E Time Division Duplex (TDD) bands are allocated band numbers from the 33-64 range as there are still unused band numbers left. This scheme is summarized in Table 12.1. 12.2.3 Impact of NSA Operation on the 5G UE RF Front-End For Non-Standalone Architecture (NSA), Evolved-Universal Terrestrial Radio Access (E-UTRA) and NR dual connectivity (EN-DC) are introduced. EN-DC/NSA uplink COV- erage benefits and principles are covered in Chapter 13. EN-DC dual uplink opera- tion is not a novelty since UL-CA is already part of LTE; however, while this feature remained optional for LTE UEs and had limited deployment, it becomes mandatory for the 5G EN-DC UE and constitutes one of the toughest RF front-end challenges. Through power amplifier nonlinearity, Figure 12.4 shows that several inter-modulation distortion (IMD) products are generated, some of which may overlap the UE's own pri- mary downlink channels and/or secondary downlink channels. IMD3 and IMD5 are the two strongest products which may create huge receiver desensitization and may violate emission requirements. For EN-DC combinations where such conditions occur, Section 12.5.4 discusses how both maximum transmit power and minimum receiver sensitivity are impacted, that is, potentially degrading both the UL and DL link budget. Figure 12.4 (left) illustrates the case of a UL MIMO-capable UE where two separate PA-filter-antenna switch modules (PAM) are available. Through limited antenna-to-antenna isolation, each radio access technology (RAT) signal reaches the other RAT PA output port, and IMDs are generated via reverse mixing. UEs with dual-PA architectures would typically generate lower IMD levels than those with the single PA architecture because the reverse interferer is attenuated by antenna isolation, while IMDs in single PA solutions are due to forward mixing (cf. Figure 12.4 (right)). 3GPP assumes 10 dB antenna isolation for MB/HB operation, while for low bands, dual antenna architecture is considered impractical due to the difficulty of creating sufficient 