re characterized by the significant growth in connectivity and traffic den- sity, network densification, and the broad range of new use cases and applications. As a result, there is a continuous need to push the performance envelope of the wireless systems to the new limits in order to satisfy the demands for greater network capacity, higher user throughput, more efficient spectrum utilization, wider bandwidths, lower latency, lower power consumption, more reliability, increased connection density, and higher mobility through virtualized and software-defined network (SDN) architectures. While extending the performance envelope of mobile networks, 5G includes intrinsic flexibility and configurabil- ity to optimize the network usage and services, accommodating a wide range of use cases, and business models. The 5G network architecture encompasses modular network functions that can be deployed, configured, and scaled on demand, in order to accommodate various use cases in a smart and cost-efficient manner. The scope of 5G is best understood by scrutinizing the main usage models targeted by this megatrend namely enhanced mobile broadband (eMBB), ultra-reliable low-latency communi- cations (URLLC), and massive machine type communications (mMTC). The high-throughput mobile broadband use case is primarily based on the evolution and enhancement of LTE tech- nology. Evolutionary nature of mobile broadband use case implies coexistence with the exist- ing radio access networks, but this consideration is only limited to sub-6 GHz RF spectrum. xxvi Introduction and Background Any mobile broadband deployments above 6 GHz are expected to use new baseband and radio technologies that improve spectral efficiency, throughput, latency, and other key perfor- mance metrics. The mission-critical machine type communication and mMTC use cases are revolutionary in nature. Technology and design choices for the latter use cases are unaffected by the burden of legacy support or backward compatibility (see Fig. 1). The Internet of Things (IoT