Attaining both Coverage and High Spectral Efficiency
with Adaptive OFDM Downlinks.
Chalmers U. of Technology,
Uppsala University and
Chalmers U. of Technology
IEEE Vehicular Technology Conference VTC2003-Fall,
Orlando, FLA, Oct. 2003. © IEEE
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.
At IEEE VTC-Fall 2003, we presented our
concept for an adaptive OFDM downlink
in four interrelated papers (see links below).
This is Paper 2 of the four papers.
It discusses the design of the adaptive OFDM
downlink and its different components.
It also suggests a frequency reuse scheme
which makes it possible to use high modulation
formats in large areas of cells, while retaining
wide area coverage (not only hot-spot coverage
with isolated access points).
A downlink radio interface is proposed for
cellular packet data systems
with wide area coverage
and high spectral efficiency.
A~slotted OFDM radio interface is used,
in which time-frequency bins are allocated
adaptively to different users
within a downlink beam, based on
their channel quality.
Fading channels generated by
vehicular 100~km/h users may be accommodated.
Frequency division duplex (FDD)
is assumed, which requires channel prediction
in the terminals and feedback of that
information to a packet scheduler
at the base station.
To attain both high spectral efficiency and
good coverage within sectors/beams,
a scheme based on coordinated scheduling between
sectors of the same site, and the employment
of frequency reuse factor above~1
only in outer parts of the sector,
is proposed and evaluated.
The resulting sector throughput
increases with the number of active users.
When terminals have one antenna and
channels are Rayleigh fading,
it results in a sector payload capacity
between 1.2 (one user)
and 2.1 bits/s/Hz/sector (for 30 users) in
an interference-limited environment.
Paper 1 at VTC2003,
on adaptive modulation, multiuser diversity
and channel variability within bins.
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.
which describes the suggested reuse scheme in detail.
of the system, presented at WWRF March 2002, and July 2002.
The adaptive OFDM downlink
briefly compared to multi-carrier CDMA.
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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