# An Internet of Things (IoT) Application on Volcano Monitoring
## Appendix A  
The LoRa solution can be labeled CDMA (Code Division Multiple Access), using different spreading factors and coding rates (see Appendix A) to multiplex signals on a single frequency. This not only increases the network capacity, but also allows for the dynamic adaptation of device data rates. Spreading a narrowband signal over a wide band results in less efficient use of the spectrum. However, this problem is typically overcome by the use of multiple orthogonal sequences. As long as multiple end devices use different channels and/or orthogonal sequences, everything can be decoded concurrently, resulting in a higher overall network capacity. The different parameters that define the characteristics of LoRa modulation are described below:  
* Transmission Power (TP) due to limits in hardware implementation is restricted from 2 dBm to 20 dBm, and for higher levels than 17 dBm, only 1% duty cycle can be used
* Carrier Frequency (CF) is the center frequency that can be programmed in steps of 61 Hz from 137 MHz to 1020 MHz. In some LoRa chips, this frequency range is limited between 860 MHz and 1020 MHz
* Bandwidth (BW): The higher it is, the higher the data rate (thus the shorter time on air); however, sensitivity decreases. LoRa provides three selectable BWs: 125 kHz, 250 kHz, and 500 kHz. Data is sent out at a chip rate equal to the bandwidth in chips per second per Hertz; a bandwidth of 125 kHz corresponds to a chip rate of 125 kcps. * Coding Rate (CR) refers to the proportion of the transmitted bits that actually carries information. Forward error correction (FEC) techniques are used in LoRa to further increase the receiver sensitivity, which is done by encoding 4-bit data with redundancies into 5-bit, 6-bit, 7-bit, or 8-bit. Using this redundancy will allow the LoRa signal to endure short interferences. The LoRa allowed coding rate values are 4/5, 4/6, 4/7, and 4/8. The more correction bits are used, the easier the data can be corrected, but the duration for the transmission is higher, and the effective data rate is lower. * Spreading Factor (SF) is the ratio between the symbol rate and chip rate (a LoRa symbol is composed of 2 SF chips). Selecting SF from 6 to 12, radio communications with different SF values are orthogonal to each other. SF must be known in advance by the transmitter and receiver in order to detect the message preamble (in other words, to detect at least 4.25 symbols), as the preamble size scales with SF, and there is no single preamble for all SFs. A higher SF increases the signal-to-noise ratio (SNR), and thus the sensitivity and range, but also increases the packet airtime. With the same BW, a longer time on air obviously results in less data transmitted per unit of time. Each increase in SF halves the transmission rate, and hence doubles the transmission duration and ultimately energy consumption. The radio communications under different SF are orthogonal to each other, and thus, the network separation by employing different SF is possible. This way, LoRa symbols can be simultaneously transmitted and received on a same channel without interference. Orthogonality can also be achieved by using different combinations between SF and BW. However, it is necessary to take into account that all the combinations are not orthogonal [93]. Moreover, communication between two elements is only possible if both have the same configuration parameters. The selection of transmission parameters has an impact on communication performance (transmission range, resilience to interference, and energy consumption of the device). In most situations, it is desirable to balance communication performance and energy consumption, as node devices are battery powered, and it is a goal to maximize lifetime. Obviously, TP has a direct impact on the energy consumption. Another factor determining the energy consumption is the required airtime to transmit a packet, which is dependent on the bitrate and packet size. The bitrate is determined by SF and BW.