Ad Hoc Networks

Published by Elsevier
Print ISSN: 1570-8705
Publications
Multi-channel wireless networks are increasingly deployed as infrastructure networks, e.g. in metro areas. Network nodes frequently employ directional antennas to improve spatial throughput. In such networks, between two nodes, it is of interest to compute a path with a channel assignment for the links such that the path and link bandwidths are the same. This is achieved when any two consecutive links are assigned different channels, termed as "Channel-Discontinuity-Constraint" (CDC). CDC-paths are also useful in TDMA systems, where, preferably, consecutive links are assigned different time-slots. In the first part of this paper, we develop a t-spanner for CDC-paths using spatial properties; a sub-network containing O(n/θ) links, for any θ > 0, such that CDC-paths increase in cost by at most a factor t = (1-2 sin (θ/2))-2. We propose a novel distributed algorithm to compute the spanner using an expected number of O(n log n) fixed-size messages. In the second part, we present a distributed algorithm to find minimum-cost CDC-paths between two nodes using O(n2) fixed-size messages, by developing an extension of Edmonds' algorithm for minimum-cost perfect matching. In a centralized implementation, our algorithm runs in O(n2) time improving the previous best algorithm which requires O(n3) running time. Moreover, this running time improves to O(n/θ) when used in conjunction with the spanner developed.
 
TCP Throughput vs. Delay Window on Chain Topology (5 flows)  
Hybrid Wired/Wireless Topology
This paper studies the TCP performance with delayed ack in wireless networks (including ad hoc and WLANs) which use IEEE 802.11 MAC protocol as the underlying medium access control. Our analysis and simulations show that TCP throughput does not always benefit from an unrestricted delay policy. In fact, for a given topology and flow pattern, there exists an optimal delay window size at the receiver that produces best TCP throughput. If the window is set too small, the receiver generates too many acks and causes channel contention; on the other hand, if set the window too high, the bursty transmission at the sender triggered by large cumulative acks will induce interference and packet losses, thus degrading the throughout. In wireless networks, packet losses are also related to the length of TCP path; when traveling through a longer path, a packet is more likely to suffer interference. Therefore, path length is an important factor to consider when choosing appropriate delay window sizes. In this paper, we first propose an adaptive delayed ack mechanism which is suitable for ad hoc networks, then we propose a more general adaptive delayed ack scheme for ad hoc and hybrid networks. The simulated results show that our schemes can effectively improve TCP throughput by up to 30% in static networks, and provide more significant gain in mobile networks. The proposed schemes are simple and easy to deploy.
 
Future sensor networks would comprise of sensing devices with energy harvesting capabilities from renewable energy sources such as solar power. A key research question in such sensor systems is to maximize the asymptotic event detection probability achieved in the system, in the presence of energy constraints and uncertainties. This paper focuses on the design of adaptive algorithms for sensor activation in the presence of uncertainty in the event phenomena. We borrow ideas from increase/decrease algorithms used in TCP congestion avoidance, and design an online and adaptive activation algorithm, that varies the subsequent sleep interval according to additive increase and multiplicative decrease based upon the sensor's current energy level. In addition, the proposed algorithm does not depend on global system parameters, or on the degree of event correlations, and hence can easily be deployed in practical scenarios. Through extensive simulations, we demonstrate that the proposed algorithm not only achieves near-optimal performance, but also exhibits more stability with respect to sensor's energy level and sleep interval variations.
 
This paper studies the problem of interference-free broadcast in wireless ad hoc networks. In particular, we are interested in asymmetric power assignments so that the induced broadcast communication graph is both, energy efficient and has a short collision-free broadcast schedule. We consider both random and deterministic node layouts and develop four different broadcast schemes with provable performance guarantees on three optimization objectives simultaneously: total energy consumption, network lifetime and collision-free schedule length. We also show some numerical results which support our findings.
 
We present a systematic analysis of insider attacks against mobile ad-hoc routing protocols, using the Ad hoc On-Demand Distance Vector (AODV) protocol as an example. It identifies a number of attack goals and then studies how to achieve these goals through misuses of the routing messages. To facilitate the analysis, we classify the insider attacks into two categories: atomic misuses and compound misuses. Atomic misuses are performed by manipulating a single routing message, which cannot be further divided; compound misuses are composed of combinations of atomic misuses and possibly normal uses of the routing protocol. The analysis results reveal several classes of insider attacks, including route disruption, route invasion, node isolation, and resource consumption. We also describe simulation results that demonstrate the impact of these attacks.
 
Wireless sensor networks have been used for many delay-sensitive applications, e.g., emergency response and plant automation. In such networks, delay measurement is important for a number of reasons, e.g., real-time control of the networked system, and abnormal delay detection. In this paper, we propose a measurement architecture using distributed air sniffers, which provides convenient delay measurement, and requires no clock synchronization or instrumentation at the sensor nodes. One challenge in deploying this architecture is how to place the sniffers for efficient delay measurement. We prove the sniffer placement problem is NP-hard and develop two algorithms to solve it. Using a combination of small-scale testbed experiments and large-scale simulation, we demonstrate that our architecture leads to accurate delay monitoring and is effective in detecting abnormal delays, and furthermore, the number of sniffers required by our sniffer placement algorithms is close to the minimum required value.
 
A new routing protocol that handles real-time and non-real time applications in wireless sensor networks (WSNs) is proposed. We employ the idea of dividing the sensor network field into grids. Inside each grid, one of the sensor nodes is selected as a master node which is responsible for delivering the data generated by any node in that grid and for routing the data received from other master nodes in the neighbor grids. For each master node, multiple paths that connect the master node to the sink are stored as routing entries in the routing table of that node. These paths are the diagonal paths between the sink and the master node. In case of congestion occurrence, a novel congestion control mechanism is also proposed in order to relieve the congested areas. Simulation results have shown that our proposed protocol has the capability to extend the lifetime of the sensor network and to utilize the available storage.
 
There is a growing need for enabling reprogramming in a working sensor network. We prefer to meet the requirements remotely instead of collecting all deployed sensors. Identifying the version difference of data items, having the same key, could significantly reduce the communication overhead, because only those out-of-date items should be updated at each sensor. Previous protocols need to exchange multiple messages to identify a version difference between two items with the same key. In this paper, we propose a reliable and energy efficient data dissemination protocol (BDP) with less propagation delay. BDP uses Bloom filters to identify a version difference between two items with the same key, and find the new one between two items having the same key but different versions. Through comprehensive simulations, we show that BDP outperforms previous work in terms of energy cost and propagation delay of updating new items with high reliability.
 
Point-to-point transmissions represent a fundamental primitive in any communication network. Despite many proposals have appeared in the literature, providing an efficient implementation of such an abstraction in mobile ad hoc networks still remains an open issue. This paper proposes a probabilistic protocol for unicast packet delivery in a MANET. Unlike the classical routing protocols, in our proposal packet forwarding is not driven by a previously computed path. Rather, the nodes of the network exploit a set of routing meta-information (called hints) to discover a path to the destination on-the-fly. This assures robustness to topological changes, while requiring a very low overhead. A node gathers hints from the nodes located within a small number of hops (called the protocol's lookahead) from itself. As showed through simulations, very good performance can be obtained with small lookahead. The main statistical properties of hints have been investigated through an analytical model, which is also reported in the paper.
 
Wireless distributed sensor networks (DSNs) are important for a number of strategic applications such as coordinated target detection, surveillance, and localization. Energy is a critical resource in wireless sensor networks and system lifetime needs to be prolonged through the use of energy-conscious sensing strategies during system operation. We propose an energy-aware target detection and localization strategy for cluster-based wireless sensor networks. The proposed method is based on an a posteriori algorithm with a two-step communication protocol between the cluster head and the sensors within the cluster. Based on a limited amount of data received from the sensor nodes, the cluster head executes a localization procedure to determine the subset of sensors that must be queried for detailed target information. This approach reduces both energy consumption and communication bandwidth requirements, and prolongs the lifetime of the wireless sensor network. Simulation results show that a large amount of energy is saved during target localization using this strategy.
 
In this paper, we propose an efficient routing solution for correlated data collection in wireless sensor networks. Our proposed routing metric considers both the interference distribution as well as the data correlation when establishing routes. An iterative, distributed solution based on local information is proposed using a game theoretic framework. Routes are chosen to minimize both the interference impact of nodes in their neighborhood and the joint entropy of multiple sources relayed through common nodes.
 
Vehicular ad hoc networks (VANETs) are usually operated among vehicles moving at high speeds, and thus their communication relations can be changed frequently. In such a highly dynamic environment, establishing trust among vehicles is difficult. To solve this problem, we propose a flexible, secure and decentralized attribute based secure key management framework for VANETs. Our solution is based on attribute based encryption (ABE) to construct an attribute based security policy enforcement (ASPE) framework. ASPE considers various road situations as attributes. These attributes are used as encryption keys to secure the transmitted data. ASPE is flexible in that it can dynamically change encryption keys depending on the VANET situations. At the same time, ASPE naturally incorporates data access control policies on the transmitted data. ASPE provides an integrated solution to involve data access control, key management, security policy enforcement, and secure group formation in highly dynamic vehicular communication environments. Our performance evaluations show that ASPE is efficient and it can handle large amount of data encryption/decryption flows in VANETs.
 
This paper proposes a new energy efficient algorithm to find and maintain routes in mobile ad hoc networks. The proposal borrows the notion of learning from a previous research on cognitive packet networks (CPN) to create a robust routing protocol. Our idea uses smart packets that exploit the use of unicasts and broadcasts to search for routes. Because unicasts impose lower overall overhead, their use is preferred. Smart packets learn how to make good unicast routing decisions by employing a combined goal function which considers both the energy stored in the nodes and path delay. The end result is a dynamic discovery of paths that offer an equilibrium between low-delay routes and an efficient use of network resources that extends the working lifetime of the network.
 
Flows transported across mobile ad hoc wireless networks suffer from route breakups caused by nodal mobility. In a network that aims to support critical interactive real-time data transactions, to provide for the uninterrupted execution of a transaction, or for the rapid transport of a high value file, it is essential to identify robust routes across which such transactions are transported. Noting that route failures can induce long re-routing delays that may be highly interruptive for many applications and message/stream transactions, it is beneficial to configure the routing scheme to send a flow across a route whose lifetime is longer, with sufficiently high probability, than the estimated duration of the activity that it is selected to carry. We evaluate the ability of a mobile ad hoc wireless network to distribute flows across robust routes by introducing the robust throughput measure as a performance metric. The utility gained by the delivery of flow messages is based on the level of interruption experienced by the underlying transaction. As a special case, for certain applications only transactions that are completed without being prematurely interrupted may convey data to their intended users that is of acceptable utility. We describe the mathematical calculation of a network’s robust throughput measure, as well as its robust throughput capacity. We introduce the robust flow admission and routing algorithm (RFAR) to provide for the timely and robust transport of flow transactions across mobile ad hoc wireless network systems.
 
In this paper, a path discovery scheme which supports QoS routing in mobile ad hoc networks (MANETs) in the presence of imprecise information is investigated. The aim is to increase the probability of success in finding feasible paths and reduce average path cost of a previously proposed ticket based probing (TBP) path discovery scheme. The proposed scheme integrates the original TBP scheme with a reinforcement learning method called the on-policy first-visit Monte Carlo (ONMC) method. We investigate the performance of the ONMC method in the presence of imprecise information. Our numerical study shows that, in respect to a flooding based algorithm, message overhead reduction can be achieved with marginal difference in the path search ability and additional computational and storage requirements. When the average message overhead of the ONMC method is reduced to the same order of magnitude of the original TBP, the ONMC method gains an improvement of 28% in success ratio and 7% reduction in the average path cost over the original TBP.
 
Due to the limited lifetime of the nodes in ad hoc network, energy efficiency needs to be an important design consideration in any routing algorithm for ad hoc and sensor networks. In most of the existing position-based routing algorithms the nodes use the maximum transmission power to discover neighbors, which may cause excessive power consumption. This paper presents several localized power-aware 3D position-based routing algorithms that increase the lifetime of a network by maximizing the average lifetime of its nodes. New algorithms are semi-beaconless, using for neighbor discovery an optimal transmission range (OR) for control packets, and, if needed, maximal transmission range (MR) during routing process, and using adjusted transmission radius for message transmission. PAGR algorithm selects neighbor closest to destination among those within OR if any exists providing progress, or otherwise among those within MR. If greedy progress is not possible, PAGR:CFace(1) variant resorts to face routing on projected network in coordinate plane until recovery is possible, at which point PAGR algorithm resumes. We evaluate our algorithms and compare their power savings with the current power-aware routing algorithms. The simulation results show a significant improvement in the overall network lifetime.
 
An efficient channel assignment strategy ensures capacity maximization in a multiradio, multichannel ad hoc network. Existing mechanisms either use a static channel assignment or a centralized process intensive system that assigns channels to individual nodes. These are not effective in a dynamic environment with multiple flows that are active at different time instants. The protocol proposed in this work (Lattice routing) manages channels of the radios for the different nodes in the network using information about current channel conditions and adapts itself to varying traffic patterns in order to efficiently use the multiple channels. Further the protocol uses multipathing, a key mechanism that is found to alleviate bottlenecks present in single path routes in such an environment. Results indicate that Lattice routing consistently outperforms it closest competitor ((MCR) Kyasanur and Vaidya (2006) [1]) across a large number of experiments.
 
Localization is crucial to many applications in wireless sensor networks. In this article, we propose a range-free anchor-based localization algorithm for mobile wireless sensor networks that builds upon the Monte Carlo localization algorithm. We concentrate on improving the localization accuracy and efficiency by making better use of the information a sensor node gathers and by drawing the necessary location samples faster. To do so, we constrain the area from which samples are drawn by building a box that covers the region where anchors’ radio ranges overlap. This box is the region of the deployment area where the sensor node is localized. Simulation results show that localization accuracy is improved by a minimum of 4% and by a maximum of 73% (average 30%), for varying node speeds when considering nodes with knowledge of at least three anchors. The coverage is also strongly affected by speed and its improvement ranges from 3% to 55% (average 22%). Finally, the processing time is reduced by 93% for a similar localization accuracy.
 
IEEE 802.11 MAC mainly relies on two techniques to combat interference: physical carrier sensing and RTS/CTS handshake (also known as “virtual carrier sensing”). Ideally, the RTS/CTS handshake can eliminate most interference. However, the effectiveness of RTS/CTS handshake is based on the assumption that hidden nodes are within transmission range of receivers. In this paper, we prove using analytic models that in ad hoc networks, such an assumption cannot hold due to the fact that power needed for interrupting a packet reception is much lower than that of delivering a packet successfully. Thus, the “virtual carrier sensing” implemented by RTS/CTS handshake cannot prevent all interference as we expect in theory. Physical carrier sensing can complement this in some degree. However, since interference happens at receivers, while physical carrier sensing is detecting transmitters (the same problem causing the hidden terminal situation), physical carrier sensing cannot help much, unless a very large carrier sensing range is adopted, which is limited by the antenna sensitivity. In this paper, we investigate how effective is the RTS/CTS handshake in terms of reducing interference. We show that in some situations, the interference range is much larger than transmission range, where RTS/CTS cannot function well. Two independent solutions are proposed in this paper. One is a simple enhancement to the IEEE 802.11 MAC protocol. The other is to utilize directional antennas. Simulation results verify that the proposed schemes indeed can help IEEE 802.11 resolve most interference caused by large interference range.
 
The paper evaluates the performance effects of exposed terminals in IEEE 802.11 ad hoc networks in finite load conditions. It derives analytical models for the estimation of channel utilization and media access delay for IEEE 802.11 ad hoc networks in finite load conditions with and without exposed terminals. The simulation results show that the analytical estimated channel utilization and media access delay metrics are fairly accurate.
 
Supporting Quality of Service (QoS) in wireless networks is a challenging problem. The IEEE 802.11 LAN standard was developed primarily for elastic data applications. In order to support the transmission of real-time data, a polling-based scheme called the point coordination function (PCF) was introduced in IEEE 802.11. However, PCF was not able to meet the desired and practical service differentiation requirements to fulfill the need of real-time data. Therefore, Task Group E of the IEEE 802.11 working group released several IEEE 802.11e drafts, whose main task is to support QoS in IEEE 802.11 LANs. The polling scheme of PCF is extended in IEEE 802.11e into the more complex hybrid coordination function (HCF). We found that HCF has several performance issues that may affect its anticipated performance. In this paper, we address these issues and propose a QoS enhancement over PCF, called enhanced PCF (EPCF) that enables Wireless LAN to send a combination of voice, data and isochronous data packets using the current IEEE 802.11 PCF. First, we compare the performance of the proposed model (EPCF) with the HCF function of the IEEE 802.11e through simulation. Second, we extend the proposed model (EPCF) to work in a multihop wireless ad hoc mode and present the advantages and limitations in this case. Simulation results demonstrate an enhanced performance of our scheme over the legacy PCF and a comparable performance to the IEEE 802.11e HCF in terms of the average delay and system throughput. However, EPCF is much simpler than HCF, provides flow differentiation, and is easy to implement in the current IEEE 802.11 standard.
 
IEEE 802.11 power save mode (PSM) is a representative of energy-saving protocols which put wireless network interfaces into sleep during idleness. To save energy, part of the performance of IEEE 802.11 is sacrificed attributed to the wake-up latency thus introduced. This paper proposes a complementary mechanism, called link-indexed statistical traffic predictor (LISP) to improve IEEE 802.11 PSM. LISP employs a simple, light-weight traffic prediction method to speed up the delivery of packets along the end-to-end path. By seeking the inherent correlation between ATIM_ACKs and incoming traffic, nodes en route stay awake in the beacon intervals in which packets are anticipated to arrive. As the result, a “freeway” is bridged for packets to rapidly traverse the route. Meanwhile, the number of duty cycles is reduced and more energy is conserved. We have conducted analytical and simulation studies and demonstrated the effectiveness of LISP. The impact of various factors is investigated, including traffic load, number of hops (of routes which connections traverse), ATIM window size and packet size, in both tandem networks and networks of arbitrary topologies.
 
Energy efficiency is one of the most important concerns in wireless networks because wireless clients usually have limited battery power. The aim of this work is to reduce energy consumption by exploiting multi-rate diversity in 802.11 wireless networks. An important observation is that “probabilistic rate combination” in transmission can significantly reduce power consumption. We formulate the energy efficient rate combination as a non-convex optimization problem. A non-cooperative rate adaptation scheme is presented to reduce power consumption without information exchange. Each node selects rate combination strategy and computes its transmission probability based on the weighted average interface queue length. Due to the well-known “rate anomaly” problem, selfish nodes may choose to transmit at a lower rate free ride from the other nodes. To mitigate this problem, we propose a joint consecutive packet transmission (CPT) and contention window adaptation mechanism (CWA). We prove the stability of our proposed algorithm, and to the best of our knowledge, this is the first control theoretical analysis on 802.11 “multi-rate” wireless networks. Simulation results show that the probabilistic rate combination can greatly save battery power, even up to 700% times compared with standard 802.11a/h protocol.
 
We develop a scalable \textit{cell-level} analytical model for multi-cell infrastructure IEEE 802.11 WLANs under a so-called Pairwise Binary Dependence (PBD) condition. The PBD condition is a geometric property under which the relative locations of the nodes inside a cell do not matter and the network is free of \textit{hidden nodes}. For the cases of saturated nodes and TCP-controlled long-file downloads, we provide accurate predictions of cell throughputs. Similar to Bonald et al (Sigmetrics, 2008), we model a multi-cell WLAN under short-file downloads as "a network of processor-sharing queues with state-dependent service rates." Whereas the state-dependent service rates proposed by Bonald et al are based only on the \textit{number} of contending neighbors, we employ state-dependent service rates that incorporate the the impact of the overall \textit{topology} of the network. We propose an \textit{effective service rate approximation} technique and obtain good approximations for the \textit{mean flow transfer delay} in each cell. For TCP-controlled downloads where the APs transmit a large fraction of time, we show that the throughputs predicted under the PBD condition are very good approximations in two important scenarios where hidden nodes are indeed present and the PBD condition does not strictly hold.
 
The distributed coordination function (DCF) mode of the IEEE 802.11 MAC standard, though proposed for medium access in wireless local area networks, is seen as the de-facto medium access standard in multi-hop wireless networks. In this paper we contend that the unique characteristics that differentiate multi-hop wireless ad-hoc networks from local area wireless networks render the IEEE 802.11 MAC protocol inefficient in ad-hoc networks. Specifically, we focus on the band of contention and the fairness model employed by the IEEE 802.11 MAC protocol in our study. We substantiate our arguments through simulations of idealized (centralized) protocols, and consider the key changes required to adapt the IEEE 802.11 MAC protocol for multi-hop wireless networks. We then propose a simple medium access scheme within the IEEE 802.11 MAC framework, called flow based medium access (FBMA) that achieves significantly better fairness properties while adhering to the purely distributed operations of the basic IEEE 802.11 MAC scheme. We demonstrate the performance of the proposed MAC protocol through simulations.
 
The IEEE 802.11e standard introduces Quality of Service support for wireless local area networks through two MAC functions: Enhanced Distributed Channel Access (EDCA) and HCF Controlled Channel Access (HCCA). While the former provides prioritized contention-based access to the medium, the latter uses a parameterized contention-free polling scheme. Several studies have proposed enhancements to EDCA or improved scheduling algorithms for HCCA to properly support VBR traffic. However, the cooperation between these functions has only marginally been considered and the solutions vary depending on specific traffic requirements.In this paper we propose a novel approach to address the problem of scheduling VBR traffic streams. Our scheduler, named Overboost, uses HCCA to negotiate a minimum bandwidth and deals with traffic streams that require more bandwidth than the negotiated one by redirecting the excess bandwidth to the EDCA function. An analytical evaluation has been conducted and the results has been corroborated by an extensive set of simulations. They show that the overall scheduler improves the performance with respect to other HCCA schedulers in terms of null rate, throughput, access delay, and queue length.
 
Vehicular ad hoc networks (VANETs) are an extreme case of mobile ad hoc networks (MANETs). High speed and frequent network topology changes are the main characteristics of vehicular networks. These characteristics lead to special issues and challenges in the network design, especially at the medium access control (MAC) layer. In this paper, we provide a comprehensive evaluation of mobility impact on the IEEE 802.11p MAC performance. The study evaluates basic performance metrics such as packet delivery ratio, throughput, and delay. An unfairness problem due to the relative speed is identified for both broadcast and unicast scenarios. We propose two dynamic contention window mechanisms to alleviate network performance degradation due to high mobility. The first scheme provides dynamic level of service priority via adaptation to the number of neighboring nodes, while the second scheme provides service priority based on node relative speed. Extensive simulation results demonstrate a significant impact of mobility on the IEEE 802.11p MAC performance, the unfairness problem in the vehicle-to-vehicle (V2V) communications, and the effectiveness of the proposed MAC schemes.
 
Wireless mesh networking based on 802.11 wireless local area network (WLAN) has been actively explored for a few years. To improve the performance of WLAN mesh networks, a few new communication protocols have been developed in recent years. However, these solutions are usually proprietary and prevent WLAN mesh networks from interworking with each other. Thus, a standard becomes indispensable for WLAN mesh networks. To meet this need, an IEEE 802.11 task group, i.e., 802.11s, is specifying a standard for WLAN mesh networks. Although several standard drafts have been released by 802.11s, many issues still remain to be resolved. In order to understand what performance can be expected from the existing framework of 802.11s standard and what functionalities shall be added to 802.11s standard to improve performance, a detailed study on the existing 802.11s standard is given in this paper. The existing framework of 802.11s standard is first presented, followed by pointing out the challenging research issues that still exist in the current 802.11 standard. The purpose of this paper is to motivate other researchers to develop new scalable protocols for 802.11 wireless mesh networks.
 
In this paper we study passive discovery of IEEE 802.15.4 networks operating in the beacon-enabled mode. The task of discovery occurs in different scenarios. One example is a simple device that wishes to associate with a specific, pre-specified PAN coordinator (targeted discovery). Another example are opportunistic relaying applications, where arbitrary foreign coordinators should be discovered (untargeted discovery). We consider a simple class of listening strategies and provide different analytical models which allow to find optimal strategies for different listening scenarios. For the case of targeted discovery without constraints on the listening costs we give a dynamic programming formulation, for targeted discovery with bounded costs we present and validate a simple model and derive the desired performance measures. For untargeted discovery we present simulation results in a mobile scenario.
 
We consider a tree network spanning a set of source nodes that generate measurement packets, a set of additional relay nodes that only forward packets from the sources, and a data sink. We assume that the paths from the sources to the sink have bounded hop count. We assume that the nodes use the IEEE 802.15.4 CSMA/CA for medium access control, and that there are no hidden terminals. In this setting, starting with a set of simple fixed point equations, we derive sufficient conditions for the tree network to approximately satisfy certain given QoS targets such as end-to-end delivery probability and delay under a given rate of generation of measurement packets at the sources (arrival rates vector). The structures of our sufficient conditions provide insight on the dependence of the network performance on the arrival rate vector, and the topological properties of the network. Furthermore, for the special case of equal arrival rates, default backoff parameters, and for a range of values of target QoS, we show that among all path-length-bounded trees (spanning a given set of sources and BS) that meet the sufficient conditions, a shortest path tree achieves the maximum throughput.
 
Sensor networks, in particular those used in embedded devices like robots, impose drastic temporal constraints and low-power consumption. The design of the physical layer and optimization of the medium access control are major keys for fulfilling these constraints. The low-power wireless personal area network IEEE 802.15.4 offers protocol and topology oriented toward this problem. However, several gaps have been identified, especially those concerning contention access phases and the lack of synchronization between star coordinators. To solve these issues, a new, fully deterministic access method has been developed, formally validated using Petri nets and quantitatively validated through a specifically-designed simulation tool. Researchers now have a real application for this newly designed protocol.
 
We develop an approximate analytical technique for evaluating the performance of multi-hop networks based on beaconless IEEE 802.15.4, a popular standard for wireless sensor networks. The network comprises sensor nodes, which generate measurement packets, relay nodes which only forward packets, and a data sink (base station). We consider a detailed stochastic process at each node, and analyse this process taking into account the interaction with neighboring nodes via certain time averaged unknown variables (e.g., channel sensing rates, collision probabilities, etc.). By coupling the analyses at various nodes, we obtain fixed point equations that can be solved numerically to obtain the unknown variables, thereby yielding approximations of time average performance measures, such as packet discard probabilities and average queueing delays. The model incorporates packet generation at the sensor nodes and queues at the sensor nodes and relay nodes. We demonstrate the accuracy of our model by an extensive comparison with simulations. As an additional assessment of the accuracy of the model, we utilize it in an algorithm for sensor network design with quality-of-service (QoS) objectives, and show that designs obtained using our model actually satisfy the QoS constraints (as validated by simulating the networks), and the predictions are accurate to well within 10% as compared to the simulation results.
 
In this paper we focus on the problems of high latency and low throughput arising from the periodic operation of MAC protocols for wireless sensor networks. In order to meet both design criteria we propose an energy-efficient, low delay, fast-periodic MAC algorithm, namely FP-MAC, that is exclusively designed for 802.15.4-like networks utilizing in full the standard’s physical layer. Our proposal relies on the short periodic communication operation of the nodes comprising the WSN. This is achieved by decreasing the actions that a node needs to perform at the start of every communication period and by incorporating a variable radio-on operation. Moreover, the algorithm introduces differences in nodes’ scheduling to further reduce delay. Local synchronization and the crucial task of determining the proper timing for transmission and reception of data is achieved through the periodic broadcast of special synchronization frames at the beginning of each on-period. FP-MAC is evaluated and compared to S-MAC and T-MAC through extensive simulations, showing a significant improvement in terms of low energy consumption and average MAC delay.
 
In future smart environments, ad hoc sensor networks will play a key role in sensing, collecting, and disseminating information about environmental phenomena. As sensor networks come to be wide-spread deployment, security issues become a central concern. So far, the main research focus has been on making sensor networks feasible and useful, and less emphasis has been placed on security. This paper analyzes security challenges in wireless sensor networks and summarizes key issues that need be solved for achieving security in an ad hoc network. It gives an overview of the current state of solutions on such key issues as secure routing, prevention of denial-of-service, and key management service.
 
Evaluation of design parameter effects on the solution.
Multiple-OLT formulation results.
First deployment example.
Second deployment example.
Hybrid Wireless–Optical Broadband Access Networks (WOBANs) are gauging momentum as flexible, bandwidth-effective, and cost-effective solutions for providing connectivity to residential users in metropolitan areas. In this work, we address the issue of designing the topology of deployed WOBANs. Namely, we consider the case where the coverage of a Ethernet-based Passive Optical Network (EPON) is extended by an additional wireless segment which features multi-hop wireless links operated either according to the IEEE 802.11 standard, or to the IEEE 802.16 one. We propose a mathematical programming model which optimizes the overall WOBAN topology in terms of deployment cost, while accounting for the specific traffic requirements of the residential users, and the specific features of the technological components. The potentials of the proposed model are showcased by deriving and commenting numerical results obtained when planning realistic WOBAN scenarios.
 
Vehicular communication systems facilitate communication devices for exchange of information among vehicles and between vehicles and roadside equipment. These systems are used to provide a myriad of services ranging from traffic safety application to convenience applications for drivers and passengers. In this paper, we focus on the design of communication protocols for vehicular access networks where vehicles access a wired backbone network by means of a multi-hop data delivery service. Key challenges in designing protocols for vehicular access networks include quick adaptability to frequent changes in the network topology due to vehicular mobility and delay awareness in data delivery. To address these challenges, we propose a cross-layer position-based delay-aware communication protocol called PROMPT. It adopts a source routing mechanism that relies on positions independent of vehicle movement rather than on specific vehicle addresses. Vehicles monitor information exchange in their reception range to obtain data flow statistics, which are then used in estimating the delay and selecting best available paths. Through a detailed simulation study using ns-2, we empirically show that PROMPT outperforms existing routing protocols proposed for vehicular networks in terms of end-to-end packet delay, packet loss rate, and fairness of service.
 
Mobile ad hoc networks (MANETs) provide an attractive solution for networking in the situations where network infrastructure or service subscription is not available. Its usage can further be extended by enabling communications with external networks such as the Internet or cellular networks through gateways. However, data access applications in MANETs suffer from dynamic network connections and restricted resources. While most of the research focuses on media (or medium) access control (MAC) and routing layer solutions, we explore the possibility of making use of data locality and the commonality in users’ interests at the application level. In this paper, we investigate how cooperative caching can be used to improve data access efficiency in MANETs. We propose COOP, a novel cooperative caching scheme for on-demand data access applications in MANETs. The objective is to improve data availability and access efficiency by collaborating local resources of mobile nodes. COOP addresses two basic problems of cooperative caching: cache resolution and cache management. To improve data availability and access efficiency, COOP discovers data sources which induce less communication overhead by utilizing cooperation zones, historical profiles, and hop-by-hop resolution. For cache management, COOP increases the effective capacity of cooperative caches by minimizing caching duplications within the cooperation zone and accommodating more data varieties. The performance of COOP is studied using mathematical analysis and simulations from the perspectives of data availability, time efficiency, and energy efficiency. The analysis and simulation results show that COOP significantly reduces response delay and improves data availability with proper settings of the cooperation zone radius.
 
In this paper, we exploit space as a new dimension in collision resolution for a carrier sense multiple access (CSMA) protocol. Most contention-based medium access control protocols resolve collisions by backing off in time. We introduce power backoff (PB), the use of transmission power control to resolve collisions by backing off in space, and incorporate it into a CSMA protocol as CSMA/PB. Through analysis and simulation, we show that collision resolution using power backoff can be remarkably successful. Simulation results show that CSMA/PB outperforms IEEE 802.11 in both static and mobile ad hoc network scenarios. CSMA/PB improves end-to-end throughput and uses less energy. The resulting gains in throughput per unit energy can be substantial.
 
Most ad hoc networks do not implement any network access control, leaving these networks vulnerable to resource consumption attacks where a malicious node injects packets into the network with the goal of depleting the resources of the nodes relaying the packets. To thwart or prevent such attacks, it is necessary to employ authentication mechanisms to ensure that only authorized nodes can inject traffic into the network. We propose LHAP, a hop-by-hop authentication protocol for ad hoc networks. LHAP resides in between the network layer and the data link layer, thus providing a layer of protection that can prevent or thwart many attacks from happening, including outsider attacks and insider impersonation attacks. Our detailed performance evaluation shows that LHAP incurs small performance overhead and it also allows a tradeoff between security and performance.
 
It has been proposed to upgrade the performance of medium access control (MAC) schemes through the use of beamforming directional antennas, to achieve better power and bandwidth utilization. In this paper, we consider a shared wireless medium as employed in a mobile ad hoc wireless network. We present and analyze a random access MAC algorithm that is combined with the use of directional beamforming formed by each transmitting mobile entity. Mathematical equations are derived to characterize the throughput performance of such a directional-ALOHA (D-ALOHA) algorithm. We describe the interferences occurring at each receiving node by considering both distance based and SINR based interference models. The D-ALOHA protocol includes the establishment of a (in-band or out-of-band) control sub-channel that is used for the transmission of location update messages. The latter is used for allowing mobile nodes to track the location of their intended destination mobiles. We present a separation property result that allows us to express the network throughput performance as a product of two factors: (1) a stationary factor that represents the system throughput performance under a perfect receiver location update process, and (2) a mobility factor that embeds the user mobility and location update processes in expressing the level of throughput degradation caused due to location update errors. We employ our derived mathematical equations, as well as carry out simulation evaluations, to present an extensive set of performance results. The throughput performance of such a beamforming based MAC protocol is characterized in terms of the system’s traffic loading conditions, the selected beamwidths of the antennas at the transmitting mobiles, the mobility levels of the nodal entities and the bandwidth capacity allocated to the control channel used for location update purposes. We show that the D-ALOHA protocol can provide a significant upgrade of network performance when the transmitting nodes adapt their beamwidth levels in accordance with our presented control scheme. The latter incorporates the involved tradeoff between the attained higher potential spatial reuse factors and the realized higher destination pointing process errors, and consequently uses nodal mobility levels and channel loading conditions as key parameters.
 
Concurrent with the rapid expansion of wireless networks is an increasing interest in providing Quality-of-Service (QoS) support to them. As a consequence, a number of medium access control protocols has been proposed which aims at providing service differentiation at the distributed wireless medium access layer. However, most of them provide only average performance assurances. We argue that average performance guarantees will be inadequate for a wide range of emerging multimedia applications and “per-flow” service assurances must be provided instead. Based on m-ary tree algorithms, we propose an adaptive and distributed medium access algorithm for single-cell ad hoc networks to provide “per-flow” service assurances to flows whose QoS requirement can be expressed as a delay requirement. Both analytical and simulation experiments are conducted to assess the performance of the proposed scheme.
 
Directional antennas have the potential to significantly improve the throughput of a wireless ad hoc network. At the same time, energy consumption can be considerably reduced if the network implements per-packet transmission power control. Typical MAC protocols for ad hoc networks (e.g., the IEEE 802.11 Ad Hoc mode) were designed for wireless devices with omnidirectional antennas. When used with directional antennas, such protocols suffer from several medium access problems, including interference from minor lobes and hidden-terminal problems, which prevent full exploitation of the potential of directional antennas. In this paper, we propose a power-controlled MAC protocol for directional antennas that ameliorates these problems. Our protocol allows for dynamic adjustment of the transmission power for both data and clear-to-send (CTS) packets to optimize energy consumption. It provides a mechanism for permitting interference-limited concurrent transmissions and choosing the appropriate tradeoff between throughput and energy consumption. The protocol enables nodes to implement load control in a distributed manner, whereby the total interference in the neighborhood of a receiver is upper-bounded. Simulation results demonstrate that the combined gain from concurrent transmissions using directional antennas and power control results in significant improvement in network throughput and considerable reduction in energy consumption.
 
Studies of ad hoc wireless networks are a relatively new field gaining more popularity for various new applications. In these networks, the Medium Access Control (MAC) protocols are responsible for coordinating the access from active nodes. These protocols are of significant importance since the wireless communication channel is inherently prone to errors and unique problems such as the hidden-terminal problem, the exposed-terminal problem, and signal fading effects. Although a lot of research has been conducted on MAC protocols, the various issues involved have mostly been presented in isolation of each other. We therefore make an attempt to present a comprehensive survey of major schemes, integrating various related issues and challenges with a view to providing a big-picture outlook to this vast area. We present a classification of MAC protocols and their brief description, based on their operating principles and underlying features. In conclusion, we present a brief summary of key ideas and a general direction for future work.
 
Recent developments in sensor technology, as seen in Berkeley’s Mica2 Mote, Rockwell’s WINS nodes and the IEEE 802.15.4 Zigbee, have enabled support for single-transceiver, multi-channel communication. The task of channel assignment with minimum interference, also named as the 2-hop coloring problem, allows repetition of colors occurs only if the nodes are separated by more than 2 hops. Being NP complete, development of efficient heuristics for this coloring problem is an open research area and this paper proposes the Dynamic Channel Allocation (DCA) algorithm as a novel solution. Once channels are assigned, a Medium Access Control protocol must be devised so that channel selection, arbitration and scheduling occur with maximum energy savings and reduced message overhead, both critical considerations for sensor networks. The contribution of this paper is twofold: (1) development and analysis of the DCA algorithm that assigns optimally minimum channels in a distributed manner in order to make subsequent communication free from both primary and secondary interference and (2) proposing CMAC, a fully desynchronized multi-channel MAC protocol with minimum hardware requirements. CMAC takes into account the fundamental energy constraint in sensor nodes by placing them in a default sleep mode as far as possible, enables spatial channel re-use and ensures nearly collision free communication. Simulation results reveal that the DCA consumes significantly less energy while giving a legal distributed coloring. CMAC, our MAC protocol that leverages this coloring, has been thoroughly evaluated with various modes in SMAC, a recent protocol that achieves energy savings through coordinated sleeping. Results show that CMAC obtains nearly 200% reduction in energy consumption, significantly improved throughput, and end-to-end delay values that are 50–150% better than SMAC for our simulated topologies.
 
Nodes in a sensor network may be lost due to power exhaustion or malicious attacks. To extend the lifetime of the sensor network, new node deployment is necessary. In military scenarios, adversaries may directly deploy malicious nodes or manipulate existing nodes to introduce malicious “new” nodes through many kinds of attacks. To prevent malicious nodes from joining the sensor network, access control is required in the design of sensor network protocols. In this paper, we propose an access control protocol based on Elliptic Curve Cryptography (ECC) for sensor networks. Our access control protocol accomplishes node authentication and key establishment for new nodes. Different from conventional authentication methods based on the node identity, our access control protocol includes both the node identity and the node bootstrapping time into the authentication procedure. Hence our access control protocol cannot only identify the identity of each node but also differentiate between old nodes and new nodes. In addition, each new node can establish shared keys with its neighbors during the node authentication procedure. Compared with conventional sensor network security solutions, our access control protocol can defend against most well-recognized attacks in sensor networks, and achieve better computation and communication performance due to the more efficient algorithms based on ECC than those based on RSA.
 
The phenomenal growth in wireless technologies has brought about a slew of new services. Incumbent with the new technology is the challenge of providing flexible, reconfigurable, self-organizing architectures which are capable of catering to the dynamics of the network, while providing cost-effective solutions for the service providers. In this paper, we focus on mesh-based multi-hop access network architectures for next generation radio access networks. Using short, high bandwidth optical wireless links to interconnect the various network elements, we propose a non-hierarchical, multi-hop access network framework. We study two generic family of mesh-based topologies: GPeterNet, a graph theoretic framework, and FraNtiC, a fractal geometric architecture, for arbitrary access network deployments. The performance of these topologies is analyzed in terms of different system metrics – topological robustness and reliability, system costs and network exposure due to failure conditions. Our analysis shows that a combination of different mesh-based multi-hop access topologies, coupled with emerging wireless backhaul technologies, can cater carrier-class services for next generation radio access networks, providing significant advantages over existing access technologies.
 
We consider the problem of media-access control in multiple-cell networks, such as ad hoc networks in which clusterheads take on a role similar to base stations. We assume that a single channel is used by all cells, and that the user populations that transmit to different base stations overlap, causing interference in the neighboring cells. Starting with a two-destination network, we introduce the “Group-Division Multiple Access” (GDMA) concept, according to which different groups of users multiplex their transmission in time while being free to use the protocol of their choice within their own group. We show that use of GDMA provides higher stable throughput than a “free-running” scheme (under which all slots are available to all users) when the First-Come First-Serve collision–resolution algorithm is used as the channel-access protocol, and we show how performance depends on the degree of overlap of communication and interference regions. Finally, we show that this approach can be applied to larger cellular-like networks as well.
 
To support energy-efficient routing, accurate state information about energy levels should be available. But due to bandwidth constraints, communication costs, high loss rate and the dynamic topology of MANETs, collecting and maintaining up-to-date state information is a very complex task. In this work, we use Optimized Link State Routing (OLSR) as the underlying routing protocol and explore the accuracy of state information under different traffic rates. We are focusing on energy level as QoS metric, which has been used for routing decisions in many energy-efficient routing protocol proposals. First, we show that the accuracy of the available nodal energy level does impact the performance of energy-efficient variations of OLSR. If nodes learn other nodes’ energy level through protocol messages, fewer packets tend to get delivered in an energy-constrained network, in particular under high traffic loads or in mobile networks. We analyzed the accuracy of the reported energy levels for the static scenarios and found that the propagated values are highly inaccurate, in particular under high traffic rates. Tuning the OLSR protocol parameters has no noticeable impact on accuracy levels. We then propose two additional techniques to increase accuracies and compare the different techniques against each other and against the basic OLSR protocol. One of the techniques, which we call smart prediction, achieves highly accurate perceived energy levels under all traffic loads. We finally show that the proposed smart prediction technique also works well for mobile networks and more heterogeneous wireless interfaces.
 
This report considers the class of applications of sensor networks in which each sensor node makes measurements, such as temperature or humidity, at the precise location of the node. Such spot-sensing applications approximate the physical condition of the entire region of interest by the measurements made at only the points where the sensor nodes are located. Given a certain density of nodes in a region, a more spatially uniform distribution of the nodes leads to a better approximation of the physical condition of the region. This report considers the error in this approximation and seeks to improve the quality of representation of the physical condition of the points in the region in the data collected by the sensor network. We develop two essential metrics which together allow a rigorous quantitative assessment of the quality of representation achieved: the average representation error and the unevenness of representation error, the latter based on a well-accepted measure of inequality used in economics. We present the rationale behind the use of these metrics and derive relevant theoretical bounds on them in the common scenario of a planar region of arbitrary shape covered by a sensor network deployment. A simple new heuristic algorithm is presented for each node to determine if and when it should sense or sleep to conserve energy while also preserving the quality of representation. Simulation results show that it achieves a significant improvement in the quality of representation compared to other related distributed algorithms. Interestingly, our results also show that improved spatial uniformity has the welcome side-effect of a significant increase in the network lifetime.
 
Directional antenna offers various benefits for wireless sensor networks, such as increased spatial reuse ratio and reduced energy consumption. In this paper, we formulate the maximum flow problem as an optimization problem in interference-limited wireless sensor networks with switched beam directional antennas. The optimization problem is solvable in the presence of an omniscient controller, but it is NP-hard. Therefore, we seek a distributed algorithm to achieve the maximum flow through jointly routing and scheduling. The maximum flow between given source destination pair is determined forwardly hop by hop and is verified by the proposed feasible condition at downstream nodes. This method works for both single-beam antenna and multi-beam antenna with some variation in the feasibility condition.
 
Top-cited authors
Kemal Akkaya
  • Southern Illinois University Carbondale
Mohamed Younis
  • University of Maryland, Baltimore County
Daniele Miorandi
  • U-Hopper srl
Sabrina Sicari
  • Università degli Studi dell'Insubria
Francesco De Pellegrini
  • Université d´Avignon et des Pays du Vaucluse