Next-generation wireless communication systems will support high-data rate services for mobile transmitters and receivers, such as those in high-speed trains, highway vehicles, and satellites. These high-mobility applications often experience time-varying channels due to high Doppler shifts, which existing modulation schemes struggle to handle. Recently, orthogonal time frequency space (OTFS) modulation has been found effective in such scenarios. This thesis investigates OTFS modulation, addressing practical challenges in its application to high-mobility communications. It also explores its adaptability with technologies like MIMO, cell-free massive MIMO, and intelligent reflecting surfaces (IRS) to enhance signal reliability and performance in future wireless networks.