Oregon State University

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PhD Oral Preliminary Examination – Wei Liu

Monday, June 11, 2012 1:00 PM - 3:00 PM

Efficient Detection and Scheduling Design for MIMO-OFDM Systems
Multiple-input multiple-output (MIMO) antennas can be exploited to provide high data rate using a limited bandwidth through multiplexing gain. MIMO combined with orthogonal frequency division multiplexing (OFDM) could potentially provide high data rate and high spectral efficiency in frequency-selective fading channels. The computational complexity of conventional algorithms for MIMO-OFDM detection is usually prohibitively high for mobile devices.

In the first part of this thesis, we firstly study the channel matrix inversion which is commonly required in various MIMO detection schemes. An algorithm that exploits second-order extrapolation in the time domain is proposed to efficiently reduce the computational complexity. This algorithm can be applied to both linear detection and non-linear detection such as ordered successive interference cancellation (OSIC) while maintaining the system performance. Second, we study the complexity reduction for Lattice Reduction Aided Detection (LRAD) of MIMO-OFDM systems. We propose an algorithm that exploits the inherent feature of unimodular transformation matrix that remains the same for relatively highly correlated frequency components. This algorithm effectively eliminates the redundant brute-force lattice reduction iterations among adjacent subcarriers. Third, we analyze the impact of channel coherent bandwidth on two LRAD algorithms. Analytical and simulation results demonstrate that carefully setting the initial calculation interval according to the coherence bandwidth is essential for these algorithms.

The second part of this thesis focuses on the efficient multi-user (MU) scheduling and coordination for MIMO-OFDM-based uplink Wireless Local Area Network (WLAN). On one hand, single-user (SU)-MIMO achieves multiplexing gain in physical (PHY) layer and MU-MIMO achieves multiplexing gain in the medium access control (MAC)layer. However, the average throughput of the system varies with different antenna numbers, number of users, channel conditions, and signal-to-noise-ratios (SNR). An efficient criteria on the dynamic switch between SU-MIMO and MU-MIMO is needed. On the other hand, conventional MU-MIMO MAC protocols involve large overhead which lowers the performance gain of concurrent transmission rendered by the multi-packet reception (MPR) capability of MIMO systems. Therefore, an efficient MU-MIMO uplink MAC scheduling scheme is of great interest for future WLANs.

Major Advisor: Huaping Liu
Committee: Thinh Nguyen
Committee: Ben Lee
Committee: Raviv Raich
GCR: Abi Farsoni

Kelley Engineering Center (campus map)
Shannon Thompson
1 541 737 7234
shannon.thompson at oregonstate.edu
Sch Elect Engr/Comp Sci
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