## 3 LoRa Modulation Evaluation
This is a pessimistic approach and represents the evaluation of a boundary situation which is, however, often met with during the practical implementations of the LoRa technology. Due to the fact that one of the main advantages of the LoRa technology consists in large communication distances of the order of tens of kilometers; the operators of these networks will choose an SF with the maximum value available and implicitly ensuring communication at long distances, from an incentive to minimize the number of gateways (e.g., because of cost) which serves a certain area. This feature determines a longer transmission time (due to the LoRa modulation mechanism) and implicitly the increase of probability of a collision occurring [28]. The results of these simulation scenarios are depicted in Figure 4.  
Thus, another varied parameter is the payload size associated with the LoRa packet ranging from the minimum value of 1 byte to a maximum LoRa specification defined value of 243 bytes. From the obtained results, it can be observed that with SIR (Signal to Interference Ratio) decrease the analyzed BER (Bit Error Rate) parameter increases, an expected aspect due to the increase of the transmission-related time. When a larger channel bandwidth is used, the performance level and the resistance to interferences is considerably enhanced. Furthermore, one can see that once the packet payload is increased, the resistance to interferences is not drastically affected, with results being similar. Since the studied scenario is of a worst-case type (e.g., use of SF12) and of best-case scenario (e.g., use of SF6), the payload influence is not a determining factor in the final overall result. This result is a surprising one, due to the fact that the answer to a wireless communication channel is oftentimes dependent on network packet dimension. A similar result has been reported in Reference [29]. Thanks to the coding and spectrum spreading mechanism patented by Semtech, the influence of payload over the level of performance is minimized. In the eventuality in which the receiver and the transmitter are synchronized, the influence of payload over performance level is minimal when talking about co-existence. Figure 5 presents the performance analysis for SF8 when using a packet payload of 60 bytes. The SF is varied from SF8 to SF10, and the analyzed communication channel bandwidth is 500 kHz. Figure 3: Bit Error Rate (BER) parameter for SF12, bandwidth (BW) = 125 kHz. The figure depicts the BER parameter when the SF12 spreading factor is used for a 125 kHz channel bandwidth. One can observe a decrease in performance. This scenario was included in order to create a more accurate overview of the impact of SF selection for LoRa sensors on the performance level of the communication link, since the previous simulation scenarios were focused on the most favorable and unfavorable use cases. Figure 4: _Cont._  
To investigate the influence of the payload on the resistance to interferences, another simulation scenario involving the BER parameter evaluation for a specific SF by varying the payload size while  
Figure 4: The analysis of performance based on SF, BW and packet payload variation. The SF is varied from SF6 to SF12 and the bandwidths analyzed are 125 kHz and 500 kHz, respectively. In the evaluation scenarios, the payload is varied from 1 byte to 243 bytes. Figure 5: The analysis of performance for SF8 when using a packet payload of 60 bytes. The SF is varied from SF8 to SF10, and the analyzed bandwidth is 500 kHz. maintaining the same BW value was performed. The payload was varied from 60 bytes to 120 bytes and 180 bytes, respectively. The selected communication channel bandwidth in this setup is 125 kHz. In Figure 6, we can observe the obtained results. As stated before, one can observe the payload does not significantly influence the performance level of communication. We consider this payload analysis to be one of the main contributions of this work.