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This paper considers a network where a node wishes to transmit a source message to a legitimate receiver in the presence of an eavesdropper. The transmitter secures its transmissions employing a sparse implementation of random linear network coding (RLNC). A tight approximation to the probability of the eavesdropper recovering the source message is provided. The proposed approximation applies to both the cases where transmissions occur without feedback, or where the reliability of the feedback channel is impaired by an eavesdropper jamming the feedback channel. An optimization framework for minimizing the intercept probability by optimizing the sparsity of the RLNC is also presented. Results validate the proposed approximation and quantify the gain provided by our optimization over solutions where non-sparse RLNC is used. [ABSTRACT FROM AUTHOR]

High-speed and low-latency communications are one of the major requirements for connected vehicle environments. Safety messages in vehicular networks must arrive on time for each vehicle, and the optimization of driving paths also strongly depends on low-latency traffic information. To comply with the demands, a base station take important roles to provide a short service delay for the vehicles, even at the expense of performance. The relationship between delay time and decoding performance at receiver sides in physical layers can be explained by the performance/complexity tradeoff as follows. To achieve better performance in terms of the minimization of word error rates in decoding, the receiver usually requires higher complexity, which results in larger delays. We analyze this tradeoff based on the receiver queue model. This paper proposes a novel algorithm to adaptively select one of receiver candidates under the constraint of queue stability so as not to degrade low-latency communications. Based on the configurable architecture for multi-input multioutput (MIMO) detectors, this paper shows that the proposed algorithm works well on adaptive MIMO detector selection. [ABSTRACT FROM PUBLISHER]

In delay-tolerant networks (DTNs), stable end-to-end connections do not always exist. Messages are forwarded, assisted by the mobility of nodes, in a store–carry–forward paradigm. The mobility of nodes in most DTNs has a certain statistical regularity; thus, using historical information in DTNs to compute the delivery quality of nodes can help to select good forwarding nodes. This paper aims to establish a routing scheme based on multihop delivery quality, which is designed to reduce the energy consumption of message forwarding while maintaining a high delivery rate. We characterized the multihop delivery quality of each node with an expected delay and an expected probability, parameterized by the remaining hop count. Based on these two quality metrics, we developed two algorithms, namely, the delay-inferred forwarding (DIF) algorithm and the probability-inferred forwarding (PIF) algorithm. The basic idea of DIF and PIF is to find the optimal forwarding path by minimizing the expected delay and by maximizing the expected probability, respectively, in the hop graph that is defined in this paper. We performed extensive trace-driven simulations to compare our algorithm to other representative routing algorithms using several real traces. We observed the following: 1) Compared with the delegation algorithm, which uses one-hop delivery quality, both DIF and PIF significantly improve the message delivery rate, and they yield more improvements as the mobility of nodes becomes more regular; and 2) compared with the state-of-the-art optimal opportunistic forwarding (OOF) algorithm, which also uses a multihop delivery quality, DIF and PIF have significantly smaller forwarding overhead (with the maximum reduction in the number of forwarding being over 40%), whereas they are quite close to OOF in terms of both delivery rate and average delay. [ABSTRACT FROM PUBLISHER]

Geocast, which consists of delivering messages to a specific location, has become an important technique with the accelerated development of the location-based services in mobile networks. Geocast in the automotive domain is of particular interest, enabling many promising applications, such as geographic advertising, location-based traffic alerts, etc. Different from the conventional geocast algorithms focusing on the distance-based approaches, in this paper, we propose a node mobility-aware and node contact-aware geocast algorithm (GeoMobCon) for urban vehicular ad hoc networks from the delay-tolerant network perspective to better deal with the high mobility and transient connectivity issues. Different levels and aspects of vehicle mobility information and self-maintained contact information are employed, making GeoMobCon simple, scalable, and communication and computation effective. Practical issues are well considered by introducing real-world trace analysis, trace-driven simulation, and efficient buffer management. Extensive performance comparisons with other protocols have been conducted to show the advantages of GeoMobCon. [ABSTRACT FROM AUTHOR]

Delay-tolerant networks (DTNs) consist of nodes moving around and occasionally coming into each other's proximity. During the limited proximity time, nodes can exchange data; this can result in a very slow data dissemination process that is usually governed by a replication-based mechanism. However, due to the long propagation delay and the large overhead associated with the replication approach, DTN delivery performance is neither efficient nor effective. To reduce the overhead, which becomes a critical aspect particularly when addressing a multicast scenario, infection recovery mechanisms have been proposed to control and reduce the number of packet copies circulating through the network. This, however, has the cost of decreasing the chances of delivering packets to all destinations. In this paper, adaptivity in infection recovery is addressed. This represents a viable solution to make transmission more reliable, hence delaying the activation of the infection recovery procedure, depending on the number of nodes, destinations, and the time. Moreover, we also propose to exploit an additional feature in data multicasting, i.e., socially aided data dissemination, where the packet dissemination procedure is not trivially epidemic, but rather exploits the intrinsic sociality of users and their interests to reduce the delivery overhead and speed up the multicast process. More specifically, we consider a procedure where users are not regarded as individual members of the network but can be aggregated into groups sharing interests, and their sociality helps the data dissemination procedure. Results of our analysis show that new sociality-aided adaptive recovery schemes can speed up the delivery process. [ABSTRACT FROM AUTHOR]

In this paper, we propose a heterogeneous framework to deliver smart grid (SG) data cost effectively. The data generated by distributed SG loads, and generation units should be delivered to the utility control center (UCC) within the tolerated delay, which is crucial for SG applications. To this end, a heterogeneous communication framework is proposed, where the cellular network (CN) provides ubiquitous yet expensive data transmission, and vehicle-assisted device-to-device (D2D) communications are leveraged to offload the CN by delivering the delay-tolerant SG data in a store–carry–forward fashion with low cost. To improve the offloading and cost performance of the proposed framework, we put effort in the following aspects: 1) optimal forwarding schemes to optimally select vehicles to carry and forward the data; and 2) mode selection and dynamic resource allocation to maximize the amount of data delivered by D2D communications, reduce the cost of SG data delivery, and guarantee the fairness among SG users. Simulation results are given to validate proposed approaches and demonstrate that the proposed framework is efficient in saving cost for the utility and offloading the CN. [ABSTRACT FROM AUTHOR]

Delay tolerant networks (DTNs) are featured by unpredictable mobility patterns and easily interrupted connections. Forwarding strategy has always been the research focus in DTNs, in order to improve a delivery ratio. An enormous amount of research works pay attention to solving the following two problems: whether to forward and how to forward. Therefore, forwarding metrics and forwarding strategies both play important roles in DTNs. In this paper, we consider a generalized random-waypoint model with heterogeneous nodes; the node's speed is regarded as the forwarding metric, which includes both short-term and long-term speed. Subsequently, we propose a theoretical, multicopy delegation forwarding based on short-term and long-term speed in DTNs (DFSL-T), which first determines a comprehensive mapping from short-term speed and long-term speed to the actual forwarding metric. Then, according to the forwarding metric and delegation forwarding strategy, DFSL-T utilizes some efficient nodes with higher forwarding metrics to assist in delivering messages, in order to improve the delivery ratio while reducing the forwarding cost. However, DFSL-T assumes that each node could achieve the average speeds of the others, which is impractical. In order to overcome this problem, we further propose a practical strategy (DFSL-P) through exchanging and evaluating the average speeds of each other. Finally, we conduct simulations based on the synthetic mobility pattern and real trace. The results show that compared with other multicopy forwarding strategies, DFSL-T and DFSL-P achieve higher forwarding efficiency, which is the result of delivery ratio divided by forwarding cost. [ABSTRACT FROM AUTHOR]

Caching-enabled device-to-device (D2D) networks have the potential to make mobile users directly fetch requested files from nearby users, resulting in low network delay. In addition, user mobility can increase the communication chances among different users, and therefore, the network delay can be further effectively reduced by proper designing the caching strategy. In this paper, mobility-aware caching strategies in D2D networks are studied to minimize the network delay. Specifically, based on the inter-contact user mobility model, the expression of the average file delivery delay is analytically obtained. Considering the limited cache capacity, a delay minimization cache placement problem considering the user mobility is investigated. To optimally solve this nonlinear integer programming problem, we reformulate it as a multistage decision problem. According to the recursive relationship between adjacent stages, dynamic programming is adopted to obtain the optimal mobility-aware caching strategy stage-by-stage. Furthermore, to lower the complexity, we also demonstrate that the original problem can be recasted as a monotone submodular function maximization problem over a matroid constraint. Then, a low-complexity greedy mobility-aware caching strategy with $(1-1/e)$ -optimality performance guarantee is put forward. Numerical results show that, in the scenario with high user mobility, the file delivery delay can be reduced by 47% with our proposed mobility-aware caching strategy, as compared with the most popular caching. Furthermore, the superiority of the proposed caching strategy is verified by real-world data set. [ABSTRACT FROM AUTHOR]

Delay-tolerant networks often adopt the message replication methodology to increase the opportunity that destinations can receive messages from a source node in a network. Repeatedly replicating messages, however, consumes significant resources such as local buffer space on nodes and internode communication bandwidth. Previous buffer management and scheduling policies mainly contributed to a simple scenario of message unicasting from a source to a singular destination in a network. When message multicasting toward multiple destinations is considered, previous solutions perform inefficiently. This paper proposes a new buffer management and scheduling policy for message multicasting in delay-tolerant networks. The proposed policy is an optimal-based design with a new utility function, which can prioritize messages in a buffer for maximizing the successful delivery rate in a network. Simulation results manifest the efficacy of the proposed scheme under different mobility benchmarks in delay-tolerant networks. [ABSTRACT FROM PUBLISHER]

We perform a study on the buffer occupancy 1 The term buffer occupancy refers to the amount (or number) of data (or packets) present in the buffer. We shall be using the terms buffer occupancy and system size interchangeably as deemed fit. and its steady-state properties in a mobile opportunistic network (MON) for different forwarding strategies. Nodes in MON adhere to replication based strategy in order to ensure reliable delivery. Such replications occur in bulks during intermittent and very short contact events, which often lead to buffer congestion in the relay nodes, thereby affecting the network performance. The state-of-the-art on buffer management in MON relies on local information exchange to measure buffer occupancy, which leads to overhead. Therefore, to find the average buffer occupancy, we first study the aggregated bulk transfer size using real-life contact traces and find that it follows a log-normal distribution. Since the contact rate has been observed to follow a Poisson distribution, we model the packet arrival process in each node as a compound Poisson process. Furthermore, the departure process is modeled as packets dropped due to time-to-live expiry, which is shown to have an exponential distribution. Using the above model, we derive the steady-state probability distribution of buffer occupancy of an arbitrary node for three different classes of replication scheme, viz., epidemic routing, probabilistic routing, and time-varying probabilistic routing. The results of this paper help in assessing how fast a node buffer gets depleted under different routing algorithms, which will help in designing better buffer management techniques and routing algorithms. [ABSTRACT FROM AUTHOR]

Mobile-relay-assisted forwarding in delay-tolerant networks (DTNs) can improve network capacity and packet delivery ratio but, at the same time, may significantly increase energy consumption at the system level. In this paper, we propose a distance-based energy-efficient opportunistic forwarding (DEEOF) framework for the broadcast transmission in mobile DTNs. DEEOF strikes a balance between energy consumption and network performance by maximizing the energy efficiency while maintaining a high packet delivery ratio. In the proposed algorithms, we define the metric of the forwarding equivalent energy efficiency distance (FEED) for broadcast transmission to quantify the transmission distances achieving the same energy efficiency at different time instances, or with different numbers of the relays in the source's transmission radius. Based on the concept of FEED, we propose two DEEOF algorithms for opportunistic broadcast forwarding, which makes the forwarding decision by comparing the current energy efficiency with the estimated future expectation and distribution, respectively. The performance improvement of the proposed DEEOF algorithms is also demonstrated by simulation, particularly for the cases in which the source has very limited battery reserves. [ABSTRACT FROM AUTHOR]

In this paper, we first challenge the accuracy of the so-called innovative assumption that is widely adopted in delay performance analysis of network-coding-based epidemic routing (NCER) in delay-tolerant networks (DTNs). We demonstrate that this optimistic assumption severely underestimates data delivery delay and solves this problem successfully by introducing an extra encounter factor $\delta$. Based on this, we propose a coloring process (CP)-based analytical model to evaluate the delay performance of NCER. Numerical results show that our CP-based method outperforms traditional ordinary differential equation (ODE)-based methods on estimating the delay performance under different network sizes. Furthermore, to mitigate potential competition among multiple data streams from different nodes, we propose a feedback-based recovery protocol (FRP) that takes advantage of finite buffer space and significantly reduces the number of ineffective transmissions between nodes. As a result, FRP can achieve much better delay performance compared with existing protocols in prior work. [ABSTRACT FROM AUTHOR]

We consider a delay-tolerant network (DTN) whose mobile nodes are assigned to collect packets from data sources and deliver them to a sink (i.e., a gateway). Each mobile node operates by using energy transferred wirelessly from the gateway. For such a network, two main issues are studied. First, when a mobile node is at the data source, this node must decide on whether to accept the packet received from the data source or not. In contrast, whenever a mobile node is at the gateway, it has to decide on whether to transmit the packets collected from the data sources or to request wireless energy transfer. Second, multiple mobile nodes can cooperate and form coalitions to help one another in the delivery of packets from their associated data sources. However, this cooperation may not be always beneficial due to the limited buffer and energy resources. Moreover, some mobile nodes may secretly decide to deviate from a given coalition, thus taking advantage of the other innocent mobile nodes. To address these two issues, this paper introduces a performance analysis and optimization framework, which is based on a joint optimization and game-theoretic framework. The optimization model is used to obtain the packet delivery policy of each individual mobile node. Then, a novel game-theoretic model, namely a repeated coalition formation game, is developed to analyze the cooperation strategies of multiple mobile nodes. [ABSTRACT FROM PUBLISHER]

This paper studies energy-efficient transmission strategies for a closed-loop downlink multiple-input–single-output (MISO) system, where a communication period consists of three phases for uplink training, downlink data sending, and base station (BS) idling. For both delay-tolerant and delay-sensitive services, the durations of the three phases are optimized, aimed at maximizing the energy efficiency (EE) of the system. To this end, we derive the approximate average net spectrum efficiency (SE) and outage probability with imperfect uplink channel estimation, which are used to characterize the quality-of-service (QoS) requirements for the two kinds of services, respectively. The impact of QoS requirement, signal-to-noise ratio (SNR), and circuit power consumption on the optimal transmission durations is analyzed. For delay-tolerant services, analytical results show that the EE-oriented design leads to a longer training duration than the SE-oriented design in general. For delay-sensitive services, it is shown that introducing BS idling is crucial in improving the EE. The challenges and opportunities of applying the proposed transmission strategies in current and future cellular systems are discussed, and the transmission strategies are extended from single-user single-service to multiuser mixed-service scenarios. Simulation results demonstrate the significant EE gain of the EE-oriented design over the SE-oriented design in both single-user and multiuser scenarios. [ABSTRACT FROM PUBLISHER]

Fountain codes have been extensively employed in delay-tolerant networks (DTNs) due to their near-capacity performance with very low encoding/decoding complexity. A decode-and-forward-based relaying strategy is ideally suited for fountain codes in such networks due to its ability to recover the source message from any subset of encoded packets with sufficient mutual information. However, the unreliable nature of the channel may lead to the starvation of some subsequent nodes with good channel conditions. By cooperation among the forwarding nodes, the overall latency of such networks can be alleviated. This paper analytically quantifies the latency of both cooperative and conventional fountain-coded delay-tolerant multihop networks by deriving the exact closed-form equations for the channel usage. The overall latency suffered by such networks forces conservation of the end-to-end delay, particularly for real-time applications. However, by constraining the total delay (the number of encoded transmissions), the performance of fountain codes deteriorates due to the lack of encoded packets for retrieving the entire source message. This degradation can be gauged by the average packet loss experienced with partial decoding of fountain codes. The exact closed-form equation for the average packet loss based on the channel usage for such delay-constrained networks (DCNs) is derived in this paper. The tradeoff between average delay and the channel usage required for successful decoding is also analyzed. It is observed that the average packet loss can be minimized by optimizing the total delay based on the performance across each link. Finally, the pros and cons of using DCNs and DTNs employing fountain codes are evaluated, and theoretical grounding to the simulated results is provided. [ABSTRACT FROM PUBLISHER]

In delay-tolerant networks (DTNs), unpredictable mobility leads to the uncertainty of network topology, and it is hard to maintain an end-to-end connection from the source to the destination. To realize the forwarding of the messages, beaconing is used to detect the contact probabilities. However, beaconing frequency not only influences the detection probability of the available communications but is concerned with the energy consumption rate as well. The higher the beaconing frequency is, the faster the energy is consumed. The energy consumption leads to the reduction of the network survival time, due to the lack of energy supply. In contrast, the lower the beaconing frequency is, the less frequently available communications are detected, which also leads to a decrease in delivery rate. Therefore, it is meaningful to find out the most suitable beaconing frequency in specific DTNs. In this paper, we propose an energy efficient dynamic beaconing control strategy in energy-constrained DTNs (DBCEC) based on the time-continuous Markov model. Six different dynamic function forms are, respectively, used to control the beaconing frequency. Simulations based on the synthetic mobility pattern and real mobility traces are conducted in the Opportunistic Network Environment (ONE), and the results show that DBCEC-E achieves a better delivery rate without affecting the average delay and the overhead ratio, compared with other beaconing control strategies. [ABSTRACT FROM AUTHOR]

With encounter-based communication introduced in intermittently connected mobile networks (ICMNs), the message dissemination in mobile Internet subscriber/publisher services can be augmented through near-distance communication of mobile nodes. Specifically, mobile nodes with Internet connectivity can help those without to obtain messages once stored and currently carried by the former. We model such a system, particularly considering the time-critical property of messages, the limited communication bandwidth, and the existence of multiple sources. Based on the model, we propose analytical methods for obtaining the performance of message delivery ratio and average delay under the 1-hop or the 2-hop relaying mode specified in this paper, respectively. Through extensive simulations, we validate the proposed methods and discuss system performance under different parameter settings and relaying schemes. [ABSTRACT FROM PUBLISHER]

In pocket switched networks (PSNs), devices carried by humans form a network environment, which utilizes both human mobility and occasional connectivity to deliver messages among mobile devices. Mobile phones are widely used in our daily lives. Therefore, the PSN composed of human-carried mobile phones will soon become an ubiquitous network environment. In this paper, we propose a communication strategy that applies the WiFi hotspot mode of a mobile phone in the PSN to realize the device-to-device communications. However, due to the lack of energy supply, a phone in hotspot mode could rapidly consume energy and shorten its battery lifetime significantly. To maximize the message dissemination scope within the limited energy constraint of each phone in PSNs, an Energy-efficient Phone-to-phone Communication method based on WiFi Hotspot (EPCWH) is presented to schedule the phone's switching between hotspot mode and client mode. Simulations based on the synthetic random-waypoint mobility pattern and real traces are conducted in an opportunistic network environment; the results show that EPCWH achieves the best performance in terms of message dissemination and energy consumption among different switching strategies. [ABSTRACT FROM PUBLISHER]

The proliferation of radio-enabled equipment, including sensors, controllers, actuators, mobile handhelds, etc., into the today's heterogeneous wireless network (HWN) has led to the support of different vertical services on-top of the same physical infrastructure. Such an approach increases the potential for enhanced multiplexing gains due to the joint utilization of multiple network tiers and their resources. However, it also links the availability of new services to the robustness of the HWN infrastructure against malicious attacks. In this paper, we study the impact of two prominent denial of service (DoS) attacks, the jamming and the black hole attack, on network coverage of multi-tier HWNs. In particular, we consider a HWN model of multiple tiers, where the locations of nodes belonging to each tier are modeled by a homogeneous Poisson point process (PPP) with known intensity. Each tier consists of regular nodes, jammers (disrupting downlink communications by transmitting at constant power), and black holes (appearing as regular nodes but without forwarding received packets to their legitimate destination). The type of a node for a given network tier is determined by a prescribed probability, whereas jammer and black hole nodes are considered to act independently from each other. We further focus on the challenging scenario where end users can access a limited number of network tiers, while we also allow different tiers to potentially utilize different spectrum bands. Assuming that successful service reception from a node belonging to a given network tier requires a minimum received signal quality threshold to be attained, we derive exact expressions and performance bounds on the coverage probability of random multi-tier HWNs with joint jamming and black hole attacks, which depend on the capability of network nodes to detect and avoid association with malicious nodes (i.e., jammers or black holes). Detailed numerical results highlight the usefulness of the proposed analysis, providing valuable insights on system design and parameterization towards enhanced network robustness. [ABSTRACT FROM AUTHOR]

In this paper, a novel reputation framework for information-centric vehicular applications leveraging on machine learning and the artificial immune system (AIS), also known as ReFIoV, is proposed. Specifically, the Bayesian learning and classification allow each node to learn as newly observed data of the behavior of other nodes become available and hence classify these nodes, meanwhile, the k-means clustering algorithm allows us to integrate recommendations from other nodes even if they behave in an unpredictable manner. The AIS is used to enhance misbehavior detection. The proposed ReFIoV can be implemented in a distributed manner as each node decides with whom to interact. It provides incentives for nodes to cache and forward others’ mobile data as well as achieves robustness against false accusations and praise. The performance evaluation shows that ReFIoV outperforms state-of-the-art reputation systems for the metrics considered. That is, it presents a very low number of misbehaving nodes incorrectly classified in comparison with another reputation scheme. The proposed AIS mechanism presents a low overhead. The incorporation of recommendations enabled the framework to reduce even further detection time. [ABSTRACT FROM AUTHOR]

In this paper, we investigate a multisource multicast network with the aid of an arbitrary number of relays, where it is assumed that no direct link is available at each S-D pair. The aim is to find the fundamental limit on the maximal common multicast throughput of all source nodes if resource allocations are available. A transmission protocol employing the relaying strategy, i.e., compute-and-forward (CPF), is proposed. We also adjust the methods in the literature to obtain the integer network-constructed coefficient matrix (i.e., a naive method, a local optimal method, and a global optimal method) to fit the general topology with an arbitrary number of relays. Three transmission scenarios are addressed. The first scenario is delay-stringent transmission, where each message must be delivered within one slot. The second scenario is delay-tolerant transmission where no delay constraint is imposed. The associated optimization problems to maximize the short- and long-term common multicast throughputs are formulated and solved, and the optimal allocation of power and time slots are presented. The third case (a general $N$-slot-delay-tolerant scenario) is also discussed, and a suboptimal algorithm is presented. Performance comparisons show that the CPF strategy outperforms conventional decode-and-forward (DF) strategy. It is also shown in the simulation that with more relays, the CPF strategy performs even better due to the increased diversity. Finally, by simulation, it is observed that, with CPF, the $N$-slot-delay-constraint case can perform close to that of the delay-tolerant case in terms of throughput, given that $N$ is relatively large. [ABSTRACT FROM PUBLISHER]

In this paper, we design and evaluate the proposed geographic-based spray-and-relay (GSaR) routing scheme in delay/disruption-tolerant networks. To the best of our knowledge, GSaR is the first spray-based geographic routing scheme using historical geographic information for making a routing decision. Here, the term spray means that only a limited number of message copies are allowed for replication in the network. By estimating a movement range of destination via the historical geographic information, GSaR expedites the message being sprayed toward this range, meanwhile prevents that away from and postpones that out of this range. As such, the combination of them intends to fast and efficiently spray the limited number of message copies toward this range and effectively spray them within range, to reduce the delivery delay and increase the delivery ratio. Furthermore, GSaR exploits delegation forwarding to enhance the reliability of the routing decision and handle the local maximum problem, which is considered to be the challenges for applying the geographic routing scheme in sparse networks. We evaluate GSaR under three city scenarios abstracted from real world, with other routing schemes for comparison. Results show that GSaR is reliable for delivering messages before the expiration deadline and efficient for achieving low routing overhead ratio. Further observation indicates that GSaR is also efficient in terms of a low and fair energy consumption over the nodes in the network. [ABSTRACT FROM PUBLISHER]

In cooperative communication networks, owing to the nodes' arbitrary geographical locations and individual oscillators, the system is fundamentally asynchronous. Such a timing mismatch may cause rank deficiency of the conventional space–time codes and, thus, performance degradation. One efficient way to overcome such an issue is the delay-tolerant space–time codes (DT-STCs). The existing DT-STCs are designed assuming that the transmitter has no knowledge about the channels. In this paper, we show how the performance of DT-STCs can be improved by utilizing some feedback information. A general framework for designing DT-STC with limited feedback is first proposed, allowing for flexible system parameters such as the number of transmit/receive antennas, modulated symbols, and the length of codewords. Then, a new design method is proposed by combining Lloyd's algorithm and the stochastic gradient-descent algorithm to obtain optimal codebook of STCs, particularly for systems with linear minimum-mean-square-error receiver. Finally, simulation results confirm the performance of the newly designed DT-STCs with limited feedback. [ABSTRACT FROM PUBLISHER]

With the growing popularization of Electric Vehicle (EVs), Electro-mobility (in terms of where to charge EV) has become an increasingly important research problem in smart cities. One of the major concerns is the anxiety of EVs, as drivers may suffer from discomfort due to long charging time. In this paper, we leverage the battery switch technology to provide an even faster charging than plug-in charging service, by cycling switchable (fully recharged) batteries at Charging Stations (CSs). Upon that, a cost-efficient Publish/Subscribe (P/S) system is provisioned, to facilitate the design of distributed charging manner for privacy guarantee. The proposed communication framework utilizes Mobile Edge Computing (MEC)-functioned Road Side Units (RSUs) to bridge, process, and aggregate the information flow between CSs and EVs. We further design an advanced reservation-based charging system, in which the knowledge of EVs' reservations is utilized to predict how likely a CS will be congested. This benefits to a smart transportation planning on where to charge, in order to improve charging comfort. Results show the advantage of our enabling technology comparing to other benchmark solutions, in terms of minimized waiting time for the battery switch (as the benefit for EV drivers), and a higher number of batteries switched (as the benefit for CSs). [ABSTRACT FROM AUTHOR]

This paper proposes an enhanced PRIvacy preserVing opportunistic routing protocol (ePRIVO) for vehicular delay-tolerant networks (VDTN). ePRIVO models a VDTN as a time-varying neighboring graph where edges correspond to neighboring relationship between pairs of vehicles. It addresses the problem of vehicles taking routing decision meanwhile keeping their information private, i.e., vehicles compute their similarity and/or compare their routing metrics in a private manner using the Paillier homomorphic encryption scheme. The effectiveness of ePRIVO is supported through extensive simulations with synthetic mobility models and a real mobility trace. Simulation results show that ePRIVO presents on average very low cryptographic costs in most scenarios. Additionally, ePRIVO presents on average gains of approximately 29% and 238% in terms of delivery ratio for the real and synthetic scenarios considered compared to other privacy-preserving routing protocols. [ABSTRACT FROM AUTHOR]

Delay-tolerant networks (DTNs) are typically sparse ad hoc networks where node density is low and contacts between nodes in the network do not occur very frequently. The existing location privacy protection methods, which require mobile nodes to collectively change their pseudonyms in special regions called mix zones, may not work well in DTNs due to their unique characteristics, including low network density and limited contact duration. In this paper, we propose a novel cooperative location privacy protection scheme, which is called AVATAR, for sparse DTNs. The main idea of AVATAR is to generate a certain number of virtual nodes in the proximity of a node and allow both virtual and real nodes to make a coordinated pseudonym change in an enlarged region, which are named virtual mix zones. Each AVATAR participant benefits from increased location privacy protection at the cost of generating a series of signed position messages, which are named footprint signatures. To stimulate each node to contribute more footprint signatures to the virtual mix zones, AVATAR proposes a reward mechanism, which is modeled as a multiunit discriminatory auction game. Extensive simulations and analysis have been provided to demonstrate the effectiveness and efficiency of the proposed scheme. [ABSTRACT FROM PUBLISHER]

In vehicle delay tolerant networks (VDTNs), current routing algorithms select relay vehicles based on either vehicle encounter history or predicted future locations. The former method may fail to find relays that can encounter the target vehicle in a large-scale VDTN, while the latter method may not provide accurate location prediction due to traffic variance. Therefore, these methods cannot achieve high performance in terms of routing success rate and delay. In this paper, we aim to improve the routing performance in VDTNs. We first analyze vehicle network traces and observe that 1) each vehicle has only a few active subareas that it frequently visits, and 2) two frequently encountered vehicles usually encounter each other in their active subareas. We then propose an active area based routing method (AAR), which consists of two steps based on the two observations correspondingly. AAR first distributes a packet copy to each active subarea of the target vehicle using a traffic-aware shortest path spreading algorithm, and then in each subarea, each packet carrier tries to forward the packet to a vehicle that has high encounter frequency with the target vehicle. In addition to the basic AAR, we further propose an advanced AAR (AAAR). In the AAAR, we improve the routing efficiency in each subarea by exploiting spatio-temporal correlation and developing three strategies for calculating spatio-temporal correlation. Extensive trace-driven simulation demonstrates that AAR produces higher success rates and shorter delay in comparison with the state-of-the-art routing algorithms in VDTNs. Also, the simulation shows that our advanced AAAR has better performances than our AAR. [ABSTRACT FROM PUBLISHER]

Delay-tolerant network (DTN) is developed to cope with intermittent connectivity and long delay in wireless networks. Due to limited connectivity, DTN is vulnerable to flooding attack in which malicious nodes flood the network with superfluous data to deplete the network resources. Existing works mitigate internal flooding attacks by rate limit to constrain the number of messages that nodes can generate per time slot. However, rate limit cannot flexibly accommodate burst traffic in which nodes may have sending demands higher than the rate limit for a short period. In this paper, we propose flooding detection based on encounter records (FDER) to detect flooding attack and yet allow legitimate burst traffic simultaneously. Nodes exchange their histories of encounter records (ER), which record the sent messages during their previous encounters. The ER history is used to infer a node's new message transmission rate over time and the number of forwarded replicas per message. The adversary nodes that send too many messages or replicas can thus be detected. Since ERs serve as useful tools for monitoring the sending behavior of nodes over a long time period, FDER could detect the burst traffic violation efficiently. We also design fairness policy (FP)—a fairness forwarding policy to ensure fairness in the delivery performance fairness between nodes with normal traffic and those with burst traffic. FP uses ER information to observe nodes’ rate of new message generation and adjust their forwarding priorities accordingly. Simulation results show that FDER can detect flooding attack at a higher accuracy and a lower delay compared to a state-of-the-art scheme with affordable overhead. Moreover, FP could mitigate the smart flooding attack and still provide the performance fairness to support bursty traffic scenario. [ABSTRACT FROM PUBLISHER]

The delay/disruption-tolerant network (DTN) was proposed as an end-to-end networking architecture for file delivery service in a stressed communication environment. A typical application of DTN technology is for reliable data delivery in deep-space vehicle communications. The main protocol of DTN, i.e., bundle protocol (BP), utilizes a store-and-forward mechanism and a custody transfer option for transmission reliability. However, little work has been done on the performance evaluation of DTN's BP in deep-space communications. In this paper, we present a study of the retransmission timeout (RTO) timer setting for the use of BP for reliable file (or data) transmission over a relay-based deep-space vehicle communication infrastructure characterized by extremely long latency, lossy data links, and highly asymmetric channel rates. Unlike most studies proposed for terrestrial Internet for which the RTO timer is set equal to or longer than the round-trip time (RTT), we propose to set the RTO timer shorter than the RTT and expect that it will increase delivery efficiency per unit of time. We intend to find an RTO timer setting for maximum data delivery performance of BP, which is considered to be an optimal RTO timer, for deep-space missions. For the first time, analytical models are built for delivery performance involving the RTO timer. Using the built models, we tune the RTO timer toward the highest data delivery performance. The models are validated by running text file transfer experiments using a PC-based testbed and tuning the RTO timer toward the best performance of BP. A performance comparison between the optimal RTO timer proposed in this study and the existing commonly used RTO timers is also presented. [ABSTRACT FROM PUBLISHER]

Delay-tolerant networks (DTNs) are an emergent communication paradigm characterized by intermittent connectivity. The nodes in DTNs can take advantage of their contact opportunities to forward messages. However, in noncooperative DTNs, the nodes may be selfish and reluctant to cooperate with each other in message forwarding. In such DTNs, stimulating cooperation among the nodes will be indispensable. Recently, many incentive mechanisms have been proposed to motivate nodes to cooperate in message forwarding. However, most of them cannot guarantee systematic security. To resolve the drawback of the previous incentive mechanisms, we first propose a credit-based rewarding scheme called the earliest path singular rewarding (EPSR) scheme to motivate the nodes to truthfully forward the messages during every contact opportunity. Then, we propose another credit-based rewarding scheme called the earliest path cumulative rewarding (EPCR) scheme by further considering that a node may get more contact information on others. We prove that both the EPSR and EPCR schemes are incentive compatible, and the payment for each delivered message is upper bounded. Furthermore, the proposed schemes can prevent selfish nodes having malicious behaviors. We have conducted real-trace-based simulations to illustrate the effectiveness of the proposed EPSR and EPCR schemes. [ABSTRACT FROM AUTHOR]

Delay-tolerant networks (DTNs) rely on the mobility of nodes and their contacts to make up with the lack of continuous connectivity and, thus, enable message delivery from source to destination in a “store–carry–forward” fashion. Since message delivery consumes resource such as storage and power, some nodes may choose not to forward or carry others' messages while relying on others to deliver their locally generated messages. These kinds of selfish behaviors may hinder effective communications over DTNs. In this paper, we present an efficient incentive-compatible (IC) routing protocol (ICRP) with multiple copies for two-hop DTNs based on the algorithmic game theory. It takes both the encounter probability and transmission cost into consideration to deal with the misbehaviors of selfish nodes. Moreover, we employ the optimal sequential stopping rule and Vickrey–Clarke–Groves (VCG) auction as a strategy to select optimal relay nodes to ensure that nodes that honestly report their encounter probability and transmission cost can maximize their rewards. We attempt to find the optimal stopping time threshold adaptively based on realistic probability model and propose an algorithm to calculate the threshold. Based on this threshold, we propose a new method to select relay nodes for multicopy transmissions. To ensure that the selected relay nodes can receive their rewards securely, we develop a signature scheme based on a bilinear map to prevent the malicious nodes from tampering. Through simulations, we demonstrate that ICRP can effectively stimulate nodes to forward/carry messages and achieve higher packet delivery ratio with lower transmission cost. [ABSTRACT FROM PUBLISHER]

In recent years, the capacity of cellular networks has hardly kept pace with the dramatic explosion of cellular traffic from emerging mobile applications. To address this issue, a number of studies have been proposed to offload the cellular traffic using delay-tolerant networks (DTNs) opportunistically formed by mobile devices. These offloading schemes rely on the assumption of small-size content, which can be entirely transmitted over a single DTN contact. However, such an assumption, which was probably valid in the past, can no longer hold with the increasing popularity of large-size multimedia contents in the future. In this paper, we propose a novel contact-duration-aware offloading scheme called Coff, which consists of several designs that are specially tailored for DTNs. First, we use content fragmentation to utilize short contacts. Second, we adopt network coding to achieve a near-optimum dissemination. Finally, we design a greedy load allocation (GLA) algorithm to achieve no less than (\mbox1-\mbox1/e) of the optimum. Extensive simulations on both synthetic and real-world traces show that Coff is more efficient than the baselines, which extend from state-of-art DTN-based offloading schemes with content fragmentation and network coding. [ABSTRACT FROM AUTHOR]

Delay-tolerant network (DTN) is a network that’s designed to operate effectively in heterogeneous networks that may lack continuous network connectivity. It is characterized by their lack of instantaneous end-to-end paths, resulting in difficulties in designing effective DTN routing protocols. Traditional routing algorithms largely rely on greedy schemes. Such schemes can not guarantee the packets will be eventually transmitted to their destinations, thereby presenting a poor transmission efficiency. Recently, the social-based method has attracted a large amount of attention in wireless network routing. It can use the community and the centrality information to increase the delivery rate of the whole network. Therefore, in this article, we introduce the social-based mechanism to our DTN routing design. Besides, how the distributed nodes can learn the collaboration strategies is another challenge. Inspired by the recent success of multi-agent learning in online control, we adopt a centralized training and distributed execution learning paradigm and design a hierarchical social-based DTN architecture. Based on this, we propose a collaborative multi-agent reinforcement learning (termed as QMIX) aided routing algorithm. [ABSTRACT FROM AUTHOR]

To provide communication services in delay-tolerant networks (DTNs) where there may exist no end-to-end paths between mobile node pairs, a variety of relaying and routing algorithms have been proposed under the assumption that the mobile nodes are homogeneously distributed in the network with the same contact rate and delivery cost. However, experimental data have revealed the heterogeneous contact rates between node pairs, and various applications of DTNs have shown that the mobile nodes often belong to different types in terms of energy consumption, communication ability, and other properties. Following the philosophy of exploiting the heterogeneous features of nodes to enhance the routing performance, we design an optimal relaying scheme for DTNs, which takes into account the nodes' heterogeneous contact rates and delivery costs when selecting relays to minimize the delivery cost while satisfying the required message delivery probability. We use the trace-driven simulations to demonstrate the effectiveness of our optimal relaying scheme in various distributions of nodes' delivery costs and mobility environments. Simulation results show that our proposed optimal relaying scheme requires the least delivery cost and achieves the largest maximum delivery probability, compared with the schemes that neglect or do not fully take into account nodes' heterogeneity. [ABSTRACT FROM PUBLISHER]

In this work, we study the problem of jamming avoidance for ensuring quality-of-service (QoS) in terms of the network lifetime and overhead in wireless sensor networks (WSNs). We propose a mobility model using Single-Leader-Multiple-Followers Stackelberg game theory to avoid the jamming affected region. In the proposed model, the centralized unit (CU) identifies the jamming affected region based on the locations of the affected nodes and acts as the leader. On the other hand, the jamming affected nodes act as followers and decide the mobility pattern, including the angle of movement, while minimizing the energy consumption and delay in packet delivery. A scheme, named M-JAW, for ensuring QoS, while avoiding jammers in WSNs, is proposed using the stated game-theoretic mobility model. Using M-JAW, the energy consumption of the overall network reduces by up to $\text{20.36}\%$ , and the network overload reduces by 44.13– $\text{50.12}\%$ , which, in turn, increases the lifetime of WSNs. [ABSTRACT FROM AUTHOR]