), which carries the necessary system information to enable a UE to access the 5G network. As described in Chapter 7, the "System information on demand" concept is introduced in 5G: only the information essential for system access is actually broadcasted continuously (periodically), while other sys- tem information is provided only on the need basis. The transport channel Broadcast Channel (BCH) is mapped on the PBCH. The modulation on the PBCH is QPSK. The BCH together with the Primary Synchronization Signal (PSS) and Secondary Syn- chronization Signal (SSS) form the SS Block, which is the fundamental 5G structure with beamforming operation as well as for the cell search and system access in general. The SS Block is shown in Figure 6.4. The PDCCH is place before the PDSCH as shown in Figure 6.5, which allows the PDCCH to carry information on the downlink scheduling for the PDSCH. Also, the uplink allocations are normally signaled on the PDCCH. The relative positions of the PDCCH and PDSCH are such that in the downlink the PDCCH is always just before the PDSCH. As described later in this chapter, the PDCCH can carry information other than the downlink or uplink allocations. 6.3 Physical Channels and Signals Primary Synchronization Signal (PSS) Secondary Synchronization Signal (SSS) Physical Broadcast 10000 Channel (PBCH) Sync block 4 symbols Figure 6.4 5G SS Block structure. Downlink control data (PDCCH) User Data (PDSCH) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Slot (14 OFDM symbols) Figure 6.5 5G downlink control and data channels. On the uplink side, the following channels are available: Physical Uplink Control Channel (PUCCH), which carriers the L1 control infor- mation (when there is no PUSCH allocation) including Hybrid Automatic Repeat Request (HARQ) feedback as well as Channel State Information (CSI). The modu- lation on the PUCCH is QPSK, or in some cases Pi/2-BPSK too. There are different types of PUCCH, which can be divided into be either short or long PUCCH, as shown in Figure 6.6. Physical Uplink Shared Chann