f the active BWP. The granularity of bandwidth allocation in NR is one PRB. For each serving cell, up to 4 downlink/uplink BWPs can be configured separately and independently for paired spectrum; nevertheless, only one BWP can be active at a given time and the UE is not expected to receive downlink/uplink physical signals/channels outside of an active BWP. For paired spec- trum, a downlink BWP and an uplink BWP are jointly configured as a pair and up to four pairs can be configured. One can configure up to four BWPs on a supplemental uplink (SUL) carrier. Different use cases of the BWP are illustrated in Fig. 3.49 [28]. In other words, a BWP is a subset of contiguous CRBs for a given numerology (note that different numerologies may be used in different BWPs) on a given RF carrier. The starting position NBWP(i) and the number of resource blocks N PRB BBP(i) in a BWP satisfy Nerid Norid(u) BWP(i) start Norid size (u), respectively. If a UE is configured with a SUL, then it can additionally be configured with up to four BWPs on the SUL with a single SUL BWP being active at a given time. As we mentioned earlier, the transmit/receive bandwidth of a UE does not need to be as large as the bandwidth of the cell and it can be adaptively adjusted according to UE New Radio Access Physical Layer Aspects (Part 1) 395 PRB N3 BWP 3 (active) PRB 1 PRB 0 BWP 2 BWP 2 PRB N2 (active) (active) PRB 1 BWP 1 BWP 1 (active) (active) PRB 0 PRB N1 PRB 1 PRB 0 Figure 3.50 Illustration of the active bandwidth part adaptation concept [12,19,28]. operational conditions. With Bandwidth Adaptation (BA), a UE's bandwidth can be resized (e.g., reduced during a period of low activity for power saving); its location can be moved in the frequency domain (e.g., to increase scheduling flexibility); and the subcarrier spacing can be changed (e.g., to allow different services). A subset of the total cell bandwidth is called a BWP and the BA is achieved by configuring the UE with different BWP(s) and notifying the UE of the instantaneous active one. Fig.