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Rapid developments in the communication arena has tremendously improved the transmission procedures today. The amount of information transmission in the commercial and military applications has grown tremendously therefore the need for security concerns have also grown simultaneously since these applications involve in the transmission of confidential contents. Information transmissions in wireless networks appear to be confidential, hence it becomes mandatory to safeguard these contents from the various available offenses by means of devising suitable security mechanisms. Various types of attacks have been observed in the ad hoc networks, namely, the active and passive types, internal and external types. Integrity, identity and privacy are the three major parameters to be ensured in the design of a secure network. This survey paper discusses about the various attacks on a network together with the essential security procedures to be incorporated for securing the network. [ABSTRACT FROM AUTHOR]

This paper studies finding the secure path according to the secrecy connectivity probability (SCP) in the multihop ad hoc networks in the presence of inhomogeneous eavesdropper clusters. We consider both random and fixed eavesdropper clusters, where the former case assumes that there is no knowledge of the locations of the clusters and the latter case assumes that the locations of the clusters can be estimated accurately. First, we derive the end-to-end SCP to characterize the secrecy performance of a given path in a general multihop wireless network with half-duplex randomize-and-forward relaying. Then, we consider a full-duplex scheme at the legitimate receiver, which receives the useful information while broadcasting a jamming signal to the potential eavesdroppers to further enhance the secrecy connectivity. Then, a novel secure routing algorithm that can provide the maximum SCP for any legitimate transmitter/receiver pair in a distributed manner is proposed. The theoretical analysis is verified by Monte Carlo simulation results. The results show that our secure routing algorithm provides similar results compared to an exhaustive search. For the random eavesdropper cluster case, the optimal route is independent of the knowledge of the cluster, which is the same as the homogeneous eavesdropper case. However, for the case where eavesdropper clusters are fixed and their locations are knowna priori, the optimal path selection depends on the radii and locations of the eavesdropper clusters and the average number of eavesdroppers in each cluster. [ABSTRACT FROM AUTHOR]

In this paper, we present a routing and interface assignment algorithm for multi-channel multi-interface (MCMI) wireless ad hoc networks. An MCMI network consists of nodes that have more than one interface, and more than one channel available for transmission. The proposed algorithm takes into account both the number of hops between the source to the destination nodes, and the effects of adjacent hop interference. The algorithm has two decoupled steps: route selection and interface assignment. The step of route selection finds the path that has the minimum lower bound among all possible routes between the source and the destination while the step of interface assignment assigns an interface to a channel on each hop on that path. The interface assignment is based on the use of the Viterbi algorithm. The use of decoupled steps makes the algorithm computationally efficient, while the use of the lower bound metrics in route selection and the Viterbi algorithm in interface assignment helps improving the global optimality of the routing. Computer simulation and examples are used to demonstrate the effectiveness and performance of the proposed technique. Comparisons are made to other existing routing techniques in the area of dynamical spectrum access. [ABSTRACT FROM AUTHOR]

A Multi-Beam Antenna (MBA) can be defined as a set of directional radio transceivers. These transceivers are facing different directions to prevent signal interference with each other. MBA nodes have two main characteristics: the Multi-Packet Transmission (MPT) capability and the Multi-Packet Reception (MPR) capability whereby a node can transmit/receive multiple packets at the same time. In this paper, we provide an analysis of how this MPT/MPR capability can be used to reduce the end-to-end delay for delivered packets in ad hoc networks. Taking beam considerations (determination of the beam in which neighbors are located) into account, we formulate the delay reduction issue as an optimization problem that we solve. Our results show that to maximally exploit the full potential of MBAs for delay reduction, the scheduling of links has to promote the formation of star nodes and keep the formation of bridges to a minimum; all of which leads to the selection of routes that very often are not the shortest. In fact, using only the shortest routes has a negative impact on the delay. However, the optimal link scheduling comes at the expense of a higher overhead in terms of the total number of packet transmissions. Furthermore, the beamwidth has a direct and significant impact on the end-to-end delay and the computation time. [ABSTRACT FROM AUTHOR]

This paper develops a stochastic geometry-based approach for the modeling and analysis of single- and multi-cluster wireless networks. We first define finite homogeneous Poisson point processes to model the number and locations of the transmitters in a confined region as a single-cluster wireless network. We study the coverage probability for a reference receiver for two strategies; closest-selection, where the receiver is served by the closest transmitter among all transmitters, and uniform-selection, where the serving transmitter is selected randomly with uniform distribution. Second, using Matern cluster processes, we extend our model and analysis to multi-cluster wireless networks. Here, two types of receivers are modeled, namely, closed- and open-access receivers. Closed-access receivers are distributed around the cluster centers of the transmitters according to a symmetric normal distribution and can be served only by the transmitters of their corresponding clusters. Open-access receivers, on the other hand, are placed independently of the transmitters and can be served by all transmitters. In all cases, the link distance distribution and the Laplace transform (LT) of the interference are derived. We also derive closed-form lower bounds on the LT of the interference for single-cluster wireless networks. The impact of different parameters on the performance is also investigated. [ABSTRACT FROM AUTHOR]

In this paper, we consider the problem of joint secure routing and transmit power optimization for a multi-hop ad-hoc network under the existence of randomly distributed eavesdroppers following a Poisson point process. Secrecy messages are delivered from a source to a destination through a multi-hop route connected by multiple legitimate relays in the network. Our goal is to minimize the end-to-end connection outage probability under the constraint of a secrecy outage probability threshold, by optimizing the routing path and the transmit power of each hop jointly. We show that the globally optimal solution could be obtained by a two-step procedure where the optimal transmit power has a closed-form and the optimal routing path can be found by Dijkstra’s algorithm. Then a friendly jammer with multiple antennas is applied to enhance the secrecy performance further, and the optimal transmit power of the jammer and each hop of the selected route is investigated. This problem can be solved optimally via an iterative outer polyblock approximation with 1-D search algorithm. Furthermore, suboptimal transmit powers can be derived using the successive convex approximation method with a lower complexity. Simulation results show the performance improvement of the proposed algorithms for both non-jamming and jamming scenarios, and also reveal a non-trivial tradeoff between the numbers of hops and the transmit power of each hop for secure routing. [ABSTRACT FROM AUTHOR]

Estimating communication latency is a challenging task in the applications of industrial Internet of things (IIoT). Mobile convergecast, as a many-to-one communication pattern, has been recently explored in mobile sensor networks for IIoT, where sensor nodes are usually in mobile status, and report the sensed data regularly or randomly to one or more stationary sinks through the multihop routing path. As convergecast becomes increasingly relevant for industrial sensing and monitoring, a critical part of empowering information aggregation is to maintain consistent transmission. Path duration is one important component of end-to-end delay for communications along the path. In this paper, a probabilistic model for mobile convergecast has been proposed and evaluated to capture path duration times, by considering parameters including network models, sensor network scope, and mobility patterns of network elements. Through experiments, it has been verified that the proposed model can provide a feasible analysis of end-to-end delays in industrial networks implementing convergecast. [ABSTRACT FROM AUTHOR]

Cache-enabled wireless networks have gained increasing popularity in recent years for facilitating the delivery of content. Most existing works assumed that the network is static without the change of users and content, which is not the case in the real world. In this paper, we study the content delivery in cache-enabled wireless networks, where the network evolves in terms of users and content. We adopt the affiliation network model to reveal the network evolution process, where new users and content are added into the network randomly and connected with existing nodes via the preferential attachment. Users with strong social relations tend to request the same content objects, thus content popularity is sharply concentrated. Therefore, caching technique is more effective. To maximize the content delivery rate, we formulate the optimization problem of caching replication jointly with routing strategy. We show that network evolution can greatly improve the content delivery rate. In particular, when per-user cache capacity is in the order of $\Theta (1)$ , per-user delivery rate can achieve constant, i.e., the network can scale. Finally, theoretical results are validated based on a real-world data set from Facebook. [ABSTRACT FROM AUTHOR]

Network location is one of the critical issues and a challenge in wireless sensor and ad hoc networks, in particular when networks are sparse. However, even in highly sparse networks, there exist well-connected subgraphs while the distribution of the networks is random. This paper introduces weighted component stitching (WCS) to find redundantly rigid components with high redundant ratios, which can be used to generate reliable local realization. Finding and ranking the redundantly rigid components is an NP-hard problem (a reduction from maximum quasi-clique). Here, we introduce a series of theorems and algorithms to carry out WCS efficiently. More precisely, we prove that each graph has a determinant number of redundantly rigid components, each redundantly rigid component is covered by a set of basic redundant components (BRCs), and each BRC contains one redundant edge. We apply constraints to merge the BRCs to form components with higher redundancy ratio and develop a greedy algorithm to merge BRCs to form locally mostly redundant components (LMRCs). Finally, we give the approximation ratio. The local coordinates of nodes are calculated by optimization in each LMRC and are synchronized with weights to produce the global coordinates of nodes in the network to overcome the sparseness of subgraphs. Extensive experiments demonstrate significant improvements in accuracy (45%–64%) using our WCS method over the state-of-the-art algorithms under various settings of network sparseness and ranging noises. [ABSTRACT FROM AUTHOR]

In the last years, the advancements in signal processing and integrated circuits technology allowed several research groups to develop working prototypes of in–band full–duplex wireless systems. The introduction of such a revolutionary concept is promising in terms of increasing network performance, but at the same time poses several new challenges, especially at the MAC layer. Consequently, innovative channel access strategies are needed to exploit the opportunities provided by full–duplex while dealing with the increased complexity derived from its adoption. In this direction, this paper proposes RTS/CTS in the Frequency Domain (RCFD), a MAC layer scheme for full–duplex ad hoc wireless networks, based on the idea of time–frequency channel contention. According to this approach, different OFDM subcarriers are used to coordinate how nodes access the shared medium. The proposed scheme leads to efficient transmission scheduling with the result of avoiding collisions and exploiting full–duplex opportunities. The considerable performance improvements with respect to standard and state–of–the–art MAC protocols for wireless networks are highlighted through both theoretical analysis and network simulations. [ABSTRACT FROM AUTHOR]

The performance of backoff scheme plays an important role in designing efficient Medium Access Protocols for ad hoc networks. In this paper, we propose an adaptive backoff scheme and evaluate the performance of the proposed scheme for ad hoc networks. The backoff mechanism devised by us grants a node access to the channel based on its probability of collision for a transmitted frame in comparison to the nodes in the two-hop contention area. We use both an analytical model and simulation experiments to evaluate the performance of our adaptive backoff mechanism in an ad hoc network. The results show that our protocol exhibits a significant improvement in power saving, end-to-end goodput, packet delivery ratio, and hop-put, compared with the existing IEEE 802.11 DCF. Copyright © 2010 John Wiley & Sons, Ltd. In this paper, we propose an adaptive backoff scheme and evaluate the performance of the proposed scheme for ad hoc networks. The backoff mechanism devised by us grants a node access to the channel based on its probability of collision for a transmitted frame in comparison to those of nodes in the two-hop contention area. We use both an analytical model and simulation experiments to evaluate the performance of our adaptive backoff mechanism in an ad hoc network. The results show that our protocol exhibits a significant improvement in power saving, end-to-end goodput, packet delivery ratio, and hop put, compared to the existing IEEE 802.11 DCF. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, we discuss distributed algorithms to construct ring-like overlays over a subset of scattered nodes in a static, random wireless ad hoc and sensor network (WASN). A ring-like overlay consists of a unidirectional ring plus side paths or loops, in which the given subset of nodes may appear multiple times. Different from a Hamiltonian cycle, a ring-like overlay is easier to construct and more efficient to operate. Yet, it can support many useful control operations in WASN such as mutual exclusion, clock synchronization, and cluster management. Compared with other topologies, a ring-like overlay allows conflict-free two-way communications, supports node ordering, and provides cost-free status feedbacks of operations. In this paper, we first present a distributed algorithm to construct a proximity-aware ring-like overlay in WASN. We then show optimization techniques to adapt the primitive overlays to meet the various application requirements. [ABSTRACT FROM AUTHOR]

Relay nodes in an ad hoc network can be modelled as fluid queues, in which the available service capacity is shared by the input and output. In this paper such a relay node is considered; jobs arrive according to a Poisson process and bring along a random amount of work. The total transmission capacity is fairly shared, meaning that, when n jobs are present, each job transmits traffic into the queue at rate 1/( n + 1) while the queue is drained at the same rate of 1/( n + 1). Where previous studies mainly concentrated on the case of exponentially distributed job sizes, the present paper addresses regularly varying jobs. The focus lies on the tail asymptotics of the sojourn time S. Using sample-path arguments, it is proven that $${\mathbb{P}\left\{ S > x \right\}}$$ behaves roughly as the residual job size, i.e., if the job sizes are regularly varying of index − ν, the tail of S is regularly varying of index 1 − ν In addition, we address the tail asymptotics of other performance metrics, such as the workload in the queue, the flow transfer time and the queueing delay. [ABSTRACT FROM AUTHOR]

Abstract: Multiple-Input and Multiple-Output (MIMO) systems are recently being recognized for achieving simultaneous transmissions on wireless channels that overlap in time. As a result, new scheduling mechanisms are required that coordinate these multiple transmissions among wireless stations which share a single wireless channel. This paper proposes a new distributed MIMO-aware medium access control (MA-MAC) protocol which allows two simultaneous transmissions overlapped in time when stations are equipped with MIMO. The proposed MA-MAC protocol is compatible with the existing IEEE 802.11 standard for wireless local area networks (WLANs). It uses weighted nulling and intelligent packet fragmentation for its operation. Detailed performance analysis of MA-MAC protocol is carried out using the NS-2 network simulator. Firstly, this paper presents the concept of weighted nulling that is necessary for simultaneous transmissions on wireless channel, followed by a detailed description of the proposed MA-MAC scheme. Secondly, it presents the performance of MA-MAC scheme under various network scenarios that includes both saturated and unsaturated conditions. This paper presents the performance improvements shown by MA-MAC when compared with an existing medium access control scheme which is also proposed for scheduling simultaneous transmissions for MIMO. [Copyright &y& Elsevier]

The mobile ad hoc wireless network (MAWN) promises to become an ever-present technology with application to a myriad of areas. This networking scheme has its roots in DoD technology, yet, the ability to measure and calculate its reliability is largely absent. This paper describes the unique attributes of the MAWN and how the classical methods for analysis of network reliability must be adjusted. The methods developed acknowledge the dynamic and scalable nature of the new networking scheme along with its absence of infrastructure and remove the need to a priori define a network configuration. The methods rely on a novel modeling approach that recognizes the effects of mobility on the formation of the network's configurations. Hence, this paper proposes a Monte Carlo simulation method that accounts for node mobility, node reliability and node performance in the network's connectivity and resultant network reliability. [ABSTRACT FROM AUTHOR]

In this paper, we study distributed opportunistic scheduling (DOS) in an ad hoc network, where many links contend for the same channel using random access. In such a network, DOS involves a process of joint channel probing and distributed scheduling. Due to channel fading, the link condition corresponding to a successful channel probing could be either good or poor. In the latter case, further channel probing, although at the cost of additional delay, may lead to better channel conditions and hence yield higher throughput. The desired tradeoff boils down to judiciously choosing the optimal stopping rule for channel probing and distributed scheduling. In this paper, we pursue a rigorous characterization of the optimal strategies from two perspectives, namely, a network-centric perspective and a user-centric perspective. We first consider DOS from a network-centric point of view, where links cooperate to maximize the overall network throughput. Using optimal stopping theory, we show that the optimal scheme for DOS turns out to be a pure threshold policy, where the rate threshold can be obtained by solving a fixed-point equation. We further devise iterative algorithms for computing the threshold. We also generalize the studies to take into account fairness requirements. Next, we explore DOS from a user-centric perspective, where each link seeks to maximize its own throughput. We treat the problem of threshold selection across different links as a noncooperative game. We explore the existence and uniqueness of the Nash equilibrium, and show that the Nash equilibrium can be approached by the best response strategy. Since the best response strategy requires message passing from neighboring nodes, we then develop an online stochastic iterative algorithm based on local observations only, and establish its convergence to the Nash equilibrium. Because there is an efficiency loss at the Nash equilibrium, we then study pricing-based mechanisms to mitigate the loss. Our results reveal that rich physical layer/MAC layer (PHY/MAC) diversities are available for exploitation in ad hoc networks. We believe that these initial steps open a new avenue for channel-aware distributed scheduling. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we analyze the average end-to-end delay and maximum achievable per-node throughput in random access multihop wireless ad hoc networks with stationary nodes. We present an analytical model that takes into account the number of nodes, the random packet arrival process, the extent of locality of traffic, and the back off and collision avoidance mechanisms of random access MAC. We model random access multihop wireless networks as open G/G/1 queuing networks and use the diffusion approximation in order to evaluate closed form expressions for the average end-to-end delay. The mean service time of nodes is evaluated and used to obtain the maximum achievable per-node throughput. The analytical results obtained here from the queuing network analysis are discussed with regard to similarities and differences from the well established information-theoretic results on throughput and delay scaling laws in ad hoc networks. We also investigate the extent of deviation of delay and throughput in a real world network from the analytical results presented in this paper. We conduct extensive simulations in order to verify the analytical results and also compare them against NS-2 simulations. [Copyright &y& Elsevier]

Wireless ad hoc networks are expected to provide broadband services parallel to their wired counterparts in near future. To address this need, MIMO (multiple-input-multiple-output) antenna techniques hold significant promise. Most previous work on capacity analysis of ad hoc networks is based on an implicit assumption that each link exclusively occupies a geometric area, referred to as exclusion region that characterizes the amount of spatial resource occupied by a link. When multiple antennas are deployed at each node, however, multiple links can transmit in the vicinity of each other simultaneously, as interference can now be suppressed by spatial signal processing. As such, the concept of "exclusion region" no longer applies. In this paper, we investigate link-layer throughput capacity of MIMO ad-hoc networks. In contrast to previous work, the amount of spatial resource occupied by each link is characterized by the actual interference it imposes on other links. To calculate the link-layer capacity, we first derive the probability distribution of post-detection SINR (signal to interference and noise ratio) at a receiver. The result is then used to calculate the number of active links and the corresponding data rates that can be sustained within an area. Our analysis shows that there exists an optimal active-link density that maximizes the link-layer throughput capacity. This will serve as a guideline for the design of medium access protocols for MIMO ad-hoc networks. To the best of knowledge, this paper is the first attempt to characterize the capacity of MIMO ad-hoc networks by considering the actual PHY-layer signal and interference model. The results in this paper pave the way for further study on network-layer transport capacity of ad-hoc networks with MIMO. [ABSTRACT FROM PUBLISHER]

In this paper, we deal with an amplify-and-forward (AF) cooperative strategy in slot-based, block-fading environments. In contrast with previous schemes, which assume a constant channel during the cooperative frame (several slots), here, we relax this constraint and assume a classical quasi-static block-fading channel (constant for one slot). This additional degree of freedom modifies the behavior of the conventional nonorthogonal AF (NAF) schemes and generates a new block-fading NAF (BFNAF) protocol, where the source can usefully retransmit the same data during the cooperative slot. This new protocol is interesting at low spectral efficiencies, where diversity against fading is more important. To overcome performance degradation, which characterizes cooperative schemes at low signal-to-noise ratios (SNR5), an adaptive version of the considered schemes is also proposed, where cooperation is activated according to the outage behavior of the direct link. Moreover, an optimal hybrid protocol that allows intelligent switching between noncooperation, NAF, and BFNAF protocols is also proposed. Another issue that is discussed throughout this paper is the optimal power allocation of the investigated schemes. The proposed power-allocation strategy uses as an optimization criterion the well-defined asymptotic expressions of the outage probabilities, which are averaged over the fading statistics. The minimization (and avoidance for the nonhybrid protocols) of the required data feedback makes it suitable for practical ad hoc networks with crucial power constraints. The enhancement of the proposed schemes and the efficiency of the power allocation policy are shown by theoretical analysis and simulation results. [ABSTRACT FROM AUTHOR]

This paper revisits the topology control problem for multi-hop wireless ad hoc networks. It accounts for the maximum number of links interfering with each node in the network, which is referred to as the interference load in the paper. Finding a topology with minimum interference load is an NP-complete problem. In this paper, we develop the essential theorems and lemmas for constructing low interference load topologies for wireless ad hoc networks. Based on the theoretical results, we provide the design guidelines for topology construction with low interference load, and propose a polynomial-time solution accordingly. The performance of the proposed mechanism is evaluated via simulations. The results show that the proposed mechanism outperforms existing work in terms of lower interference load even using the maximum transmission power in the generated topology. [ABSTRACT FROM PUBLISHER]

For today's mobile applications in ubiquitous/pervasive environments, the classical client-server approach with tightly-coupled components does not suit anymore. Instead, new ways of information passing between such mobile components have to be searched: components will often have no dedicated communication partner, but rather send data into a certain direction in order to inform all participants in a specific area about an event or a status. This process is called data dissemination. In this paper we introduce a new data dissemination protocol named AutoCast. Unlike other approaches, AutoCast is flexible enough to support a broad variety of different types of mobile applications. The paper presents the major design decisions taken for AutoCast and the protocol features in detail. A thorough evaluation shows the effectiveness and efficiency of the new protocol. [ABSTRACT FROM AUTHOR]

Abstract: This paper shows a novel self-organizing approach for routing datagrams in ad hoc networks, called Distributed Ant Routing (DAR). This approach belongs to the class of routing algorithms inspired by the behavior of the ant colonies in locating and storing food. The effectiveness of the heuristic algorithm is supported by mathematical proofs and demonstrated by a comparison with the well-known Ad hoc On Demand Distance Vector (AODV) algorithm. The differences and the similarities of the two algorithms have been highlighted. Results obtained by a theoretical analysis and a simulation campaign show that DAR allows obtaining some important advantages that makes it a valuable candidate to operate in ad hoc networks and the same method helps in the selection of the algorithm parameters. Since the approach aims at minimizing complexity in the nodes at the expenses of the optimality of the solution, it results to be particularly suitable in environments where fast communication establishment and minimum signalling overhead are requested. These requirements are typical of ad hoc networks with critical connectivity, as described in the paper. Thus the performance of the proposed algorithm are shown in ad hoc networks with critical connectivity and compared to some existing ad hoc routing algorithms. [Copyright &y& Elsevier]

In this paper, we consider the neighbor discovery problem in wireless ad hoc networks with directional antennas. One key performance measure is how long it takes to discover all the neighbors given that nodes do not have priori knowledge where their neighbors are. One common impression is that algorithms using directional transmission/receive take longer time than those algorithms using omni-antennas. In this paper, we prove that this is not the case. Furthermore, most of the proposed algorithms are 1-way only, which is not suitable for networks with directional antennas. We first propose three 2-way random neighbor discovery algorithms (based on the algorithms in [Vasuden et al., 2005]), two of which may still use omni-antennas in certain stages of the algorithms and a new scan based algorithm. Then we derive analytical expressions for the average number of slots required to discover all the neighbors for the three 2-way random algorithms and for two scan based algorithms. Analytic and simulation results are presented to compare 4 of the algorithms. From the numerical results, we conclude that scan-based all-directional algorithms give the best performance among all the algorithms considered. If designed properly, all-directional algorithms can discover neighbors in less time than those algorithms using omni-directional antennas. [ABSTRACT FROM PUBLISHER]

In this two-part paper, we propose a decentralized strategy, based on a game-theoretic formulation, to find out the optimal precoding/multiplexing matrices for a multipoint-to-multipoint communication system composed of a set of wideband links sharing the same physical resources, i.e., time and bandwidth. We assume, as optimality criterion, the achievement of a Nash equilibrium and consider two alternative optimization problems: 1) the competitive maximization of mutual information on each link, given constraints on the transmit power and on the spectral mask imposedby the radio spectrum regulatory bodies; and 2) the competitive maximization of the transmission rate, using finite order constellations, under the same constraints as above, plus a constraint on the average error probability. In this first part of the paper, we start by showing that the solution set of both noncooperative games is always nonempty and contains only pure strategies. Then, we prove that the optimal precoding/multiplexing scheme for both games leads to a channel diagonalizing structure, so that both matrix-valued problems. can be recast in a simpler unified vector power control game; with no performance penalty. Thus, we study this simpler game and derive sufficient conditions ensuring the uniqueness of the Nash equilibrium. Interestingly, although derived under stronger constraints, incorporating for example spectral mask constraints, our uniqueness conditions have broader validity than previously known conditions. Finally, we assess the goodness of the proposed decentralized strategy by comparing its performance with the performance of a Pareto-optimal centralized scheme. To reach the Nash equilibria of the game, in Part II, we propose alternative distributed algorithms, along with their convergence conditions. [ABSTRACT FROM AUTHOR]

Abstract: Physical-layer (pulse-coupled) techniques for distributed synchronization in wireless networks are attracting significant attention for their efficiency and scalability. In this paper, the model of pulse-coupled discrete Phase Locked Loops is reviewed and further investigated in two directions. At first, we extend the characterization of (frequency or phase) synchronous states and convergence conditions from homogeneous networks, where all the nodes have the same power constraints, to more general heterogeneous networks. Towards this goal, we build on recent results on algebraic graph theory for generally non-bidirectional graphs, and derive: (i) necessary and sufficient conditions for global synchronization of the network; (ii) closed-form expressions for the asymptotic values of frequency and phases, as a function of the network topology. In the second part of the paper, an application of pulse-coupled synchronization is considered, namely data collection in a sensor network. The energy efficiency of two medium access protocols for data collection from a set of randomly located sensors to an access point is compared: (i) basic ALOHA (which does not require time synchronization among the sensors); (ii) slotted ALOHA, where time synchronization is achieved via pulse-coupled clocks. Analysis shows that the energy spent for maintaining synchronization in slotted ALOHA pays off in terms of total energy consumption with respect to basic ALOHA provided that the number of sensors is sufficiently small. Moreover, the energy gain is proved to depend explicitly on the system load (in terms of packets /s), hardware and topology of the network. [Copyright &y& Elsevier]

Wireless Sensor Networks (WSN) are a field in the computer science that the last years have been the center of research in lot of research centers and universities around the world. The advantages of this technology are a lot, small size, energy saving, long range coverage, small cost etc. One of the biggest advantages is scalability. Scalability means that a network with wireless nodes can be expanded as big as we want. Wireless sensor networks can be used in big variety of areas: rom agricultural to military applications and from in house applications to industrial applications. This paper is (one overview??) reported in the techniques and communications protocols of the WSN and demonstrates the use of wireless sensor networks for the building environment monitoring paper presents a new editing method for the Bulletin of the Transilvania University of Brasov. The intention is to obtain a better quality of the presentation. This version took into consideration a lot of papers from similar scientific bulletins. [ABSTRACT FROM AUTHOR]

In ad hoc networks, CSMA/CA is a widely used MAC layer protocol. There has been considerable work on the performance evaluation of this protocol. But most work is confined to saturation performance of single-hop ad hoc networks. In this paper, we employ a linear feedback model to evaluate the performance for CSMA/CA according to the Poisson distributed traffic in both single-hop and multi-hop ad hoc networks. To the best of our knowledge, this is the first attempt to analytically evaluate the performance for CSMA/CA protocol under a general assumption about the traffic. This paper also gives analytical results, showing the impact of RTS/CTS. Although RTS/CTS do add the overhead to the system, they become essential when either the hidden terminal problem is dominant, or the traffic is heavy, or the packet length is very large. This paper also shows that the performance degrades dramatically in multi-hop ad hoc networks when the number of competing nodes increases, which implies that the scalability is still a major problem in ad hoc networks. To validate our analytical results, we have done extensive simulations, and it is observed that the simulation results match the analytical results very well. Copyright © 2006 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, we consider a MAC protocol for ad hoc networks where nodes are equipped with multiple antennas, and communications are spatially multiplexed using the Bell labs layered space time (BLAST) system. The contribution of this paper is twofold. First, we introduce two different analytical models aimed at predicting the propagation of detection errors within the BLAST receiver, the first based on a Gaussian approximation of the detection errors, and the second on the weighed enumeration of error configurations. A simplification of the latter, with lower complexity, is also obtained and compared to the original model. We then use these analytical tools to assess the performance of a cross-layer MAC protocol, and compare it with fully detailed simulations. Since the analytical tools replace the simulation of the physical layer, the proposed semianalytical approach is much faster than the bit-by-bit simulations. Numerous results are provided for the network performance assessment, showing that our semianalytical approach is able to predict network behavior with very good accuracy, but much lower complexity. [ABSTRACT FROM PUBLISHER]

In ad hoc wireless networks, it is crucial to minimize power consumption while maintaining key network properties. This work studies power assignments of wireless devices that minimize power while maintaining κ-fault tolerance. Specifically, we require all links established by this power setting be symmetric and form a κ-vertex connected subgraph of the network graph. This problem is known to be NP-hard. We show current heuristic approaches can use arbitrarily more power than the optimal solution. Hence, we seek approximation algorithms for this problem. We present three approximation algorithms. The first algorithm gives an O(κα)-approximation where α is the best approximation factor for the related problem in wired networks (the best α so far is O (log κ).) With a more careful analysis, we show our second (slightly more complicated) algorithm is an O(κ)-approximation. Our third algorithm assumes that the edge lengths of the network graph form a metric. In this case, we present simple and practical distributed algorithms for the cases of 2- and 3-connectivity with constant approximation factors. We generalize this algorithm to obtain an O (κ2c+2)-approximation for general κ-connectivity (2 ≤ c ≤ 4 is the power attenuation exponent). Finally, we show that these approximation algorithms compare favorably with existing heuristics. We note that all algorithms presented in this paper can be used to minimize power while maintaining κ-edge connectivity with guaranteed approximation factors. Recently, different set of authors used the notion of κ-connectivity and the results of this paper to deal with the fault-tolerance issues for static wireless network settings. [ABSTRACT FROM AUTHOR]

Advances in clock synchronization techniques allow an approximated global time in ubiquitous environments. This paper presents an event stream-based online algorithm that fuses the data reported from the processors in such a network to detect time-based predicates. The algorithm has low space, time, and message complexities. The paper also considers the detection of simultaneous events as a special case. [ABSTRACT FROM AUTHOR]

This paper considers the security of sensor network applications. Our approach creates multicast regions that use symmetric key cryptography for communications. Each multicast region contains a single keyserver that is used to perform key management and maintain the integrity of a multicast region. Communications between two multicast regions is performed by nodes that belong to both regions. To ease the network management burden, it is desirable for the networks to self-organize into regions and dynamically select their keyservers. This paper shows how to determine the number of keyservers (k) to use and the size in the number of hops (h) of their multicast regions. We find that power consumption issues provide a natural trade-off that determines optimal values for these parameters. Analysis of one application shows an increase in system security with 70-80% less power overhead than existing security approaches. [ABSTRACT FROM AUTHOR]

Biological systems present remarkable adaptation, reliability, and robustness in various environments, even under hostility. Most of them are controlled by the individuals in a distributed and self-organized way. These biological mechanisms provide useful resources for designing the dynamical and adaptive routing schemes of wireless mobile sensor networks, in which the individual nodes should ideally operate without central control. This paper investigates crucial biologically inspired mechanisms and the associated techniques for resolving routing in wireless sensor networks, including Ant-based and genetic approaches. Furthermore, the principal contributions of this paper are as follows. We present a mathematical theory of the biological computations in the context of sensor networks; we further present a generalized routing framework in sensor networks by diffusing different modes of biological computations using Ant-based and genetic approaches; finally, an overview of several emerging research directions are addressed within the new biologically computational framework. [ABSTRACT FROM PUBLISHER]

Anonymity and authenticated key exchange should be paid much more attention in secure mobile ad hoc routing protocols, especially in privacy-vital environment. However, as far as we know, few papers on secure routing protocols have addressed both the anonymity and authenticated key exchange. Therefore, in this paper, we present a new secure anonymous routing protocol with authenticated key exchange for ad hoc networks. In comparison with other previous secure routing protocols, our proposed protocol not only provides the anonymity to the route from the source to the destination, but also integrates the authenticated key exchange into the routing algorithm. [Copyright &y& Elsevier]

We consider a wireless ad hoc network where each node employs a single-beam directional antenna and is provisioned with limited energy. We are interested in an online routing algorithm for successive multicast communication requests with the aim of maximizing the network lifetime. The beam-forming property, which is associated with single-beam directional antennas, introduces some unique problems that do not exist for omnidirectional antennas and, therefore, significantly increases the design space for routing algorithms. The contributions of this paper are twofold. First, we provide some important theoretical understanding on various multicast problems and deduce that even an offline version of this problem is NP-hard. Second, we develop a highly competitive online routing algorithm that takes the network lifetime consideration directly into iterative calculations and show that an algorithm that is designed under this methodology provides consistently better performance than the current state-of-the-art algorithm that only considers remaining energy. The theoretical results and routing algorithm in this paper offer some important insights on algorithm design for energy-constrained wireless ad hoc networks with directional antennas. [ABSTRACT FROM AUTHOR]

Energy efficient communication is a fundamental problem in wireless ad-hoc and sensor networks. In this paper, we explore the feasibility of a distributed beamforming approach to this problem, with a cluster of distributed transmitters emulating a centralized antenna array so as to transmit a common message signal coherently to a distant base station. The potential SNR gains from beamforming are well-known. However, realizing these gains requires synchronization of the individual carrier signals in phase and frequency. In this paper we show that a large fraction of the beamforming gains can be realised even with imperfect synchronization corresponding to phase errors with moderately large variance. We present a master-slave architecture where a designated master transmitter coordinates the synchronization of other (slave) transmitters for beamforming. We observe that the transmitters can achieve distributed beamforming with minimal coordination with the base station using channel reciprocity. Thus, inexpensive local coordination with a master transmitter makes the expensive communication with a distant base station receiver more efficient. However, the duplexing constraints of the wireless channel place a fundamental limitation on the achievable accuracy of synchronization. We present a stochastic analysis that demonstrates the robustness of beamforming gains with imperfect synchronization, and demonstrate a tradeoff between synchronization overhead and beamforming gains. We also present simulation results for the phase errors that validate the analysis [ABSTRACT FROM PUBLISHER]

The IEEE 802.16 protocol for wireless broadband access (wirelessMAN) has been standardized recently. In order to improve network coverage and scalability, mesh mode is supported in 802.16. In the mesh mode, all nodes are organized in an ad hoc fashion and use a pseudo-random function to compete for their transmission opportunities based on the scheduling information in the two-hop neighborhood. In this paper, we develop a stochastic model for the distributed mesh mode scheduler. With this model, we analyze the scheduler performance under various conditions, and the analytical results match very well with the ns-2 simulation results. The analytical model developed in this paper is instrumental in optimizing the IEEE 802.16 mesh network performance. To the best of our knowledge, this work is the first one theoretically investigating the IEEE 802.16 mesh mode scheduling performance [ABSTRACT FROM PUBLISHER]

In multi-hop ad hoc networks, stations may pump more traffic into the networks than can be supported, resulting in high packet-loss rate, re-routing instability and unfairness problems. This paper shows that controlling the offered load at the sources can eliminate these problems. To verify the simulation results, we set up a real 6-node multi-hop network. The experimental measurements confirm the existence of the optimal offered load. In addition, we provide an analysis to estimate the optimal offered load that maximizes the throughput of a multi-hop traffic flow. We believe this is a first paper in the literature to provide a quantitative analysis (as opposed to simulation) for the impact of hidden mires and signal capture on sustainable throughput. The analysis is based on the observation that a large-scale 802.11 network with hidden nodes is a network in which the carrier-sensing capability breaks down partially. Its performance is therefore somewhere between that of a carrier-sensing network and that of an Aloha network. Indeed, our analytical closed-form solution has the appearance of the throughput equation of the Aloha network. Our approach allows one to identify whether the performance of an 802.11 network is hidden-node limited or spatial-reuse limited. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we consider on-line disjoint path routing in energy-constrained ad hoc networks. The objective is to maximize the network capacity, i.e. maximize the number of messages routed successfully by the network without any knowledge of future disjoint path connection request arrivals and generation rates. Specifically, in this paper we first present two centralized on-line algorithms for the problem. One is based on maximizing local network lifetime, which aims to minimize the transmission energy consumption, under the constraint that the local network lifetime is no less than γ times of the optimum after the realization of each disjoint path connection request, where γ is constant with 0< γ ⩽1. Another is based on the exponential function of energy utilization at nodes, and the competitive ratio of this latter algorithm is also analyzed if admission control mechanism is employed. We then conduct extensive experiments by simulations to analyze the performance of the proposed algorithms, in terms of network capacity, network lifetime, and the transmission energy consumption for each disjoint path connection request. The experimental results show that the proposed algorithms outperform those existing algorithms that do not take into account the power load balancing at nodes in terms of maximizing the network capacity. [Copyright &y& Elsevier]

In this paper, we consider the problem of rate/distortion with side information available only at the decoder. For the case of jointly Gaussian source X and side information Y, and mean-squared error distortion, Wyner proved in 1976 that the rate/distortion function for this problem is identical to the conditional rate/distortion function RX∣Y, assuming the side information Y is available at the encoder. In this paper we construct a structured class of asymptotically optimal quantizers for this problem: under the assumption of high correlation between source X and side information Y, we show there exist quantizers within our class whose performance comes arbitrarily close to Wyner's bound. As an application illustrating the relevance of the high-correlation asymptotics, we also explore the use of these quantizers in the context of a problem of data compression for sensor networks, in a setup involving a large number of devices collecting highly correlated measurements within a confined area. An important feature of our formulation is that, although the per-node throughput of the network tends to zero as network size increases, so does the amount of information generated by each transmitter. This is a situation likely to be encountered often in practice, which allows us to cast under new—and more "optimistic"—light some negative results on the transport capacity of large-scale wireless networks. [ABSTRACT FROM AUTHOR]

This paper presents an ad-hoc sensor network especially developed for a disaster relief application that provides the rescue teams with a quickly deployable, cost-effective, and reliable tool to collect information about the presence of people in a collapsed building space and the state of the ruins. The hardware/software architecture of the wireless sensor nodes is developed for a low-cost design implementation. Energy efficiency is another objective of this paper, achieved by the combination of a low-power-mode algorithm and a power-aware routing strategy. A selected set of simulation studies indicate a reduction in energy consumption and a significant increase in node lifetime whereas network performance is not affected significantly. Finally, a lightweight management architecture is presented to facilitate autonomous management of ad-hoc sensor networks [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the impact of variable-range transmission power control on the physical and network connectivity, on network capacity, and on power savings in wireless multihop networks. First, using previous work by Steele [18], we show that, for a path attenuation factor α = 2, the average range of links in a planar random network of A m² having n nodes (Multiple line equation(s) cannot be represented in ASCII text). We show that this average range is approximately half the range obtained when common-range transmission control is used. Combining this result and previous work by Gupta and Kumar [8], we derive an expression for the average traffic carrying capacity of variable-range-based multihop networks. For α = 2, we show that this capacity remains constant even when more nodes are added to the network. Second, we derive a model that approximates the signaling overhead of a routing protocol as a function of the transmission range and node mobility for both route discovery and route maintenance. We show that there is an optimum setting for the transmission range, not necessarily the minimum, which maximizes the capacity available to nodes in the presence of node mobility. The results presented in this paper highlight the need to design future MAC and routing protocols for wireless ad hoc and sensor networks based, not on common-range which is prevalent today, but on variable-range power control. [ABSTRACT FROM AUTHOR]

Bluetooth networks can be constructed as piconets or scatternets depending on the number of nodes in the network. Although piconet construction is a well-defined process specified in Bluetooth standards, scatternet formation policies and algorithms are not well specified. Among many solution proposals for this problem, only a few of them focus on efficient usage of bandwidth in the resulting scatternets. In this paper, we propose a distributed algorithm for the scatternet formation problem that dynamically constructs and maintains a scatternet based on estimated traffic flow rates between nodes. The algorithm is adaptive to changes and maintains a constructed scatternet for bandwidth-efficiency when nodes come and go or when traffic flow rates change. Based on simulations, the paper also presents the improvements in bandwidth-efficiency and reduction in energy consumption provided by the proposed algorithm. [ABSTRACT FROM AUTHOR]

In third generation (3G) wireless data networks, multicast throughput decreases with the increase in multicast group size, since a conservative strategy for the base station is to use the lowest data rate of all the receivers so that the receiver with the worst downlink channel condition can decode the transmission correctly. This paper proposes ICAM, Integrated Cellular and Ad hoc Multicast, to increase 3G multicast throughput through opportunistic use of ad hoc relays. In ICAM, a 3G base station delivers packets to proxy mobile devices with better 3G channel quality. The proxy then forwards the packets to the receivers through an IEEE 802.11-based ad hoc network. In this paper, we first propose a localized greedy algorithm that discovers for each multicast receiver the proxy with the highest 3G downlink channel rate. We discover that due to capacity limitations and interference of the ad hoc relay network, maximizing the 3G downlink data rate of each multicast receiver's proxy does not lead to maximum throughput for the multicast group. We then show that the optimal CAM problem is NP-hard, and derive a polynomial-time 4-approximation algorithm for the construction of the multicast forest. This bound holds when the underlying wireless MAC supports broadcast or unicast, single rate or multiple rates (4(1 + ϵ) approximation scheme for the latter), and even when there are multiple simultaneous multicast sessions. Through both analysis and simulations, we show that our algorithms achieve throughput gains up to 840 percent for 3G downlink multicast with modest overhead on the 3G uplink. [ABSTRACT FROM AUTHOR]

This paper proposes a new approach that applies multibeam directional antennas to controlling topology by reducing the power intensity directionally instead of omnidirectionally. In contrast to omnidirectional topology control, which reduces transmission power (and, thus, the resulting transmission range) in all directions, the proposed approach maintains the original power range in certain directions while clearing the power intensity in other directions. This paper shows that the proposed approach and the omnidirectional topology control approach are equivalent in terms of the probability distribution of the number of symmetric neighbors in their resulting topologies. Major benefits of this approach include reduced and steady hop count, power saving independent of the number of neighbors within the original power range, and symmetric link in terms of SNR quality, as compared to omnidirectional topology control approaches. Simulation studies have demonstrated these benefits and highlighted its trade-offs. [ABSTRACT FROM AUTHOR]

Although individual node cooperation is necessary for the correct execution of network protocols in mobile ad hoe networks (MANETs), it is not always guaranteed. In this paper, we present a node reputation scheme aiming at reinforcing node cooperation in MANETs with centralized control. This scheme was designed for centralized ad hoc network architecture (CANA), an ad hoc enhancement to the HIPERLAN/2 WLAN standard. Misbehavior detection techniques for protocol attacks in both the cluster formation and data transmission phases of the network operation are developed. Statistical methods for selecting the optimal parameters of the reputation scheme are investigated and their efficiency is illustrated through theoretical analysis and simulation results. Throughout this paper, the specific aspects of CANA that impose particular design decisions are outlined and the applicability of our scheme to other network architectures is discussed. [ABSTRACT FROM AUTHOR]

Recently, it became apparent that group-oriented services are one of the primary application classes targeted by MANETs. As a result, several MANET-specific multicast routing protocols have been proposed. Although these protocols perform well under specific mobility scenarios, traffic loads, and network conditions, no single protocol has been shown to be optimal in all scenarios. The goal of this paper is to characterize the performance of multicast protocols over a wide range of MANET scenarios. To this end, we evaluate the performance of mesh and tree-based multicast routing schemes relative to flooding and recommend protocols most suitable for specific MANET scenarios. Based on the analysis and simulation results, we also propose two variations of flooding, scoped flooding and hyper flooding, as a means to reduce overhead and increase reliability, respectively. Another contribution of the paper is a simulation-based comparative study of the proposed flooding variations against plain flooding, mesh, and tree-based MANET routing. In our simulations, in addition to "synthetic" scenarios, we also used more realistic MANET settings, such as conferencing and emergency response. [ABSTRACT FROM AUTHOR]

This paper examines flexibility in ad hoc networks and suggests that, even with cross-layer design as a mechanism to improve adaptation, a fundamental limitation exists in the ability of a single optimization function, defined a priori, to adapt the network to meet all quality-of-service requirements. Thus, code implementing multiple algorithms will have to be positioned within the network. Active networking and programmable networking enable unprecedented autonomy and flexibility for ad hoc communication networks. However, in order to best leverage the results of active and programmable networking, metrics that indicate the nature and location of required flexibility need to be developed. The primary contribution of this paper is to propose a metric that couples network topological rate of change with the ability of a generic service to move itself to an optimal location in concert with the changing network. This metric points to a fundamental tradeoff among adaptation (changing service location), performance (sophistication or estimated minimum code size of the service), and the network's ability to tune itself to a changing ad hoc network topology. [ABSTRACT FROM AUTHOR]

This paper investigates the issues of QoS routing in CDMA/TDMA ad hoc networks. Since the available bandwidth is very limited in ad hoc networks, a QoS request between two nodes will be blocked if there does not exist a path that can meet the QoS requirements, even though there is enough free bandwidth in the whole system. In this paper, we propose a new scheme of using multiple paths between two nodes as the route for a QoS call. The aggregate bandwidth of the multiple paths can meet the bandwidth requirement of the call and the delays of these paths are within the required bound of the call. We also propose three strategies by which to choose a set of paths as the route, namely, shortest path first (SPF), largest bandwidth first (LBF), and largest hop-bandwidth first (LHBF). Extensive simulations have been conducted to evaluate the performance of the three strategies in comparison with a traditional single path routing algorithm. The simulation results show that the proposed multiple paths routing scheme significantly reduces the system blocking rates in various network environments, especially when the network load is heavy. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes an ad hoc networking scheme and routing protocol for emergency communications. The objective of the network is to collect damage assessment information quickly and stably in a disaster. The network is configured with a hybrid wireless network, combining ad hoc networks and a cellular network to maintain connectivity between a base station (BS) and nodes even in a disaster. In the event that a direct link between the BS and a node is disconnected due to damage or obstacles, the node switches to the ad hoc mode, and accesses the BS via neighboring nodes by multihopping. The routing protocol proposed in this paper discovers and builds a route by way of monitoring neighbors’ communications instead of broadcasting a route request packet. The network employs a dedicated medium access control protocol based on TDM (Time Division Multiplexing) for multihopping in ad hoc networks to maintain accessibility and to perform a short delay. Experiments showed that approximately 90% of nodes are capable of reaching the BS within a few hops, even in conditions where only 20% of nodes maintain direct connections to the BS. In addition, the results showed that it is feasible for the network to operate in a short delay for delivering a packet to the BS. However, throughput is not retrieved sufficiently due to the restriction of the access protocol, whereas reachability does improve sufficiently. Therefore, the network is suitable for collecting damage assessment information and transmitting urgent traffic quickly and stably, while the data is restricted to a small amount. [Copyright &y& Elsevier]

Abstract: IEEE 802.11 and Mote devices are today two of the most interesting wireless technologies for ad hoc and sensor networks respectively, and many efforts are currently devoted to understanding their potentialities. Unfortunately, few works adopt an experimental approach, though several papers highlight that popular simulation and analytical approximations may lead to very inaccurate results. In this paper we discuss outcomes from an extensive measurement study focused on these technologies. We analyze the dependence of the communication range on several parameters, such as node distance from the ground, transmission data rate, environment humidity. Then, we study the extent of the physical carrier sensing zone around a sending node. On the basis of these elements, we provide a unified wireless link model for both technologies. Finally, by using this model we analyze well-known scenarios (such as the hidden node problem), and we modify the traditional formulations according to our experimental results. [Copyright &y& Elsevier]