## 1 Introduction  
A mobile sensor network (MSN) [1; 2; 3] has opened a great promising area for various applications, such as localization, target tracking, disaster recovery, or search and rescue operations in a wild area where communication infrastructures can not be used. In such a network, a stable multi-hop communication is required for the effective operations of mobile sensors. For example, in search and rescue operations, mobile sensors which are carried by unmanned vehicles or emergency crew members need to send task-related data such as continuous images or real-time videos to the sink (base station) or other mobile sensors to share findings or status of the wounded personnel. Unfortunately, in a practical deployment for those operations, the performance of MSN is significantly degraded due to poor quality wireless links and link breakage, resulting from high node mobility, time-varying channel properties, and geographical constraints (e.g., obstacles). As a result, the network may not be able to provide a desired quality for the end-to-end data transfer. Due to high node mobility, routing protocols [4] that have been proposed for traditional wireless sensor networks are not suitable for MSNs. Instead, mobile ad-hoc routing protocols (e.g., AODV [5], DSR [6], OLSR [7], and greedy forwarding based schemes [8, 9]) may be used for MSNs. However, those protocols try to find a route by taking into consideration only the _given_ network topology. As a result, if the selected best path contains a wireless link with a poor quality and an alternative path cannot be discovered in the given topology, the network performance on the path will be limited by the link with the lowest quality. Even in the case that every link on the path initially has a good quality, it is possible that the quality of links can be lowered due to the lengthened distance between communicating peers as nodes move. In this paper, the use of robotic nodes is considered to overcome the limitations of existing ad hoc routing protocols. More specifically, in order to address of the low performance of MSN and provide a high-quality and mission-critical data transfer service, we propose a novel routing and relaying architecture namely _RoCoMAR_ (Robots' Controllable Mobility Aided Ad hoc Routing) that uses controllable mobility of robotic nodes, _i.e._, RoCoMAR controls the motion of robotic nodes during the network lifetime with the objective of maximizing the network throughput. To achieve the objective, RoCoMAR repeatedly performs _link reinforcement_ process until the required performance is achieved or no more performance gain can be obtained. In the link reinforcement process, the link with the lowest quality on the path is identified and a robotic node is placed at an optimal position to create high quality relay links that will replace the poor quality link. In this paper, PDR (packet delivery ratio) is used as an indicator of a link quality. On duty as a relay, the robotic node also performs _adaptive link maintenance_, where the robotic node keeps adjusting its position according to the network topology change due to movements of regular MSN nodes (e.g., sensor devices that are carried by unmanned vehicles or personnel such as crew members). The robotic node resigns as a relay if the quality of the original link, which used to have a poor quality, becomes high enough due to node mobility. In other words, a robotic node adaptively determines not only its position but also whether or not it should stay as a relay according to the network topology change. Figure 1 illustrates the overview of RoCoMAR. As shown in the example in Figure 1, the link with the lowest quality is identified and replaced with new links. For example, on the path from node \(S_{1}\) to the base-station (sink or command center), the link between node \(S_{1}\) and node \(C\) has the poorest quality. Then, a robotic node \(R_{1}\) is relocated between node \(S_{1}\) and node \(C\) and two new relay links will be created via node \(R_{1}\).