SYSC 4607 – Lecture 17 Outline

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					    SYSC 4607 – Slide Set 17 Outline
   Review of Previous Lecture
   Variable-Rate Variable-Power MQAM
   Channel Estimation Error and Delay
    Review of Previous Lecture

   Adaptive modulation varies modulation
    parameters relative to fading to improve
    performance
   Adaptive Techniques
    - Variable-Rate
    - Variable-Power
    - Variable-Rate Variable-Power
  Adaptive Coding and Modulation
- Requires reliable feedback channel and accurate channel estimation
- Increases transmitter and receiver complexity
Variable-Rate Variable-Power MQAM
Variable-Rate Variable-Power MQAM
Formulation of Optimization
Formulation of Optimization
Optimal Adaptive Scheme
Optimal Adaptive Scheme
Spectral Efficiency
Channel Inversion with Fixed Rate
Discrete-Rate Adaptation
Constellation Restriction
Rate and Power Adaptation
      (Five Regions)
Power Adaptation
Average Rate
Spectral Efficiency in Rayleigh Fading
Update Rate in Adaptive Modulation

Rate at which constellation size changes should be
much more than a symbol time.
Channel Estimation Error and Delay
Channel Estimation Error and Delay


Pb 



                                    (for constant )
Estimation errors within 0.5 dB - 1 dB may be tolerated.
Channel Estimation Error and Delay
Channel Estimation Error and Delay
                   Main Points
   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.
   Constellations cannot be updated faster than 10s to 100s
    of symbol times: OK for most Dopplers.
   Estimation error and delay can lead to irreducible error
    floors.

				
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