# Fast Deployment of a UWB-Based IPS for Emergency Response Operations
## 2 State of the Art
### Indoor Positioning Systems (IPSs)  
Since its release for civilian use in the 1990s, GPS's indisputable success in outdoor positioning and navigation systems has been mainly substantiated by its global availability and cost-effectiveness. Nonetheless, degradation or even unavailability of satellite signals in indoor scenarios make GPS unsuitable for the stringent accuracy requirements of fine localization. To be more specific, the typical accuracy for a smartphone's GPS receptor ranges from 5 to 10 meters depending on the environmental conditions, whereas most indoor applications preferably require mean accuracies around 1 to 2 m [16; 17]. The need for filling the gap left by GPS resulted in the emergence of the IPS concept, which encompasses any automatic system responsible for identifying, locating, and tracking people and objects within a pre-defined area on a real-time basis. Depending on the kind of technology and density of the deployed sensing devices, an IPS may provide different ways to express position and accuracy levels [18]:  
* **Absolute position:** The coordinates (and altitude) of the tracked object. The accuracy is measured quantitatively; for instance, from _meter-level_ to _centimeter-level_. * **Relative position:** The 2D or 3D distance to a fixed point. The accuracy is also expressed quantitatively. * **Symbolic position:** It implies the presence of the item in a specific area (for instance, _zone-level_ places it on the correct floor or within a pre-determined subarea, while _room-level_ does so in a specific room) or near something or someone. The current study only considers the use of an IPS to estimate the exact position of a person/object. It leaves out of the scope the usage of an IPS for proximity detection (e.g., _location at choke points_), where the outcome is to determine _what specific location you are near_. A large variety of IPS technologies has been proposed over the years, but none of them has achieved high prevalence over the rest [19]. Such is the heterogeneity of these technologies that they can be classified into the following fields: infrared, ultrasound, audible sound, magnetic field, optical and vision, radio frequency (RF), visible light, dead reckoning, and hybrid [20]. Figure 1 compares two of the most important features (range and accuracy) of the main positioning technologies. Infrared, ultrasound, optical and vision, and visible light technologies can only provide positioning estimations in line-of-sight (LOS) conditions; that is, when no obstacles or walls stand between the IPS infrastructure and the device or person to locate. This is particularly limiting in ER operations, as it would entail the installation and calibration of such a great amount of devices inside the target indoor environments, which, in addition, usually have poor visibility and acoustic conditions. Conversely, RF systems perform better in such environments, due to their ability to operate in non-line-of-sight (NLOS) conditions. In particular, most of the proposed wireless technologies to build an IPS over them are short-range (e.g., RFID, BLE, UWB, WiFi, and ZigBee) (see Table 1 for further details), because emerging long-range IoT technologies (e.g., Sigfox, LoRa, IEEE 802.11 ah, and Weightless, among others) report a low accuracy, especially in indoor environments [22]. Regardless, the unpredictable propagation of wireless signals and the associated delay deterioration in the presence of obstacles and/or interference have typically represented the main challenges for all these technologies [23]. of these systems is the fast-growing drift over time when operating alone, which requires either periodic recalibrations or combination with other technologies. Lastly, NASA has pioneered the use of probes to generate quasi-static magnetic fields that are read with a sensor placed outside the target scenario [26]. Unlike radio waves, these magnetic fields are not disturbed by metallic or other structures commonly found in building environments.