 interna- tional agreement is reached [30]. The 3.4-3.6 GHz range is practically globally harmonized, which can drive the economies of scale needed for low-cost devices. A number of countries are exploring whether a portion of other bands could be used such as 3.8-4.2 GHz and spectrum in the 4-5 GHz range, in particular 4.8-4.99 GHz region. There are also numerous other mobile bands in the 1-6 GHz range that are currently used for 3G and 4G services which should be gradually repurposed for 5G use. Due to its favorable properties such as radio wave propagation and available bandwidth, the bands in the range of 3300-4200 and 4400-4990 MHz will be the primary spectrum under 6 GHz for the introduction of 5G. Parts of the band between 3300-4200 MHz and 4400-4990 MHz are being considered for the first field trials and United States FCC, https://www.fcc.gov/. Ixxxiv Introduction and Background introduction of 5G services in a number of countries and regions in the world, including Europe (3400-3800 MHz), China (3300-3600, 4400-4500, 4800-4990 MHz), Japan (3600-4200, 4400-4900 MHz), Korea (3400-3700 MHz), and the United States (3100-3550, 3700-4200 MHz). The above 6 GHz spectrum comprises a combination of licensed and unlicensed mobile bands. There are several mmWave bands including 24.25-27.5, 31.8-33.4, 37-43.5, 45.5-50.2, 50.4-52.6, 66-76, and 81 - 86 GHz which have been identified for sharing studies by WRC-15 that must be ratified by WRC-19 for worldwide allocation. However, some countries are also investigating other mobile bands above 6 GHz for 5G services, which are not being considered at WRC-19. The 28 GHz band is of particular interest as it has been permitted for 5G use in the United States and is being closely examined by Japan and Korea. This would complement the 24 GHz band, which is being studied at WRC-19 and is supported in the European Union, because the same equipment could easily support both bands thus helping to lower device costs. Fig. 19 illustrates the frequency ranges that are being studied for