*3.7.2 CSI-RS based single user MIMO*

**Figure 18** shows a typical downlink transmission CSI-RS based SU/MU-MIMO scheme. First of all, UE needs to know the **H** matrix. The gNB is obligated to transmit CSI-RS ports so that UE can observe the full MIMO channel matrix. UE calculates the channel matrix and reports PMI, RI and CQI to gNB.

In the equivalent MIMO channel, we have *NL*data streams, corresponding to *NL*layers. Each *i*-th diagonal element of **D**, *λi*, represents the *i*-th layer's channel magnitude; **w***i*, the i-th column vector of **W**, is the beamforming weights for the *i*-th layer.

UE reports gNB is its preferred PMI but gNB is not obligated to apply the precoding indicated by the PMI, and the gNB does not provide the UE with explicit

**Figure 17.** *Downlink single user MIMO operation.*

**Figure 18.**

*CSI reporting and equivalent channel for SU-MIMO.*

information regarding the precoding procedure. The UE relies upon using the Demodulation Reference Signal (DMRS) when decoding the PDSCH.

CSI-RS single user MIMO scheme uses type I codebook which is based upon a specific set of assumed antenna configurations. The antenna configurations are Single Panel and Multi Panel as described in **Tables 6** and **7**.

For codebook type I single panel: MIMO ranks: 1 to 8; CSI RS Ports: 2, 4, 8, 12, 16, 24, 32.

For codebook type I multi panel: MIMO ranks: 1 to 4; CSI RS Ports: 8, 16, 32.
