Summary: Inter­Carrier Interference in MIMOOFDM
Anastasios Stamoulis, Suhas N. Diggavi, and Naofal Al­Dhahir
AT&T Shannon Laboratory
Florham Park, NJ 07932
Abstract
In this paper, we examine multicarrier transmission over time­varying channels. We first develop a
model for such a transmission scheme and focus particularly on MIMO OFDM. Using this method, we
analyze the impact of time­variation within a transmission block (time variation could arise both from
Doppler spread of the channel and from synchronization errors). To mitigate the effects of such time­
variations, we propose a time­domain approach. We design ICI­mitigating block linear filters, and we
examine how they are modified in the context of space­time block­coded transmissions. Our approach
reduces to the familiar single­tap frequency­domain equalizer when the channel is block time­invariant.
Channel estimation in rapidly time­varying scenarios becomes critical, and we propose a scheme for es­
timating channel parameters varying within a transmission block. Along with the channel estimation
scheme, we also examine the issue of pilot tone placement and show that in time­varying channels it
may be better to group pilot tones together into clumps equispaced onto the FFT grid; this placement
technique is in contrast to the common wisdom for time­invariant channels. Finally, we provide numer­
ical results illustrating the performance of these schemes, both for uncoded and space­time block­coded
systems.
Parts of this paper will appear in WCNC'02 and ICC'02.

Source: Al-Dhahir, Naofal - Department of Electrical Engineering, University of Texas at Dallas

Collections: Engineering