t. Internet of Things 755 In the in-band operation, the assignment of resources between LTE and NB-IoT is not fixed. However, as we mentioned earlier, some of the physical LTE RBs cannot be used for NB- IoT deployment. The NB-IoT system is designed to operate in the following LTE operating bands: 1, 2, 3, 4, 5, 8, 11, 12, 13, 14, 17, 18, 19, 20, 21, 25, 26, 28, 31, 66, 70, 71, 72, 73, and 74 [1]. 3GPP specifications do not specify how to allocate the RBs between LTE and NB-IoT. However, downlink synchronization and paging can only be established on certain RBs. The RBs located at the center of the band cannot be used due to LTE transmission of the downlink synchronization signals and broadcast channel. Owing to capacity limitations, NB-IoT is not designed for 1.4 MHz channel bandwidth. The RBs allocated for a cell connection are referred to as anchor carriers. For the actual exchange of data (in the connected state), other RBs (non-anchor carriers) can be assigned. For an LTE service provider, the in-band option provides the most efficient NB-IoT deploy- ment scenario because if there is no IoT traffic, the PRB(s), available for an NB-IoT carrier, may be allocated to LTE services. Note that NB-IoT can be fully integrated with the exist- ing LTE infrastructure. This allows the base station scheduler to multiplex LTE and NB- IoT traffic in the same spectrum. Fig. 6.6 shows the results of a coexistence study where the impact of NB-IoT uplink transmission in in-band and guard-band modes on an LTE [victim] system throughput is given in terms of cumulative distribution function (CDF) of throughput. The results suggest that there is a negligible impact on LTE operation as a result of NB-IoT deployment [17]. 6.2.3 Protocol Structure The NB-IoT protocol stack is a functionally reduced version of the LTE protocols. The NB-IoT further uses a different bearer structure. SRBs are partly reused from LTE; that is, the SRBO is used for RRC messages transmitted over the common control channel, and the SRB1 is used for transport o