Download
1 / 21
210 likes | 404 Views
SYSC 4607 – Lecture 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
E N D
SYSC 4607 – Lecture 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 • 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 - Without transmitter channel knowledge same performance as receiver diversity - With channel knowledge - Alamouti scheme - full diversity gain similar to receiver MRC, 3 dB lower array gain
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
Adaptive Coding and Modulation - Requires reliable feedback channel and accurate channel estimation - Increases transmitter and receiver complexity
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.
