# Narrowband Internet of Things (NB-IoT):
## 3 Narrowband-IoT Protocol Stack
### Media Access Control Layer
#### 3.2.1 Radio Resource Allocation  
In NB-IoT, resource allocation is the key feature to ensure the expected massive connections in a cell. Tone allocations, PRBs, repetition number options, power configurations, subframes, or time slots, etc. must be optimized to maximize performance with minimum possible resources. Since NB-IoT is intended for low rate, less frequent time insensitive applications but with the required performance metrics, better radio resource management will ensure the optimal resource usage for expected throughput, spectral efficiency, and coverage enhancement. In [68], the authors discussed the impact of interference for partial deployment of NB-IoT such that if one PRB is used for NB-IoT in some of the cells, that same PRB could be used for LTE in other cells for the in-band mode of NB-IoT operation. In such a deployment, possible co-channel interference may appear between NB-IoT UE and LTE UE. The authors modeled the partial deployment in percentile such that 100%, 75%, 50%, 25% represent the percentage of cells where NB-IoT enabled. Their results were analyzed by means of cumulative density functions (CDF) of respective SINR detected and maximum coupling loss achieved. The work demonstrates possible NB-IoT interference between NB-IoT and another NB-IoT UEs from adjacent cells and between NB-IoT and LTE from the adjacent cell. The simulation is performed for the in-band mode of operation where both NB-IoT and LTE UEs share the same PRB. They proposed the PRB blanking i.e., blanking the resources that are used by NB-IoT to not be used by LTE, not even being used for CRS. Blanking of these resources will omit the interference from LTE UEs and will result in NB-IoT only access to this PRB. However,the paper did not consider the performance degradation due to reduced available radio resources after when resource blanking is applied. In [69], the authors formulated an analytical model to characterize the maximum achievable data rate, then investigated the impact of intercell interference in a multicell environment (for in-band and standalone scenarios), and finally proposed an iterative algorithm which uses cooperative approach which takes into consideration the overhead of control channels, repetition number, intercell interference as well as time offset. The proposed sub-optimal solution ensured better radio resource allocation, which raised the data rate by 8% and reduced the overall device energy consumption by 17% with respect to the non-cooperative approach. In [82], the authors presented preliminary results of RSSI and detected SNR by developing a DORM (integrateD cOmpact naRrowband plattorM) node which was deployed on a university campus to test its practical feasibility in different indoor scenarios.Their SNR and RSSI values were observed to be in the range of 18 dB to 23 dB and \(-65\) dBm to \(-70\) dBm, respectively, which shows its suitability for indoor coverage. The RSSI and SNR values variations are considered to be due to different elevations that the nodes are, with respect to the serving base station. However, the paper does not explain the channel estimation and measurements quality and their impact on the achievable throughput, moreover their paper does not cover the outdoor deployment and the impact of repetition on the overall devices' energy consumption when devices are located in different indoor environments. In [70], the authors introduced the NB-IoT radio access strategy in detail and studied the NB-IoT scheduling problem. Their primary objective is to lower the number of used radio resource while each device's data requirement can still be satisfied. They furthermore formulated the NB-IoT scheduling problem and proposed an efficient algorithm to overcome such a problem. Their simulation results show that they could minimize the number of NPDCCH periods (NPs) used to satisfy each device's data requirement. However, the repetition number is given according to the distance between the base station and the device.