Definition of channel bandwidth and transmission bandwidth configuration for in-band/guard- band NB-loT operation [1]. DC subcarrier is 180 kHz. As a result, the PRB indices 30, 35, 40, and 45 are all centered at 2.5 kHz from the nearest 100 kHz grid. It can be shown that for LTE carriers of 10 and 20 MHz, there exists a set of PRB indices that are all centered at 2.5 kHz from the nearest 100 kHz grid, whereas for LTE carriers of 3, 5, and 15 MHz bandwidth, the PRB indices are centered approximately 7.5 kHz away from the 100 kHz raster. It must be noted that none of the middle six PRBs of the LTE carrier can be assigned as an NB-IoT anchor car- rier (e.g., PRB_25 of 10 MHz LTE, despite the fact that its center is 2.5 kHz away from the nearest 100 kHz raster). This is due to the fact that LTE synchronization and broadcast channels occupy the resource elements in the middle six PRBs. Similar to the in-band deployment, an NB-IoT anchor carrier in the guard-band is required to have center fre- quency no more than 7.5 kHz distant from the 100 kHz raster. The NB-IoT cell search and initial acquisition are designed for a UE to be able to synchronize to the network in the presence of a raster offset up to 7.5 kHz. Multi-carrier operation of NB-IoT is also sup- ported. Since one NB-IoT anchor carrier is necessary to enable UE initial access/synchroni- zation, the additional carriers do not need to be near the 100 kHz raster grid. These additional carriers are referred to as secondary carriers. As we mentioned earlier, NB-IoT carrier occupies 180 kHz of bandwidth, which corresponds to one PRB in an LTE system [2]. With this selection, the following operation modes are possible (see Fig. 6.4): Standalone: A scenario where currently used GSM frequencies with 200 kHz bandwidth can be utilized for NB-IoT deployment. Guard-band: A deployment scenario which utilizes the unused RBs within an existing LTE carrier's guard-band. In-band: A scenario where PRBs within an existing LTE channel bandwidth are utilized for NB-IoT deploymen