# UWB Localization with Battery-Powered Wireless Backbone for Drone-Based Inventory Management
## 5 System Performance Evaluation
### Current Consumption  
Because UWB is known to be very energy consuming, it is advantageously to disable the UWB radio as much as possible, instead relying on the sub-GHz radio to wake the anchor nodes when needed.  
* The current consumption for transmission and reception on the UWB radio are depending on several PHY settings. Higher frequency channels consume more power than lower frequency channels. Long preamble, payload length and high datarate results in longer packet duration and thus more current demand. The exact current consumption in TX and RX can be found in the Decawave DW1000 user manual [32], and varies between 48 and 117 mA. In contrast, the UWB radio-chip consumes only 1 \(\upmu\)A in SLEEP-mode and only 100 nA in DEEPSLEEP (the chip can be woken up by setting a programmed sleep count or by using an external pin. This requires only the low power oscillator and the internal sleep counter to be active. To enable external micro-controller access, the lowest power state is the INIT-state, which consumes 4 mA. For full speed SPI access and internal clock, the IDLE-mode consumes 12 mA.)
* Also the current consumption of the CC1200 depends on the chosen output power (up to 16 dB) and the PHY settings of the radio. The consumption for the chip for reception varies from 17 to 23 mA and for transmission from 34 to 45 mA [35]. In SLEEP mode, it only consumes 0.5 \(\upmu\)A.  
The anchors can set their UWB radio in SLEEP-mode while they are not selected by the tag. Therefore, they only listen on the beginning of the superframe for the synchronization message using the sub-GHz radio. If we compare this to most UWB solutions, this is a significant reduction in current consumption, since these are constantly listening for preambles (which is the most energy consuming  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{2}{c}{**Theoretic Update**} & \multicolumn{2}{c}{**Experimental Update**} \\  & **Frequency [Hz]** & \multicolumn{2}{c}{**Frequency [Hz]**} \\ \hline  & Min. & Max. & Min. & Max. \\ Basic & 125 & 790 & 65 & 127 \\ Optimization I & 206 & 1035 & 98 & 178 \\ Optimization II & 284 & 1841 & 136 & 276 \\ Optimization III & 343 & 2892 & 166 & 372 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Localization update frequency for the UWB localization system, both theoretically (ignoring hardware dependent delays) and experimentally.  
\begin{table}
\begin{tabular}{l c c c} \hline \hline  & \(slot_{awb}\) & \(slot_{sync}\) & \(slot_{report}\) \\ \hline Slowest setting & 5400 \(\upmu\)s & 6800 \(\upmu\)s & 4000 \(\upmu\)s \\ Fastest setting & 2400 \(\upmu\)s & 3800 \(\upmu\)s & 2800 \(\upmu\)s \\ \hline \hline \end{tabular}
\end{table}
Table 7: Slot sizes for experimental update frequency.  
operation of UWB) of possible UWB-messages. The same is true for anchors which are selected to range with. These will only power on the UWB radio on the slots they are supposed to range on. The current consumption on the tag is much higher, since the tag is constantly transmitting or receiving to range with the anchors.  
The resulting current consumption (when more interested in the required power, the given current can be multiplied with the required voltage, which is 3.3 V) of the UWB radio and sub-GHz for the most energy consuming configuration (e.g., slowest setting) is shown in Table 8. Most commercial and academic anchor nodes continuously consume on average about 130 mA. In contrast, our anchor nodes consume only 3.4 mA when they are stand-by, and 26.6 mA when they are selected for ranging.