Waveform design for interference cancellation in next-generation wireless systems, which includes precoding and modulation, aims to achieve orthogonality among data signals/symbols across all Degrees of Freedom (DoF). Conventional methods struggle with non-stationary channel states due to high mobility, density, and time-varying multipath propagation. In this article, we review the HOGMT-Precoding and MEM modulations for non-stationary channels. We also discuss practical challenges and future directions.