# A Compact Low-Power LoRa IoT Sensor Node with Extended Dynamic Range for Channel Measurements
## 5 Conclusions  
An autonomous LoRa-compatible wireless sensor node for the IoT was designed, fabricated, calibrated and tested. This node is not only unique in its ability to perform channel characterization in both the 434 MHz and 868 MHz ISM-bands, it can also accurately measure received power levels over a large dynamic range. A feat which is possible thanks to the stepped attenuators implemented in this design and the calibration of the unit performed in the lab.  
Furthermore, several design choices (such as the addition of a real-time clock with a dedicated interrupt line and a supercapacitor buffering the supply voltage) were made to increase the autonomy of the node, enabling prolonged measurement campaigns to take place. Moreover, both the incorporation of various other peripheral components and the fact that this custom hardware is significantly smaller than a development board or software radio show that this system qualifies for a very broad range of LoRa research applications.  
The correct operation of the node was successfully validated by performing both indoor and outdoor test measurements. In these measurement campaigns, the expected superiority of the 434 MHz band for long-range communication links was repeatedly confirmed. Moreover, with measured received power values ranging from \(-140\) dBm to \(-70\) dBm, the need for and usefulness of an enhanced dynamic range for channel measurements was clearly illustrated.  
The outdoor tests have also provided insight into the difference in link quality between the 434 MHz and 868 MHz LoRa channels. With an additional distance of 1.6 km to the transmitter, the standard deviation of the SNR of the packets received by receiver RX1 exhibited an increase of 1.29 dB for the 434 MHz band and 3.98 dB for the 868 MHz band when compared to the SNR of the packets received by the more nearby RX2. When comparing rainfall and temperature data to the signals measured outdoors, a correlation was found between a sudden drop in signal and an episode of rainfall. This indicated that the behavior of the antenna, which was placed outside of the building, had changed substantially due to the water present on it. No correlation was found between the outdoor temperature fluctuation and the measured signal levels.  
Indoor measurements indicated that the presence of people in a building also has a measurable influence on the quality of the LoRa link. When considering the 434 MHz band, the average standard deviations of the received powers measured by day differ from these measured by night or in the weekend by approximately 2 dB for both indoor receivers. For the 868 MHz band, these differences amount to approximately 3 dB for both receivers.  
In conclusion, the system successfully recorded several propagation characteristics in both the 434 MHz and 868 MHz ISM-bands over a wider dynamic range than achievable with off-the-shelf LoRa units.  
Conceptualization, P.V.T.; Formal analysis, H.R.; Funding acquisition, H.R.; Investigation, T.A. and P.V.T.; Methodology, T.A., P.V.T. and H.R.; Resources, H.R.; Software, P.V.T.; Supervision, P.V.T. and H.R.; Validation, T.A. and P.V.T.; Visualization, T.A.; Writing--original draft, T.A.; Writing--review & editing, T.A., P.V.T. and H.R.  
This work was partly funded by the Research Foundation--Flanders (FWO) through the \"MUlti-SErvice WIreless NETwork\", FWO-FRS Excellence of Science--EOS project.  
We thank our colleagues at the public observatory [PERSON] of Ghent University, www.armandpien.be, for allowing us to use their excellent location to install the LoRa transmitter used for the outdoor measurements in this paper.  
The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.