dio node, such as: - HI information (HARQ Indicator) concerning the positive ACK or negative NACK acknowledgment in response to data received on the PDSCH physical channel; - the ratio of the CSI (Channel State Information) signal used by the gNB to define the transmission mode, as well as the coding and modulation scheme; - the SR (Scheduling Request) to obtain tempo-frequency resources on the PUSCH physical channel. The PUCCH and PUSCH physical channels can be multiplexed in the FDM (Frequency Division Multiplex) or TDM (Time Division Multiplex) time domain. 4.5. Downlink transmission 4.5.1. Synchronization signal The SSB block consists of multiplexing physical PSS/SSS synchronization signals with the physical broadcast channel PBCH. The PSS/SSS signals are mapped to 127 contiguous subcarriers and two symbols. The BCCH channel uses 240 contiguous subcarriers and two symbols. The SSB block is formed by multiplexing the SSS/PSS signals with the PBCH channel. The SSB block is mapped to 240 subcarriers and four symbols (Figure 4.8). One or more SSB blocks are transmitted in an SSB burst confined in a half-frame. 104 NG-RAN and 5G-NR An SSB block is periodically transmitted with a configurable period between 5 ms and 160 ms. The configuration of the SSB burst corresponds to the temporal position of the blocks in a half-frame and to the periodicity of the block. The configuration of the SSB burst is transmitted to the mobile in the SIB1 message for 5G-SA and in the RRC Reconfiguration message for 5G-NSA. 4.5.1.1. Physical PSS signal The physical PSS signal performs the following functions: - frequency synchronization; - time synchronization at the level of the OFDM symbol, the time interval (slot) and the half-frame (periodicity 5 ms); - the determination of the value N(2) . The physical PSS is generated from a pseudo-random sequence of 127 bits (Figure 4.7). Figure 4.7. PSS signal generation Register initialization: [x(6) x(5) x(4)x(3)x(2) x(1) x(0)]=[1110110] At each clock rising edge, the bit x(6) is generated by 