# Location-Aware Point-to-Point RPL in Indoor IR-UWB Networks
## 2 Related Works  
The improvement of the route quality performance for RPL and P2P-RPL depends on the network topology for route discovery. The cost associated with the P2P-RPL route discovery is very costly in terms of energy consumption especially for LLNs, because all nodes in the network need to participate in the formation of temporary DODAGs during the route discovery. The Lightweight On-demand Ad hoc Distance vector routing protocol, Next Generation (LOADng) is an ad hoc on-demand distance vector routing for LLNs [12]. LOADng supports P2P, point-to-multipoint (P2 MP), and MP2P traffic patterns. LOADng disseminates the route discovery packets throughout the whole network like P2P-RPL. Geographic routing uses the location information of nodes to forward data packets with the greedy algorithm. A node chooses the closest node to the destination as the next hop to forward the data packets. Geographic routing shows the routing problem for the selection of the stable next hop in LLNs. Geographic routing has to exchange the one hop or even two hop neighbor table periodically to update the location information through the whole network. The cost is huge in terms of energy consumption for LLN environments [13]. Energy-Efficient Region-based Routing Protocol for Low-Power and Lossy Networks (ER-RPL) is designed to use the existing DODAG structure of RPL for the P2P route discovery [4]. Through the self-localization procedure, only a portion of nodes perform the route discovery packet forwarding. The region-based route discovery and region-to-region routing without route discovery procedure are introduced. A distributed self-regioning algorithm is proposed to estimate the region of each node. In ER-RPL, the estimated location accuracy severely depends on the network configurations, which may result in the routing performance degradation from the inaccurate location information. [PERSON] et al. proposed Mobility-Aware Energy-Efficient Routing (MAEER) by using the position information of each node in the network [14]. MAEER provides mobility support and P2P route discovery with low energy consumption. The location information comes from the distributive self-regioning based on simple DV-hop algorithm. MAEER keeps track of location information of each node and provides DODAG Information Solicitation (DIS) and DODAG Information Object (DIO) managements. If the nodes are not distributed uniformly, DV-hop based localization scheme gives the inaccurate location information for each node. RPL routing for mobile low power wireless sensor networks using Corona mechanism (Co-RPL) is based on the Corona algorithm to estimate the location of each node [15]. DAG root sends DIO periodically without trickle timer for continuous configuration changes. The DIO transmission interval is controlled based on the speed of the nodes. RPL protocol can capture the frequent topology changes. Co-RPL suffers from the high power consumption and the large amount of control overhead due to the periodical broadcasting. [PERSON] et al. proposed KP-RPL which exploits a positioning method based on the confidence regions defined by the mobile nodes in order to manage node mobility [16]. The standard Kalman filter predicts the position and enhances the accuracy. The standard Kalman filter is applied for the linear model, the non-linear trajectory of mobile nodes causes the inaccurate positioning results. The direct path UWB signal attenuation due to obstacles reduces the possibility of direct path signal detection at the receiver, which degrades the accuracy of the flight time-based ranging method [11]. The failure of direct path signal detection significantly deteriorates the inter-node distance measurement performance in multilateration based positioning algorithms [17]. This problem is more serious in UWB devices, which have to follow the power spectral density (PSD) regulation to mitigate the interference problem with other narrowband systems.