A 01-quick-introduction-to-digital-communication-system

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Quick Introduction to Digital Communication System

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A 01-quick-introduction-to-digital-communication-system

  1. 1. A-01: Quick Introduction to Communication System Author 10/3/2013 1
  2. 2. Communication System • Source encoder converts message into message signal or bits. • Transmitter converts message signal or bits into format appropriate for channel transmission (analog/digital signal). • Channel introduces distortion, noise, and interference. • Receiver decodes received signal back to message signal. • Source decoder decodes message signal back into original message.
  3. 3. Analog vs. Digital System • Analog Signals – Value varies continuously • Digital Signals – Value limited to a finite set – Digital systems more robust • Binary Signals – Has at most 2 values – Used to represent bit values – Bit time T needed to send 1 bit – Data rate R=1/T bps
  4. 4. Performance Metric • Analog communication systems – Metric is fidelity (the ability of the receiver to reproduce all the modulating frequency equally). • Digital communication systems – Metrics are data rate and of bit error rates (BER). – Without noise, never make bit errors. – With noise, BER depends on signal and noise ration (SNR), data rate, and channel characteristics.
  5. 5. Digital Modulation • Most information today is in bits. • Baseband modulation converts bits into analog signals. • Rectangular pulse don’t have good BW properties. • Nyquist pulse allow tradeoff of bandwidth characteristic to timing errors
  6. 6. Digital Modulation
  7. 7. BPSK, QPSK, QAM
  8. 8. Harmonic Signals in Nyquist-Pulse • Good BW performance, poor harmonic interference. • Harmonic signals create interference (e.g. Inter-Symbol Interference).
  9. 9. Solution to Nyquist Inter Symbol Interference
  10. 10. What is OFDM?
  11. 11. Difference between OFDM and OFDMA
  12. 12. LTE Downlink OFDMA

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