mimo_4 - Broadband MIMO-OFDM Wireless Communications GORDON...

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Broadband MIMO-OFDM Wireless Communications GORDON L. STÜBER, FELLOW, IEEE, JOHN R. BARRY, MEMBER, IEEE, STEVE W. MCLAUGHLIN, SENIOR MEMBER, IEEE, YE (GEOFFREY) LI, SENIOR MEMBER, IEEE, MARY ANN INGRAM, SENIOR MEMBER, IEEE, AND THOMAS G. PRATT, MEMBER, IEEE Invited Paper Orthogonal frequency division multiplexing (OFDM) is a popular method for high data rate wireless transmission. OFDM may be combined with antenna arrays at the transmitter and receiver to increase the diversity gain and/or to enhance the system capacity on time-variant and frequency-selective channels, resulting in a multiple-input multiple-output (MIMO) config- uration. This paper explores various physical layer research challenges in MIMO-OFDM system design, including physical channel measurements and modeling, analog beam forming tech- niques using adaptive antenna arrays, space–time techniques for MIMO-OFDM, error control coding techniques, OFDM preamble and packet design, and signal processing algorithms used for per- forming time and frequency synchronization, channel estimation, and channel tracking in MIMO-OFDM systems. Finally, the paper considers a software radio implementation of MIMO-OFDM. Keywords— Adaptive antennas, broadband wireless, mul- tiple-input multiple-output (MIMO), orthogonal frequency division multiplexing (OFDM), software radio, space–time coding, syn- chronization. I. INTRODUCTION Orthogonal frequency division multiplexing (OFDM) has become a popular technique for transmission of signals over wireless channels. OFDM has been adopted in several wireless standards such as digital audio broadcasting (DAB), digital video broadcasting (DVB-T), the IEEE 802.11a [1] local area network (LAN) standard and the IEEE 802.16a [2] metropolitan area network (MAN) standard. OFDM is also being pursued for dedicated short-range communications (DSRC) for road side to vehicle communications and as a potential candidate for fourth-generation (4G) mobile wireless systems. Manuscript received June 23, 2003; revised November 3, 2003. This work was supported in part by the Yamacraw Mission (http://www.yamacraw.org) and in part by the National Science Foundation under Grant CCR-0121565. The authors are with the School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332 USA. Digital Object Identifier 10.1109/JPROC.2003.821912 OFDM converts a frequency-selective channel into a parallel collection of frequency flat subchannels. The sub- carriers have the minimum frequency separation required to maintain orthogonality of their corresponding time domain waveforms, yet the signal spectra corresponding to the different subcarriers overlap in frequency. Hence, the available bandwidth is used very efficiently. If knowledge of the channel is available at the transmitter, then the OFDM transmitter can adapt its signaling strategy to match the channel. Due to the fact that OFDM uses a large collection of narrowly spaced subchannels, these adaptive strategies
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mimo_4 - Broadband MIMO-OFDM Wireless Communications GORDON...

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