nature2 N - Point Root ZC PRACH receiver architecture 1 sequence Sampling rate fIFFT Hybrid time-frequency method Power delay profile calculation Cyclic Subcarrier Linear Insert Decimation prefix demapping Energy filter zeros detection removal Numerically controlled Root ZC oscillator sequence PRACH receiver architecture 2 Figure 4.84 Example PRACH transmitter and receiver structure 15]. front-end at the system sampling rate, the power delay profile calculation, and signature detection. The two approaches differ only in the computation of the subcarriers carrying the PRACH signal(s). The frequency-domain method computes the full range of subcarriers used for uplink transmission over the system bandwidth from 0.8 ms-long received input samples. As a result, the PRACH subcarriers are directly extracted from the set of uplink subcarriers, which does not require any frequency shift or time-domain filtering but involves an extremely large DFT computation. Note that even though DFT size NDFT = n2m, and we New Radio Access Physical Layer Aspects (Part 2) 627 can use fast and effcient DFT computation algorithms, the DFT computation cannot start until the complete sequence is stored in memory, which increases the processing delay. 4.2.3.2.1 Four-Step Random-Access Procedure From the UE physical layer perspective, the RACH procedure consists of transmission of random-access preamble (Msg1) in a PRACH occasion, receiving random-access response message via PDCCH/PDSCH (Msg2), and transmission of Msg3 in PUSCH, and receiving PDSCH for contention resolution. If the random-access procedure is initiated by a PDCCH command, the PRACH preamble is transmitted with the same subcarrier spacing. The random-access procedure comprises four steps. However, before the UE can attempt to access the network, it must synchronize to the downlink and receive the SI via PBCH and PDCCH/PDSCH. Upon receiving the SI, the UE would have the knowledge of PRACH con- figuration and transmission parameters such as PRACH preamble format, time-frequency re