retically valid only on the tempo-frequency resources to which the reference signal is mapped. However, due to the stationarity in time and frequency, the estimate remains valid for the duration of a slot, on a block resource for an antenna port. When two signals are transmitted on different antenna ports, the propagation channel differs; however, in the case of the quasi-stationary channel, the signal distortion is similar from one antenna port to another. Thus, the estimation of the propagation channel of the signal emitted by one antenna can be used for the estimation of the propagation channel of the signal emitted on the other antenna. This technique is called QCL (Quasi-CoLocation) mode. 6.2.1. Downlink transmission Symbols produced by modulation are distributed over spatial layers, and then precoded before being assigned to resource elements by antenna port. NG-RAN and 5G-NR DM-RS CSI-RS1 Mapping Modulated symbol of codeword 0 Mapping to Modulated symbol of spatial layers Precoding codeword 1 Mapping DM-RS CSI-RSn Figure 6.11. MIMO transmitter scheme The precoded symbols are associated with reference signals (RS) to form antenna ports. Table 6.2 shows the association of the antenna ports and the downlink reference signals. The DM-RS associated with the PDSCH can be transmitted over eight spatial layers on antenna ports from 1000 to 1007 for the DM-RS type 1 configuration and from 1000 to 1011 for the DM-RS type 2 configuration (see Chapter 4). The PT-RS associated with the PDSCH is a repetition of the DM-RS on antenna ports 1000 to 1005. The DM-RS associated with the PDCCH is only transmitted over a single 2000 antenna port. The Synchronization Signal Block (SSB) is transmitted on only one antenna port 4000. Antenna port Reference signal P1000-P1011 DM-RS (PDSCH) P1000-P1005 PT-RS (PDSCH) P2000 DM-RS (PDCCH) P3000-P3031 CSI-RS P4000 Block SSB P5000 Table 6.2. Mapping of antenna ports and reference signals in downlink transmission 5G-NR Radio Interface - MIMO and Beamforming 6.2.1.1. The CSI-RS physical sig