# Secure Authentication and Credential Establishment in Narrowband IoT and 5G
## 5 Architecture Description and Evaluation
### Performance Analysis with Real Devices  
For the purpose of validating the proposal, the most relevant performance parameters of NB-IoT in recent literature were considered [42]. The requirements of IoT deployments identified are as follows: (i) an extended coverage range, (ii) device cost, (iii) efficient energy management, and (iv) scalability to serve a massive amount of devices per cell. Regarding NB-IoT energy management, 3 GPP introduced two power saving schemes in Releases 13 and 14, i.e., PSM and eDRX. These modes allow the UE to enter a state where monitoring the signaling and scheduling information is not needed [43]. There is already research available on the energy performance of NB-IoT with regard to this. For instance, the authors in [44] presented empirical power consumption measurements on early, commercially available NB-IoT hardware. The results show that a device transmitting 100 bytes of payload every 24 h can operate for more than 12 years with a C-cell battery. The authors of [43] presented and validated a model of NB-IoT performance with regard to battery lifetime and latency. The results indicated that power does not grow in a linear manner in terms of packet length; instead, it is worsened due to the segmentation of longer packets. Moreover, adverse channel conditions will require retransmissions that increase power consumption. The work in [45] presented an analytical model to measure the impact of channel conditions on NB-IoT communications. The results show that, at a Maximum Coupling Loss (MCL) of 145 dB or more, the performance of the system starts to be affected with regard to battery lifetime and latency. At a 164 dB MCL, the battery lifetime is reduced by 90% compared to ideal conditions. In addition, devices that report periodically in shorter intervals will consume more energy. This is because most of the power is consumed during transmission [46]. Similarly, scalability is also one of the design goals of NB-IoT. It is aimed to serve 40 devices per household--in urban areas similar to London, this equals approximately 50,000 devices per base station [47]. In addition, the authors in [48] provided an analysis of NB-IoT performance in terms of capacity for realistic use case scenarios. They measured the performance of channel occupancy of both  
Figure 5: The proposed architecture for lightweight authentication and key establishment over NB-IoT.  
downlink and uplink with regard to different device transmission intervals and base station density. Their results suggest that a system is able to cope with up to 12,000 packets per hour per base station.  
After evaluating all the aforementioned works, a reduced message size and a reduced number of packets required were considered as apt performance indicators for this validation process. It has reasonably been shown that they are tightly related to the energy, scalability, and latency performance of NB-IoT communication systems.  
In order to validate the proposed architecture, a real-life implementation was carried out as a proof of concept. As a result, a testbed was built with real hardware while taking into consideration the constrained nature of IoT devices. Thus, the hardware was chosen with the specific purpose of replicating the characteristics of a typical scenario. An analysis of different parameters of a practical nature for the scenario are presented next.