erators turned to RAN sharing models, which is also often encouraged by regulators. With RAN sharing, a portion of resources of a network deployed by operator A can be leased to operator B, as shown in Figure 2.7. Different standardized and proprietary RAN sharing options exist, ranging from just shar- ing a cell site, to sharing a base station, to sharing a base station and the spectrum. Many operators deploy 4G using RAN sharing, and we expect this trend to continue with 5G. The concept of a neutral host takes the RAN sharing idea one step further, allowing for cell site and RAN infrastructure sharing between operators, with the main difference between them being that the RAN is owned and operated by some other entity than a mobile operator. Neutral host RAN infrastructure is a single, shared network solution provided to all MNOs by a third party (e.g. a venue owner) and can be used, for example, to resolve poor wireless coverage and capacity inside buildings or other busy locations, such as stadiums. Shared RAN Shared eNB/gNB F1 of Operator A F2 of Operator A Figure 2.7 RAN sharing. 2 Market Drivers Figure 2.8 Neutral host network deployment. Vendors Venue Owners Neutral MNO 1 Small Vendors MNO 4 Various different neutral host approaches are used to provide wireless services in dif- ferent environments, such as DASs and small cells, which are described in more detail in Sections 4.6 and 4.7. Figure 2.8 illustrates the neutral host ecosystem concept, in which small cell or DAS vendors provide the infrastructure, a venue owner builds and operates a network (perhaps using a third-party integrator), and MNOs lease capacity on that shared network to serve their users. The term neutral host is often associated with small cells and, indeed, it is expected that most initial neutral host deployments will use small cells; however, there are no technical barriers to deploy the same concept in the macro network. While the concept of neutral host is not new and not unique to 5G, as for example some CBRS networks are expect