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Lect-21_07 - 5 Why Digital(contd • Image stored in...

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1 The Noise objective was 3pW/km. The total noise power measured at the end of 6400 km was 8000 pW, which is less than 3pW/km. The (S/ N) O was 40 dB. 2 coaxial ’tubes’ required for 10,800 channels, one for ‘Go’ and the other for ‘Return’. For L5 - 22 ‘tubes’ are there with 2 spare ‘tubes’. Total Capacity – 1,08,000 VF Channels. (Operational since 1974)
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2 Lecture - 21 Noise Figure, Noise Temperature 24-02-2007
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4 Why Digital? Regeneration – digital coding of signals involves two states and shape of the pulse is not important as long as energy is the same. Digital Signals are more immune to noise In analog Communication noise is cumulative. Distortion cannot be corrected. Digital circuits are more reliable Digital hardware allows more flexible implementation Time Division Multiplexing (TDM) is simpler than FDM. Different types of signals can be treated as identical signals. Digital techniques lend themselves naturally to signal processing functions – coding, encryption etc.
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Unformatted text preview: 5 Why Digital? (contd.) • Image stored in digital form can be reproduced without deterioration • Disadvantages: • They require more bandwidth. Efficient compression techniques are coming up at the cost of increased complexity of implementation. • They tend to get more signal processing intensive. • Synchronization is a problem – Bit Synch, clock synch, frame synch. etc. More bandwidth may be required. • Degradation in S/N is not graceful. 6 7 8 Formatting of Information Signals 9 Sampling • Instantaneous Sampling • Natural Sampling • Flat Top Sampling 10 Instantaneous Sampling 11 Flat Top Sampling 12 Distortion due to finite width of Pulse during Sampling Aperture Effect in Flat Top Sampling 13 14 PCM Generation 15 Quantization – Uniform and non-uniform 16 A- law and µ - law Characteristics 17 µ - law Characteristics m = x/x max ; v = y/y max 18 A- law and µ - law Characteristics...
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