n or undercompensation of the carrier frequency. As a result, the symbol timing drifts in either the forward or backward direction depending on whether the carrier frequency was over- compensated or undercompensated. This may cause a severe degradation in the performance of NPBCH detection. During cell selection, the UE measures the received power and quality of the NRS. These values are then compared to cell-specific thresholds provided by the SIB1-NB. If the UE is in coverage of a cell, it will try to camp on it. Depending on the received NRS power, the UE may have to start a cell reselection. The UE compares this power to a reselection thresh- old, which may be different for the intra-frequency and the inter-frequency scenarios. All required parameters are received from the serving cell; thus there is no need to acquire sys- tem information from other cells. Among all cells fulfilling the cell-selection criteria, the UE ranks the cells with respect to the excess power over a threshold. A hysteresis is added in this process in order to prevent frequent cell reselection, and also a cell-specific offset may be applied for the intra-frequency scenarios. In contrast to LTE, there are no priorities for different frequencies. The UE selects the highest ranked cell which is deemed suitable. In NB-IoT, random-access procedure serves multiple purposes such as initial access when establishing a radio link and scheduling request. Among others, the main objective of ran- dom access is to achieve uplink synchronization, which is important for maintaining uplink orthogonality in NB-IoT. As shown in Fig. 6.23, the contention-based random-access proce- dure in NB-IoT consists of four steps: (1) UE transmits a random-access preamble; (2) the network transmits a RAR message that contains the timing advance command and schedul- ing of uplink resources for the UE to use in the third step; (3) the UE transmits its identity Internet of Things NB-loTUE NB-IoTeNB INPSS,NSSS,NPBCH,SIB1 SIB2 parameters Random access RACH preamble preamb