# Experimental Evaluation of a LoRa Wildlife Monitoring Network in a Forest Vegetation Area
## 5 Experimental Results and Discussion
### Experimental Results
#### 5.1.2 Effects of the CR  
Figures 11-13 show the \(PDR\) for a 17 bytes LoRa transmitted packet obtained for transmissions from POS C, POS F & POS 3 to the gateway for different combinations of \(SF\) and \(CR\) values in both 433 and 868 MHz frequency bands. The CR values measured are \(CR=5\) (the least level of redundancy) and \(CR=8\) (the highest level of redundancy). Looking at the graph, it is clear that there is an advantage of using a higher code rate to improve the obtained \(PDR\). These experimental results conform to the simulations reported in [55], which pointed out that higher \(CR\) values (increased redundancy in the packet) guarantee, at the cost of an increased time-on-air (ToA), a substantial increment in the \(PDR\) when the \(SNR\) is near the threshold, and hence an increased robustness of LoRa to fluctuation in the channel attenuation.  
Figure 11: PDR vs. \(SF\) varying the \(CR\) in POS C **(a)** 433 MHz **(b)** 868 MHz.  
Figure 10: PDR vs. \(SF\) in POS 2 with CR = 4/5, BW = 125 KHz for **(a)** 433 MHz band **(b)** 868 MHz band.  
At a higher code rate, the improved forward error correction (FEC) allows more bits to be recovered: fewer packets are corrupted and discarded by the CRC, thus resulting in a higher \(PDR\). An example is demonstrated in Figure 12(a),b, which shows that for an SF value of 8 in the 433 MHz and \(SF\) value of 10 in the 868 MHz both in POS 3, communication was only possible when using the highest level of redundancy (\(CR=8\)). Despite this, the connectivity was patchy, with only a small fraction of packets being delivered successfully, close to 22% and 18% respectively. No communication was impossible for an \(SF\) value of 12 at POS D, irrespective of the CR value. It should be noted that, in almost all tested configurations, even though it is not reported, that the measured \(SNR\) for each packet, despite that better \(PDR\) is marginally but still significantly lower, using a higher \(CR\).  
Figure 14 shows the received signal strength indicator at the receiver for transmissions from POS 2 with different combinations of SF and CR values in both 433 and 868 MHz frequency bands. As evident from this figure, signal strength values around the -125 dBm mark were observed for this location, indicating that this link is operating close to its edge (communication drops off beyond -135 dBm).  
The figure also shows the differences when operating in different frequency bands. In addition, a strong signal is registered by the receiver with the average RSSI around the -113 dBm mark for the 433 MHz band. A setting with \(SF=10\) and \(CR=5\) emerges as the best choice when operating in the 868 MHz band for POS 2 to achieve the best possible performance with the least time on air. Nonetheless, the other two alternatives (\(SF=9\)) and (\(SF=8\)) could also be used. However, this would depend on the application's  
Figure 12: PDR vs. \(SF\) varying the \(CR\) in POS F (**a**) 433 MHz (**b**) 868 MHz.  
Figure 13: PDR vs. \(SF\) varying the \(CR\) in POS 3 (**a**) 433 MHz (**b**) 868 MHz.  
tolerance to packet loss. If an application does not demand high levels of delivery accuracy and packet loss is tolerable, then a more aggressive setting could also be used. Therefore, the choice of settings boils down to the demands of the application and what can be practically delivered in the given deployment scenario.