e type communications (mMTC) [1, 2]. eMBB is expected to support much higher down- link/uplink peak data rates (up to 100 times) than the long-term evolution (LTE) system, which requires a flexible physical layer configuration, e.g. a large subcarrier spacing (SCS) to counteract the Doppler spread of the fast fading channel, and a small SCS for higher robustness to the long delay spread channel. URLLC caters to applications/services where extremely high reliability and low end-to-end delays are required, e.g. vehicle to vehicle (V2V) services; hence, the SCS needs to be large enough to meet stringent latency require- ments. On the other hand, mMTC is designed to support a connection density of up to 106 devices/km²; thus, delay-tolerant devices with long symbol duration (and hence small SCS) is an important precondition [1]. Considering the high cost and deployment complexity, it is not feasible to have separate radio designs for different services. Therefore, mixed numerology, wherein services with different physical signaling formats operate on a common underlying physical layer, is proposed as one of the most promising techniques to support the diverse requirements in 5G. Besides, with mixed numerology, inter-numerology interference (INI) will be generated because different symbols and SCS for different services will adversely affect the system orthogonality [3]. Hence, a key challenge for designing a mixed numerology system is to minimize the performance degradation caused by INI. In comparison with adding a guard band (GB) between services (which will reduce the spectrum utilization efficiency), Radio Access Network Slicing and Virtualization for 5G Vertical Industries, First Edition. Edited by Lei Zhang, Arman Farhang, Gang Feng, and Oluwakayode Onireti. © 2021 John Wiley & Sons Ltd. Published 2021 by John Wiley & Sons Ltd. 3 Windowed OFDM for Mixed-Numerology 5G and Beyond Systems a more practical and attractive way is to design new waveforms with lower out of band emission (OoBE) [4]. A variety of new wav