ill open to different solutions and the most important drivers appear to be market demand, time to market, and efficient spectrum utilization. The requirements for 5G are derived from the use cases that consider how the 5G system will provide services to the end user and what services are provided. The use cases are grouped into broad categories in order to contrast the differences in their require- ments. A number of use cases are related to scenarios where the user selects from a number of network options, depending on service, performance, cost, or user preferences. When the service transfers from one network configuration to another, one of the important considera- tions is the degree of network interoperability. One of the 5G promises was to provide a unified experience for users across multiple devices. From an operator's point of view, 5G also aims to unify multiple access types into a single core network as well as requirements for interoperability for one device operating on different access technologies; this also introduces requirements for service continuity between devices. 5G systems provide the user with the ability to transfer existing service xxxiv Introduction and Background sessions from one device to another device with a minimal perceptible service interruption to the user. The modern cities of this era greatly depend on a number of critical infrastructure to func- tion properly: electricity, water, sewer, gas, etc. Critical infrastructure monitoring is a cum- bersome undertaking, often requiring service levels achievable only by dedicated wireline connectivity. For instance, in order to detect a fault in high-voltage transmission lines and be able to take corrective actions to prevent cascading failures, the required communication latency is beyond what current wireless networks can achieve. Similarly, structural monitor- ing requires the provisioning of a large number of low-data-rate battery-powered wireless sensors, and today's wireless networks are not optimized to support this deploymen