physical separation between antennas in a smartphone at low frequencies, and therefore only single PA architectures are assumed for LB. When these emissions become too difficult to handle, the UE is allowed to request Single Uplink Operation (SUO), whose concept is illustrated in Figure 12.5. LTE 5G LTE 5G 5G TX Antennal (XXX) Freq. Freq. At Af Af Freq. Af Af Af Af Af FDD duplexer LTETX Antenna2 5G, LTE Freq. +IMDs FDD duplexer LTE 5G FDD duplexer Freq. Af Af Af Af Af At Af Af Figure 12.4 Dual uplink inter-modulation distortion (IMD) products for dual-PA architecture for (left) inter-band and some intra-band cases, (right) single PA UE architecture for intra-band EN-DC. LTE PDSCH/PDCCH LTE PUSCH/PUCCH/SRS Slot number LTE DL band LTE UL band TDM UL transmissions Slot number NR 15kHz TDD Freq. Freq. NR PDSCH/PDCCH NR PUSCH/PUCCH/SRS Slot number e.g. band 3 e.g. band n78 NR 30kHz DL/UL 10 ms Figure 12.5 Solving dual uplink transmission IMD issues using Single Uplink Operation: example of an FDD-TDD EN-DC combination with 15 and 30 kHz SCS for 5G. Receive slots: light gray, transmit slots: dark gray, special slots (TDD): dashed. 12.2 Impact of New Physical Layer on RF Performance SUO uses Time Division Multiplexing (TDM) to avoid 5G and LTE UL simultaneous transmissions and therefore eliminates any two carrier related IMDs. It is also used for UEs which are not capable of performing dynamic power sharing (DPS), as explained in Section 12.5. To optionally request SUO, the UE needs to fulfill two conditions: 1. The UE's own LTE or NR primary downlink channels are victim of either an IMD2 or IMD3 product. 2. IMD3 products are only considered when LTE and 5G UL transmissions operate either both in the "low frequency range" (i.e. 410-960 MHz), or when both operate in the mid-band range (i.e. 1427-2690 MHz). This is justified by the fact that interferers cannot be suppressed easily due to their close proximity in the frequency domain. SUO may also be allowed when emission requirements are difficult to meet, such as intra-b