Change search
ReferencesLink to record
Permanent link

Direct link
Multiuser diversity orthogonal frequency division multiple access systems
KTH, Superseded Departments, Signals, Sensors and Systems.
2004 (English)Licentiate thesis, monograph (Other scientific)
Abstract [en]

Multiuser diversity can be used to significantly increase system throughput in wireless communication systems. The idea is to schedule users when they experience good channel conditions and let them wait when the channels are weak. In this thesis, several aspects on multiuser diversity OFDMA systems are investigated. An adaptive reduced feedback scheme for multiuser diversity OFDMA is proposed. It significantly reduces the total feedback overhead while maintaining a multiuser diversity gain. The scheme uses clusters of sub-carriers as feedback units and only feeds back information about the fading peaks. Furthermore, an opportunistic beamforming scheme for clustered OFDM is presented and evaluated. A key aspect of the opportunistic beamforming scheme is that it increases the frequency fading of users with relatively flat channels, which increases the likelihood of being scheduled. Scheduling is an important aspect of multiuser diversity. A modified proportional fair scheduler is proposed in this thesis. It incorporates user individual target bit-rates and delays and a tunable fairness level. These features makes the scheduler more attractive for future mixed service wireless systems. The use of the feedback information in the opportunistic beamforming process is discussed and evaluated. This extra information can help to increase the performance of unfairly treated users in the system. Several aspects of the proposed system are evaluated by means of simulation, using the 3GPP spatial channel model. In the simulations, the clustered beamforming performs better than three comparison systems. The modified proportional fair scheduler manages to divide the resources according to the user targets, while at the same time exploiting the multiuser diversity as well as the standard proportional fair algorithm. The thesis also includes results on coded packet error rate estimation from a channel realization by means of a two dimensional table. This can be useful in large network simulations as well as in designing adaptive modulation schemes.

Place, publisher, year, edition, pages
2004. , vi, 91 p.
Trita-S3. SB, ISSN 1103-8039 ; 0465
Keyword [en]
Keyword [sv]
National Category
Signal Processing
URN: urn:nbn:se:kth:diva-352OAI: diva2:9334
Available from: 2005-08-01 Created: 2005-08-01 Last updated: 2012-03-21

Open Access in DiVA

fulltext(1846 kB)3166 downloads
File information
File name FULLTEXT01.pdfFile size 1846 kBChecksum SHA-1
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Svedman, Patrick
By organisation
Signals, Sensors and Systems
Signal Processing

Search outside of DiVA

GoogleGoogle Scholar
Total: 3166 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 664 hits
ReferencesLink to record
Permanent link

Direct link