and scheduling complexity. New Radio Access Physical Layer Aspects (Part 2) gNB MAC UE MAC DL-SCH/PCH Transport Blocks Information Element CRC Calculation + Attachment Payload Generation + Multiplexing Scrambling LDPC Graph Selection CRC Calculation + Attachment CRC Calculation + Attachment Code Block Segmentation HARQ ACK/NACK Channel Coding (LDPC Encoding) Channel Coding (Polar Encoding) Channel Coding (Polar Encoding) Channel Decoding (LDPC Rate Matching + HARQ Rate Matching Rate Matching Decoding) + HARQ Buffer HARQ ACK/NACK Interleaving + Scrambling + CCE-to-REG Mapping Modulation Scrambling Scrambling De-scrambling + De-interleaving Layer Mapping QPSK Modulation QPSK Modulation Demodulation Antenna Port Mapping SS Block Generation Layer De-mapping CSI Estimation Reference Signal Generation Precoding DM-RS/CSI-RS/PT-RS/TRS MIMO Detection/Equalization Reference Signal Virtual/Physical Resource Configuration Channel Element Mapping Resource De-mapping Estimation OFDM Modulation + CP CP Removal OFDM Insertion PBCH Detection Demodulation Downlink TX Beamforming RX Beamforming Synchronization IQ Modulation/RF Up-conversion/ LNA and RX Filter/IQ PA and TX Filter Demodulator/Down-conversion Figure 4.1 Overall downlink physical layer processing [5]. 4.1.2 Reference Signals To facilitate estimation of the multipath communication channel and reliable, coherent detection of traffic/control channels, an OFDM system makes use of reference signals (or pilot subcarriers). The pilot subcarriers provide estimate of the channel frequency response at the pilot locations over the time-frequency resource grid. It is possible to estimate the channel at other time-frequency locations using interpolation techniques. Using predefined pilot subcarriers to estimate the channel matrix, it is possible to equalize the effects of the channel and to reduce noise and interference effects on the received resource blocks. The NR specifications include several types of reference signals that are configured and trans- mitted in different manner