Next generation wireless communication networks are expected to be multi- functional to support emerging requirements, e.g. high data transmission rates, high-quality wireless connectivity supporting a large number of devices, and highly accurate and robust sensing capability. To realize these demands, cutting- edge technologies such as integrated sensing and communication (ISAC), massive multiple-input multiple-output (MIMO), satellite communications, and full-duplex (FD) communications system requires further exploration and development. Specifically, challenges persist in optimizing these systems. In mono-static ISAC system, radar returns are drowned by the strong residual self interference (SI) stemming from the transmitter. ISAC satellite communications systems encounter challenges on interference control and power limitations. Massive MIMO systems confront the high power consumption and receiver analog-to-digital converter (ADC) saturation. Additionally, FD communica- tion systems face the difficulties of suppressing SI. To overcome the mentioned challenges, this thesis introduces novel approaches, which are based on con- vex optimization techniques and unlimited sensing theorem. Subsequently, this thesis provides introductions to the background context, followed by a thorough review of the techniques utilized in the proposed solutions. In the following chapters, explanations of these solutions are presented. Finally, this thesis wraps up with a comprehensive conclusion.