The base station architecture deployment options in case of Non-standalone deployment are depicted in Figures 1, 2 and 3 below. Option 3, Option 3a and Option 3x.
The options listed in Figure 1, 2 and 3 are known as E-UTRA - New Radio Dual Connectivity (EN-DC). E-UTRA refers to the 4G air-interface and New Radio refers to the 5G air-interface. This naming convention orders the air interface technologies according to Master Node followed by Secondary Node. In case of EN-DC --- E-UTRA is the Master Node so is named first.
UEs which support EN-DC are required to be capable of receiving downlink data at the same time across 4G and 5G air-interfaces. In 3GPP release 15, EN-DC bands for up to 5 different operating bands are included.
Generally UEs which support EN-DC are required to be capable of transmissiting uplink data at the same time across 4G and 5G air interfaces.
A UE with 2 transmitters can generate inter-modulation products which fall within the UE's receive bandwidth. In other words, UE can desensitise itself by generating interference (inter-modulation products) within its own downlink receiver.