To cope with the different 5G NR use cases and demands per service, 3GPP defines the concept of bandwidth parts (BWP). Each BWP has a fixed numerology (fixed subcarrier spacing, number and location of the resource block, symbol duration, etc.).
User equipment (UE) can be configured with up to four carrier bandwidth parts in downlink/uplink, but at any given time only a single downlink/uplink carrier bandwidth part can be active. The downlink control information (DCI), radio resource control (RRC) or a timer can trigger the switch of the active BWP (see Figure 1).
Another significant difference between LTE and 5G NR is the position of the synchronization signals, namely the primary (PSS) and secondary synchronization signals (SSS) within the carrier. Synchronization signals are very important. They are the first information that mobile devices need to identify in order to access the network.
In LTE, the sync signals are always located in the center of the carrier bandwidth; this makes them easy to find. In 5G NR, the sync signals are part of the SS/PBCH block (also called synchronization signal block, SSB) containing the physical broadcast channel (PBCH) information. These SS/PBCH blocks can be located at multiple positions all over the carrier bandwidth and are broadcast periodically as defined symbols in the radio frames and different beams versus time (see Figure 2).