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Maximizing Througput with Adaptive
M-QAM Based on Imperfect Channel Predictions.
Mikael Sternad,
and
Sorour Falahati,
IEEE Symposium on Personal, Indoor and Mobile
Radio Communications PIMRC 2004
,
Barcelona, Sept. 2004.
© IEEE
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Outline:
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The Wireless IP project studies
problems that are crucial in the evolution of UMTS towards high
data rates, as well as in future 4G technologies aimed at
rapidly mobile terminals. The goal is to attain higher
througputs for packet data in particular in downlinks,
without bandwidth expansion and while providing acceptable
quality of service for various classes of traffic.
At IEEE VTC-Fall 2003, we presented our
concept for an adaptive OFDM downlink
in four interrelated papers (see links below).
An important aspect is here how link adaptation
schemes will perform when the channel state
predictions on which they are based are erroneous.
This is investigated in the present paper, and we
also investigate the effect of channel prediction
errors on the resulting multiuser diversity gain
when allocating resources by opportunistic scheduling.
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Abstract:
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Uncoded adaptive M-QAM transmission
over flat Rayleigh fading channels is here
optimized in a novel way
in the presence of channel
prediction errors.
The modulation rate is determined
based on the predicted channel state.
The modulation rate limits
are adjusted by maximizing the
throughput in error-free link-level
frames, averaged over the pdf of the
true channel state.
No bit error rate
constraint is imposed. This approach is
appropriate when fast link-level
retransmissions can be used to
attain required error levels.
The resulting scheme is evaluated analytically
in a multiuser environment where predictive
link adaptation is used in combination with
a scheduling strategy that
provides multiuser diversity gain.
Prediction errors
typical of prediction 1/3 wavelength
ahead in space will then result in only
8\% - 12\% reduction in the spectral
efficiency, as compared to a case with
perfectly known channels.
The resulting performance is very robust with
respect to the prediction error variance
assumed when optimizing the rate
adaptation scheme.
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Related publications:
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Proc. of the IEEE (Dec. 2007)
invited paper on
adaptive transmission in beyond-3G wireless systems.
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Paper 1 at VTC2003,
on adaptive modulation, multiuser diversity
and channel variability within bins.
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Paper 2 at VTC2003,
on the OFDM downlink and cell planning for high SIR.
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Paper 3 at VTC2003,
on OFDM channel estimation and channel prediction.
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Paper 4 at VTC2003,
on optimizing M-QAM with trellis-coded modulation
under BER constraints, based on uncertain channel predictions.
(We then obtain a scheme which is "afraid" of fading dips,
in contrast to the present results.)
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Channel Power Prediction,
by using unbiased predictors and advanced regressor noise reduction.
(VTC 2002-Fall.)
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Optimizing uncoded adaptive M-QAM ,
by taking the power prediction error into account (GlobeCom03).
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Optimizing uncoded adaptive M-QAM ,
(IEEE Trans. COM 2004).
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Source:
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Pdf, (155K)
Postscript (224K)
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The Wireless IP Project Homepage
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Main
entry in list of publications
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