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UBC Theses and Dissertations

Signal design for MIMO-OFDM systems Chen, Harry Zhi Bing


Orthogonal frequency division multiplexing (OFDM) combined with multiple-input multiple-output (MIMO) wireless technology is an attractive air-interface solution for wireless systems. The time-selective and dispersive nature of the wireless channel, however, poses challenges for signal design. To address these challenges, this dissertation investigates several physical layer aspects of signal design for MIMO-OFDM systems. To improve the information outage rate of certain MIMO systems with low-rank channel matrices, we propose two novel channel augmentation schemes, namely, the complex virtual antenna (CVA) and the real virtual antenna (RVA) schemes. For Bell labs space-time (BLAST) type architectures, both the CVA and the RVA schemes are more robust to channel correlations than a previously proposed scheme. For performance enhancement of coded MIMO-OFDM, we consider wrapped space-frequency coding (WSFC) and coded vertical BLAST (V-BLAST) with adaptive bit loading (ABL) and optimize both schemes. We show that bit-loaded WSFC and V-BLAST optimized for coded MIMO-OFDM can achieve error rate performances close to that of quasi-optimal MIMO-OFDM based on single value decomposition (SVD) of the channel, while their feedback requirements for loading are low. To exploit the spatial and frequency diversity in coded MIMO-OFDM systems, we propose cyclic space-frequency (CSF) filtering, which is applicable to both traditional MIMO systems with co-located transmit antennas and cooperative diversity systems with distributed transmit antennas. We further propose a robust CSF filtering scheme, which exploits imperfect channel state information at the transmitter (CSIT) and takes into account the reliability of the CSIT. To further improve robustness, we combine CSF filtering with space-time block coding (STBC) in the frequency domain. We also propose a linear prediction method for improving the quality of the CSIT via post-processing. For these CSF filtering schemes, design criteria are derived, closed-form solutions are given for certain special cases, and various design methods are provided for the general case. Simulation results confirm that robust CSF filtering is a promising solution for wireless communication systems.

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