## 3 Results  
### Network Performance  
The application should use as few resources of the mobile network as possible. A design aspect of the protocol is therefore a low message size. Table 1 contains the frequencies and sizes of the messages sent within the UTM network. During the test, the bit rates for all network subscribers, both in the UL (UE to base station) and in the DL (base station to UE), were determined.  
To determine the transit times in the UTM network, the server was set up as a reference timer with which all participating clients synchronised themselves. In addition, all messages were time-stamped before being sent by the transmitting unit. Based on the time of message creation and message receipt, the runtime of the data packets in the network could be estimated.  
All UTM participants were simultaneously connected directly via the radio interface of the mobile network. An additional VPN was required for communication with each other. However, the VPN leads to higher trip times of the network participants in the designed architecture. In addition, it could be observed that the UART microcontroller interface between the single board computer and the LTE module also leads to additional  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Message Type** & **Refresh Rate [Hz]** & **Message Size [Byte]** & **Note** \\ \hline UavTelmetry & 2.0 & 214 & - \\ UavStatus & 2.0 & 116 & - \\ TrafficInfoRequest & 1.0 & 107 & Radius = 500 m \\ AirspaceInfoRequest & 0.2 & 107 & Radius = 500 m \\ TrafficInfo & 1.0 & 278 & 1 nearby aircraft \\ AirspaceInfo & 0.2 & 41 & 1 nearby airspace \\ OperatorCommand & - & 87 & As required \\ AtcCommand & - & 87 & As required \\ FlightPlan & - & 1875 & As required \\ \hline \hline \end{tabular}
\end{table}
Table 1: Parameters used for the prototypical UTM Network.  
Figure 9: The experimental setup including the virtual controlled airspace (UniBw CTR), the positions of the devices involved and the recording components.  
delays within the MMT. The trip times are shown in Table 2. On the contrary, an end-to-end Round Trip Time (RTT) between a COTS UE and the CN was measured in the range of 20 ms to 35 ms.  
Tables 3 and 4 show the measured SNRs in UL and the bit rates in UL and DL. The SNR > 10 dB allows the use of the 16-QAM modulation in the UL during the field trial. A Channel Quality Indicator (CQI) between 14 and 15 was reported by UEs. This is an indicator how good the communication channel quality is. 15 and 14 are the largest CQI values where usually 256-QAM modulation is chosen for the DL. The SNR measured at the base station and the CQI shows that the signal strength at the receivers was sufficient during the over-the-air test. As shown in Table 3, a virtual UAS was used in V4, which was simulated on the device of User2 at a higher update frequency (10 Hz instead of 2 Hz), hence increasing its bit rates in DL as well as in UL significantly.  
In addition, the maximum TCP throughput was evaluated using the NR UE with iPerf3. 138.7 Mbps in the DL and 25.1 Mbps in the UL could be achieved on the 40 MHz TDD carrier. According to [36] the measured TCP throughput is close to the maximum value for QAM-64 modulation considering a 40 MHz TDD Single Input Single Output (SISO) carrier with the highest Modulation and Code scheme index.