 EnodeB for LTE-Advanced and Beyond project. His main research interests include self-organizing cellular networks, energy-efficient networks, multiple-input multiple-output systems, wireless blockchain networks, network slicing, and cooperative communications. He has published more than 60 technical papers in scholarly journals and international conferences. He has served as technical program committee member of several IEEE conferences and as reviewer for several IEEE and other top journals. He received an Exemplary Reviewer Award from the IEEE Transaction on Wireless Communications in 2017. Preface The move toward an always-connected society, where people and machines concurrently interact with multiple devices, requires future networks to be highly flexible, combining multiple standards and architectures, while simultaneously providing services to multiple users of various types and traffic requirements (massive machine type communications (mMTC), vehicle-to-vehicle (V2V) communications, etc.). Moreover, future networks are expected to provide orders of magnitude improvement to such heterogeneous networks in key technical requirements such as throughput, number of connected devices, latency, and reliability. It is cumbersome to design a unified all-in-one radio that meets the extreme require- ments for all types of services. For instance, an MTC service might require an multicarrier system with smaller subcarrier spacing (thus longer symbol duration in the time domain) than the current standards to support massive delay-tolerant devices, while V2V commu- nication necessitates significantly larger frequency subcarrier spacing (thus shorter sym- bol duration) to satisfy the stringent delay requirements and provide robustness against Doppler spread. Moreover, some other configurations, such as waveform, should be dynam- ically optimized/selected to adapt to the traffic type, wireless channel, and user mobility. On the contrary, designing separate service systems that run on separate infrastructures make the oper