# UWB Localization with Battery-Powered Wireless Backbone for Drone-Based Inventory Management
## 5 System Performance Evaluation
### Maximum Communication Range  
The maximum communication range determines how many anchor nodes should be installed, which is crucial for cost-efficient deployments in large warehouses. The maximum communication and maximum interference range is defined by the threshold value for distance or sensitivity power level after which the packet cannot be decoded or detected anymore. The sensitivity level can vary when the modulation setting is changed [32], and the distance threshold can increase when increasing  
\begin{table}
\begin{tabular}{l c c c c c c} \hline \hline  & & \multicolumn{2}{c}{**Stand-by Anchor**} & \multicolumn{2}{c}{**Active Anchor**} & \multicolumn{2}{c}{**Always-RX Anchor**} \\
**Power State** & \(\mathbf{I_{\text{arg}}}\) **[mA]** & \multicolumn{2}{c}{**(No Slot)**} & \multicolumn{2}{c}{**(One Slot)**} & \multicolumn{2}{c}{**(Traditional Approach)**} \\ \cline{3-7}  & \% & **mA** & \% & **mA** & **\%** & **mA** \\ \hline UWB RX & 133 & - & - & 10.3 & 13.699 & 89.1 & 118.51 \\ UWB TX & 102 & - & - & 5 & 5.1 & 10.9 & 11.12 \\ UWB SLEEP & 0.001 & 100 & 0.001 & 84.7 & 0.001 & - & - \\ SubGHz RX & 23 & 14.8 & 3.404 & 14.9 & 3.427 & - & - \\ SubGHz TX & 45 & - & - & 9.8 & 4.41 & - & - \\ SubGHz SLEEP & 0.005 & 85.2 & 0.004 & 75.3 & 0.004 & - & - \\
**Superframe** & & 100 & **3.409** & 100 & **26.641** & 100 & **129.63** \\ \hline \hline \end{tabular}
\end{table}
Table 8: Current consumption of the anchor nodes in different power states with different MAC implementations. The last line shows the total current consumption for the complete superframe.  
Figure 7: Cumulative distribution function of the ranging errors for different ranging distances.  
tx transmission power level. The signal power that arrives at the receiver has suffered from path loss can be expressed Friis' path loss formula:  
\[P_{r}[dBm]=P_{t}[dBm]+G[dB]-L[dB]-20\log_{10}(\frac{4\pi f_{c}d}{c}) \tag{14}\]  
where \(P_{r}\) and \(P_{T}\) are the received and the transmitted power, \(G\) includes the antenna gains, L includes any PCB losses in the system, \(f_{c}\) is the center frequency of the channel and \(d\) is the distance in meters between the transmitter and the receiver.  
Because typical radio waves are reflected and obstructed by all objects illuminated by the transmitter antenna, the signal is also exposed to the two ray ground model. The total received energy can be modeled as the vector sum of the direct transmitted wave and one ground reflected wave. The two waves are added constructively or destructively depending on their phase difference at the receiver. The magnitude and phase of the direct transmitted wave varies with distance traveled. The magnitude of the reflected wave depends on total traveled distance and the reflection coefficient.  
Figure 7(a) shows the path loss for the UWB radio calculated both theoretically (green line) and validated experimentally (red dots). Our current UWB board with omni-directional antenna allows reliable ranging up to 80 m, and occasionally (disregarding the Fresnel zone) up to 220 m. Figure 7(b) shows that the theoretical range of the sub-GHz radio goes up to several kilometers. As such, it is possible to install large warehouses without requiring excessive number of anchor nodes or cabling.