anel and N2 being the number of rows per panel. 170 NG-RAN and 5G-NR In Figure 6.9, the antenna structure is (1,8,2) on the left and (2,4,2) on the right. In Figure 6.10, the antenna structure is (2,8,2). Anterna Antenna W1.2 W2.2 W3.2 W4.2 W5.2 W W7.2 W8.2 W2.1 W3.1 W4.1 W5.1 W6.1 W7.1 W8.1 RF chains TXU/TRU TXU J/TRU RF chains TXU / TRU TXU / TRU Single-panel: Full connection model Sub-array: Partitioning antenna model Figure 6.9. Single panel and sub-array panel Antenna W6.W7.2 W1.1 W2.1 W3.1 W4.1 W5.1 W6.1 W7.1 W8.1 RF chanel TXU/TRU TXU/TRU TXU/TRU TXU/TRU Multi-panels Figure 6.10. The structure of multi-panels 6.2. Antenna port The MIMO mechanism and the beamforming mechanism are based on knowledge of the propagation channel. On the uplink (UL), the mobile uses the reference signals sent by the base station to estimate the propagation channel. 5G-NR Radio Interface - MIMO and Beamforming On the downlink (DL), the base station uses the following: - the reference signals transmitted by the mobile; - and/or the measurement report made by the mobile from the reference signals sent by the base station (feedback method). The CSI (Channel State Information) measurement report is transmitted from the mobile to the base station via a control information message on the UCI (Uplink Control Information) uplink. The CSI-RS reference signals for the downlink or SRS for the uplink channel are used for the equalization of channel Matrix H. The particularity of the TDD duplexing mode in 5G is the ability to use reference signals transmitted by the mobile. The concept of antenna port refers to a logical antenna carrying a reference signal associated or not with physical channels. The antenna port can correspond to several physical antennas, and the receiver estimates the propagation channel between the logical transmitting antenna and the receiving antenna. Knowing the reference signal, the receiver reconstructs the transfer function of the propagation channel from the distortion of the received signal. This estimate is theo