- 2078 Kartik · 2+2 marks
Digital transmission system; analog vs digital
Short answer
A digital system samples and PCM-encodes analog data, then line-codes or modulates both analog-derived bits and digital data. Digital transmission offers regeneration, error control, encryption, constant quality, and TDM, but uses more bandwidth; analog is simpler, less bandwidth, but noise accumulates and quality degrades.
Draw the block diagram of a digital transmission system that can be used to transmit analog as well as digital data. Compare and contrast analog and digital transmission techniques with at least five distinguishing characteristics.
Block diagram of a digital transmission system for analog and digital data
Analog source -> LPF -> Sampler -> Quantiser -> Encoder (PCM) -+
v
Digital source ------------------------------------> Line coder/Modulator
|
Channel
|
Analog output <- LPF <- DAC <- Decoder <- Regenerator/Demodulator
Digital output <------------------------------------+
Analog data is sampled (above twice the highest frequency), quantised and encoded into bits (PCM); digital data goes directly to the line coder or modulator (ASK, FSK, PSK). At the receiver the signal is regenerated, decoded and, for analog data, converted back by a DAC and filter.
Comparison
| Point | Analog transmission | Digital transmission |
|---|---|---|
| Signal | Continuous in time and amplitude | Discrete levels (bits) |
| Noise effect | Noise adds up and cannot be removed | Regenerated by repeaters, errors can be detected and corrected |
| Bandwidth | Less | More (for PCM) |
| Equipment | Amplifiers, simple | Converters, repeaters, more complex |
| Security / processing | Difficult to encrypt and process | Easy encryption, compression, multiplexing (TDM) |
| Quality over distance | Degrades | Constant (regenerated) |
| Examples | AM/FM radio, old telephone | Digital telephony, Ethernet, mobile data |
✓ Answer checked by Claude Sonnet 5.5
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