## 2 Related Work  
### Open Source Hardware  
A plethora of UWB localization systems already exist. However, the majority is commercialized and not intended for scientific research purposes. This paper mainly focuses on open source systems. An overview of these systems is given in Table 1. The EVB1000 board from Decawave is also included in the comparison, as this board is specifically developed for research purposes and is purchasable in kits of four devices for $990. The PolyPoint project [10] introduced multiple antennas to avoid the effect of polarization mismatch between sender and receiver. The Atlas project [11] designed a UWB node starting from the DWM1000 [12], in combination with the STM32F103C8T6 Evaluation Board known as \"Blue Pill\". Both the hardware [13] and accompanying localization software [14] are open source. Different drivers for the DW1000 and DWM1000 [12] are written and are publicly available on GitHub [15; 16]. The GitHub library [17] contains hardware design files. \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Project**} & \multirow{2}{*}{**Academic/**} & \multirow{2}{*}{**External**} & \multirow{2}{*}{**Extra**} & \multicolumn{3}{c}{**Open Source**} \\ \cline{5-8}  & & & & & **HO** & **Localization** & **IoT Network** \\ \hline PolyPoint [10] & academic & & ✓(BLE) & ✓ & ✓ & \\ Atlas [13; 14] & academic & & ✓ & ✓ & & \\ Arduino DW1000 [15] & academic & & & & ✓ & \\ DecaDuino [16] & academic & & & & ✓ & \\ KDWM1000 [18] & academic & & & ✓ & ✓ & \\ uwb\_localization [17] & academic & & ✓(Arduino Mini) & ✓ & & \\ EVB1000 [12] & commercial & ✓ & & & & \\ \hline Wi-PoS & academic & ✓ & ✓(sub-GHz & ✓ & ✓ & ✓ \\  & & & and 2.4 GHz) & & & \\ \hline \end{tabular}
\end{table} 
Table 1: Overview of existing open source UWB localization systems. Wi-PoSSupports several extra radio modules, an external antenna interface, and Open Source Hardware, localization algorithm, and network stack. The unique features of Wi-PoS, emphasized in the introduction, are included in Table 1. The majority of the hardware solutions is based on the DWM1000 module with integrated surface mount dielectric (SMD) chip antenna and does not support flexible interfacing with external antennas. The use of an external antenna inherently complicates the design of the RF front end, but many use cases can benefit from it. Mobile nodes typically require omnidirectional antennas, while anchor nodes can benefit from directional antennas. The influence of the integration platform will be minimized during antenna design, requiring tailoring for specific use cases. The only localization system that also includes this feature is the evaluation board from Decawave (EVB1000). The integration of sub-GHz is a unique feature. Some other UWB localization solutions use an extra radio, but with a shorter range wireless technology. The range of sub-GHz (>1.5 km) is significantly bigger than the WiFi range (>150 m), improving the scalability of the localization system [19] and developing localization systems with large coverage areas. A mobile tag can communicate with a central routing node at large distances, allowing the central node to control the localization schemes [7]. The presented hardware platform was evaluated on different performance characteristics. Several research papers have already been published about the comparison of different UWB localization systems. The Bespoon, Decawave, and Ubisense systems are compared in Reference [20], while other published work comparing different UWB localization systems, includes Reference [21, 22]. These comparative studies mainly focus on the achieved ranging accuracy in different operating conditions, but they use different ranging techniques (angle of arrival, time of flight), or the various UWB localization systems are compared in different measurement environments. The general conclusion the researchers take is that the Decawave system is slightly better in line-of-sight (LOS) conditions and more reliable in non-line-of-sight (NLOS) than the other systems (Bespoon and Ubisense).