Mumbai university > Electronics and telecommunication Engineering > Sem 6 > Television Engineering

Marks: 05

Years: May 2016

• Japan had been the pioneer in developing HDTV systems. They first developed Hi-Vision (an acronym of HIgh definition teleVISION) in 1979.

• The system used 1125 lines (1035 active lines), 5:3 aspect ratio, a bandwidth of 20MHz for luminance signal and 7MHz for chrominance signal (about 4 times the bandwidth used by the traditional SDTV) and dot interleaving in addition to line interleaving.

• It was based on division of a carrier frequency into multiple frequencies and then modulating each frequency using frequency modulation and transmitting them using time division multiplexing.

• This Hi-Vision system also came to be known as MUSE (an acronym of MUltiple Sub-Nyquist Encoding).

• Most of the video signal was contained in low frequencies and so it was not necessary to use the Nyquist sampling rate for the highest video frequency of 5MHz.

• Lower frequency content could be easily recovered by using low sampling rate called sub-Nyquist rate.

• Despite this innovation, transmission bandwidth was quite high as analog frequency modulation was used.

• At that time, digital modulation for video signals was not available.

• So the video signal was digitized for multiplexing and recording purpose but for transmission it had to be converted back to analog signal for modulating radio frequency carriers using frequency modulation.

• Hence it was not suitable for terrestrial broadcast but was alright at that time for satellite relay systems which were capable of accommodating quite high bandwidths.

• Satellite broadcast suited Japan very well as the whole island could be covered by a single satellite.

• Japan started broadcasting Hi-Vision TV to its subscribers in 1995.

• With the growing popularity of HDTV broadcasts, demand for channels increased and the broadcast satellite system could not cope up; so Japan discontinued satellite broadcast of Hi-Vision from October 1, 2007.

• Despite the deficiency of high bandwidth, it is latently true that without the pioneering Hi-Vision, modern high definition digital TV broadcast would not have been in use so soon.