Degrees of freedom in adaptive modulation: a unified view

We examine adaptive modulation schemes for flat-fading channels where the data rate, transmit power, and instantaneous BER are varied to maximize spectral efficiency, subject to an average power and BER constraint. Both continuous-rate and discrete-rate adaptation are considered, as well as average...

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Bibliographic Details
Published in:IEEE transactions on communications Vol. 49; no. 9; pp. 1561 - 1571
Main Authors: Seong Taek Chung, Goldsmith, A.J.
Format: Journal Article
Language:English
Published: New York IEEE 01.09.2001
The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subjects:
Adaptation
Bit error rate
Channel estimation
Channels
Constellation diagram
Constraints
Degrees of freedom
Delay estimation
Estimation error
Fading
Feedback
Mathematical analysis
Modulation
Modulation coding
Optimization
Power system reliability
Spectra
Transmitters
ISSN:0090-6778, 1558-0857
Online Access:Get full text
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Summary:We examine adaptive modulation schemes for flat-fading channels where the data rate, transmit power, and instantaneous BER are varied to maximize spectral efficiency, subject to an average power and BER constraint. Both continuous-rate and discrete-rate adaptation are considered, as well as average and instantaneous BER constraints. We find the general form of power, BER and data rate adaptation that maximizes spectral efficiency for a large class of modulation techniques and fading distributions. The optimal adaptation of these parameters is to increase the power and data rate and decrease the BER as the channel quality improves. Surprisingly, little spectral efficiency is lost when the power or rate is constrained to be constant. Hence, the spectral efficiency of adaptive modulation is relatively insensitive to which degrees of freedom are adapted.
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ISSN:0090-6778
1558-0857
DOI:10.1109/26.950343