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Dear all,
Khaled Hassan Shawky (EECS@IUB) will give a talk in the EECS seminar
Time: 10. 2. 2005 13:00
Place: ClamV Seminar Room (120@R1)
Title: User Scheduling for Multi User Access OFDM Systems
Speaker: Khaled Hassan Shawky
Abstract:
The orthogonal frequency division multiplexing (OFDM) system is the most
promising communication system for future solutions that support high data
rates and resist severe channel conditions. The multiple access techniques
for OFDM systems benefits from multi-user diversity, a form of diversity
inherent in wireless networks provided by time varying channels across
different users. This multi-user diversity benefits from faded channel taps,
by smart-scheduling different users, which increases the data rate and
throughput. The scheduling is done by tracking the channel fluctuations of
each user and arranging the transmissions for the different users on the
basis of the highest instantaneous channel power. As the fluctuations of the
channel increases, the probability of scheduling users with high
instantaneous channel power increases, and the instantaneous throughput of
the system increases. The proposed scheme increases the fluctuations of the
flat-fading channel to ensure higher instantaneous channel gain at the
receiver antenna.
Scheduling takes place at the base station during the downlink transmission
by providing feedback information from the mobile station to the base
station. For simplicity, the scheduler task is repeated exactly in the same
manner during the uplink transmission. In this work, the users are scheduled
for higher throughput, the throughput being the principal performance
measure. The throughput difference in the uplink and downlink has been
evaluated for different duplexing schemes, the time division duplexing (TDD)
and the frequency division duplexing (FDD). It is demonstrated that the
performance of TDD scheme is much better than that of the FDD method, given
that the uplink and the downlink are using the same channel conditions
different time slots.
Different multiple access techniques viz., frequency division multiplexing
(FDMA) and the time division multiplexing (TDMA) have also been implemented
and their effect on the multiuser system performance have been observed. The
performance of the system is found to be critically depending on the
multiple access techniques used where the scheduling criteria is affected by
the multiple access techniques. It is also demonstrated that the multi-user
diversity gains performance from the FDMA rather than over TDMA.
[for more information see http://eecs.iu-bremen.de/seminar]
Michael Kohlhase
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Prof. Dr. Michael Kohlhase, Office: Research 1, Room 62
Professor for Computer Science Campus Ring 12,
School of Engineering & Science D-28758 Bremen, Germany
International University Bremen tel/fax: +49 421 200-3140/-493140
http://www.faculty.iu-bremen.de/mkohlhase <m.kohlhase@xxxxxxxxxxxx>
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