issue. Another was zoning regulations and other permissions that often cause major delays in building infrastructure. Officials in cities with historic buildings were reluctant to have equipment mounted on them. In residential areas, neighbors don't want antennas near their homes because of fears that the radiation from antennas may be harmful. It took years to negotiate these issues with municipalities. Running fiber required permission from cities to use their rights of way. In cities with fiber already running in conduits under the ground, mobile providers negotiate the monthly fees that municipalities charge in return for space to lay fiber within these conduits. In an effort to speed up the process, telecom and cellular firms lobbyed the FCC to issue rules that restrict local municipalities from oversight of 5G gear. In 2018 the FCC issued rules that eliminate the majority of these delays in getting permission to place 5G gear by restrictions on local cities www.TechnicalPDF.com and towns efforts to impose fees and zoning rules on 5G infrastructure. Frequency- and Time-Division Air Interfaces in The 3GPP standards group has defined two different air interfaces for LTE. An air interface is the way signals are transmitted between cell sites and user equipment. The most common air interfaces are Frequency Division Multiplexing and Time Division Multiplexing. Frequency-Division Multiplexing (FD-LTE) is the most commonly implemented air interface. FD-LTE uses one frequency band for down-link from the cell site to the user device and another set of frequencies on the uplink from the user device to the network. Frequency-Division Multiplexing (FDM) requires paired frequencies, which means that one spectrum band is used for the downlink and another band is used for the uplink. See Figure 7-11 for an example of FDM and TDM. When mobile carriers that use FD-LTE acquire new spectrum, they obtain one band specified by the government for uplink service and a different band specified for downlink service. Most of the rest