ons of FR1 and FR2 bands, and thus no MSD or MPR/A-MPR is needed in 38.101-3 for this case. It is to be noted, though, that in Release 16 there are studies underway for the fre- quency range 7.125-24.25 GHz which will probably result in single and dual UL issues if operated concurrently with either FR1 or FR2. 12.6 Examples of UE Implementation Challenges 12.6.1 More Antennas, More Bands to Multiplex, and More Concurrency The latest LTE phones already represented a significant challenge in terms of RF front-end architecture with a large number of bands and band combinations, and 4x4 DL MIMO supported in a number of MB and HB bands. However, bands were limited to up to 2.7 GHz in the expectation of some implementation supporting Band 42 in Japan, and dual UL-CA was not implemented. With the advent of 5G, even without considering the addition of mmWave, the RF front-end sees yet another step up in complexity with the addition of the 3.5 and 4.5 GHz bands, which have mandatory support for 4 X 4 DL MIMO but will most probably support 2 X 2 UL MIMO. 5G NSA operation adds further complexity as additional transmitter paths and improved filter performance are required to handle the challenging EN-DC out-of-band emissions. 12.6 Examples of UE Implementation Challenges Table 12.11 FR1 RF front-end filter count in high-end smartphone - antenna multiplexing and band. 2019 4G phone (34 cellular bands) 2020 5G phone (35 cellular bands) Nplexing Primary Diversity/MIMO Primary Diversity/MIMO Filters Total Band Group FDD Tx FDD Rx TDD Diversity/MIMO FDD Tx FDD Rx TDD Diversity/MIMO Total Grand Total Table 12.11 only illustrates the increase in complexity in terms of the number of filters, limited to FR1, needed to implement a 2019 high-end 4G smartphone on the right and a 2020 high-end 5G smartphone on the right. First, the multiplexing of the different subbands, bands, and modes to antennas increases the overall number of paths from 16 to 20, thus allowing up to 20 paths to operate concurrently. This is essentially due to the ad