Creating Diversity with Precoding for IEEE 802.11a based MIMO-OFDM Systems


Existing wireless local area networks (WLAN) support data rates from 11 MBit/s (IEEE 802.11b) to 54 MBit/s (IEEE 802.11a/g). In order to offer rate-consuming wireless multimedia applications, future WLAN systems will have to support much higher data rates and an improved link reliability. Recent research results have demonstrated that multiple-input multiple-output (MIMO) communication systems are able to substantially increase the data rate (bit/sec) and/or to improve the transmission quality (bit error rate) in a wireless point-to-point link without additional expenditure in power or bandwidth [1], [2]. The Communication Technology Laboratory (CTL) is working on the project " Future MIMO-WLAN " , the aim of which is to enhance the IEEE 802.11a technology using multiple antenna arrays.
A novel precoding method has been proposed in [3]. This method enables several independant users to communicate with a base station, creating a set of virtual parallel single-input single-output (SISO) links. For the moment the obtained diversity per user is 1. It would be interesting to increase the system diversity, and thus to improve the system performance in terms of symbol error rate. A possible method for this consists in adding additional antennas to the system. When more antennas than data streams are present in the system a scheme could be employed to exploit these additional degrees of freedom. So far a selection combining scheme has been implemented but it only leads to a coding gain.
In this project you will propose, investigate and compare innovative schemes to improve the MIMO-OFDM system performance.
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[1] A. Paulraj, R. Nabar and D. Gore, Introduction to Space-Time Wireless Communications. Cambridge University Press, 2003.
[2] I. E. Telatar, Capacity of Multi-Antenna Gaussian Channels, technical report, AT&T Bell Laboratories, 1995.
[3] E. Auger, B. Rankov, M. Kuhn and A. Wittneben, Time Domain Precoding for MIMO-OFDM Systems, proceedings of the 10th International OFDM-WOrkshop, 2005.

Type Student project (Semesterarbeit)
Semester Winter 2005-2006
Subject area MIMO communication systems, channel estimation, gains
Type of work 50% Theory, 50% Software (Matlab)
Students Regula Gönner, Dominik Schatzmann
Supervisor Dr. Etienne Auger
Professor Prof. Dr. Armin Wittneben