Adaptive TDMA/OFDMA for Wide-Area
Coverage and Vehicular Velocities.
Chalmers Univ. of Technology and
Dresden, June 19-23 2005.
Adaptive communication systems allocate (schedule) time,
frequency and antenna resources based on channel quality
and user requirements. They enable efficient resource utilization
and multi-user scheduling gains, when channels to different
terminals fade independently.
In systems based on time division
multiple access/ adaptive OFDM (TDMA/OFDMA),
time-frequency resources (chunks) are allocated.
This provides a flexible small-scale granularity of the resources,
ideal for transmitting small as well as large packets.
Based on the results obtained within the
Swedish Wireless IP project, we are assessing the
feasibility of such methods in novel broadband radio
interfaces within the EU FP6 Integrated Project WINNER.
We here investigate adaptive downlinks and uplinks based on
fast scheduling and link adaptation, also for users at vehicular
speeds, with a non-adaptive fall-back mode for very fast
The non-adaptive fall-back mode design is
outside the scope of this paper, but should be based on time,
frequency and space diversity techniques.
Allocation of fast
fading channels requires channel prediction. The signal to
interference and noise ratio (SINR) is to be predicted for
all potential resources in future transmission.
In the proposed downlink, each terminal predicts the
SINR over a major part of the total bandwidth.
All active terminals report source coded SINR
values or source coded suggested modulation
formats over a shared uplink control channel.
A resource scheduler, located close to one or several radio
access points, allocates the downlink resources.
Within the EU FP6 Integrated Project WINNER,
adaptive transmission is investigated as a key technology
for boosting the spectral efficiency of a new radio interface for
4G systems. Adaptive allocation of time-frequency chunks in
an OFDM-based system offers a significant potential, but
also poses challenges.
Within work package two of WINNER,
we study critical issues such as the feasibility of adaptive
transmission over fading downlink/uplink channels to/from
vehicular terminals, the corresponding required channel
prediction accuracy, and the required feedback control bandwidth.
This paper summarizes recent results obtained within
WINNER, and related results obtained within the
Swedish Wireless IP project.
Proc. of the IEEE (Dec. 2007)
invited paper on
adaptive transmission in beyond-3G wireless systems,
with later results.
by modfied coding schemes (VTC06-Spring).
Adaptive modulation systems
for predicted wireless channels. IEEE TCOM 2004 paper
presenting the method for adjusting modulation rate limits.
Channel Power Prediction,
by using unbiased predictors and
advanced regressor noise reduction (VTC 2002-Fall).
PhD Thesis on channel prediction,
by Torbjörn Ekman.
Paper 1 at VTC2003,
on adaptive modulation, multiuser diversity
and channel variability within bins.
Paper 2 at VTC2003,
on the OFDM downlink and cell planning for high SIR.
Paper 3 at VTC2003,
on OFDM downlink channel estimation and channel prediction.
Paper 4 at VTC2003,
on the impact of prediction errors on the adaptive modulation.
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