# Location-Aware Point-to-Point RPL in Indoor IR-UWB Networks
## 4 Location-Aware P2P-RPL for Indoor IR-UWB Based Network with Self Localization
#### Location-Aware P2P Route Discovery Forwarding Zone  
As the results of self-localization are obtained, all nodes have their own up-to-date position state. LA P2P-RPL defines the route discovery packet forwarding zone based on the position states of the source and destination nodes. If the estimated region of a node belongs to the route discovery forwarding zone, the node forwards a P2P route discovery packet to its neighbor nodes. The operation for LA P2P-RPL route discovery forwarding zone is shown in Figure 6.  
Assume that the source node (Src) tries to find the P2P route path to the destination node (Dst). In Figure 6, the Src sends the measurement request which includes its position state to the Dst along the existing DAG. Upon receiving the measurement request, the Dst checks whether the accumulated path cost inside the request message satisfies the constraints or not. If the cost is not satisfied to the constraints, the Dst initiates the LA P2P-RPL route discovery. As shown in Figure 6, the Dst defines the forwarding zone for P2P route discovery as the rectangular region that includes the current estimated position states of the Src and Dst nodes. We denote the forwarding zone position state \(\mathbf{x}_{  
Figure 6: The operation for Route Discovery Packet Forwarding Zone of Location-Aware (LA) P2P-RPL (**a**) Measurement request procedure (**b**) Forwarding zone determination (**c**) Route discovery packet forwarding (**d**) Data transmission.  
\[\mathbf{x}_{fwd}=\begin{bmatrix}x_{lb,fwd}\\ x_{ub,fwd}\\ y_{lb,fwd}\\ \end{bmatrix}=\begin{bmatrix}min(x_{lb,s},x_{lb,d})\\ max(x_{ub,s},x_{ub,d})\\ min(y_{lb,s},y_{lb,d})\\ max(y_{ub,s},y_{ub,d})\\ \end{bmatrix} \tag{19}\]  
where \(lb\), \(ub\), \(s\), \(d\) denotes low bound, upper bound, source, destination, respectively.  
Then, the Dst node initiates the route discovery by constructing a temporary DODAG rooted at itself. Since the P2P path between the Src and the Dst is required over asymmetric links and RPL routes are optimized for upward routing, we set the Dst node as the root to improve the end-to-end delivery in LLNs. Before disseminating a P2P-DIO message, the Dst node piggybacks \(\mathbf{x}_{fwd}\) on the message. Upon receiving P2P-DIO from its neighbor node, the intermediate node follows the procedure which is described in Figure 5. The node joins P2P route discovery only if there is an intersection between its estimated region and the forwarding zone. In Figure 6c, if the nodes that are not belong to the route discovery forwarding zone receive the P2P-DIO packet from the neighbor node, they simply discard the forwarding packet. Consequently, only small number of nodes which belong to the route discovery forwarding zone participate in the route discovery process, which reduces the network-wide route discovery packet flooding significantly. Once the Src node receives the P2P mode DIO message, the P2P path is established as the upward route to the root (Dst) of the temporary DODAG from the Src node as shown in Figure 6d. Then, the Src node sends the data packet along the discovered route to the Dst node.