osition of the DM-RS resource elements in the frequency domain vary depending on the subcarrier shift, which is determined by the physical cell identity known to the UE after the PSS/SSS demod- ulation. The DM-RS of PBCH is modulated by a pseudo-noise random binary sequence and carries the index of the half radio frame as well as partial information on the index of the associated SS/PBCH block. 3 5G System Overview 3.5.4.2 Random Access Channel Similar to LTE, Release-15 NR enables a UE to access a cell by using a four-step RACH procedure, that is, synchronization signal detection, broadcast information acquisition, connection establishment using random access, and contention resolution. However, configuration of the signals and transmissions is different from LTE. In particular, for msg2 (Message 2) transmission from a UE to a gNB, the Physical Random Access Channel (PRACH) supports long and short sequences (preambles) (3GPP TS 38.211). For the long sequence four preamble formats are supported, mainly targeting FR1 deployment scenarios with large cells. These formats inherit the LTE PRACH design principles and support SCS of 1.25 or 5 kHz. For the short sequences nine preamble formats are supported in NR, targeting small/regular cells and indoor deployment scenarios. Short PRACH formats are based on a new structure and can be used for both FR1 and FR2. Short preamble formats are constructed by the composition of multiple shorter OFDM symbols per PRACH preamble and are transmitted using the same SCS as the shared channel, i.e. 2H . 15 kHz, = 0,1,2,3. This structure offers several benefits including possible support of Rx beam sweeping at gNB, robustness in the scenarios with time varying channels, single Fast Fourier Transform operation with uplink data, etc. The additional details of the supported PRACH formats are summarized in Table 3.5.3. The generic structure of the PRACH preamble in NR is shown in Figure 3.5.6, where the number of sequences (SEQ), CP duration, and guard period (GP) duration depend on the Ta