l channels and signals Mapping the CSI-RS to antennas The CSI-RS is mapped to antenna ports and antenna ports are mapped to physical antennas. However, the details of mapping are not specified: Channel sounded by means of the CSI-RS CSI-RS# Port #1 CSI-RS #1 Port #2 M-post CSI-RS Port #M CSI-RS #2 N physical antennas Figure 6.6 - CSI-RS antenna mapping The implementation-specific relation is modeled by the F matrix here. The device estimates the composite channel, including F. Quasi-Colocation (QCL) relations describe what assumptions the device may make about F. Let's move to the next downlink physical signal, the TRS, which is new in NR. The TRS NR has no Cell Specific Reference Signal (CRS) to use for fine time-frequency tracking. Therefore, the TRS is employed to track time, frequency, delay spread, and Doppler spread more efficiently. The TRS is managed as device-specific. An example of the TRS format is illustrated here: 10ms, 20ms, 40ms or 80ms TRS burst periodicity Configurable TRS symbol One or two slot TRS burst positions: (4,8), (5,9) or (6,10) Fixed TRS inter symbol distance 10FDM symbols Fixed TRS subcarrier distance- = 4 subcarriers - CSI-RS resource #3 CSI-RS resource #4 CSI-RS resource #1 CSI-RS resource #2 Configure TRS subcarrier offset OFDM Symbol index within slot Slot number within TRS burst Figure 6.7 - TRS format example 5G Air Interface and Physical Layer Procedures - Part 3 A TRS can be configured in different ways. For instance, it can consist of bursts of four consecutive OFDM symbols in two consecutive slots. Another typical configuration is a TRS burst of two TRS symbols in two adjacent slots. Let's move to the next downlink physical signal, PTRS, which is also new in NR. A device can be configured in downlink and uplink with PTRS to track phase variations, mainly for high bands: Subcarriers DM-RS PT-RS Symbols Figure 6.8 - PTRS occurring every second PRB and every symbol PTRS is dense in time and occurs every second or every fourth symbol depending on the scheduled Modulation and Cod