DIGITAL TELEVISION-TRANSMISSION AND RECEPTION

INTRODUCTION As in other areas of electronics, digital technology has made its impact on television transmission and reception enabling gradual transition from analog to digital from of signal processing. This has resulted in much improved TV pictures and sound output quantity. While digital transmission via satellites is now common, the means to do so by terrestrial means is also picking up. Both analog and digital receiver are in use at the receiving end.

DIGITAL SYSTEM HARDWARE Analog signals can have any amplitude but in the digital system information is represented in a discrete form for which most common is the binary format. Memory devices: operation on digital data which need storage, sequencing and retrieval are carried out with special circuit called memory devices. The basic units for these circuits are logic gates and flip-flops. Clock pulses: the free running multi-vibrator is mostly used to generate CLOCK pulses at the desired rate. Registers: a register is an array of flip-flops, all triggered by a common clock.

In digital system hardware there are various devices and techniques are used such as data encryption, digital computer, CPU, microprocessor, microcomputer, A/D & D/A converters. Data communication: for processing or transmission of data in digital form, it is necessary to have a code to represent various numbers or letters.

Analog to digital (A/D) converters:

Digital to analog (D/A) converter:

SIGNAL QUANTISATION AND ENCODING Video signal quantization: It has been practically verified that sampling of analog video at 256 levels is sufficient to make the reproduced signal to be almost undetectable from the original signal.

Encoder:

DIGITAL SATELLITE TELEVISION The four stages of digital satellite transmission are, 1) signal encoding 2) processing 3) modulation 4) transmission Signal processing: the three stages of signal processing are, a) data compression b) data encryption c) data packetizing

Digital satellite reception and decoding:

DIRECT TO HOME SATELLITE TELEVISION The DIRECT TO HOME satellite broadcast system enables viewers to receiver many channels of high quality TV programs via high powered KU-BAND satellites. For DTH service, ku-band frequencies are preferred because these are not prone to interference from ground point to point communication and also need smaller diameter dish antenna. Low powered ku-band transmit in the 11.7 to 12.5GHZ range & new high powered range is 12.2 to 12.7GHZ for efficient operation of DTH transmissions.

DIGITAL TV RECEIVER The functions of various VLSI chips used in the receiver are described by, 1) video codec 2) video processor 3) deflection processing unit 4) audio codec 5) audio processor 6) central control unit

MERITS OF DIGITAL TV RECEIVERS Digital TV receiver have the following merits in terms of overall performance, picture quality and sound reproduction. 1) reduced ghosts 2) reduced of 50Hz flicker 3) high resolution pictures 4) pictures in pictures (PIP) 5) slow motion action 6) easy adoption to additional displays 7) reduced operational instability 8) improved reception in fringe areas

DIGITAL TERRESTRIAL TV (DTT) Digital terrestrial television (DTTV or DTT) is a technological evolution of broadcast television and an advancement over analog television. DTTV broadcasts land-based (terrestrial) signals. Digital TV transmission by terrestrial means commenced on same selected channels more than two decades back when digital receiver beams available to reproduce high quality pictures and stereo sound output.  The advantages of digital terrestrial television, are similar to digital versus analog in platforms such as cable, satellite, and all telecommunications; the efficient use of spectrum and provision of more capacity than analog, better quality images, and lower operating costs for broadcast and transmission (after the initial upgrade costs).

Transmission: DTTV is transmitted on radio frequencies through terrestrial space in the same way as standard analog television, with the primary difference being the use of multiplex transmitters to allow reception of multiple channels on a single frequency range (such as a UHF orVHF channel) known as subchannels. Reception: DTTV is received either via a digital set-top box (STB), TV gateway or integrated tuner included with television sets, that decodes the signal received via a standard television antenna. Some set-top-boxes and TV gateways include digital video recorder (DVR) functionality.

REFERENCES Modern Television Practice(Fourth revised edition) - R.R.Gulati , New Age International Publishers. Audio and Video Systems(Second Edition) - R.G.Gupta, McGraw Hill Education Limited. https://en.wikipedia.org/wiki/Digital_terrestrial_television