Efficient Closed-Loop Schemes for MIMO-OFDM-Based WLANs
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Efficient Closed-Loop Schemes for MIMO-OFDM-Based WLANs Xiayu Zheng,1 Yi Jiang,2 and Jian Li1 1 Department 2 Department
of Electrical and Computer Engineering, University of Florida, Gainesville, FL 32611-6130, USA of Electrical and Computer Engineering, University of Colorado, Boulder, CO 80309-0425, USA
Received 28 December 2005; Revised 18 July 2006; Accepted 13 August 2006 The single-input single-output (SISO) orthogonal frequency-division multiplexing (OFDM) systems for wireless local area networks (WLAN) defined by the IEEE 802.11a standard can support data rates up to 54 Mbps. In this paper, we consider deploying two transmit and two receive antennas to increase the data rate up to 108 Mbps. Applying our recent multiple-input multipleoutput (MIMO) transceiver designs, that is, the geometric mean decomposition (GMD) and the uniform channel decomposition (UCD) schemes, we propose simple and efficient closed-loop MIMO-OFDM designs for much improved performance, compared to the standard singular value decomposition (SVD) based schemes as well as the open-loop V-BLAST (vertical Bell Labs layered space-time) based counterparts. In the explicit feedback mode, precoder feedback is needed for the proposed schemes. We show that the overhead of feedback can be made very moderate by using a vector quantization method. In the time-division duplex (TDD) mode where the channel reciprocity is exploited, our schemes turn out to be robust against the mismatch between the uplink and downlink channels. The advantages of our schemes are demonstrated via extensive numerical examples. Copyright © 2006 Xiayu Zheng et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
The single-input single-output (SISO) orthogonal frequency-division multiplexing (OFDM) systems for wireless local area networks (WLAN) defined by the IEEE 802.11a standard can support data rates up to 54 Mbps [1]. Improving the data rate to over 100 Mbps is a major goal of the next-generation WLANs [2, 3]. The multiple-input multipleoutput (MIMO) communication technology is widely regarded as a key to achieve such a high data rate. Assuming that the channel state information (CSI) is available at both the transmitter and the receiver, the MIMO channel can be decoupled, using singular value decomposition (SVD), into multiple orthogonal subchannels (or eigenmodes) on each subcarrier [4]. To maximize the channel throughout, power allocation and bit loading should be applied to the subchannels in both the spatial and frequency domains (see, e.g., [5] and the references therein). However, bit loading is often not adopted in practice, such as in the IEEE 802.11 standards, due to its complexity. If the same constellation is used across all the subchannels, the weaker eigenmodes corresponding to the smaller singular values of the channel matrices tend to experience deeper fading [4], which degr
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