Node Relocation Techniques for Wireless Sensor Networks: A Short Survey <s> I. INTRODUCTION <s> This paper describes the concept of sensor networks which has been made viable by the convergence of micro-electro-mechanical systems technology, wireless communications and digital electronics. First, the sensing tasks and the potential sensor networks applications are explored, and a review of factors influencing the design of sensor networks is provided. Then, the communication architecture for sensor networks is outlined, and the algorithms and protocols developed for each layer in the literature are explored. Open research issues for the realization of sensor networks are also discussed. <s> BIB001 </s> Node Relocation Techniques for Wireless Sensor Networks: A Short Survey <s> I. INTRODUCTION <s> This paper presents Span, a power saving technique for multi-hop ad hoc wireless networks that reduces energy consumption without significantly diminishing the capacity or connectivity of the network. Span builds on the observation that when a region of a sharedchannel wireless network has a sufficient density of nodes, only a small number of them need be on at any time to forward traffic for active connections. Span is a distributed, randomized algorithm where nodes make local decisions on whether to sleep, or to join a forwarding backbone as a coordinator. Each node bases its decision on an estimate of how many of its neighbors will benefit from it being awake, and the amount of energy available to it. We give a randomized algorithm where coordinators rotate with time, demonstrating how localized node decisions lead to a connected, capacity-preserving global topology. Improvement in system lifetime due to Span increases as the ratio of idle-to-sleep energy consumption increases. Our simulations show that with a practical energy model, system lifetime of an 802.11 network in power saving mode with Span is a factor of two better than without. Additionally, Span also improves communication latency and capacity. <s> BIB002 </s> Node Relocation Techniques for Wireless Sensor Networks: A Short Survey <s> I. INTRODUCTION <s> Wireless sensor networks are poised to increase the efficiency of many military and civil applications, such as disaster management. Typically sensors collect data about their surrounding and forward that data to a command center, either directly or through a base-station. Due to inhospitable conditions, these sensors are not always deployed uniformly in an area of interest and some sensors can be unreachable because they are too distant from the base-station or simply because there exist obstacles in their path. This paper focuses on reducing the sensitivity of the operation and monitoring of sensor networks to the ambiguity of the propagation model of the radio signal. We define ‘agent’ sensors, which monitor the health and relay messages to and from unreachable sensors. We form groups of sensors around these agents while considering the load on each agent. An energy-aware routing of data collected by and relayed by these agents is performed. Our approach localizes communication which reduces the amount of sensor energy expended in transmission, enables efficient monitoring of sensor resources and health status and allows optimal management of deployed sensors for increased network lifetime. The approach is validated by the simulation results. <s> BIB003 </s> Node Relocation Techniques for Wireless Sensor Networks: A Short Survey <s> I. INTRODUCTION <s> The effectiveness of wireless sensor networks (WSNs) deployed in search and rescue, battlefield reconnaissance, surveillance, and other applications depends on inter-node interaction and maintaining network connectivity. While connectivity can be provisioned at startup, then sustained through careful coordination when nodes move, the network can be partitioned if a node suddenly fails. This paper presents recovery through inward motion (RIM), a distributed algorithm to efficiently restore network connectivity after a node failure. Instead of performing a network-wide analysis to assess the impact of the node failure and set a course of action, RIM triggers a local recovery process by relocating the neighbors of the lost node. RIM minimizes messaging overhead and reduces the distance that individual nodes travel during the recovery. Simulations validate RIM's performance. <s> BIB004 </s> Node Relocation Techniques for Wireless Sensor Networks: A Short Survey <s> I. INTRODUCTION <s> The major challenge in designing wireless sensor networks (WSNs) is the support of the functional, such as data latency, and the non-functional, such as data integrity, requirements while coping with the computation, energy and communication constraints. Careful node placement can be a very effective optimization means for achieving the desired design goals. In this paper, we report on the current state of the research on optimized node placement in WSNs. We highlight the issues, identify the various objectives and enumerate the different models and formulations. We categorize the placement strategies into static and dynamic depending on whether the optimization is performed at the time of deployment or while the network is operational, respectively. We further classify the published techniques based on the role that the node plays in the network and the primary performance objective considered. The paper also highlights open problems in this area of research. <s> BIB005 </s> Node Relocation Techniques for Wireless Sensor Networks: A Short Survey <s> I. INTRODUCTION <s> Mobility has been introduced to sensor networks through the deployment of movable nodes. In movable wireless networks, network connectivity among the nodes is a crucial factor in order to relay data to the sink node, exchange data for collaboration, and perform data aggregation. However, such connectivity can be lost due to a failure of one or more nodes. Even a single node failure may partition the network, and thus, eventually reduce the quality and efficiency of the network operation. To handle this connectivity problem, we present PADRA to detect possible partitions, and then, restore the network connectivity through controlled relocation of movable nodes. The idea is to identify whether or not the failure of a node will cause partitioning in advance in a distributed manner. If a partitioning is to occur, PADRA designates a failure handler to initiate the connectivity restoration process. The overall goal in this process is to localize the scope of the recovery and minimize the overhead imposed on the nodes. We further extend PADRA to handle multiple node failures. The approach, namely, MDAPRA strives to provide a mutual exclusion mechanism in repositioning the nodes to restore connectivity. The effectiveness of the proposed approaches is validated through simulation experiments. <s> BIB006 </s> Node Relocation Techniques for Wireless Sensor Networks: A Short Survey <s> I. INTRODUCTION <s> A dynamic energy-efficient network model that can reduce the energy dissipation of sensor nodes while improving on WSN lifetime is proposed. The Harmony Search Optimization Algorithm is the core that the model is built on it.The proposed model employs two approaches named a mobile base station and a cluster-based network technique to reduce the communicating distances between sensor nodes and their base station.The cluster-based network technique seeks to build a dynamic network infrastructure where the optimal number of clusters and their members is predicted.The mobile base station algorithm seeks to find the near optimal location (i.e. center) between the cluster heads that represent each cluster and the base station in a manner that can reduce the communicating distances and to be closer to all of them.The proposed dynamic network model runs into rounds including the sensing and sending stages until the last node dies. In wireless sensor networks (WSNs), the location of the base station (BS) relative to sensor nodes is an important consideration in conserving network lifetime. High energy consumption mainly occurs during data communication between sensor nodes and the BS, in both single and multi-hop infrastructures. A WSN design with dynamic BS relocation is therefore desirable as this may prolong the network operational lifetime. However, positioning the BS next to each sensor node may cause data gathering latency. The reorganization of sensor nodes into clusters and the choice of a delegate node from each cluster, known as a cluster head (CH), as a communicator between each cluster and the moving BS appears to avoid this latency problem and enhance the energy utilization in WSNs. In this paper, we propose an energy-efficient network model that dynamically relocates a mobile BS within a cluster-based network infrastructure using a harmony search algorithm. First, this model allocates sensor nodes into an optimal number of clusters in which each sensor node belongs to the most appropriate cluster. Following this, the optimal CHs are chosen from the other clusters sensors in order to evenly distribute the role of the CHs among the sensors. This infrastructure changes dynamically based on the number of alive nodes, so that load balancing is achieved among sensor nodes. Subsequently, the optimal location of the moving BS is determined between the CHs and the BS, in order to reduce the distances for communication. Finally, sensing and data transmission takes place from each sensor node to their respective CH, and CHs in turn aggregate and send this sensed data to the BS. Simulation results show very high levels of improvements in network lifetime, data delivery and energy consumption compared to static and random mobile BS network models. <s> BIB007 </s> Node Relocation Techniques for Wireless Sensor Networks: A Short Survey <s> I. INTRODUCTION <s> Abstract In this paper we study an opportunistic geographically constrained information sharing paradigm known under the name Floating Content (FC), considering two different mobility models that describe the behavior of pedestrians. We assume that users carrying their smartphones walk from one location to another and then stop for a while. Information transfers take place in the periods when users pause between movements. We develop analytical models to compute the performance metrics that characterize FC in this case and we validate analytical results with data collected during an experiment performed in a university campus. The comparison proves the accuracy of our analytical models. Moreover, results unveil the key relevance for FC performance of group dynamics in user movements. <s> BIB008 </s> Node Relocation Techniques for Wireless Sensor Networks: A Short Survey <s> I. INTRODUCTION <s> With the development of autonomous unmanned intelligent systems, such as the unmanned boats, unmanned planes and autonomous underwater vehicles, studies on Wireless Sensor-Actor Networks (WSANs) have attracted more attention. Network connectivity algorithms play an important role in data exchange, collaborative detection and information fusion. Due to the harsh application environment, abnormal nodes often appear, and the network connectivity will be prone to be lost. Network self-healing mechanisms have become critical for these systems. In order to decrease the movement overhead of the sensor-actor nodes, an autonomous connectivity restoration algorithm based on finite state machine is proposed. The idea is to identify whether a node is a critical node by using a finite state machine, and update the connected dominating set in a timely way. If an abnormal node is a critical node, the nearest non-critical node will be relocated to replace the abnormal node. In the case of multiple node abnormality, a regional network restoration algorithm is introduced. It is designed to reduce the overhead of node movements while restoration happens. Simulation results indicate the proposed algorithm has better performance on the total moving distance and the number of total relocated nodes compared with some other representative restoration algorithms. <s> BIB009
Wireless Sensor Network (WSN) is marked as an influential technology and considered as a well-established research area for its wide range of applications. WSN while having certain lower energy and reasonable densely inactive compact mobile nodes is typically organized well in the practices like environment reconnaissance, to assign data and manage communications amongst one another via radio-based technology BIB006 . WSN is known to be very useful in the environments where human intervention is mostly impractical like wild fire detection, battlefield surveillance, deep ocean exploration, etc. BIB001 . Mainly, these sensor nodes applications are associated with armed forces, households, or medical care. Moreover, in the armed services, for instance, through its timely practice, defective endurance quality, and independent operation, WSN has revealed its extraordinary applicability relating the systems of armed forces involving inspection, scheming, communication, targeting, and commanding. In health applications, these nodes help monitor the patients and support the patients with special needs (disabled). Besides, these sensor nodes are influential in the areas of commerce and finance like in supply chain management, etc. Moreover, they can also be utilized for monitoring the areas affected by disaster BIB008 . Fig. 1 shows the sensors random deployment in a region. All of these nodes are responsible for performing the given task independently in a distributed manner and communicate with each other using multi-hop communication. Sensor nodes send back the sensed data to the sink node in a multi-hop fashion as shown in Fig. 1 . Eventually, this data is sent to the user by means of internet afterwards BIB006 . The dynamic relocation of sensors in the operation of the network is very significant to enhance its performance BIB007 . During the operation of WSN, some of the redundant sensors located at different locations will likely be repositioned in order to replace the sensors with depleted batteries for rectification of network stability  . Besides, this type of dynamic repositioning might be appropriate in a mechanism that supports the target movement; also the moveable ones BIB009 . To further clarify, it approaches forth, eventually gets feasible to reposition particular sensor nodes close-by to the target to attain the improvement of node's data accuracy. In relevant applications BIB002 and in order to maintain the availability, installing base-station into secure position from ambiguous targets like a tank of an enemy, at the present, could be a better accomplishment BIB003 . The resolution of the disputation to reposition dynamic sensor node has been analyzed in BIB004 BIB005 . This work is sponsored by Jouf University Saudi Arabia, under the research project number 40/117.  In the sensor node repositioning, it is conceivable to handle the dynamic variation in the network resource surrounding environment as it is dissimilar from the initial deployment. In this article many technical issues are highlighted for sensor node relocation. These technical issues define where to move the sensor node and how to accomplish the network when the sensor node is mobile?  Several dynamic node positioning techniques are compared and reviewed based on their application, objective, and methodology. As a result, it is supposed that the sensor nodes which are movable can probably be dynamically relocated in order to fill the connectivity and coverage by managing the variations in the user importance.  The problem of managing multi-node reposition is acknowledged as an open research area and an important attention is paid to this interesting and challenging area. The rest of the paper is organized as follows. Nodes repositioning issues are summarized in section II. Dynamic node repositioning schemes are discussed in section III and subsequently, section IV concludes this paper.