# A Systematic Analysis of Narrowband IoT Quality of Service
## 5 Discussion  
In this section, the real-life performance of NB-IoT is discussed and correlated with the 3 GPP requirements [4] and existing system-level simulations [1]. Table 4 provides an overview of the most relevant QoS parameters, which were used to discuss the suitability of NB-IoT in different scenarios. For example, in smart metering applications, four transmission categories were identified depending on the functionality of the end device:  
* Uplink transfer of individual sensor data from a single sensor
* Downlink transfer of individual commands
* Uplink transfer of small packets from many sensors
* Transfer of software updates in the downlink and bulk data to the cloud in the uplink \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Metric** & **3 GPP Specification [4]** & **Simulated Performance [1]** & **Measured Performance** \\ \hline MCL (dB) & 164 & 164 & 163.5 \\ Max. uplink & 62.5 1  & 62.6 1  & 22.6 2 \\ throughput (kbps) & 27.2 1  & 26.2 1  & 23.0 \\ Min. data rate (kbps) & & UL: 0.320 & \\ (164 dB MCL) & 0.160 & DL: 0.370 & \textgreater{}0.707 @ 160 dB MCL \\ Exception report & & & UL: 11.2, DL: 0.610 \\ latency (s) (164 dB MCL) & 10 & 8.0 & for user traffic \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of different NB-IoT QoS parameters in a guard-band deployment. The first transmission category corresponded to a typical IoT use case, which was a single sensor transmitting data to the cloud for further processing and storage. Sensors are commonly deployed in hard to reach locations, such as basements and metal enclosures. NB-IoT was designed to provide long-range communication with 164 dB MCL. While this coverage was confirmed in the simulations as shown in Table 4, the measurements showed that the MCL could be reduced by interference, with an observed best case MCL of 163.5 dB. The second important QoS criterion was latency. For NB-IoT, an exception report latency of 10 s was defined, which was fulfilled in a simulated environment at 8.0 s. In most real-world applications however, the latency of regular user traffic is of interest. NB-IoT provided a low user traffic latency at high signal levels with an uplink median of 535 ms for ECL0 transmissions. Below the noise floor, ECL2 was employed, and the latency increased significantly to a median of 11.2 s. Since there were many samples with a latency of tens of seconds, the application must be designed accordingly. For applications that employ exception reports, no latency benefit was found, which suggested that this functionality may not have been implemented in the network under investigation. Furthermore, the high repetition count (up to 128) and corresponding high output power (up to 23 dBm) decreased the battery life of sensors without a mains connection. Since the long-term measurement revealed more stable radio conditions during night time, it might be beneficial for sensors in extreme coverage to collect sensor readings and transmit them at night. No packet loss was observed for transmissions of individual packets, which relaxed the need for application layer retransmissions. In the second category, an actuator received commands from a control server on the Internet. The traffic patterns and QoS requirements matched those of the sensors closely, except that commands were transferred in the downlink direction. As such, most of the QoS conclusions made for the transmission of sensor data also applied to actuators. For good signal levels with ECL0, NB-IoT provided very low median downlink latencies of 179 ms. In extreme coverage scenarios with ECL2, the target latency was still satisfied at a median of 610 ms. As such, NB-IoT fulfilled the need for transferring commands to actuators. For the third category, a deployment of many sensors in a limited area was considered. One NB-IoT UE could aggregate and transmit all sensor readings. In this use case, many small packets would be sent within a short period of time, so the system bandwidth was an important QoS characteristic.