A system and method for reducing the OFDM out-of-band emissions (OOBE) and Inter-Numerology Interference (INI) in a mixed-numerology OFDM-based system by utilizing a transmitter windowing operation that smooths the inherent rectangular pulse shape of the OFDM signals. The technique retains the main design of the OFDM receivers and provides backward compatibility for the existing OFDM-based systems. The guard band and the multi-window parameters that control the guard duration are jointly optimized regarding the numerology, the use case and the power offset between the users. To fully exploit and further increase the potential of adaptive guards, an interference-based scheduling algorithm is proposed as well.