 is multiplied by the cyclically shifted sequence. The cyclic shift varies between symbols and slots. The higher layers may impose a limitation that disallows some of the cyclic shifts available in a cell. In addition, a spreading with an orthogonal sequence is applied. The PUCCH formats 1, 1a, and 1b carry three reference symbols per slot in case of a normal cyclic prefix (located on SC-FDMA symbols 2, 3, and 4 as shown in Figure 9-78). For PUCCH formats 1a and 1b, when both ACK/NACK and SR are transmitted in the 476 CHAPTER 9 The IEEE 802. 16m Physical Layer (Part I) Physical Uplink Control Channel Demodulation Reference Signal for PUCCH 1 ms sub-frame (2 slots) FIGURE 9-78 Structure of physical uplink control channel for frame structure type 1 and PUCCH format 1, 1a, and 1b same subframe, the UE transmits ACK/NACK on its assigned ACK/NACK resource for negative SR transmission, and transmits ACK/NACK on its assigned SR resource for positive SR transmission. In PUCCH formats 2, 2a, and 2b, the bits for transmission are first scrambled and QPSK modulated. The resulting symbols are then multiplied with a cyclically shifted Zadoff-Chu type of sequence, where again the cyclic shift varies between symbols and slots [30]. PUCCH formats 2, 2a, and 2b carry two reference symbols per slot in case of normal cyclic prefix (located on SC-FDMA symbol numbers 1, 5). A resource block can either be configured to support a mix of PUCCH formats 2/2a/2b and 1/1a/lb, or to support formats 2/2a/2b exclusively [102]. As mentioned earlier, 3GPP LTE supports intra-subframe and inter-subframe frequency hopping, which is configured per cell by higher layers. Either both intra-subframe and inter-subframe hopping or only inter-subframe hopping is supported. In intra-subframe hopping or inter-slot hopping, the UE hops to another frequency allocation from one slot to another within one subframe. In inter-subframe Table 9-25 PUCCH Formats and Contents Number of Bits per PUCCH Format Contents Modulation Scheme Subframe Scheduling Request (SR) 