FFT-based frequency domain filter design for multichannel overlap-windowed-DFTs-OFDM signals

5G NR (New Radio) employs OFDMA (Orthogonal Frequency Division Multiple Access) for both uplink and downlink where sub-carrier spacing can be modified. To enable flexible uplink access for IoT (Internet of Things) in beyond 5G, it is required to accommodate various types of mobile terminals from low to high-speed transmission. When sub-channel spacing is different and/or transmission timing is asynchronous in adjacent channels, OFDMA signals will not be orthogonal with each other and channel filtering is required to reduce ACI (Adjacent channel interference). Supposing joint use of OW-DFTs-OFDM (Overlap-Windowed Discrete Fourier Transform spreading OFDM) signals for low PAPR (Peak to Average Power Ratio) and FFT (Fast Fourier Transform) based filter-bank for flexible channel filtering, this paper discusses FFT-based frequency domain filter design for receiving multi-channel OW-DFTs-OFDM signals to avoid performance degradation due to ACI and ISI (Inter-Symbol Interference).