Impact of Multiuser Diversity and Channel
Variability on Adaptive OFDM.
Chalmers U. of Technology,
Chalmers U. of Technology and
Multi-Carrier Spread Spectrum Workshop
for Future Generation Wireless Systems
Oberpfaffenhofen, Germany, Sept. 17-19 2003.
The Swedish 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,
bandwidth expansion and while providing acceptable
quality of service for various classes of traffic.
This paper outlines the adaptive OFDM downlink
which is one focal point of our research.
At IEEE VTC-Fall 2003, we presented our
concept for an adaptive OFDM downlink
in more detail,
in four interrelated papers (see links below).
In this paper we describe an OFDM based 4G downlink
for a wide area coverage and high mobility system.
User data are multiplexed and OFDM modulated
such that the user with the best predicted channel
conditions are always using the channel. This user
employs the linear modulation scheme that
maximizes the spectral efficiency. We show
that the system obtains a sector capacity that is
significantly better than current 3G systems.
Various combinations of OFDM and CDMA are
also discussed and it is concluded that it is difficult
to motivate the significantly increased
complexity of such schemes.
Moreover, we also doubt that these combinations
can increase spectral efficiency when predicted
channel information is utilized at the transmitter.
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 channel estimation and channel prediction.
Paper 4 at VTC2003,
on the impact of prediction errors on the adaptive modulation.
of the system, presented at WWRF March 2002, and July 2002.
An overview of the Wireless IP Project (RVK02)
Proc. of the IEEE (Dec. 2007)
invited paper on
adaptive transmission in beyond-3G wireless systems.
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