# Experimental Evaluation of a LoRa Wildlife Monitoring Network in a Forest Vegetation Area
## 2 State-of-the-Art and Related Works
### LPWAN Technologies for Smart Agriculture and Wildlife Monitoring  
Following the rapid IoT market expansion, LPWAN has become one of the faster-growing areas in IoT, especially for smart agriculture applications. The choice of a LPWAN technology is dependent on the specific application area and its specific requirements such as data rate, range, energy budget, frequency band, bidirectionality, network, cost, scalability, security, among others. The classification of existing LPWAN technologies is illustrated in Figure 1. The LPWAN technologies can be broadly classified into two categories, 3 GPP technologies (e.g., NB-IoT, LTE-M-IoT, EC-GSM-IoT) and non-3 GPP technologies (e.g., LoRa, Sigfox, Ingenu RPMA, DASH7). We only describe in detail LoRa and LoRaWAN, where other LPWAN technologies mentioned in Figure 1 are referenced in [11; 12; 21; 22; 23; 24; 25]. LoRa has robustness over a long distance due to the chirp spreading spectrum (CSS), where the physical channel is logically separated by the spreading factors (SF) due to their orthogonality. The carrier frequency varies over a designated amount of time, thus achieving low power and long-range communication links [15]. A network structure based on LoRaWAN protocol consists of four individual layers, namely the end devices, the gateway, the network server and the application server. A brief description of each layer is highlighted below:  
Figure 1: Low Power Wide Area Network Classification. * _End Nodes_ are devices embedded with LoRa chips. There are 3 classes of end-devices: Class A (for All), B (for Beacon) and C (for Continuously listening), each associated with a different operating mode. The devices broadcast their sensor values to all gateways in all range which forward data packets to a single network server over an IP based network. * _Gateways_ are intermediate devices running an operating system that forward data packets coming from the end nodes to a network server over an IP-based backhaul network. In a LoRaWAN deployment, there can be multiple gateways receiving data packets from a LoRa end device. Usually, LoRa gateways are publicly available and transparently connected to a cloud community service. * _Network Server_ performs a lot of functions, such as filtering redundant packets, performing an adaptive rate, performing security checks and generally managing the network. * _Application Server_ is responsible for the encryption, decryption, and processing of data from the network server. The application server allows users to access and manage the gateway, nodes and applications. The LoRa technology is defined by the main parameters, which are spreading factor, bandwidth and code rate, which are configured to adapt to the working scenario. We briefly describe each parameter below:  
* _Bandwidth (BW)_ is the range of transmission frequencies varying between 7.8 kHz and 500 kHz. The greater the bandwidth value is, the more the transmitted data, thus reducing transmission time and resulting in lower sensitivity. * _Spreading factor (SF)_ characterizes the number of bits sent in each LoRa symbol. SF take values between 7 and 12 resulting in different time-on-air (_ToA_), thus, varying receiver sensitivity. Having a higher \(SF\) such as \(SF=12\) denotes a longer range with low bit rate and better receiver sensitivity. The relationship between the LoRa transmission (_ToA_) and the used LoRa parameters is denoted as \(\textit{ToA}=2^{SF}/BW\). * _Transmitted Power (TP)_: By default, the maximum effective isotropic radiated power (EIRP) for LoRa end-device operating in the 433 MHz and 868 MHz band are 12.15 dBm and 16 dBm respectively. * _Code rate (CR)_ is related to the number of redundant bits used to improve the packet error rate in the presence of noise and interference. In other words, LoRa provides forward error correction capability by adding extra redundant bits to improve the robustness of transmission. The possible values of \(CR\) are \(4/5\), \(4/6\), \(4/7\) and \(4/8\).