ency hopping Frequency hopping Figure 4.79 Time-frequency structure of PUCCH format 1 [6]. New Radio Access Physical Layer Aspects (Part 2) 611 Unlike LTE, where PUCCH frequency-hopping was always done at the slot boundary, the NR provides additional flexibility by allowing variable PUCCH duration depending on the scheduling decisions and overall system configuration. Furthermore, since the devices are supposed to only transmit within their active bandwidth part, hopping is typically not between the edges of the overall carrier bandwidth as in LTE. Therefore, frequency hopping is configurable and determined as part of PUCCH resource configuration. The position of the hop is obtained from the length of PUCCH. If frequency hopping is enabled, one orthogonal block-spreading sequence is used per hop. 4.2.3.1.3 PUCCH Format 2 Structure and Physical Processing PUCCH format 2 is a short PUCCH format which is used to carry more than two uplink control bits, for example, CSI report and HARQ acknowledgments, or HARQ acknowledg- ments per se. An SR can also be included in the bits and jointly encoded. If the payload to be transmitted by PUCCH format 2 is too large, the CSI reports are not transmitted in order to make room for more important HARQ acknowledgment bits. The overall PUCCH format 2 physical layer processing is depicted in Fig. 4.80. A CRC is added for large payload sizes UCI bits Channel coding Scrambling sequence modulation PUCCH Scrambled allocated modulated and bandwidth encoded UCI bits -Slot- DM-RS Figure 4.80 Processing and mapping of PUCCH format 2 [6]. 612 Chapter 4 and the resulting block of bits are encoded using Reed-Muller - codes20 for payload sizes up to 12 bits or polar codes for larger payloads. The encoded block is scrambled and QPSK modulated. The scrambling sequence is based on the device identity (C-RNTI) together with the physical-layer cell identity (or a configurable virtual cell identity), ensuring inter- ference randomization across cells and devices using the same set of time-frequency r