DMA symbols per slot. As shown in Fig. 6.20, the SC-FDMA symbols used for DMRS transmission depend on the subcarrier spacing. The DMRS symbols are constructed from a base sequence multiplied by a phase factor. They have the same modulation as the associated data channel. For 3.75 kHz subcarrier 15 kHz subcarrier 3.75 kHz subcarrier 15 kHz subcarrier spacing spacing spacing spacing Figure 6.20 Resource elements used for DMRS in NPUSCH format 1 and 2 [2]. Internet of Things NPUSCH format 2, DMRS symbols are spread with the same orthogonal sequence as defined for the LTE PUCCH formats 1, 1a, and 1b. 6.4 Layer 2/3 Aspects As in physical layer, there has been a number of changes in LTE L2/L3 operation to enable NB-IoT including introduction of new RRC messages and information elements. Some of the baseline LTE functions are not supported in NB-IoT including public safety notifica- tions, inter-RAT mobility, and security activation for transfer of RRC context information, measurement configuration and reporting, and self-configuration and self-optimization as well as measurement logging and reporting for network performance optimization. The UE in RRC_CONNECTED can be configured, via UE-specific RRC signaling, with a non- anchor carrier for all unicast transmissions. The UE in RRC_IDLE, based on broadcast/mul- ticast signaling, can use a non-anchor carrier for single-cell point-to-multipoint reception. The UE in RRC_IDLE can, based on broadcast signaling, use a non-anchor carrier for pag- ing reception. The UE in RRC_IDLE or RRC_CONNECTED, based on broadcast signaling, can use a non-anchor carrier for random access. If the non-anchor carrier is not configured for the UE, all transmissions occur on the anchor carrier. 6.4.1 HARQ Protocol and Scheduling To enable low-complexity UE implementation, NB-IoT allows only one HARQ process in both downlink and uplink, and allows longer UE decoding time for both NPDCCH and NPDSCH. Asynchronous, adaptive HARQ procedure is adopted to support scheduling flexi- bility. An example is 