mimo-ofdm_2 - IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 50,...

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IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 50, NO. 9, SEPTEMBER 2002 1471 MIMO-OFDM for Wireless Communications: Signal Detection With Enhanced Channel Estimation Ye (Geoffrey) Li , Senior Member, IEEE , Jack H. Winters , Fellow, IEEE , and Nelson R. Sollenberger , Fellow, IEEE Abstract— Multiple transmit and receive antennas can be used to form multiple-input multiple-output (MIMO) channels to increase the capacity by a factor of the minimum number of transmit and receive antennas. In this paper, orthogonal frequency division multiplexing (OFDM) for MIMO channels (MIMO-OFDM) is considered for wideband transmission to mitigate intersymbol interference and enhance system capacity. The MIMO-OFDM system uses two independent space-time codes for two sets of two transmit antennas. At the receiver, the independent space–time codes are decoded using prewhitening, followed by minimum- Euclidean-distance decoding based on successive interference cancellation. Computer simulation shows that for four-input and four-output systems transmitting data at 4 Mb/s over a 1.25 MHz channel, the required signal-to-noise ratios (SNRs) for 10% and 1% word error rates (WER) are 10.5 dB and 13.8 dB, respectively, when each codeword contains 500 information bits and the channel’s Doppler frequency is 40 Hz (corresponding normalized frequency: 0.9%). Increasing the number of the receive antennas improves the system performance. When the number of receive antennas is increased from four to eight, the required SNRs for 10% and 1% WER are reduced to 4 dB and 6 dB, respectively. Therefore, MIMO-OFDM is a promising technique for highly spectrally efficient wideband transmission. Index Terms— Multiple-input multiple-output channels (MIMO), orthogonal frequency division multiplexing (OFDM), parameter estimation, wireless communications. I. INTRODUCTION H IGH DATA-RATE wireless access is demanded by many applications. Traditionally, more bandwidth is required for higher data-rate transmission. However, due to spectral limitations, it is often impractical or sometimes very expensive to increase bandwidth. In this case, using multiple transmit and receive antennas for spectrally efficient transmission is an alternative solution. Multiple transmit antennas can be used either to obtain transmit diversity, or to form multiple-input multiple-output (MIMO) channels. Many researchers have studied using multiple transmit an- tennas for diversity in wireless systems. Transmit diversity may be based on linear transforms [1] or space–time coding Paper approved by C. Tellambura, the Editor for Modulation and Signal De- sign of the IEEE Communications Society. Manuscript received May 2, 2000; revised May 27, 2001. This paper was presented in part at ICC’01, Helsinki, Finland, June 2001. Y. Li is with the School of Electrical and Computer Engineering,
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This note was uploaded on 09/21/2010 for the course ECE 567 taught by Professor Attkin during the Spring '10 term at Academy of Design Tampa.

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mimo-ofdm_2 - IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 50,...

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