MOBILE COMPUTING

A TABU SEARCH ALGORITHM FOR CLUSTER BUILDING IN WIRELESS SENSOR NETWORKS

Abstract—The main challenge in wireless sensor network deployment pertains to optimizing energy consumption when collecting data from sensor nodes. This paper proposes a new centralized clustering method for a data collection mechanism in wireless sensor networks, which is based on network energy maps and Quality-of-Service (QoS) requirements. The clustering problem is modeled as a hypergraph partitioning and its resolution is based on a tabu search heuristic. Our approach defines moves using largest size cliques in a feasibility cluster graph. Compared to other methods (CPLEX-based method, distributed method, simulated annealing-based method), the results show that our tabu search-based approach returns high-quality solutions in terms of cluster cost and execution time. As a result, this approach is suitable for handling network extensibility in a satisfactory manner.

A GEN2-BASED RFID AUTHENTICATION PROTOCOL FOR SECURITY AND PRIVACY

EPCglobal Class-1 Generation-2 specification (Gen2 in brief) has been approved as ISO18000-6C for global use, but the identity of tag (TID) is transmitted in plaintext which makes the tag traceable and clonable. Several solutions have been proposed based on traditional encryption methods, such as symmetric or asymmetric ciphers, but they are not suitable for low-cost RFID tags. Recently, some lightweight authentication protocols conforming to Gen2 have been proposed. However, the message flow of these protocols is different from Gen2. Existing readers may fail to read new tags. In this paper, we propose a novel authentication protocol based on Gen2, called Gen2þ, for low-cost RFID tags. Our protocol follows every message flow in Gen2 to provide backward compatibility. Gen2þ is a multiple round protocol using shared pseudonyms and Cyclic Redundancy Check (CRC) to achieve readerto- tag authentication. Conversely, Gen2þ uses the memory read command defined in Gen2 to achieve tag-to-reader authentication. We show that Gen2þ is more secure under tracing and cloning attacks.

ROUTE STABILITY IN MANETS UNDER THE RANDOM DIRECTION MOBILITY MODEL

A fundamental issue arising in mobile ad hoc networks (MANETs) is the selection of the optimal path between any two nodes. A method that has been advocated to improve routing efficiency is to select the most stable path so as to reduce the latency and the overhead due to route reconstruction. In this work, we study both the availability and the duration probability of a routing path that is subject to link failures caused by node mobility. In particular, we focus on the case where the network nodes move according to the Random Direction model, and we derive both exact and approximate (but simple) expressions of these probabilities. Through our results, we study the problem of selecting an optimal route in terms of path availability. Finally, we propose an approach to improve the efficiency of reactive routing protocols.

GREEDY ROUTING WITH ANTI-VOID TRAVERSAL FOR WIRELESS SENSOR NETWORKS

Abstract—The unreachability problem (i.e., the so-called void problem) that exists in the greedy routing algorithms has been studied for the wireless sensor networks. Some of the current research work cannot fully resolve the void problem, while there exist other schemes that can guarantee the delivery of packets with the excessive consumption of control overheads. In this paper, a greedy antivoid routing (GAR) protocol is proposed to solve the void problem with increased routing efficiency by exploiting the boundary finding technique for the unit disk graph (UDG). The proposed rolling-ball UDG boundary traversal (RUT) is employed to completely guarantee the delivery of packets from the source to the destination node under the UDG network. The boundary map (BM) and the indirect map searching (IMS) scheme are proposed as efficient algorithms for the realization of the RUT technique. Moreover, the hop count reduction (HCR) scheme is utilized as a short-cutting technique to reduce the routing hops by listening to the neighbor’s traffic, while the intersection navigation (IN) mechanism is proposed to obtain the best rolling direction for boundary traversal with the adoption of shortest path criterion. In order to maintain the network requirement of the proposed RUT scheme under the non-UDG networks, the partial UDG construction (PUC) mechanism is proposed to transform the non-UDG into UDG setting for a portion of nodes that facilitate boundary traversal. These three schemes are incorporated within the GAR protocol to further enhance the routing performance with reduced communication overhead. The proofs of correctness for the GAR scheme are also given in this paper. Comparing with the existing localized routing algorithms, the simulation results show that the proposed GAR-based protocols can provide better routing efficiency.

CELL BREATHING TECHNIQUES FOR LOAD BALANCING IN WIRELESS LANS

Abstract—Maximizing network throughput while providing fairness is one of the key challenges in wireless LANs (WLANs). This goal is typically achieved when the load of access points (APs) is balanced. Recent studies on operational WLANs, however, have shown that AP load is often substantially uneven. To alleviate such imbalance of load, several load balancing schemes have been proposed. These schemes commonly require proprietary software or hardware at the user side for controlling the user-AP association. In this paper we present a new load balancing technique by controlling the size of WLAN cells (i.e., AP’s coverage range), which is conceptually similar to cell breathing in cellular networks. The proposed scheme does not require any modification to the users neither the IEEE 802.11 standard. It only requires the ability of dynamically changing the transmission power of the AP beacon messages. We develop a set of polynomial time algorithms that find the optimal beacon power settings which minimize the load of the most congested AP. We also consider the problem of network-wide min-max load balancing. Simulation results show that the performance of the proposed method is comparable with or superior to the best existing association-based methods.

LOCAL CONSTRUCTION OF NEAR-OPTIMAL POWER SPANNERS FOR WIRELESS AD-HOC NETWORKS

We present a local distributed algorithm that, given a wireless ad hoc network modeled as a unit disk graph U in the plane, constructs a planar power spanner of U whose degree is bounded by k and whose stretch factor is bounded by 1 + (2sin pi/k)p, where k ges 10 is an integer parameter and p isin [2, 5] is the power exponent constant. For the same degree bound k, the stretch factor of our algorithm significantly improves the previous best bounds by Song et al. We show that this bound is near-optimal by proving that the slightly smaller stretch factor of 1 + (2sin pi/k+1)p is unattainable for the same degree bound k. In contrast to previous algorithms for the problem, the presented algorithm is local. As a consequence, the algorithm is highly scalable and robust. Finally, while the algorithm is efficient and easy to implement in practice, it relies on deep insights on the geometry of unit disk graphs and novel techniques that are of independent interest.

BIASED RANDOM WALKS IN UNIFORM WIRELESS NETWORKS

A recurrent problem when designing distributed applications is to search for a node with known property. File searching in peer-to-peer (P2P) applications, resource discovery in service-oriented architectures (SOAs), and path discovery in routing can all be cast as a search problem. Random walk-based search algorithms are often suggested for tackling the search problem, especially in very dynamic systems-like mobile wireless networks. The cost and the effectiveness of a random walk-based search algorithm are measured by the excepted number of transmissions required before hitting the target. Hence, to have a low hitting time is a critical goal. This paper studies the effect of biasing random walk toward the target on the hitting time. For a walk running over a network with uniform node distribution, a simple upper bound that connects the hitting time to the bias level is obtained. The key result is that even a modest bias level is able to reduce the hitting time significantly. This paper also proposes a search protocol for mobile wireless networks, whose results are interpreted in the light of the theoretical study. The proposed solution is for unstructured wireless mobile networks.

INFORMATION CONTENT-BASED SENSOR SELECTION AND TRANSMISSION POWER ADJUSTMENT FOR COLLABORATIVE TARGET TRACKING

For target tracking applications, wireless sensor nodes provide accurate information since they can be deployed and operated near the phenomenon. These sensing devices have the opportunity of collaboration among themselves to improve the target localization and tracking accuracies. An energy-efficient collaborative target tracking paradigm is developed for wireless sensor networks (WSNs). A mutual-information-based sensor selection (MISS) algorithm is adopted for participation in the fusion process. MISS allows the sensor nodes with the highest mutual information about the target state to transmit data so that the energy consumption is reduced while the desired target position estimation accuracy is met. In addition, a novel approach to energy savings in WSNs is devised in the information-controlled transmission power (ICTP) adjustment, where nodes with more information use higher transmission powers than those that are less informative to share their target state information with the neighboring nodes. Simulations demonstrate the performance gains offered by MISS and ICTP in terms of power consumption and target localization accuracy.

ENERGY MAPS FOR MOBILE WIRELESS NETWORKS:COHERENCE TIME VERSUS SPREADING PERIOD

We show that even though mobile networks are highly unpredictable when viewed at the individual node scale, the end-toend quality-of-service (QoS) metrics can be stationary when the mobile network is viewed in the aggregate. We define the coherence time as the maximum duration for which the end-to-end QoS metric remains roughly constant, and the spreading period as the minimum duration required to spread QoS information to all the nodes. We show that if the coherence time is greater than the spreading period, the end-to-end QoS metric can be tracked. We focus on the energy consumption as the end-to-end QoS metric, and describe a novel method by which an energy map can be constructed and refined in the joint memory of the mobile nodes. Finally, we show how energy maps can be utilized by an application that aims to minimize a node’s total energy consumption over its near-future trajectory.

RANDOMCAST: AN ENERGY EFFICIENT COMMUNICATION SCHEME FOR MOBILE AD HOC NETWORKS

In mobile ad hoc networks (MANETs), every node overhears every data transmission occurring in its vicinity and thus, consumes energy unnecessarily. In IEEE 802.11 Power Saving Mechanism (PSM), a packet must be advertised before it is actually transmitted. When a node receives an advertised packet that is not destined to itself, it switches to a lowpower sleep state during the data transmission period, and thus, avoids overhearing and conserves energy. However, since some MANET routing protocols such as Dynamic Source Routing (DSR) collect route information via overhearing, they would suffer if they are used in combination with 802.11 PSM. Allowing no overhearing may critically deteriorate the performance of the underlying routing protocol, while unconditional overhearing may offset the advantage of using PSM. This paper proposes a new communication mechanism, called RandomCast, via which a sender can specify the desired level of overhearing, making a prudent balance between energy and routing performance. In addition, it reduces redundant rebroadcasts for a broadcast packet and thus saves more energy. Extensive simulation using ns-2 shows that RandomCast is highly energy-efficient compared to conventional 802.11 as well as 802.11 PSM-based schemes, in terms of total energy consumption, energy goodput and energy balance.

NETWORKING

RESEQUENCING ANALYSIS OF STOP-AND-WAIT ARQ FOR PARALLEL MULTICHANNEL COMMUNICATIONS

In this paper, we consider a multichannel data communication system in which the stop-and-wait automatic-repeat request protocol for parallel channels with an in-sequence delivery guarantee (MSW-ARQ-inS) is used for error control. We evaluate the resequencing delay and the resequencing buffer occupancy, respectively. Under the assumption that all channels have the same transmission rate but possibly different time-invariant error rates, we derive the probability generating function of the resequencing buffer occupancy and the probability mass function of the resequencing delay. Then, by assuming the Gilbert–Elliott model for each channel, we extend our analysis to time-varying channels. Through examples, we compute the probability mass functions of the resequencing buffer occupancy and the resequencing delay for time-invariant channels. From numerical and simulation results, we analyze trends in the mean resequencing buffer occupancy and the mean resequencing delay as functions of system parameters. We expect that the modeling technique and analytical approach used in this paper can be applied to the performance evaluation of other ARQ protocols (e.g., the selective-repeat ARQ) over multiple time-varying channels. Index Terms—In-sequence delivery, modeling and performance, multichannel data communications, resequencing buffer occupancy, resequencing delay, SW-ARQ.

SECURE AND POLICY-COMPLIANT SOURCE ROUTING

In today’s Internet, inter-domain route control remains elusive; nevertheless, such control could improve the performance, reliability, and utility of the network for end users and ISPs alike. While researchers have proposed a number of source routing techniques to combat this limitation, there has thus far been no way for independent ASes to ensure that such traffic does not circumvent local traffic policies, nor to accurately determine the correct party to charge for forwarding the traffic. We present Platypus, an authenticated source routing system built around the concept of network capabilities, which allow for accountable, fine-grained path selection by cryptographically attesting to policy compliance at each hop along a source route. Capabilities can be composed to construct routes through multiple ASes and can be delegated to third parties. Platypus caters to the needs of both end users and ISPs: users gain the ability to pool their resources and select routes other than the default, while ISPs maintain control over where, when, and whose packets traverse their networks. We describe the design and implementation of an extensive Platypus policy framework that can be used to address several issues in wide-area routing at both the edge and the core, and evaluate its performance and security. Our results show that incremental deployment of Platypus can achieve immediate gains.

RESOURCE ALLOCATION IN OFDMA WIRELESS COMMUNICATIONS SYSTEMS SUPPORTING MULTIMEDIA SERVICES

We design a resource allocation algorithm for down-link of orthogonal frequency division multiple access (OFDMA) systems supporting real-time (RT) and best-effort (BE) services simultaneously over a time-varying wireless channel. The proposed algorithm aims at maximizing system throughput while satisfying quality of service (QoS) requirements of the RT and BE services. We take two kinds of QoS requirements into account. One is the required average transmission rate for both RT and BE services. The other is the tolerable average absolute deviation of transmission rate (AADTR) just for the RT services, which is used to control the fluctuation in transmission rates and to limit the RT packet delay to a moderate level. We formulate the optimization problem representing the resource allocation under consideration and solve it by using the dual optimization technique and the projection stochastic subgradient method. Simulation results show that the proposed algorithm well meets the QoS requirements with the high throughput and outperforms the modified largest weighted delay first (M-LWDF) algorithm that supports similar QoS requirements.

ANALYSIS OF SHORTEST PATH ROUTING FOR LARGE MULTI-HOP WIRELESS NETWORKS

In this paper, we analyze the impact of straight line routing in large homogeneous multi-hop wireless networks. We estimate the nodal load, which is defined as the number of packets served at a node, induced by straight line routing. For a given total offered load on the network, our analysis shows that the nodal load at each node is a function of the node’s Voronoi cell, the node’s location in the network, and the traffic pattern specified by the source and destination randomness and straight line routing. In the asymptotic regime, we show that each node’s probability that the node serves a packet arriving to the network approaches the products of half the length of the Voronoi cell perimeter and the load density function that a packet goes through the node’s location. The density function depends on the traffic pattern generated by straight line routing, and determines where the hot spot is created in the network. Hence, contrary to conventional wisdom, straight line routing can balance the load over the network, depending on the traffic patterns. Index Terms—Analysis, geometric probability, multi-hop wireless network, routing, simulations.

SINGLE-LINK FAILURE DETECTION IN ALL-OPTICAL NETWORKS USING MONITORING CYCLES AND PATHS

In this paper, we consider the problem of fault localization in all-optical networks. We introduce the concept of monitoring cycles (MCs) and monitoring paths (MPs) for unique identification of single-link failures. MCs and MPs are required to pass through one or more monitoring locations. They are constructed such that any single-link failure results in the failure of a unique combination of MCs and MPs that pass through the monitoring location(s). For a network with only one monitoring location, we prove that three-edge connectivity is a necessary and sufficient condition for constructing MCs that uniquely identify any single-link failure in the network. For this case, we formulate the problem of constructing MCs as an integer linear program (ILP). We also develop heuristic approaches for constructing MCs in the presence of one or more monitoring locations. For an arbitrary network (not necessarily three-edge connected), we describe a fault localization technique that uses both MPs and MCs and that employs multiple monitoring locations. We also provide a linear-time algorithm to compute the minimum number of required monitoring locations. Through extensive simulations, we demonstrate the effectiveness of the proposed monitoring technique.

VIRUS SPREAD IN NETWORKS

We study how the spread of computer viruses, worms, and other self-replicating malware is affected by the logical topology of the network over which they propagate. We consider a model in which each host can be in one of 3 possible states – susceptible, infected or removed (cured and no longer susceptible to infection). We characterize how the size of the population that eventually becomes infected depends on the network topology. Specially, we show that if the ratio of cure to infection rates is larger than the spectral radius of the graph, and the initial infected population is small, then the final infected population is also small in a sense that can be made precise. Conversely, if this ratio is smaller than the spectral radius, then we show in some graph models of practical interest (including power law random graphs) that the final infected population is large. These results yield insights into what the critical parameters are in determining virus spread in networks.

PRESTO: FEEDBACKDRIVEN DATA MANAGEMENT IN SENSOR NETWORKS

This paper presents PRESTO, a novel two-tier sensor data management architecture comprising proxies and sensors that cooperate with one another for acquiring data and processing queries. PRESTO proxies construct time-series models of observed trends in the sensor data and transmit the parameters of the model to sensors. Sensors check sensed data with model-predicted values and transmit only deviations from the predictions back to the proxy. Such a model-driven push approach is energyefficient, while ensuring that anomalous data trends are never missed. In addition to supporting queries on current data, PRESTO also supports queries on historical data using interpolation and local archival at sensors. PRESTO can adapt model and system parameters to data and query dynamics to further extract energy savings. We have implemented PRESTO on a sensor testbed comprising Intel Stargates and Telos Motes. Our experiments show that in a temperature monitoring application, PRESTO yields one to two orders of magnitude reduction in energy requirements over on-demand, proactive or model-driven pull approaches. PRESTO also results in an order of magnitude reduction in query latency in a 1% duty-cycled five hop sensor network over a system that forwards all queries to remote sensor nodes.

EXPLICIT LOAD BALANCING TECHNIQUE FOR NGEO SATELLITE IP NETWORKS WITH ON-BOARD PROCESSING CAPABILITIES

Non-geostationary (NGEO) satellite communication systems offer an array of advantages over their terrestrial and geostationary counterparts. They are seen as an integral part of next generation ubiquitous communication systems. Given the non-uniform distribution of users in satellite footprints, due to several geographical and/or climatic constraints, some Inter-Satellite Links (ISLs) are expected to be heavily loaded with data packets while others remain underutilized. Such scenario obviously leads to congestion of the heavily loaded links. It ultimately results in buffer overflows, higher queuing delays, and significant packet drops. To guarantee a better distribution of traffic among satellites, this paper proposes an explicit exchange of information on congestion status among neighboring satellites. Indeed, a satellite notifies its congestion status to its neighboring satellites. When it is about to get congested, it requests its neighboring satellites to decrease their data forwarding rates by sending them a self status notification signaling message. In response, the neighboring satellites search for less congested paths that do not include the satellite in question and communicate a portion of data, primarily destined to the satellite, via the retrieved paths. This operation avoids both congestion and packet drops at the satellite. It also ensures a better distribution of traffic over the entire satellite constellation. The proposed scheme is dubbed “Explicit Load Balancing” (ELB) scheme. While the multi-path routing concept of ELB has many advantages, it may lead to persistent packet reordering. In case of connection- oriented protocols, this phenomenon results in unnecessary shrinkage of the data transmission rate. A solution to this issue is also incorporated in the design of ELB. The interactions of ELB with mechanisms that provide different QoS by differentiating traffic (e.g., Differentiated Services) are also discussed. The good performance of ELB, in terms of better traffic distribution, higher throughput, and lower packet drops, is verified via a set of simulations using the Network Simulator (NS).

DELAY ANALYSIS FOR MAXIMAL SCHEDULING WITH FLOW CONTROL IN WIRELESS NETWORKS WITH BURSTY TRAFFIC

We consider the delay properties of one-hop networks with general interference constraints and multiple traffic streams with time-correlated arrivals. We first treat the case when arrivals are modulated by independent finite state Markov chains. We show that the well known maximal scheduling algorithm achieves average delay that grows at most logarithmically in the largest number of interferers at any link. Further, in the important special case when each Markov process has at most two states (such as bursty ON/OFF sources), we prove that average delay is independent of the number of nodes and links in the network, and hence is order-optimal. We provide tight delay bounds in terms of the individual auto-correlation parameters of the traffic sources. These are perhaps the first order-optimal delay results for controlled queueing networks that explicitly account for such statistical information. Our analysis treats cases both with and without flow control.

PARALLEL AND DISTRIBUTED SYSTEMS

COMPACTION OF SCHEDULES AND A TWO-STAGE APPROACH FOR DUPLICATION-BASED DAG SCHEDULING

Many DAG scheduling algorithms generate schedules that require prohibitively large number of processors. To address this problem, we propose a generic algorithm, SC, to minimize the processor requirement of any given valid schedule. SC preserves the schedule length of the original schedule and reduces processor count by merging processor schedules and removing redundant duplicate tasks. To the best of our knowledge, this is the first algorithm to address this highly unexplored aspect of DAG scheduling. On the average, SC reduced the processor requirement 91%, 82% and 72% for schedules generated by PLW, TCSD and CPFD algorithms, respectively. SC algorithm has a low complexity (O(|N |3) ) compared to most duplication based algorithms. Moreover, it decouples processor economization from schedule length minimization problem. To take advantage of these features of SC, we also propose a scheduling algorithm SDS, having the same time complexity as SC. Our experiments demonstrate that, schedules generated by SDS are only 3% longer than CPFD (O(|N |4) ), one of the best algorithms in that respect. SDS and SC together form a two-stage scheduling algorithm that produces schedules with high quality and low processor requirement, and has lower complexity than the comparable algorithms that produce similar high quality results.

DEPENDABLE AND SECURE COMPUTING

THE EFFECTIVENESS OF CHECKSUMS FOR EMBEDDED NETWORKS

Embedded control networks commonly use checksums to detect data transmission errors. However, design decisions about which checksum to use are difficult because of a lack of information about the relative effectiveness of available options. We study the error detection effectiveness of the following commonly used checksum computations for embedded networks: exclusive or (XOR), two’s complement addition, one’s complement addition, Fletcher checksum, Adler checksum, and cyclic redundancy codes (CRC). A study of error detection capabilities for random independent bit errors and burst errors reveals that XOR, two’s complement addition, and Adler checksums are suboptimal for typical application use. Instead, one’s complement addition should be used for applications willing to sacrifice error detection effectiveness to reduce compute cost, Fletcher checksum for applications looking for a balance of error detection and compute cost, and CRCs for applications willing to pay a higher compute cost for further improved error detection

INFORMATION FORENSICS AND SECURITY

SPREAD SPECTRUM WATERMARKING SECURITY

This paper presents both theoretical and practical analyses of the security offered by watermarking and data hiding methods based on spread spectrum. In this context, security is understood as the difficulty of estimating the secret parameters of the embedding function based on the observation of watermarked signals. On the theoretical side, the security is quantified from an information-theoretic point of view by means of the equivocation about the secret parameters. The main results reveal fundamental limits and bounds on security and provide insight into other properties, such as the impact of the embedding parameters, and the tradeoff between robustness and security. On the practical side, workable estimators of the secret parameters are proposed and theoretically analyzed for a variety of scenarios, providing a comparison with previous approaches, and showing that the security of many schemes used in practice can be fairly low.