## 7 Results and Discussion
Figure 22 shows the same relationship with the exception that it shows the packet loss at the dedicated DASH7 gateways. Note that the packet loss is generally lower compared to Figure 21. It is noteworthy that the majority of packet loss occurs when there is NLOS. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & & \multicolumn{2}{c}{**CH 0**} & \multicolumn{2}{c}{**CH 93**} & \multicolumn{2}{c}{**CH 186**} \\ \hline  & &  
Eventually, we found that there was less packet loss at the DASH7 gateways compared to the post-processed data in GNU Radio of the indoor data set. The findings for the suburban data set are slightly different. At certain locations and channels, the software processing outperformed the DASH7 gateways. But in other cases, it performed equally or worse. There are diverse factors that can explain the cause of it. Firstly, multipath, difference in noise floor, and other signals such as LoRa were randomly seen within the data set, which affected the transmitted signals and, therefore, can explain the packet  
Figure 21: An overview of the relationship between distance and packet loss based on measurements from the suburban environment. The data for each received channel were captured by the SDR. The “N” stands for NLOS locations. Figure 22: An overview of the relationship between distance and packet loss based on measurements from the suburban environment. The data for each received channel were captured by dedicated DASH7 gateways. The “N” stands for NLOS locations. loss. Also, at channel 0, other signals were observed occasionally. Another reason why the gateway outperformed the SDR recordings was due to sensitivity. It is found that the receiver sensitivity of the B-L072Z-LRWAN1 board was \(-137\,\mathrm{dBm}\). The sensitivity of the applied SDR was not advertised and depended on multiple factors. However, we believe that the sensitivity of the SDR was worse, taking into account the large bandwidth compared to a dedicated, small bandwidth device. Another explanation for the increased data loss is time variances between the packets within one recording. We observed that these dynamic time variances between consecutive packets were between \(1\,\mathrm{ms}\) and \(2\,\mathrm{ms}\). This caused phase shifts in comparison to the locked frequency and phase of the local oscillator, which caused the intermediate frequency to be affected by each received packet. We observed that more or even other packets were decoded successfully by changing the phase offset of the local oscillator. Another observation within the recordings was a recurring static frequency deviation of about \(1.5\,\mathrm{kHz}\) that needed to be adjusted at the first mixing stage in the receiver flow-graph. This is a Center Frequency Offset (CFO), which is caused by the frequency deviation of the Temperature Compensated Crystal Oscillator (TCXO) of the B-L072Z-LRWAN1 boards (STMicroelectronics, Geneva, Switzerland), which operates at \(32\,\mathrm{MHz}\). This TCXO provides a clock signal to the SX1276 transceiver chip (Semtech, Camarillo, CA, USA) and is used by the DASH7 transmitters and gateways. According to the datasheet, these crystals have a deviation of two parts per million (ppm) [30].