p the terminal take the temporal variation of the propagation channel into account. The reservation of resource elements for the DM-RS allows the reference signal to be transmitted on several antenna ports simultaneously without interference. Symbol DM-RS Type A - Single-symbol Type A - Double-symbol Type A - Additional single-symbol Figure 4.11. Additional DM-RS mapping on antenna port 0 5G-NR Radio Interface - The Physical Layer In addition, to support different MIMO transmission modes, it is necessary to simultaneously transmit the DM-RS signals associated with the PDSCH channel, without interfering with each other through frequency division multiplexing (FDM) or through multiplexing by code (CDM). In the frequency domain, two types of configuration are defined to indicate the frequency density: - type 1 configuration: six subcarriers per RB and per antenna port at the location k = 4n + 2k '+ , k' and A take the value 0 or 1; - type 2 configuration: four subcarriers per RB and per antenna port, with two contiguous REs at the location k = 6n + k '+ A. Symbol DM-RS Type 1-Single-symbol - Type 2 - Single-symbol Type 2 - Double symbol Figure 4.12. Mapping of DM-RS in the frequency domain Symbol DM-RS Port 1000 Port 1001 Port 1002 Port 1003 Figure 4.13. Multi-port mode (4 DM-RS) in the case of type 1 single-symbol configuration By implementing frequency shift or code multiplexing: - type 1 allows four DM-RS signals to be multiplexed (Figure 4.13) if a single symbol is mapped (single-symbol) and eight DM-RS in the double-symbol case are transmitted on antenna ports 1000-1007; NG-RAN and 5G-NR - type 2 allows 6 DM-RS signals to be multiplexed if a single symbol is mapped (single-symbol) and 12 DM-RS signals in the double-symbol case are transmitted on antenna ports 1000-1011. Type 1 Symbol DM-RS code (CDM) Orthogonality in code Orthogonality in frequence Type 2 Figure 4.14. Multi-port double-symbol (Table 7.4.1.1.2-1/2 TS 38.211) Orthogonality on each antenna port is obtained in the frequency domain by transmitting t