D-BLAST OFDM with Channel Estimation
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D-BLAST OFDM with Channel Estimation Jianxuan Du School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0250, USA Email: [email protected]
Ye (Geoffrey) Li School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0250, USA Email: [email protected] Received 28 January 2003; Revised 26 September 2003 Multiple-input and multiple-output (MIMO) systems formed by multiple transmit and receive antennas can improve performance and increase capacity of wireless communication systems. Diagonal Bell Laboratories Layered Space-Time (D-BLAST) structure offers a low-complexity solution for realizing the attractive capacity of MIMO systems. However, for broadband wireless communications, channel is frequency-selective and orthogonal frequency division multiplexing (OFDM) has to be used with MIMO techniques to reduce system complexity. In this paper, we investigate D-BLAST for MIMO-OFDM systems. We develop a layerwise channel estimation algorithm which is robust to channel variation by exploiting the characteristic of the D-BLAST structure. Further improvement is made by subspace tracking to considerably reduce the error floor. Simulation results show that the layerwise estimators require 1 dB less signal-to-noise ratio (SNR) than the traditional blockwise estimator for a word error rate (WER) of 10−2 when Doppler frequency is 40 Hz. Among the layerwise estimators, the subspace-tracking estimator provides a 0.8 dB gain for 10−2 WER with 200 Hz Doppler frequency compared with the DFT-based estimator. Keywords and phrases: MIMO, OFDM, channel estimation.
1.
INTRODUCTION
Multiple-input and multiple-output (MIMO) systems formed by multiple transmit and receive antennas are under intense research recently for its attractive potential to offer great capacity increase. Space-time coding, proposed in [1], performs channel coding across the space and time to exploit the spatial diversity offered by MIMO systems to increase system capacity. However, the decoding complexity of the space-time codes is exponentially increased with the number of transmit antennas, which makes it hard to implement real-time decoding as the number of antennas grows. To reduce the complexity of space-time based MIMO systems, diagonal Bell Laboratories layered space-time (D-BLAST) architecture has been proposed in [2]. Rather than try to optimize channel coding scheme, in D-BLAST architecture, the input data stream is divided into several substreams. Each substream is encoded independently using one-dimensional coding and the association of output stream with transmit antennas is periodically cycled to explore spatial diversity. Orthogonal frequency division multiplexing (OFDM) systems have the desirable immunity to intersymbol interference (ISI) caused by delay spread of wireless channels. Therefore, the combination of D-BLAST with OFDM is an attractive technique for high-speed transmission over frequency-
selective fading wireless channels. As in [3], when combining D-BLAST st
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