Cooperation in Delay-Tolerant Networks With Wireless Energy Transfer: Performance Analysis and Optimization

Data collection is a fundamental and important issue in wireless sensor networks. Recent research has shown that using mobile nodes to collect and carry data in WSNs has many advantages over static multi-hop routing. In this paper, we focus on the problem of reducing the number of mobile nodes require by data collection in WSNs. Each mobile node visits the sensor nodes, that assigned to it, every t seconds to pick up the cached data. The data gathered by mobile nodes far away from the base station are transferred to the base station through mobile nodes closer to the base station. We formally prove that the problem of data collection in WSNs with the minimum mobile nodes is NP hard. In order to reduce the number of mobile nodes, We propose two algorithms. One tries to reduce the number of mobile nodes and optimize their travel paths, and the other one carefully schedules the movement of all mobile nodes to make sure that they can cooperate with each other to transfer all gathered data to the base station. Our simulation results show that our approach can notably reduce the number of required mobile nodes as much as 46%.

We derive theoretical bounds on expected hitting times in densely covered delay-tolerant networks (DTNs). We consider a number of fixed (data collector) nodes deployed in the DTN region, and a number of mobile (data generator) nodes that move freely in the region according to Brownian motion. As it moves, each mobile node is assumed to continuously generate and buffer data. When a mobile node comes within the communication coverage range of a data collector node, it downloads its buffered data to it. Otherwise, it keeps generating and buffering its data. In this paper, we derive analytic bounds on the amount of time a mobile node spends without communication coverage. Then, using these derived bounds, we derive sufficient conditions on node density that statistically guarantee that the expected hitting times remain below a given threshold.

Recently, there has been focus on augmenting Delay/Disruption Tolerant Networks (DTNs) with easily deployable stationary relay nodes making an unconnected infrastructure to facilitate the data delivery by increasing forwarding opportunities. Relay nodes are capable of downloading, storing, and forwarding the data messages from/to the mobile nodes. Placing the relay nodes is an important issue in DTNs as the performance of the network is dependent to their positions. Relay placement is an NP-hard problem hence it makes it a more complicated issue in DTNs. Existing works in the literature are based on simulation which are suffering from computational complexities dictated by simulation. Moreover, they are optimizing the relay placement only based on specific scenarios. In this paper, we propose a generic analytical model in order to evaluate the performance of DTNs in presence of relay nodes. Our model is dependent on the mobile nodes' mobility pattern, and we consider the case when the mobile nodes move according to the random waypoint model. In order to use the proposed model for placing the relays efficiently, we utilize two heuristic approaches. The first approach is based on optimization of the network performance using simulated annealing and the second one relies on a greedy approach to find the best location for each relay one at a time. Our simulation results show that our approaches outperform the simulation based approaches in terms of data delivery performance.

There is a lack of reliable tools for evaluating the performance of Delay Tolerant Networks (DTN). Frequently, the researchers use small-scale real networks or one of the few available DTN simulators. This work presents an alternative approach for conducting performance evaluation studies of DTN, following a recent movement of the scientific community with respect to the use of hybrid environments in order to achieve realism in the studies. We propose, implement and validate the Virtualized DTN Testbed (VDT) as a means to construct a virtualized testbed completely in software that takes into account a real instance of the operating system and applications that run inside the mobile nodes, as well as a robust model of the wireless channel. The results show that VDT can accurately reproduce both the mobility of nodes, and the contact opportunities obtained in experiments of a real testbed. Moreover, we identified some implementation problems in the real experiments, that after some fixing strategies allowed us to identify the occurrence of several contacts not registered previously.

The fast mobile internet protocol version 6 (FMIPv6) was suggested as a fast handover mechanism over the mobile wireless Internets in order to reduce the handover latency of a mobile node (MN). However, FMIPv6 was originally designed to deal with single MN's. In mobile wireless Internet, a multiple MNs may do a handover at the same time as a consequence of its movement from one network to another new one. This will therefore lead to the bandwidth waste and low handover performance. This paper intends to propose a multiple handover-based mobile node (MHB-MN) control method and an enhanced FMIPv6 mechanism in order to resolve the abovementioned problem. The proposal of such an MHB-MN method aims at having one mobile node work as a guide for a group of neighboring MNs. This means that the guide of MN prepares itself for a handover before actually taking the initial steps of the actual handover operation. Based on obtained results, it is plainly observable that by MHB-MN method, the handover initiation time, handover latency and handover control messages can be reduced compared to those of FMIPv6. Furthermore, the contention of the wireless channel for multiple MNs can be improved by the use of fewer control messages. Finally, the paper introduces an analytical model to show that by enabling the MHB-MN method and enhancing the FMIPv6 method, a multiple of nodes can perform rapid handover processes with low handover latency compared to that of the FMIPv6 technique.

ExMin: A routing metric for novel opportunity gain in Delay Tolerant Networks

In infrastructure-lacking environments, like military areas of operation, the intermittent availability of backhaul networks leads to greater reliance on peer to peer data exchange. In such settings, mobile nodes use Delay Tolerant Network (DTN) protocols for exchanging location specific data. High transmission delay, packet loss and intermittent connectivity increases the need for efficient data transmission in such scenarios. In this paper, we evaluate network coding for efficient data exchange between mobile wireless nodes under the presence of an intermittent backhaul network, like a satellite or cellular link. We analyze the upper bound of savings achievable with network coding for single-hop packet transmission, and introduce a network coding algorithm focused on reducing the required number of packet transmissions in such a setting. Evaluation of our proposed data exchange protocol shows how network coding can be applied to reduce transmission delay and minimize the dependency on an intermittent backhaul network in a communication scenario typical of a military environment.

Delay-tolerant networking (DTN) is an architecture to enable data communications between isolated or remote regions, where long delays and intermittent connectivity can be tolerated. An emerging class of DTN, called vehicular DTNs (VDTN), exploits transportation systems as the transport layer to transfer data. In these networks, vehicles (e.g., busses, boats, trains) act as mobile nodes and carry data messages around. Mobile nodes can exchange data messages using devices called relay nodes. Relay nodes, placed in strategic positions along vehicle routes, have the capability to download, store, and upload the data messages from/to the mobile nodes. An important issue in VDTN is the optimal placement of the relay nodes such that delay-tolerant connectivity in VDTN is ensured at minimum cost. In this paper we show that the problem of optimal relay node placement is an NP-hard problem. Other contributions of this paper are the formulation of the relay node placement problem using ILP and the proposal of heuristic algorithms solving the optimization problem. Using simulation results, we compare the performance of each algorithm under different network constraints, such as node storage capability and network topology.

Devices in disruption tolerant networks (DTNs) must be able to communicate robustly in the face of short and infrequent connection opportunities. Unfortunately, one of the most inexpensive, energy-efficient and widely deployed peer-to-peer capable radios, Bluetooth, is not well-suited for use in a DTN. Bluetooth's half-duplex process of neighbor discovery can take tens of seconds to complete between two mutually undiscovered radios. This delay can be larger than the time that mobile nodes can be expected to remain in range, resulting in a missed opportunity and lower overall performance in a DTN. This paper proposes a simple, cost effective, and high performance modification to mobile nodes to dramatically reduce this delay: the addition of a second Bluetooth radio. We showed through analysis and simulation that this dual radio technique improves both connection frequency and duration. Moreover, despite powering two radios simultaneously, nodes using dual radios are more energy efficient, spending less energy on average per second of data transfered.

Nowadays, Delay Tolerant Network plays an important role in improving the communication between the network nodes. Applications of Delay Tolerant Network are disaster recovery, vehicular communication, sensor networks, interplanetary networks, and communication in remote and rural areas. Routing is one of the important tasks for enhancing the energy effectiveness of data transmission among the mobile nodes under network congestion and dynamic topology. Machine Learning-based routing algorithms are used for improving network communication in Delay Tolerant Networks. Its objective is to reduce the delay, minimize the overhead, reduce energy consumption, improve throughput, minimize packet loss, and efficient data transmission. This paper presents a comprehensive review of routing algorithms using machine learning for Delay Tolerant Networks.

Delay Tolerant Network (DTN) is a sparse and intermittently connected mobile wireless network where reliable communication and end-to-end connectivity cannot be assured. In DTN, a node delivers messages to the destination using store and forward scheme. Messages are copied and transferred to multiple relay-nodes in order to increase the opportunity for that message to reach the intended destination. Contact is the time duration for which two or more mobile nodes encounter each other within their radio transmission ranges, and are able to transfer messages. Due to arbitrary node movement, contact time will be varied, and is unlikely to be predictable. In this paper, we propose a fuzzy decision mechanism we called “fuzzy-spray”, to improve the routing and packet transfer efficiency in DTN environment. Fuzzy-spray can reduce overall latency in DTN by intelligently selecting appropriate messages to send to the relay-node during its next contact time. It uses fuzzy logic to prioritize messages that are stored in the buffer, based only on local parameters from each message, namely forward transmission count and message size. There is no need to know a priori information about network such as node mobility model, or node-distribution across the deployed area. The simulation results show that fuzzy-spray has the best performance in terms of overall speed of delivery, and lowest average message delay compared with other existing algorithms.

Delay tolerant network is a mobile ad hoc network where there are no predefined routes from one node to another, which is used in disaster and emergency communications. Here, we concentrate the analysis of node contact on contact duration aware routings techniques and address the issues of variation of mobile nodes, message copies and buffer size using ONE simulator. We observe that contact increases per hour with the increase of mobile nodes, while goes up and down for varying message copies and remains approximately the same for buffer size, i.e., buffer size does not affect the achievement of contacts. While, inter-contact time (ICT) is high at the beginning of communication for three cases, i.e. for varying message copies, mobile nodes and buffer size. Higher contact time results in higher ICT and number of contacts for varying mobile nodes, while it remains slightly changed for varying message copies and fixed for varying buffer size.

The Internet of Things (IoT) is going to develop integrated and organised networks of all things and beings in the world enabling autonomous computing and information communication for the creation of new values in the future. For such networks by IoT that accept a certain level of communication delay, but that must realise highly-reliable message forwarding, Delay Tolerant Network (DTN) gives a possible solution. Recently, DTN has attracted attention as a future network under challenged network environments where communication delay, disruption, and disconnect frequently occurs. In this chapter, we review some routing protocols for efficient message forwarding in DTN. We also review some mobility models often used for simulating motions of mobile nodes to evaluate the performance of DTN. In this review, we propose our mobility model called Homesick Levy Walk that mimics human mobility patterns of an universal scale-free property of the frequency of human contacts. After this, we also propose our utility-based routing protocol which maximises the expected number of selected relay nodes being likely to encounter a destination node under sequential encounters with nodes. We evaluate the performance of our routing protocol by comparing with some performance measures of some existing routing protocols under the condition that the Homesick Levy Walk is adopted as mobility model. We show that our protocol is comparable to others in arrival rate of messages under a smaller number of message forwarding.We also find that the performance of our protocol is stable up to a few hundred mobile nodes and tends to be scalable with the number of nodes.

With the development of mobile Internet, wireless communication via mobile devices has become a hot research topic, which is typically in the form of Delay Tolerant Networks (DTNs). One critical issue in the development of DTNs is routing. Although there is a lot research work addressing routing issues in DTNs, they cannot produce an advanced solution to the comprehensive challenges since only one or two aspects (nodes' movements, clustering, centricity and so on) are considered when the routing problem is handled. In view of these defects in the existing works, we propose a novel solution to address the routing issue in social DTNs. By this solution, mobile nodes are divided into different clusters. The scheme, Spray and Wait, is used for the intra-cluster communication while a new forwarding mechanism is designed for the inter-cluster version. In our solution, the characteristics of nodes and the relation between nodes are fully considered. The simulation results show that our proposed scheme can significantly improve the performance of the routing scheme in social DTNs.

The broadcast diffusion of messages in Delay Tolerant Networks (DTNs) is heavily dependent on nodes mobility, since protocols must rely on contact opportunities among devices to diffuse data. This work is a first effort to study how the dynamics of nodes affect both the effectiveness of the broadcast protocols in diffusing data, and their efficiency in using the network resources. The paper describes three control mechanisms. The mechanisms characterize a family of protocols able to achieve some awareness about the surrounding environment, and to use this knowledge in order to keep the broadcast overhead low, while ensuring high node coverage. Simulation results identify the winning mechanisms to diffuse messages in DTNs under different conditions.