Ultra Dense Networks: General Introduction and Design Overview

This chapter provides an overview of ultra dense networks (UDNs) from several viewpoints. It introduces the application scenarios identified for UDN, as well as the typical services for each scenario. The chapter describes the potential challenges for deployment and operation of UDNs, including site acquisition and expenditure, network operation and management, interference management, mobility management, and backhaul resources. Extensive research related to interference management has been performed in academia, industry, and standardization bodies such as the Third Generation Partnership Project (3GPP). In wireless networks, site rental and equipment cost accounts for most capital expenditure. The chapter addresses some other issues, including synchronization, energy efficiency, flexible duplex and potential solutions for site acquisition for UDNs. Licensed spectrum will remain a dominant spectrum-assignment approach in 5G, but there is clear value in the introduction of spectrum-sharing functionality in UDNs, since power levels are lower and deployment is more localized.