broadcasters such as ESPN, Discovery and Fox, direct-to-home (DTH) service providers like DirecTV have also started HDTV distribution. In fact, satellite service providers like PanAmSat have complete satellite neighbourhoods marked for HDTV distribution to the US domestic market.
Interestingly, out of the 18 digital TV formats specified by the Advanced Television Systems Committee in the US, six are HDTV formats. For digital television, there are two digital video formats - standard definition and high definition.
There’s a basic difference between standard definition and high definition. As standard definition signals use less bandwidth than high definition, it’s possible to broadcast multiple programmes in a multi-channel mode. HDTV, on the other hand, requires much higher data rates due to higher resolution and wider screen formats.
The presentation deals with digital video formats, digital video broadcasting, advanced TV systems, digital audio, data transmission requirements, higher order modulation, among others.
Here are some facts. Analog TV signal standards in use are NTSC in the US; PAL and SECAM in the rest of the world. It has been mandated in the US that NTSC analog TV off-the-air broadcasts must not occupy more than 6 mhz channel bandwidth limitation. So, to enhance TV signal quality, broadcasters have made a transition to digital video format. The format, according to Dr Ramani, allows broadcasters to offer enhanced video services while operating within the allocated channel bandwidth.
Coming to digital video broadcasting (DVB), Dr Ramani said the project is an industry-led consortium of over 300 broadcasters, manufacturers, network operators, regulatory bodies and others in over 40 countries designing global standards for the delivery of digital television and data services. An open standard, DVB can deliver to homes any digitised content including HDTV.
About the Advanced Television Systems Committee (ATSC), Dr Ramani said it is a non-profit organisation developing voluntary standards for digital television including standards for HDTV.
The ATSC standard is based on the MPEG-2 compression scheme. MPEG specifies several compression options for various applications, according to Dr Ramani.
He said that after a performance comparison of various systems, the ATSC selected the Dolby AC-3 surround sound system.
As for transmission, data rate requirements for transmission of HDTV signals vary depending on the profile and resolution. Said Dr Ramani that typical HDTV distribution using 4:2:2 profile requires about 20 to 45 mbps data rate depending on the compression ratio. “This requires use of efficient bandwidth saving techniques.”
The use of higher order modulations in the satellite digital world is a way to satisfy the demand for transmitting increasing data rates for HDTV distribution, pointed out Dr Ramani. But there are challenges in implementing higher order modulation schemes, he said. The advantages of higher order modulation in satellite applications can be seen in two ways. One, it’s possible to increase the data rate to improve the quality of signal as in the case of HDTV distribution. Two, it can increase the number of channels per transponder.