the TPMI is used to indicate the preferred precoder over the SRS ports in the configured single SRS resource. The TPMIs are supposed to be wideband, and while frequency-selective TPMIs might provide further performance improvement, the cost of signaling such information would be tremendously high as the baseline wideband information would be multi- plied by the number of subbands. The gNB indicates the SRI and TPMI to the UE, and hence the UE has now the nec- essary information for performing codebook-based uplink transmission. 6.13 Channel Coding with 5G gNB transmitter SRS resource 1 SRS resource 2 SRS resource 3 SRS resource 4 SRI, TPMI, rank Figure 6.44 Codebook-based UL transmission procedure. What we have been describing above is depicted in Figure 6.44. In this example, the UE transmits four SRS resources, and the gNB identifies the second resource as the best. Further, the rank and precoder are computed for this SRS resource. The gNB indicates to the UE the SRI (which means that the second SRS resource is to be used), the computed TPMI, and rank (Figure 6.44). Under the codebook-based operation, three forms of transmission are possible in the uplink: Full coherence: All the ports can be transmitted coherently. Partial coherence: Port pairs can be transmitted coherently. This can happen when the UE has calibrated antenna ports within a panel but also has multiple panels not calibrated to one another. Coherent transmission occurs inside a panel where an SRS resource is configured as such. Non-coherent: No port pairs can be transmitted coherently. In this case, the trans- mit chains of the UE operate in a more independent fashion, and there is no phase adjustment between them. 6.12.5.2 Non-Codebook-Based Uplink Transmission When non-codebook-based transmission is used, the UE would precode the PUSCH transmission, but only SRI information is used, and hence no Transmit PMI (TPMI) is indicated by the gNB, as in codebook-based transmission. Again, as in codebook-based transmission, only wideband operation is po