, and 5G deployments are no exception to this. We differentiate between: licensed spectrum that is owned by large operators deploying (typically) nationwide networks, licensed spectrum that is owned by private companies, and unlicensed spectrum that is available to any anybody adhering to spectral usage models. Spectral allocations change over time, Fig. 1-4 showing key global 5G spectrum alloca- tions around 2020: Chapter 1 Open radio access network overview 0 GHz 1 GHz 2 GHz 3 GHz 4 GHz 5 GHz 6 GHz 7 GHz 20 GHz 30 GHz 40 GHz 50 GHz 3.4 - 24.25 40.5- -27.5 -33.4 27.5- 5.925-7.125 28.35 24.25 37 43.5 -27.5 27.5- 27.0- 3.6-4.1 24.25- 3.3 4.2 4.4-5 -33.4 FIGURE 1-4 Global 5G spectrum allocations. Note that, licensed or unlicensed, mmWave spectrum is unmistakably linked to 5G, given that wide spectrum is the only way to provide the 10X promised throughput that 5G pro- mises over 4G/LTE deployments. LTE, Long-Term Evolution Licensed operator spectrum As we will discuss later, the 5G waveform is not significantly more efficient ( ~ 10%) com- pared to the 4G waveform. If the spectrum is not being made more broadly available by industry regulators (United States: FCC), the chances for successful deployment of 5G are limited. The first and most obvious path to making more spectrum available is freeing up pre- viously un- or under-utilized spectrum. Consider the 3.x GHz band that has traditionally been used for everything from fixed wireless access to satellite services. Different slices of this spectrum have been made available across the globe for licensing by wireless opera- tors. This spectrum has relatively large bandwidth (typically up to 100 MHz) and reason- able propagation characteristics. This spectrum is considered the cornerstone of 5G deployment. In addition, the existing 2G, 3G, and 4G spectrum is slowly being repurposed for 5G use. The 2G (GSM) bands may still have legacy use (IoT and other purposes) but 3G spectrum is underutilized and can be repurposed for 5G deployment. In addition, technologies such as 