o (NR), because they are TDD, requires phase/time. LTE (4G) networks that use frequency division duplex (FDD) radios normally only require frequency. LTE-A networks might require phase/time depending on the services and radio methods being enabled. Features such as Multimedia Broadcast Multicast Service (MBMS), enhanced inter- cell interference coordination (eICIC), Coordinated Multipoint (CoMP), and Carrier Aggrega- tion (CA) normally require phase/time. Sophisticated antenna techniques such as multiple input, multiple output (MIMO) require phase alignment, although the requirement to be phase-aligned might apply only to the antenna array connected to a single radio. Note that MIMO normally does not apply to low-frequency bands because the antenna array ends up being very large (low frequency means long wavelength means large antenna arrays). Any radio transmission scenario that mentions a single frequency network (SFN) requires phase synchronization. Note that broadcasting also uses this technology, SO digital radio and television transmitters normally require phase synchronization. Deployments of small cells generally requires phase, especially when interference coordination is part of the integration of small cells into the network (see the next section, "Small Cells Versus Macro Cells"). Many techniques to do with determining the position/location of the user equipment (UE) re- quire phase alignment, but especially when using Observed Time Difference of Arrival (OTDOA). Please see Chapter 10 for detailed coverage on timing requirements for mobile technologies. At least for the early deployments of 5G, there are three generally recognized use cases: eMBB (enhanced mobile broadband) and fixed wireless access (FWA), the focus of 3GPP Re- lease 15 (Rell5). FWA is where a 5G network is used to provide communications services to a fixed location, like home broadband. uRLLC (ultra-reliable and low-latency communications), the focus of Release 16 (Rel16). mMTC (massive machine-type communications) and industrial Int