# A Systematic Analysis of Narrowband IoT Quality of Service
## 1 Introduction  
In recent years, the rise of the Internet of Things (IoT) and its associated platforms has directed the interest of researchers and companies alike to the exchange of information between IoT endpoints such as sensors and servers. These communication patterns are referred to as Machine Type Communication (MTC) [1]. The communication requirements within the MTC category are diverse; therefore, it is common to distinguish between cMTC (critical MTC) and mMTC (massive MTC) technologies. A widespread mMTC use case is Wireless Sensor Networks (WSNs), which consist of many battery powered devices distributed across heterogeneous environments. The diverse applications of WSNs have sparked the development of a new group of IoT-centric access technologies. Low-Power Wide Area Networks (LPWANs) provide long-range communication for many devices simultaneously, while enabling battery life for many years. In general, LPWANs can be categorizedbased on the license of the occupied spectrum. Unlicensed technologies, such as LoRaWAN [2], work in the license-free and region-specific Industrial, Scientific, and Medical (ISM) and Short-Range Devices (SRD) bands. Licensed technologies are standardized by an industry consortium such as the Third Generation Partnership Project (3 GPP) [3] and are commonly deployed by Mobile Network Operators (MNOs) along with existing mobile networks. Some LPWANs are developed based on existing standards, such as LTE Cat-M1 [1]; others, like Narrowband IoT (NB-IoT) [1], are referred to as clean-slate technologies and do not retain full compatibility with existing technologies. As a result, these standards interfere with neighboring networks. NB-IoT has emerged from a 3 GPP study on cellular IoT technologies [4] and was first standardized as part of LTE Release 13 (Rel-13) [5]. It is designed to integrate with existing GSM and LTE networks and provide a long-range, energy-efficient mobile service, with a Maximum Coupling Loss (MCL) of 164 dB and up to 10 years of battery life. Additionally, NB-IoT supports massive device densities and guarantees delivery of high-priority exception reports within 10 seconds. In the future, NB-IoT will be part of the 5G architecture, providing support for mMTC use cases [6]. Whenever new mobile network standards are introduced, their performance is approximated in system-level simulations, which include the air interface, as well as higher protocol layers. In the case of NB-IoT, extensive simulations have already been performed for different scenarios [1, 6]. NB-IoT Rel-13 has been implemented by MNOs and gained considerable interest; however, little attention has been paid to systematic real-life QoS evaluations. While some measurements have been done, not all of them were performed in a real-world environment, which is essential to verify the end-user QoS. [PERSON] et al. [7] analyzed attachment delay, latency, and message overhead under laboratory conditions. The analysis was based on five samples per measurement, which is a relatively low sample size. [PERSON] et al. [8] performed long-term analysis of NB-IoT Signal-to-Noise Ratio (SNR) and Received Signal Strength Indicator (RSSI) on different floors of a university building. The evaluation showed that SNR and RSSI levels changed during the day. The authors proposed that this may be caused by LTE activity generated by mobile network users. [PERSON] et al. [9] analyzed NB-IoT coverage in indoor, outdoor, and underground scenarios. The results indicated that NB-IoT worked well for indoor and outdoor scenarios, while underground coverage was limited to locations close to the base station, which is referred to as eNodeB in LTE systems. [PERSON] et al. [10] performed analysis on energy consumption, reliability, and latency in NB-IoT networks. While these measurements were performed in an operative network, the authors focused on the power consumption of NB-IoT, and they found no correlation between the repetitions caused by the Enhanced Coverage Level (ECL) and latency.