# Fast Deployment of a UWB-Based IPS for Emergency Response Operations
## 4 Implementation
### Deployment  
A set of 6 anchors was deployed on the outside of the testbed building with a twofold objective: (1) ensuring that the beacons emitted by the _master_ are received by all the other anchors (whether directly or retransmitted by the _relays_) and (2) reaching full UWB coverage inside the building. To achieve this, apart from the _master_, two anchors needed to be set as _relays_, while the rest acted as _slaves_ (see Figure 6a). Note that a _relay_ is just an anchor that also retransmits beacons coming from the _master_.  
To facilitate the propagation of UWB signals not only on the ground floor of the building but also on the first floor, the anchors were mounted on tripods at a height of 2-3 m and their antennas always pointed at the center of the building. Such a height of the deployed infrastructure ensured visibility among the anchors, thus contributing to accelerate UWB network establishment and avoid synchronization problems. Nevertheless, the lack of height diversity limited tag positioning to X-Y coordinates. Figure 6b,c show the anchor deployment on the front and back side of the building, respectively.  
Figure 5: Interior of the building. (**a**) Ground floor. (**b**) First floor.  
As a rule of thumb, there is a series of recommendations to be applied in the anchor deployment of the proposed UWB-based IPS:  
* The UWB network infrastructure shall consist of at least 4 anchors (though multilateration can be achieved with only 3 elements, the extra one adds redundancy to the positioning system).
* The deployed anchors shall encircle the target building.
* The distance between two adjacent anchors shall be less than 30 m in LOS conditions.
* If the _master_ anchor is further than 30 m from an anchor or it has NLOS conditions, _relays_ shall be employed to ensure that the latter is properly receiving synchronization beacons.
* The anchors shall be placed at a height greater than 2 m to facilitate UWB signal propagation inside the building.
* Three consecutive anchors shall never be placed aligned in the same axis, because the multilateration algorithm could produce duplicate mirror positions or experience convergence issues.  
As for the GNSS-RTK self-location system, apart from the satellites and the GNSS ground-based reference station(s), the on-field deployed infrastructure comprises a single portable GNSS-RTK module, which minimizes the total cost. Nevertheless, there is scope to embed this module into each operating anchor and create a more compact device in future versions of this IPS.  
The GNSS-RTK module should be initially powered on for about 5 min in order to configure itself, that is, start detecting GNSS signals and receiving RTK corrections. Once the anchors are deployed, the GNSS-RTK module is connected to them consecutively. Each time the GNSS-RTK module is connected to an anchor, the latter sends its corresponding ID to the module and, after that, the self-location system starts.  
From that moment on, the GNSS-RTK module stores positions for one minute and then evaluates if they are accurate enough according to a predefined threshold. If so, the positioning is considered successful, so the module can be disconnected from the current anchor and moved to another one. Otherwise, the GNSS-RTK module should be disconnected and reconnected to the same anchor to restart the self-location system.  
Figure 6: Anchor deployment. (**a**) Top view. (**b**) Front view of the building. (**c**) Back view of the building.