DESIGN AND DEVELOPMENT OF SUB NYQUIST D P C M SYSTEM FOR COLOUR SIGNALS

Abstract

With the tremendous advances in digital technology, work on the digital coding of picture signals has been going on for many years, initially for transmission applications and more recently for signal processing. The goal of picture digitaliza-tion is to reach a satisfying level of bandwidth efficiency and achieve through digital transmission a level of quality and resolution of the picture signal that is higher than what is +©ssibie with current airialog ttansmiss.ion chaiifiels The advantages of digital transmission are well known, namely that digitally coded signals are inherently highly re-sistant to the effects of noise and distortion encountered in transmission systems and can be regenerated for long-distance transmission. Accordingly the quality of television signals transmitted in digital form is usually determined by the cod-ing methods used rather than the link itself. Digital transmi-ssion of video signals is therefore attractive. Digital net-works, in which digital television can take its place alongside telephony and data without special treatment, are being esta-blished around the world by the telecommunication authorities. As increasing use is being made of digital processes for pro-gramme origination, digital transmission between studiO3 or to broadcast transmittors would form a logical step in the process of evolution towards all digital operation. However, straightforward digital coding of colour video signals generates a signal having a high bit rate which, if transmitted, is rather wasteful of channel capacity. Possible ways of reducing bit rate required for.video signals have there-fore received much attention. One of the bit rate reduction technique used in these transmission systems is sub-Nyquist sampling. Therefore in this dissertation the sub-Nyquist DPCM system has been chosen. The main purpose of this dissertation is to review sub-Nyquist sampling and various picture coding techniques. Design and Hardware implementation of sub-Nyquist DPCM system is also considered. The system has been implemented with ordinary com-ponents and TTL integrated circuits. The sampling rate of 8.86 MHz has been chosen with 3 bit coding, which results in a bit rate of 26.58 Mbit/s. The system has been tested for sinusoidal signal of frequency 800 KHz and colour video signal