 since the mobile is able to control the relative phase of the signals between each antenna; - partial coherence: some pairs of antenna ports can transmit broadband signals coherently; - non-coherence: no antenna can transmit broadband signals coherently with another antenna. Digital precoding involves selecting a precoding code for the uplink. This code is defined either from the measurements of the uplink channel carried out at the base station, or from the measurements of the downlink channel carried out by the mobile, assuming the reciprocity of the transmission channel. The SRS allows the base station to estimate the uplink channel before configuring the PUSCH channel transmission mode. The mobile must be configured to transmit multiple SRSs (SRS multi-port) in order to use the MIMO mechanism. 5G-NR Radio Interface - MIMO and Beamforming The CSI-RS allows the mobile to estimate the downlink channel and, by reciprocity, this allows the uplink channel to be considered the same. Two PUSCH multi-antenna configuration modes are defined as follows: - transmission based on the codebook (codebook-based) to implement the MIMO or beamforming mechanism; - transmission not based on the codebook (non-codebook-based) to implement beamforming. Codebook-based transmission is the mode chosen by the base station when uplink SRS reference signal measurements are required. For the non-codebook-based transmission mode, the base station sets the number of RI (Rank Indicator) spatial layers (two or four) and indicates to the mobile the index of the PMI code table. The information is carried by the DCI 0 descending control information message and contained in the UL Grant resource allocation request. The mobile will apply the code imposed by the gNB to both the PUSCH channel and the DM-RS reference signal. For the non-codebook-based transmission, the base station assumes transmission channel reciprocity. In this mode: 1) the mobile selects the code that seems most appropriate for the beamforming mechanism from the CSI-RSs transmitt