# HelpResponder--System for the Security of First Responder Interventions
## 2 State of the Art
### Location Estimation for Navigation and Firefighter Tracking  
On the one hand, regarding the navigation time in a burning building, researchers in [20] developed a platform to reduce the time with a multi-agent simultaneous localisation and mapping (SLAM) technique. The results indicated that the built map was more accurate than the map obtained using the conventional TSD-SLAM. Additionally, it builds the merged map more correctly by determining the proper parameters for online map merging. The problem is that SLAM is not the optimal solution when fire and smoke are present because typical SLAM revisits in closed trajectories cannot be done. It is necessary to explore other mixed solutions in this scenario [21]. On the other hand, there are some works [22; 23] that describe rescue operations and security issues due to earthquakes, harsh climate, etc. Supplying location and tracking systems is essential to save firefighters' lives during fire operations and speed up the rescue intervention. These works explained the deployment and monitoring of environmental parameters in outdoor environments. Future developments will include the implementation of the system in a heterogeneous scenario with obstacles. It will allow studying the behavior of the system reacting to different propagation of the IoT nodes signal and the obstacle avoidance movement for autonomous navigation systems and firefighters. Moreover, for beacon-based indoor locations, the most commonly used wireless technologiesare WiFi, Bluetooth, and ultrasound [24; 25; 26], with ultrasound being the most accurate at centimeter-level RF-based solutions (WiFi and BLE), achieving accuracies of about 2 m. For instance, in [25], the authors used a network of beacons (fixed devices on the wall based on Bluetooth Low Energy) that remained connected to the device they wanted to locate, continuously estimating its position. However, this system's location depends on many parameters, such as interference, temperature, obstacles, and the signal's range. In the case of using the Zigbee positioning system in real Non-Line-of-Sight (NLOS) conditions, such as in large buildings with multiple walls that the RF signal has to penetrate, the accuracies dropped significantly to a minimum positioning error of 2 m [26]. There are other approaches to determine locations in indoor environments, such as those using LoRa (Long Range). Despite its robustness in open areas to provide stable and efficient communication, the use of Lora technologies in indoor environments is in an initial state and requires further study regarding the effect of signal propagation obstacles. Inertial sensing devices have many advantages, such as making sense independent from the environment. Many positioning proposals include the INS (Inertial Navigation System) approach, known as PDR (pedestrian dead-reckoning) when applied to monitor people while walking. An INS/PDR location solution uses inertial sensors, such as accelerometers and gyroscopes, usually integrated into an Inertial Measurement Unit (IMU). Data obtained from these sensors need post-processing, which includes integration calculations, gravity compensation, bias removal, and filtering to get proper motion (3D position) and pose (3D orientation) information [27]. There are numerous projects in this area. New Round-Trip Time-of-Flight technology such as Ultra-Wide-band (UWB) ranging is also a good complement for improving positioning accuracy at a decimeter error level [28]. Additionally, to remove the drift in inertial estimations, such as the principal building direction approach (iHDE and MiHDE) and the simulation of IMU signals for particular IMU fixes on a person's body [29]. Other heuristics using an IMU and beacons (RFID, WiFi, BLE) are combined in [30; 31], which decreases the positioning error to less than 1 m. They compare different algorithms for step detection, stride calculation, and positioning, achieving maximum errors of 5% of the total travelled distance and using a low-priced Inertial Measurement Unit (IMU).