## 3 LoRa Modulation Evaluation
The capture effect can be defined as the capacity of the receiver to decode a packet even when a collision between multiple packets occurs (usually the packet with the higher Signal-to-Noise Ratio is decoded). The spreading factors and settings, such as the bandwidth of the LoRa communication channel allow the theoretical orthogonal transmissions between the LoRa sensors; this aspect can prevent interferences between networks, but those mechanisms require further in-depth study and analysis. Concomitantly, the evaluation of the orthogonality of combinations between the spreading factor and communication channel bandwidth is analyzed in this work. Despite all this, the evaluation of performance level when it comes to simultaneous communications with the same or a different SF within the same LoRa communication channel represents a notable challenge. Furthermore, when a traffic increase occurs, this avalanche collision effect (particular to ALOHA network types characteristic of LoRa networks) triggers a decrease in performance level [21; 22]. The LoRa specification, as defined by Semtech, has seven spreading factors (SF6-SF12) and four different channel bandwidths (62.5 kHz, 125 kHz, 250 kHz and 500 kHz) following Semtech-defined LoRa specifications. In practice and current hardware implementations, SF can be varied from 7 to 12 with the employed BWs being 125 kHz, 250 kHz and 500 kHz. As per channel allocation possibilities are specified by one of the IoT platform named TTN (The Things Network) [23], there are a number of 9 channels that are defined in the EU zone within the SRD860 unlicensed frequency band that make the uplink operation possible. By the same specification, the 250 kHz channel bandwidth can be used only within channel number 2 with a central frequency of 868.3 MHz. Channel number 9 (with a central frequency of 868.8 MHz) is used for high-speed transmission and uses FSK (Frequency-Shift-Keying) modulation. Between specific spreading factors and various bandwidths, theoretical orthogonality and more importantly, non-orthogonality can be easily determined. Not all combinations of SF and BW are orthogonal [24]. Theoretically, if the same SF is used on the same communication channel, the level of performance decreases dramatically, as the orthogonality conditions are not met [25]. The LoRa communication model presented in Reference [26] has been integrated and modified in the present analysis. The initial model could only generate LoRa packets with a payload of 20 bytes. Due to the characteristics particular to the LoRa communication model, it is very probable that when two signals both modulated with the same spreading factor collide, the strongest of these signals will be correctly demodulated, due to the capture effect. The main drawback of the initial model [26] is in the lack of a modification option for the payload of the packet. Another drawback is the fact that the user cannot change the bandwidth of the communication channel. Considering those drawbacks, the first part of this paper presents the improvements in the model. Thus, the initial model [17], has been improved with the following additions: The packet payload customization, bandwidth of the communication channel and the central frequency of the communication channel selection. These improvements grant the model a high degree of adaptability, creating a powerful instrument in the evaluation of LoRa scalability. The modulated packet is then interfered in turn with a random LoRa packet modulated by a spreading factor, so that all possible variations are analyzed. The interfering packet is sent at random moments in time with an SIR (Signal-to-Interference Ratio) which increases by a 1 dB step starting from -30 dB. By implementing this mechanism, the BER (Bit Error Rate) characteristic can be determined, as a result of comparing later demodulated bits to initial modulated ones. It can be concluded that, the lower the spreading factor that interferes with the communication, the higher the SIR threshold necessary to obtain an admissible BER value.