# Tracking and Monitoring System Based on LoRa Technology for Lightweight Boats
## 3 LoRa  
LoRa is a novel transmission technology that enables long communications of more than 10 miles with reduced power consumption that permits battery's lifetimes of about 10 years [7]. To achieve these goals, LoRa makes use of a series of strategies: (i) reduced transmission bit-rates; (ii) use of low frequency bands (sub-GHz bands); and (iii) limited end-devices' communication capabilities. Regarding the former, LoRa employs limited data-rates of few kilobits per second (kbps) that allow the use of high-sensitive receivers. Thereby, the receiving equipment is capable of decoding the transmitted information when it is received at a very low signal-level. This transmission robustness is enabled by the characteristics of the LoRa modulation, which is a proprietary modulation by Semtech (Camarillo, CA, USA) based on the Chirp Spread Spectrum (CSS) modulation technique [26]. The use of low frequency bands (868 MHz and 911 MHz in Europe and America, respectively) improves the transmission range and penetration in comparison with other typical higher frequency bands such as 2.4 GHz [27]. In addition, low frequency instruments are cheaper than those operating at higher frequencies. It is important to note that LoRa uses Industrial, Scientific, and Medical (ISM) frequency bands, which are unlicensed, so anyone can freely transmit on them. Finally, in order to save energy, the communications in LoRa systems are limited in two different ways. First, the use of unlicensed frequency bands that host a great amount of devices, so that the number of messages that each node can send per day is limited for avoiding the overload of the band (duty cycle). In addition, the payload length of each packet is also limited due to the low data-rate of the transmissions. The use of long packets would lead to very long time-on-airs hence occupying the shared transmission medium for a very long time. Observe that both transmission limitations help to reduce the power consumption of the communication modules.  
One of the most valued characteristics of LoRa is its adaptability to different transmission needs. To this end, LoRa presents three configuration parameters, namely, Spreading Factor (SF), Coding Rate (CR), and bandwidth (BW). The SF indicates the grade of spreading of the transmitted signal with respect to the original one--the longest spreading, the greatest transmission robustness, but the lowest effective data-rate. The CR determines the amount of redundant information included in the transmitted packet. This extra information is employed for reconstructing the received data in case of receiving the packet partially corrupted. Employing high CR leads to an improved system robustness but at the expense of introducing extra overhead in the communication process. Finally, LoRa permits the use of different BW, although the most employed is 125 kHz. Other values such as 250 kHz or 500 kHz are also supported.  
From a network architecture perspective, there is an upper layer so-called LoRaWAN (LoRa Wide Area Network) that defines the network topology or security mechanisms, among other aspects (Figure 2). Similar to all LP-WAN solutions, LoRaWAN proposes a star or star-of-stars topology (Figure 3). This architecture is enabled by the long links established between the gateway or base station and the end-nodes. This configuration avoids complex network organizations such as mesh or hierarchical networks because the end-devices directly communicate with the base station without the support of the rest of nodes composing the network. Note that, although in our real deployment we adopted the LoRaWAN architecture (all the boats directly connected to a common gateway), from a networking point of view, we just made use of the LoRa layer, hence avoiding extra overhead introduced by LoRaWAN.  
Figure 2: LoRaWAN (Long Range Wide Area Network) stack.