Impacts of errors in carrier frequency and channel knowledge and their countermeasures

Moving to higher carrier frequency and using advanced communications schemes that exploit channel state information (CSI) at the transmitter can bring higher data rates but also come with issues such as larger carrier frequency offset (CFO) and vulnerability to CSI uncertainty. Such issues are further accentuated by mobility of wireless devices and downscaling of semiconductor devices. This dissertation studies the ramifications of these issues and designs schemes to overcome them.;CFO causes spectrum misalignment of transmitter and receiver filters. We present an exact signal model for orthogonal frequency division multiplexing (OFDM) systems with CFO. The exact signal model incorporates effects of the CFO-induced spectrum misalignment that is often overlooked by existing works. Impacts of the overlooked misalignment on existing CFO estimators are investigated. New CFO estimation and compensation methods based on the exact signal model are proposed and compared with the existing approaches. Guidelines on pilot signal designs under the exact signal model are also provided.;In addition, we study CSI acquisition and the impact of CSI uncertainty on transmission schemes such as interference alignment (IA) and relays with transmit maximal ratio combining beamforming (TMRC-BF). IA is known to have high degrees of freedom (DoF) with global CSI at the transmitter (CSIT). The CSIT comes with costs. We consider the effective DoF achieved by IA when the CSIT is acquired by training and feedback. We find optimal number of feedback bits and number of participating user pairs that maximize the effective DoF. We study the reliability of IA which is little known in existing literature. IA's error performance and sensitivity to CSI uncertainty are analyzed and compared with conventional orthogonal transmission schemes. We also design bit loading algorithms and a new adaptive transmission scheme which yield significant improvement in error performance and robustness to CSI uncertainty over the existing IA schemes. For relay with TMRC-BF, we consider a relay clustering system using TMRC-BF at the relays and address channel estimation at the destination. A cluster pairing scheme with corresponding pilot designs is proposed, which reduces both necessary pilot overhead and computational complexity by half.