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Digital vs analog communication; DCS block diagram

Short answer

Digital systems use discrete symbols, offer high noise immunity via regenerative repeaters, error control, security, and easy TDM multiplexing but require more bandwidth. The DCS block diagram includes source encoder (compression), channel encoder (error correction), modulator/demodulator, channel, and synchronization blocks.

List the differences between digital communication system and analog communication system. Draw functional block diagrams of DCS and explain the significance of each major blocks.

Digital vs analog communication

PointAnalog communicationDigital communication
SignalContinuous in time and amplitudeFinite set of symbols (e.g. 0/1)
Noise immunityLow; noise accumulatesHigh; regenerative repeaters remove noise
Error controlNot possibleError detection and correction codes
SecurityHard to encryptEasy encryption
MultiplexingFDMTDM, easy integration of voice, video, data
BandwidthLessMore (e.g. PCM voice 64 kb/s)
HardwareAnalog circuits, driftVLSI, DSP, cheap and flexible
Quality measureSNRBit error rate (BER)

Functional block diagram of a digital communication system

 Source->[Format]->[Source enc]->[Encrypt]->[Channel enc]
                                                  |
                       [Modulator]<-[Multiplex]<--+
                            |
                         CHANNEL  <- noise, fading
                            |
                       [Demod/Detect]->[Demux]-->+
                                                  |
 Sink<-[Format]<-[Source dec]<-[Decrypt]<-[Channel dec]

Significance of each block

  1. Information source and formatting: the source gives analog or digital data. Formatting converts it to digital form by sampling, quantization and coding (PCM), producing a bit stream.
  2. Source encoder: removes redundancy to reduce the bit rate, e.g. Huffman coding, DPCM, MP3, JPEG. This saves bandwidth and power.
  3. Encryption: scrambles data with a key so that only authorized receivers can read it; gives privacy and authentication.
  4. Channel encoder: adds controlled redundancy (parity, Hamming, CRC, convolutional codes) so that the receiver can detect and correct errors caused by noise.
  5. Multiplexer / multiple access: combines several users' bit streams (TDM, CDMA) to share one channel efficiently.
  6. Modulator: maps bits onto waveforms suitable for the channel; baseband line codes (NRZ, Manchester) or band-pass schemes (ASK, FSK, PSK, QAM). It also allows efficient radiation and frequency allocation.
  7. Channel: the physical medium (wire, fibre, radio). It attenuates, distorts (ISI) and adds noise and interference.
  8. Demodulator / detector: includes filtering (matched filter), sampling, synchronization and decision devices to recover bits from the noisy waveform with minimum error.
  9. Receiver-side blocks (demultiplex, channel decoder, decryption, source decoder, formatting): reverse the transmitter operations: separate users, correct errors, decrypt, expand compressed data and convert back to analog (D/A, filtering) for the user.
  10. Synchronization (carrier and symbol timing) runs throughout the receiver and is essential for correct detection.

✓ Answer checked by Claude Opus 5.5 (high effort)

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