## 3 Implementation of X-IoCA for SAR Missions: SAR-IoCA
### Internet of Robotics Things
#### 3.1.2 A Hybrid and Heterogenous Wireless Transceiver Network (H2 WTN)  
The proposed H2 WTN implementation considers two different technologies (LoRa and BLE). We selected LoRa as an appropiate LPWAN technology due to its low-power and long-range properties [52; 53; 54; 55], which are suitable for many applications [56]. Thus, we propose a LoRa H-WSN that makes use of the LoRaWAN protocol using class A devices, which is the lowest power consumption way of generating traffic [57; 58], suitable for soft real-time applications [59]. Moreover, LoRa technology enables geolocation techniques without GPS by fingerprinting [60], Kalman filtering [61], or multilateration algorithms using concentrator-nodes timestamps from the received packets [62]. Furthermore, a short-range network based on BLE allows BLE receivers to detect close agents carrying BLE transmitters through their corresponding static media access control (MAC).  
H2 WTN transceivers serve to detect and locate agents or victims while transmitting environmental information about their surroundings. An H-WSN, composed of static and mobile sensor-nodes based on LoRa technology, provides both MEC centers (FCC and BCC) with relevant information about the surroundings of the SAR agents. In addition, this LoRa H-WSN (Figure 3) provides the MEC centers with information for identifying risks in the area of operations. For example, the internal accelerometer of a sensor-node could detect an earthquake; temperature and humidity sensors could detect a fire; rain gauges could detect possible floods; or noise and gases sensors could detect risks related to terrorist attacks. To respond to this diversity of scenarios, event activation was implemented through the use of these LoRa sensor-nodes, which are grouped together, forming sensory groups (SG), in different locations in the terrain, either static or carried by an agent (rescue dog, UGV or UAV [63]). LoRa packets are received from concentrator-nodes, which can also be mobile or static. The information captured by this H-WSN is managed at the MEC centers.  
Moreover, a network of BLE transceivers was deployed to emulate victims in the area of operations, whether they are on the surface or buried. The network is composed of several ESP32 boards, acting as transmitter beacons, capable of keeping their MAC fixed, which is not possible with smartphones. The detection elements are different BLE scanners onboard robotic agents capable of detecting the presence of potential victims (PV) in their coverage area, as their MAC does not change. An external database is synchronized with each of the scanners, which communicate their data via MQTT and storing the information on an SD card. Furthermore, the position of the robots was known at all times with differential GPS, as well as that of the BLE nodes, which we obtained when they were placed on the terrain, so ground truth for relative positions was available. In addition to real time BLE Meshlium scans, offline data analysis could also be performed with BLE ESP32 RSSI readings stored in the SD cards. This network complements the LoRa network, resulting in a hybrid and heterogeneous wireless transceiver network, where the BLE devices focus on PV detecting, while the LoRa sensor nodes are used to detect risks and plan paths for the UGVs.