Student Project

Impact of Partial Channel State Information on Time-Domain Precoding for MIMO-OFDM


Existing wireless local area networks (WLAN) support data rates from 11 MBit/s (IEEE 802.11b) to 54 MBit/s (IEEE 802.11a/g). 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. The focus of the KTI project with Ascom AR\&T is to enhance the IEEE 802.11a technology by the use of multiple antenna arrays and to develop new concepts for future high-speed wireless LANs. Hereby, the goal is to make a maximal reuse of the current IEEE802.11a technology in order to provide compatibility with standard IEEE 802.11a products and to simplify the implementation. In order to provide a maximum reuse of current IEEE802.11a technology we are developing a transparent MIMO sublayer which decouples the 802.11a signal generation from the spatial multiplexing of the data as much as possible. The advantage is that several existing chipsets of 802.11a may be plugged to a MIMO front-end which further process the signals in order to support a proprietary spatial multiplexing mode. Target data rates range from 200 Mbit/s to 380 Mbit/s. Several IEEE802.11a chipsets are connected to the MIMO front end which multiplexes the independent data streams spatially, i.e., the signals are transmitted over the same frequency and time slot. In order to separate the signals at the receiver the transmitter learns the channel and precodes (pre-equalizes) the data prior to submission. Since we use complete 802.11a baseband chipsets we assume that we only have access to the time-domain OFDM baseband signal (post-IFFT). Therefore, the precoding operation has to be applied in time-domain.

Problem Formulation. Recently we have developed a time-domain (TD) based precoding scheme for MIMO-OFDM that removes multi-stream interference (MSI) without trying to eliminate the intersymbol-interference (ISI) that remains per stream. The ISI removal is done by the OFDM chipsets at the transmitter and receiver which turn the frequency-selective channel into a set of frequency-flat channels. For the precoding scheme perfect channel state information (CSI) at the transmitter was assumed. The goal of this project is to evaluate the performance in terms of error probabilities for the case of imperfect and/or partial CSI at transmitter. The performance study shall be mainly done by MATLAB simulations and where possible by analytical evaluation.

Subject area MIMO-OFDM, IEEE802.11a, Channel Estimation, Precoding
Type of work 40% Theory, 60% MATLAB
Supervisors Dr. Boris Rankov, Dr. Etienne Auger
Student Nadim El Guindi
Professor Prof. Dr. Armin Wittneben