# 3D Void Handling Geographic P2P-RPL for Indoor Multi-Hop IR-UWB Networks
## 4 Performance Evaluation  
The performance results of the cooperative multi-hop self-positioning system and the GVA-P2P-RPL protocol in 3D IR-UWB networks are evaluated. Both experiments are simulated by configuring the radio characteristics of Decawave's DW1000 UWB radio chip [22], which follows the IEEE 802.15.4 standard [23,24]. To apply real UWB device's network delay characteristics in the routing simulations, we calculated transmission delays of the P2P-DIO message and P2P-DRO message according to the model of the UWB frame transmission time (Figure 12) in the configured UWB parameter setting (Table 2). According to the model, a P2P-DIO message of 66 bytes payload requires PPDU (PHY protocol data unit) frame transmission delay of 276.7 us and a P2P-DRO message of 38 bytes requires a PPDU frame transmission delay of 233.6 us. To validate the PPDU frame transmission delay calculation results of the model, a testbed experiment with Decawave DW1000 modules was conducted, where we measured the end-to-end network delay for hop lengths varying from 1 to 4 between the source node and the destination node. As a result, an average one-hop network delay of 259.3 us was obtained. Since the average of the calculated P2P-DIO message and P2P-DRO message transmission delay is 255.2 us, the average of the sum of the one-hop processing delay, queuing delay and propagation delay is approximately 4.1 us.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline UWB Channel Number & 5 \\ Center Frequency & 6489.6 MHz \\ Band & 6240–6739.2 MHz \\ Bandwidth & 499.2 MHz \\ Pulse Repetition Frequency (PRF) & 16 MHz \\ Data Rate & 6.81 Mbps \\ Number of symbols in the preamble & 128 \\ Transmission time of the Synchronization Header (SHR) (\(T_{SHR}\)) & 135.13 us \\ Transmission time of the PHY Header (PHR) (\(T_{PHR}\)) & 21.54 us \\ Data symbol duration (\(T_{dsym}\)) & 128.21 ns \\ \hline \hline \end{tabular}
\end{table}
Table 2: UWB parameter setting.  
Figure 11: Adaptive listen-only periods for adaptive trickle timer in 3D GVA-P2P-RPL.  
The self-positioning simulation is implemented and conducted on Java. For routing performance evaluation, the route discovery success ratio, routing overheads, route discovery time and hop count are selected as the main routing performance metrics. The route discovery success ratio result shows the reliable routing ability of the proposed algorithm in both void-free and void-apparent networks. The low routing overhead result is presented to prove the high energy efficiency for operations. The low route discovery time is observed, which shows the fast routing ability in real-time implementations. The proposed algorithm achieves a slightly higher hop count than the other compared routing protocols, which indicates that it can still discover near-optimal routes with much low routing overheads. P2P-RPL, PF-P2P-RPL and ER-RPL results are compared to prove the strengths of the proposed GVA-P2P-RPL routing algorithm against the state-of-the-art RPL-based P2P routing methods. The routing simulations are implemented on the Cooja network simulator on the Contiki operating system platform [25]. P2P-RPL simulation is conducted on the P2P-RPL standard implementation [26] which is a modified version of the ContikiRPL [25] library. PF-P2P-RPL, ER-RPL and GVA-P2P-RPL simulations are conducted by modifying the P2P-RPL standard implementation.