Channel Update Scheme for MIMO-OFDM System with Time Domain Precoder


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. The precoder requires a reliable channel state information (CSI) to counter the channel effect on the signal. So far the precoder has been calculated before each transmission of an orthogonal frequency division multiplexing (OFDM) symbol. But this operation is time consuming and should therefore only be realized when the system symbol error rate (SER) is rising above a given threshold.
In this project you will design, program and simulate a scheme regulating the CSI update to improve the MIMO-OFDM system performance. At the end of this project you should be able to answer following questions: when must the CSI be updated? which protocol should be used between the receiver and the transmitter? how does the system performance behave when a set of precoding matrices is used?

[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 Patrik Bichsel, Thomas Hartmeier
Supervisor Dr. Etienne Auger
Professor Prof. Dr. Armin Wittneben