Advanced Data-Aided Channel Estimation Techniques for MIMO-OFDM Wireless Systems

Abstract

This thesis presents a comprehensive investigation into the development of low-complexity and spectrum-efficient wireless channel estimators. In this regard, we examine two technologies: orthogonal frequency-division multiplexing (OFDM) and multiple-input multiple-output (MIMO). OFDM splits the entire bandwidth into a number of overlapping but orthogonal subchannels, offers better resilience to multipath fading, and enables higher spectral efficiency. MIMO, on the other hand, provides both diversity gain and multiplexing gain in wireless communication systems. To propose novel solutions for accurate channel estimation in MIMO-OFDM systems, we dive deep into the theoretical analysis of different channel estimation techniques. The analysis allows us to identify that data-aided channel estimation (DACE) schemes can improve channel estimation accuracy without compromising the spectral efficiency of the wireless systems. In this regard, we propose two DACE schemes: a receiver-based DACE scheme and a transmitter-based DACE scheme. The former intelligently detects the most reliable data carriers at the receiver of an OFDM system and incorporates them with known pilot symbols to accurately estimate the wireless channel. The latter, on the other hand, selects peak-power carriers at the transmitter of an OFDM system, avoiding multiple distance calculations at the receiver, which significantly reduces the computational complexity of traditional receiver-based DACE schemes. We also employ nonlinear companding techniques to mitigate the high peak-to-average power ratio (PAPR) in OFDM systems. In addition, we introduce an optimal comb-type pilot pattern for the DACE scheme, utilizing a single pilot subcarrier with maximum uniform pilot spacing. The proposed pilot pattern eliminates the need for an excessive number of pilots to accurately estimate fast-fading channels, thus reducing the pilot overhead, and significantly improving the spectral efficiency of MIMO-OFDM systems. Furthermore, we evaluate the performance of the proposed transmitter-based DACE scheme under various channel conditions. Considering both Rayleigh and Rician fading channels, we analyze system performance with different numbers of channel taps. It is found that the proposed DACE scheme performs equally well under both Rayleigh and Rician fading channel conditions, provided that an appropriate number of channel taps is utilized for the given OFDM subcarriers. This demonstrates the adaptability and effectiveness of the DACE scheme in diverse channel conditions. Using both least square (LS) and linear minimum mean square error (LMMSE) channel estimation methods, we validate our solutions through formal analysis and simulations. Compared to state-of-the-art solutions, the proposed channel estimators improve channel estimation accuracy, reduce system complexity and pilot overhead, and increase the spectral efficiency of wireless communication systems. This research not only meets its intended objectives but also lays the foundation for future research in joint channel estimation and pilot design in emerging wireless communication systems.