ction while lower antenna gain is seen in other directions. When both elevation and horizontal beamforming are utilized (FD-MIMO), the maximum beamforming gain can be obtained in each direction via beam tracking proce- dures. Beamforming can improve the link budget and can increase signal-to-interference- plus-noise ratio (SINR) performance. Moreover, the interference between different systems in the unlicensed band can be minimized using highly directional antennas due to the signif- icantly lower collision probability compared to the omnidirectional transmission cases. As a result, higher spatial reuse would be possible, increasing the system throughput as well as improving spectrum efficiency. Some licensed frequency bands are designated for commercial use while others are desig- nated for public safety. The assignment of a frequency band to a user allows the user to uti- lize that frequency and bandwidth for stated purposes using predefined emission parameters. Licensed spectrum allows exclusive use of certain frequencies in specific geo- graphic locations, meaning that when someone is granted the right by a regulatory body to communicate at certain frequencies and in certain locations, everyone else is prohibited from using that frequency in that location. In contrast, in the spectrum that is designated as license-exempt or unlicensed, users can operate without a license but must comply with the regulatory constraints. For instance, the regulations limit the transmit power and the effec- tive isotropic radiated power (EIRP) to minimize interference to other cochannel systems. The unlicensed frequency bands were originally allocated for industrial, scientific, and med- ical (ISM bands) applications. IEEE Standards Association: https://standards.ieee.org/findstds/standard/802.11ad-2012.html Operation in Unlicensed and Shared Spectrum 847 To coexist with Wi-Fi in the unlicensed spectrum, some enhancements in the LTE and NR systems were required including a mechanism for channel sensing based on LBT, dis- contin