# A Systematic Analysis of Narrowband IoT Quality of Service
## 6 Conclusions  
In this paper, a detailed evaluation of the end-user QoS of the NB-IoT LPWAN standard was presented. One of the first systematic analyses of the relevant physical and application layer QoS parameters was conducted in a real network. Moreover, the influence of these parameters on the end-user QoS was studied in the uplink and downlink direction.  
Different experiments were conducted to verify the performance of NB-IoT in a public network using commercially available hardware. Analyzing the NB-IoT coverage showed that the 3 GPP target MCL of 164 dB [4] was closely approximated, but could be reduced by external interference. The necessary high receiver sensitivity was achieved by using discrete levels of signal repetitions, which were referred to as ECL. Using the highest repetition level ECL2, signals below the noise floor could be detected, which allowed sensor installations under difficult conditions.  
On the other hand, the number of ECL repetitions was a tradeoff between system latency and coverage. In the downlink direction, NB-IoT maintained a latency below one second in all coverage scenarios. In the uplink, NB-IoT provided low latency for ECL0 and ECL1 transmissions. However, when ECL2 was used below the noise floor, the latency increased to tens of seconds. This behavior could be attributed to the high number of signal repetitions and the allocation of individual subcarriers over a longer duration. Configuring the modem to send exception messages as specified by the 3 GPP requirements did not improve the latency, which might be because the mobile network did not yet implement this functionality.  
NB-IoT provided a consistent data rate over a wide range of signal levels. In the downlink direction, the throughput of 23.0 kbps was within the expected range. However, in the uplink, the data rate depended on the allocation scheme. The obtained throughput of 22.6 kbps was significantly lower than the theoretical maximum for a transmission using 12 subcarriers, which requires further investigation in a future work.  
Overall, NB-IoT satisfied most of the theoretical 3 GPP QoS requirements [4] in a commercial deployment and was a suitable technology for a wide range of sensor applications. The QoS might be reduced for signal levels below the noise floor, which must be taken into consideration during application development. In the case of smart metering, four transmission categories were analyzed, and NB-IoT was verified to be appropriate if latency values above 10 s were acceptable for signal levels below the noise floor.  
In future research, NB-IoT will be compared to other LPWAN technologies in the context of smart metering use cases. This analysis will include the currently unavailable NB-IoT non-IP optimizations, as well as the 3 GPP Release 14 improvements.  
**Author Contributions:** Conceptualization, A.P.M., J.-A.F.-P., J.C.-B., and U.B.; methodology, A.P.M. and U.B.; software, A.P.M.; validation, A.P.M., J.-A.F.-P., J.C.-B., and U.B.; formal analysis, A.P.M. and U.B.; investigation, A.P.M.; resources, U.B.; data curation, A.P.M.; writing, original draft preparation, A.P.M. and U.B.; writing, review and editing, A.P.M., J.-A.F.-P., J.C.-B., and U.B.; visualization, A.P.M.; supervision, U.B.; project administration, U.B.; funding acquisition, U.B. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by Bundesministerium fur Wirtschaft und Energie (BMWI), Germany, under Grant Number FKZ 03 ET1607A. The APC was funded by University of Jaen, Spain.  
**Acknowledgments:** The authors would like to thank Technische Hochschule Mittelhessen for providing materials and [PERSON] for technical support during the measurements.  
**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; nor in the decision to publish the results.