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SYSC 4607 – Slide Set 16 Outline

SYSC 4607 – Slide Set 16 Outline. Review of Previous Lecture Adaptive Modulation and Coding Adaptive Techniques - Variable-Rate Techniques - Variable-Power Techniques - Variable-Rate Variable-Power MQAM. Review of Previous Lecture. Combining Techniques

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SYSC 4607 – Slide Set 16 Outline

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  1. SYSC 4607 – Slide Set 16 Outline • Review of Previous Lecture • Adaptive Modulation and Coding • Adaptive Techniques - Variable-Rate Techniques - Variable-Power Techniques - Variable-Rate Variable-Power MQAM

  2. Review of Previous Lecture • Combining Techniques • Performance of Selection Combining Diversity in Fading - Combiner SNR is maximum of branch SNRs - CDF easy to obtain, pdf found by differentiating - Diminishing returns with number of antennas • Performance of MRC Diversity in Fading - Hard to get pdf of output SNR, except Rayleigh fading • Equal Gain Combining is simpler than Maximal Ratio - Harder to analyze - Performance about 1 dB worse than MRC • Transmit Diversity - With transmitter channel knowledge same performance as receiver diversity - Without channel knowledge - Alamouti scheme - full diversity gain similar to receiver MRC, 3 dB lower array gain

  3. Adaptive Modulation and Coding • Changing modulation and coding relative to fading. (Transmitter uses channel fade level to adapt.) • Parameters to adapt: - Constellation size - Transmit power - Instantaneous BER - Symbol time - Coding rate/scheme • Optimization criterion: - Maximize throughput - Minimize average power - Minimize average BER

  4. Adaptive Coding and Modulation - Requires reliable feedback channel and accurate channel estimation - Increases transmitter and receiver complexity

  5. Adaptive Techniques

  6. Variable-Power Techniques(Channel Inversion)

  7. Variable-Rate Variable-Power MQAM

  8. Variable-Rate Variable-Power MQAM

  9. Formulation of Optimization

  10. Formulation of Optimization

  11. Optimal Adaptive Scheme

  12. Optimal Adaptive Scheme

  13. Spectral Efficiency

  14. Channel Inversion with Fixed Rate

  15. Discrete-Rate Adaptation

  16. Constellation Restriction

  17. Rate and Power Adaptation (Five Regions)

  18. Power Adaptation

  19. Average Rate

  20. Spectral Efficiency in Rayleigh Fading

  21. Main Points • Adaptive modulation varies modulation parameters relative to fading to improve performance • Adaptive MQAM uses capacity-achieving power and rate adaptation, with power penalty K. • Adaptive MQAM comes within 5-6 dB of capacity • Discretizing the constellation size results in negligible performance loss.

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