# Collision Avoidance Geographic P2P-RPL in Multi-Hop Indoor Wireless Networks
## 2 Research Background
Geographic routing makes use of the locations of the nodes and relies mainly on a simple greedy forwarding strategy. In a greedy forwarding scheme, a router simply forwards a data packet to the neighbor that is closest to the destination. The geographic routing approach is largely known by its low control packet overhead, low route stretch, and scalability. However, this approach assumes sufficient network density, accurate localization, and significant link reliability. The existence of unreliable links leads to a drastic reduction of the packet delivery ratio or increased energy consumption if a retransmission mechanism is used [18]. [PERSON] et al. presented a geographic approach for large-scale 6 LoWPAN networks [19]. To better support P2P communication, they integrate a GOAFR (Greedy Other Adaptive Face Routing) algorithm [20] in the RPL protocol. The GOAFR algorithm is able to get closer to the optimum path with a high link density. On the other hand, in networks with low link density, RPL performs better and may find shorter paths than GOAFR. The loca tion inaccuracy causes routing failure. [PERSON] et al. combined RPL with geographic routing for P2P communication, where only nodes on the way to the destination node joined the route discovery procedure [21]. These geographic routing approaches, however, have the limitation that all nodes in the network must be static and need to have prior knowledge of the location. The use of mobile nodes is possible only when they are one hop away from a static node. [PERSON] et al. designed the Energy-Efficient Region-based Routing Protocol for Low-Power and Lossy Networks (ER-RPL), which exploits the region features of static networks to suppress flooding overhead [13]. ER-RPL obtains the location of each node through a self-configuration localization scheme and is designed to limit the search space for P2P route discovery by using the position information of each node in the network. The approach aims to reduce the amount of control packet overhead and energy consumption without harming the network's reliability. In ER-RPL, a network area is divided into a configurable number of non-overlapping regions, and each node belongs to one region. A distributed self-regioning algorithm based on a simple DV-hop algorithm is proposed for nodes to estimate the regions of themselves. Based on the estimated region information, only a portion of nodes join the route discovery procedure and forward route discovery packets. [PERSON] et al. proposed energy-efficient region source routing (ER-SR), which exploits a distributed energy region algorithm [22]. Based on the residual energy of the nodes, the proposed routing scheme selects a part of nodes with high energy as the source routing nodes and only source routing nodes participating in source routing procedure. The other nodes join the region of source routing node and transmit the data packet through the source routing node. The accuracy of the estimated region information severely depends on the network configurations. If the nodes are distributed non-uniformly, DV-hop-based localization schemes provide inaccurate location information for each node, resulting in routing performance degradation. To reduce the cost of P2P-RPL route discovery in terms of the control packet overhead, energy consumption, and fast network convergence time, we exploited the IR-UWB-based cooperative multi-hop positioning with smartphone INS tracking by particle filtering. The Collision Avoidance Geographic P2P-RPL algorithm is proposed with limiting the network search space for the desired route discovery based on the location information of the source and destination nodes. To decrease the delay in propagating P2P-DIO transmissions for route discovery, the listen-only period of the trickle algorithm is selected dynamically based on the physical location information of each node.