Spectrum and Energy Efficient Designs for Next Generation Wireless Communication Systems

Millimeter wave (mmWave) and Tera-Hertz (THz) communications are promising technologies for next generation wireless communication systems. However, their transceivers suffer high cost and high power consumption. On the other hand, the coexistence between wireless communication systems and wireless passive services (i.e., radio astronomy systems (RASs)) is an issue. This dissertation develops spectrum and energy efficient designs for mmWave/THz transceivers and proposes a new coexistence paradigm between wireless communication systems and RAS. The first part of the dissertation proposes hybrid analog-digital precoding designs for multiuser millimeter wave systems with different hardware complexities and different types of channel knowledge to enhance physical layer security and maximize average network sumrate. The proposed hybrid precoders achieve performance comparable to that of the fully digital precoding with much hardware-complexity reduction. The second part of the dissertation studies nonlinear THz communication systems by incorporating the nonlinearity aspects of the low-cost THz devices and the inphase and quadrature (I/Q) imbalance effect into the signal model. The proposed precompensation schemes overcome the prominent problems experienced in the existing THz systems, namely severe nonlinear distortions of the modulation symbols as well as spectral spreading and/or large spectrum sidelobes, and mitigate the I/Q imbalance effect. The third part of the dissertation proposes a new spectrum sharing paradigm between cellular wireless communications (CWC) and radio astronomy systems (RAS) which enables geographical and spectral coexistence between CWC and RAS. The proposed paradigm offers: 1) certain guaranteed spectrum access to RAS, which is impossible in the existing paradigm, 2) capability to handle higher peak and mean traffics to CWC under spectrum restructuring of both CWC and RAS bands, and 3) overall improved spectrum utilization. Furthermore, a shared spectrum access strategy for RAS and WiFi systems is also developed by modifying the distributed medium access protocol.