rce block Scheduled bandwidth Figure 4.4 Illustration of PT-RS structures in time and frequency domain [6]. mapped to are given by k=kRE + where mod KPT-RS if NRB mod KPT-RS 0; otherwise, mod(NRB mod KPT-RS) [6]. In the latter equation, NRNTI denotes the RNTI associated with the DCI scheduling of the transmission; KPT-RS E {2,4}, and is the DM-RS port associated with the PT-RS port. The density of PT-RS in time and frequency domain is configurable to address different scenarios (e.g., different carrier frequency, modulation and coding scheme, and hardware quality). The PT-RS patterns in time and frequency domains are illustrated in Fig. 4.4. 4.1.2.3 Channel State Information Reference Signals The CSI-RS in NR is used for downlink CSI estimation. It further supports RSRP measure- ments for mobility and beam management (including analog beamforming), time/frequency tracking for demodulation, and uplink reciprocity-based precoding. The CSI-RS is UE-specific; nevertheless, multiple users can share the same CSI-RS resource. The NR defines zero-power and non-zero-power CSI-RS. When a zero-power CSI-RS is configured, the resource elements (designated to CSI-RS) are not used for PDSCH transmission. In this case, the zero-power CSI-RS is used to mask certain resource elements, making them unavailable for PDSCH mapping. This masking not only supports transmission of UE- specific CSI-RS, but also the design allows introduction of new features while maintaining backward compatibility. The NR supports flexible CSI-RS configurations. A CSI resource can be configured with up to 32 antenna ports with configurable density. In the time domain, a CSI-RS resource may start at any OFDM symbol of a slot and span 1, 2, or 4 426 Chapter 4 CDM2 pattern CDM4 pattern CDM8 pattern (OFDM symbols) Table 2-Row10-FD2/TD2/CDM4 12 Ports Table 2-Row11-FD/CDM2 16 Ports Table 2-Row13-FD/CDM2 24 Ports Figure 4.5 Example locations of CSI-RS in time and frequency [6]. OFDM symbols depending on the number of configured antenna ports. The CSI-RS can be p