NB-IoT applications. The mapping of a transport block spans NSF subframes. The trans- port block is repeated providing NRP identical copies using a subframe interleaving mecha- nism for an optimized reception at the NB-IoT UE, as shown in Fig. 6.16. Both values, NSF and NRP, are signaled via DCI. The resulting subframe sequence is mapped to NSFNRP conse- cutive subframes defined for NPDSCH (see Fig. 6.16). For the downlink, there is no auto- matic acknowledgment to a transmission and the eNB indicates this information in DCI. In that case, the UE transmits the acknowledgment using NPUSCH format 2. The associated timing and subcarrier mapping is indicated in this DCI, as well. There is a multi-carrier sup- port for all operation modes, which means that another carrier may be used when the UE is in 768 Chapter 6 the connected state. In the idle state, the UE camps on the NB-IoT carrier from which it received the synchronization signals and broadcast information, that is, the anchor carrier. The UE then waits to receive the paging message or to start system access for mobile- originated data or signaling transmission, both by transmitting a preamble on the associated uplink carrier provided in SIB2-NB broadcast message. The smallest scheduled RU varies depending on the subcarrier spacing and the number of tones. The reliability is obtained through repetitions where in the downlink up to 2048 repe- titions are possible and in the uplink up to 128 repetitions are permissible (see Tables 6.4 and 6.5). The SIB1-NB broadcast message is transmitted over NPDSCH. It has a period of 256 radio frames and is repeated 4, 8, or 16 times. The TBS and the number of repetitions are indi- cated in the MIB-NB. In general, 4, 8, or 16 repetitions are possible, and four TBSs of 208, 328, 440, and 680 bits are defined, respectively. The radio frame on which the SIB1-NB starts is determined by the number of repetitions and NNcell ID The fourth subframe is used for SIB1-NB in all radio frames transmitting SIB1-NB. As the other transmissio