# Device-Free Localization and Identification Using Sub-GHz Passive Radio Mapping
## 2 Experimental Setup and Methodology
### Experiment Environment and Description  
We installed our RF sensor network and performed our experiments in a 42 m\({}^{2}\) office environment. Tables and other furniture were present near the windows, but the vast majority of the environment was unobstructed. Fifteen small, colorful cones were placed inside the environment to indicate possible locations where targets could be present. A schematic overview of the node locations and potential target locations is shown in Figure 2. Figure 3 shows a photograph of the environment.  
Figure 2: A schematic overview of the experimental environment.  
Each experimental measurement consisted of a human target being present at one of the fifteen locations indicated by the cones, while the RF sensor network collected RSS data. The duration of a measurement depended on whether the data was to be used for training (fingerprint database creation) or for evaluation. Training measurements lasted for 30 s during which the participant was instructed to randomly rotate and move in place. Each evaluation measurement took only 10 s and the participants had to stand still while facing the offices shown in the photograph in Figure 3. In practice, this led to approximately 50 measurement vectors for each evaluation measurement and 150 measurement vectors for each training measurement.  
Figure 4 uses data from the 868 MHz 30-second training measurements to illustrate the impact the presence of a target can have on the signal strengths of the communication links, which is the crux of the entire passive fingerprinting technique. This figure shows the average RSS values with which communication between node 1 and every other node occurs, for four different locations at which a target could be present. The impact of target presence in the direct line-of-sight of a link tends to be rather intuitive. For example, when a target is present in the upper or lower left corner of the environment, the link formed by nodes 1 and 12 is attenuated by 4 to 7 dB when compared to a target being present in the upper or lower right corner. Less intuitive differences which are likely the result of complex multipath effects exist as well, as illustrated by the link between nodes 1 and 4. When a target is present in the lower left corner, the link is attenuated by 3 to 4 dB when compared to all other scenarios, despite the target not being located in the direct line-of-sight. A major advantage of a fingerprinting approach lies in the fact that all of these aspects do not need to be explicitly modeled.  
For all of our experiments, we had the help of six volunteers who acted as human targets. Some of them differed significantly from each other in regards to body type. Table 1 shows the weight and height of each participant as measured at the time of the experiments. Training measurements were performed for four of the participants, while evaluation measurements were performed for all 6. The main reason for doing so was that we also wished to investigate the presence of targets for whom no training data existed.  
All of the collected RSS data was stored in a database from which it could be retrieved for later analysis.  
An overview of the most important experiment parameters can be found in Table 2. In the next section, we will describe the analyses we performed regarding target localization.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Participant \#** & **1** & **2** & **3** & **4** & **5** & **6** \\ \hline Height (cm) & 159 & 191 & 183 & 180 & 169 & 186 \\ \hline Weight (kg) & 55.6 & 103.4 & 86.3 & 92.4 & 59.4 & 92.5 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Height and weight of the six volunteers who participated in our experiments.  
Figure 3: A photograph of the office environment. It should be noted that both the nodes and cones had not yet been placed in their final locations as indicated by the schematic overview in Figure 2.