# A Systematic Analysis of Narrowband IoT Quality of Service
## 3 Experimental Setup and Methods  
The complexity of mobile networks makes a systematic QoS evaluation challenging for end-users. In most cases, the measurements performed by the base station cannot be obtained from the network. As a result, QoS parameters such as the received signal level and quality, SNR, eNodeB transmission power, \begin{table}
\begin{tabular}{c c c} \hline \hline  & **NPUSCH 164 dB MCL** & **NPDSCH 164 dB MCL** \\  & **Ref. Performance** & **Ref. Performance** \\ \hline Transmit Power \(P_{TX}\) (dBm) & 23 & 35 \\ TBS (Bit) & 1000 & 680 \\ Repetitions \(N_{Rep}\) & 32 (max. 128) & 128 (max. 2048) \\ Resource Units \(N_{RUl}\) & 10 & 8 \\ BLER (\%) & 10 & 10 \\ \(SNR_{min}\) (dB) & \(-\)13.8 & \(-\)14.7 \\ Noise Figure NF (dB) & 5 & 7 \\ Interference Margin (IM) (dB) \({}^{1}\)(1) & 0 & 0 \\ Sensitivity \(P_{RX,min}\) (dBm) & \(-\)141 & \(-\)129 \\ MCL (dB) & 164 & 164 \\ \hline \hline \end{tabular}  
* In mobile networks, additional interference degrades the MCL, especially in dense urban areas.  
\end{table} 
Table 2: Reference link budget configuration achieving the minimum requirement of MCL = 164 dB for 5G mMTC systems as defined by IMT-2020 [19] with 32 and 128 repetitions in uplink and downlink (adapted from [6]). as well as various radio configuration parameters like the number of ECL repetitions are not available to estimate the network performance. However, modems perform extensive lower layer measurements for channel estimation, which can be employed to understand the system behavior under different coverage situations. Furthermore, the application layer measurements can be used to analyze the data rates and latency. In this section, the setup used for the experiments is presented. All measurements in this research were performed from an end-user perspective, without access to the base station or control of the serving network. As such, the experiments could be reproduced by application developers and could be employed to estimate the QoS that could be expected for a given use case in different coverage scenarios. Most physical radio parameters, such as ECL and the number of repetitions, were controlled by the serving network or the eNodeB. One notable exception was the UE transmission power (\(P_{TX,UE}\)), which was set by the UE algorithm, but was subject to cell-specific and user limits. In this evaluation, the maximum user limit of 23 dBm was used. Figure 5 shows the architecture used for measuring the physical and application layer NB-IoT QoS parameters. The architecture consisted of the following elements:  
1. A measurement computer controlled the NB-IoT modem via a USB connection. A UDP client was running on the computer to send and receive test packets. 2. The NB-IoT modem connected to the public NB-IoT network and performed lower layer measurements. The Exelonix NB1 DEV kit [20], which is based on the uBlox SARA-N211 modem [21], was selected for the physical layer measurements due to its wide range of reported QoS values. 3. A RF shielding box prevented the mobile carrier signal from coupling into the modem board when high attenuation was applied. 4. A Wavetek 5080.1 step attenuator (0-81 dB attenuation, \(f_{max}=1000\) MHz) allowed simulating different signal levels. Figure 5: The measurement architecture used for the physical and application layer evaluations. * A Delock 88571 omnidirectional antenna (A = -0.8-0.2 dBi) was connected via a coaxial cable to the step attenuator. * The eNodeB was the MNO base station providing the NB-IoT carrier signal. * The MNO backbone contained provider internal functionality, such as subscriber management and packet routing. * A whitelisted server was required by the MNO as a packet destination for security reasons. The server ran a UDP server to send and receive test traffic. * A Network Time Protocol (NTP) server was part of the same local network as the measurement computer and the whitelisted server. It was used to synchronize the real-time clocks and enabled high-precision latency measurements.