[show abstract][hide abstract] ABSTRACT: Heterogeneous conditions can occur in multi-hop wireless networks due to a variety of factors such as variations in transmission power and signal propagation environments. Directed links can occur when the environment and/or the nodes are heterogeneous. In this paper, we examine the network connectivity for heterogeneous multi-hop wireless networks and propose an algorithm to identify the connectivity of the network. We follow this with a numerical study of the connectivity in random topologies. Lastly, we propose two schemes for constructing additional links to enhance the connectivity of the network. Our proposed schemes identify the links to be improved or created via a cluster based approach.
Communications (ICC), 2011 IEEE International Conference on; 07/2011
[show abstract][hide abstract] ABSTRACT: The inherent channel characteristics of impulse-based UWB networks affect the MAC layer performance significantly. Most previous studies on evaluating MAC protocols are based on prolonged simulations and do not account for the multiple access interference due to multipath delay spread. In this work, we develop CTU, an analytical framework for Capturing the Throughput dependencies in UWB networks, while taking into account the PHY layer effects. The key attributes of CTU are: 1) It is modular; it can be easily modified to provide a basis for evaluating a wide range of MAC protocols for impulse-based UWB networks. The only requirements are that the MAC protocol under study be based on time-hopping and the modulation scheme be pulse position modulation; these are common design decisions in UWB networks. 2) It considers the channel characteristics in addition to MAC layer effects; CTU correlates probabilistically the multipath delay profile of the channel with the packet error rate. We employ CTU to evaluate the performance of different generic medium access procedure. We compare the results with those from extensive simulations and show the high accuracy of CTU. We use CTU to assess the impact of various system parameters on the MAC layer performance; we make several interesting observations that are discussed in depth.
IEEE Transactions on Mobile Computing 06/2011; · 2.40 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this paper, we develop a performance modeling technique for analyzing the time varying network layer queueing behavior of multihop wireless networks with constant bit rate traffic. Our approach is a hybrid of fluid flow queueing modeling and a time varying connectivity matrix. Network queues are modeled using fluid-flow based differential equation models which are solved using numerical methods, while node mobility is modeled using deterministic or stochastic modeling of adjacency matrix elements. Numerical and simulation experiments show that the new approach can provide reasonably accurate results with significant improvements in the computation time compared to standard simulation tools.
[show abstract][hide abstract] ABSTRACT: Recent work on cooperative communications has demonstrated benefits in terms of improving the reliability of links through diversity and/or increasing the reach of a link compared to a single transmitter transmitting to a single receiver (single-input single-output or SISO). In one form of cooperative transmissions, multiple nodes can act as virtual antenna elements and provide such benefits using space-time coding. In a multi-hop sensor network, a source node can make use of its neighbors as relays with itself to reach an intermediate node, which will use its neighbors and so on to reach the destination. For the same reliability of a link as SISO, the number of hops between a source and destination may be reduced using cooperative transmissions. However, the presence of malicious or compromised nodes in the network impacts the use of cooperative transmissions. Using more relays can increase the reach of a link, but if one or more relays are malicious, the transmission may fail. In this paper, we analyze this problem to understand the conditions under which cooperative transmissions may fare better or worse than SISO transmissions.
Collaborative Computing: Networking, Applications and Worksharing (CollaborateCom), 2010 6th International Conference on; 11/2010 · 1.11 Impact Factor
[show abstract][hide abstract] ABSTRACT: In order to effectively deploy survivability techniques to improve the resilience of mobile ad hoc networks, one must be able to identify all the weak points of the network topology. The weak or critical points of the topology are those links and nodes whose failure results in partitioning of the network. Here we propose a new algorithm based on results from algebraic graph theory, that can find the critical points in the network for single and multiple failure cases. Utilizing this algorithm we present numerical results that examine how the number of critical points varies with nodal density. Secondly, we propose three localized topological control schemes to improve the network connectivity around critical points to lessen their importance and improve the network resilience. Numerical studies to evaluate the proposed schemes under node and link failure network conditions are presented.
Design of Reliable Communication Networks, 2009. DRCN 2009. 7th International Workshop on; 11/2009
[show abstract][hide abstract] ABSTRACT: Jamming attacks are considered one of the most devastating attacks as they are difficult to prevent and sometimes hard to detect. In this paper we consider the impact of the placement and range of limited-range jammers on ad hoc networks. Limited range jammers are more difficult to detect as they use transmission powers similar to that of regular nodes (or perhaps even smaller transmit powers). The attacker can locate his jammer(s) randomly in the network. Alternatively, jammers can be placed at strategic locations. For instance, intuitively, this can be nodes with the highest traffic inputs/outputs (discovered by sensing the traffic flow in the network). Using OPNET, we perform extensive simulations to show how significant such strategically placed attacks can be compared to random placement of limited-range jammers on both TCP and UDP traffic.
[show abstract][hide abstract] ABSTRACT: We propose a novel framework that combines probabilistic transmission with Latin squares characteristics to tune channel access, meeting various demands in network performance (Energy vs. Delay). The proposed technique is decentralized, scalable, and has low overhead. We develop an analytical model to estimate the network performance and validate the benefits of the proposed framework via simulation-based experiments.
Sensor Technologies and Applications, 2009. SENSORCOMM '09. Third International Conference on; 07/2009
[show abstract][hide abstract] ABSTRACT: Detecting malicious packet dropping is important in ad hoc networks to combat a variety of security attacks such as blackhole, greyhole, and wormhole attacks. We consider the detection of malicious packet drops in the presence of collisions and channel errors and describe a method to distinguish between these types. We present a simple analytical model for packet loss that helps a monitoring node to detect malicious packet dropping attacks. The model is analyzed and evaluated using simulations. The results show that it is possible to detect malicious packet drops in the presence of collisions and channel errors.
Communications, 2009. ICC '09. IEEE International Conference on; 07/2009
[show abstract][hide abstract] ABSTRACT: We introduce a distributed grid-based scheduling access scheme that mitigates high data loss in data intensive sensor networks. Our approach alleviates transmission collisions by applying virtual grids and adopting Latin Squares Characteristic to time slot assignments. We demonstrate that our technique efficiently handles sensor mobility with acceptable data loss and low overhead.
Mobile Data Management, 2008. MDM '08. 9th International Conference on; 05/2008
[show abstract][hide abstract] ABSTRACT: The inherent channel characteristics of impulse-based UWB networks affect the MAC layer performance significantly. Previous studies on evaluating MAC protocols are based on prolonged simulations, and do not account for the multiple-access interference that arises due to multipath delay spread. In this work, we develop CTU, an analytical framework that captures the performance of MAC protocols, while taking into account the underlying PHY layer effects. The key attributes that make CTU novel are: (a) It is modular and therefore flexible; it can be easily modified to provide a basis for characterizing and evaluating a wide range of MAC protocols designed for impulse-based UWB networks. The only requirements are that the MAC protocol under study be based on time-hopping, and the modulation scheme be pulse position modulation; these are common design decisions in most impulse based UWB networks, (b) It considers the channel characteristics in addition to MAC layer effects; in particular, CTU correlates probabilistically the multipath delay profile of the channel with the packet error rate. We employ CTU to evaluate the performance of a generic medium access procedure. We compare the results with those from extensive simulations and show the high accuracy of CTU. We use CTU to assess the impact of various system parameters on the MAC layer performance; we make several interesting observations that are discussed in depth.
INFOCOM 2008. The 27th Conference on Computer Communications. IEEE; 05/2008
[show abstract][hide abstract] ABSTRACT: Analytical models to evaluate and predict "precision" performance of indoor positioning systems based on location fingerprinting are lacking. Such models can be used to improve the design of positioning systems, for example by eliminating some fingerprints and reducing the size of the location fingerprint database. In this paper, we develop a new analytical model that employs proximity graphs for predicting performance of indoor positioning systems based on location fingerprinting. The model allows computation of an approximate probability distribution of error distance given a location fingerprint database based on received signal strength and its associated statistics. The performance results from the simulation and the analytical model are found to be congruent. This model also allows us to perform analysis of the internal structure of location fingerprints. We employ the analysis of the internal structure to identify and eliminate unnecessary location fingerprints stored in the database, thereby saving on computation while performing location estimation.
Pervasive Computing and Communications, 2008. PerCom 2008. Sixth Annual IEEE International Conference on; 04/2008
[show abstract][hide abstract] ABSTRACT: In this paper, we introduce novel probabilistic transmission protocols for data intensive wireless sensor networks. The protocols combine a randomized transmission scheme with scheduling based on heuristics to alleviate network performance degradation due to excessive collisions and retransmissions. In particular, by utilizing local information about sensor neighbors, our protocols minimize collisions in areas with high channel contention. The simulation results of our hybrid techniques show improved performance of data delivery and reduced energy consumption compared to carrier-sensing based IEEE 802.15.4 CAP mode and time-division based DRAND.
Advanced Information Networking and Applications Workshops, 2007, AINAW '07. 21st International Conference on; 06/2007
[show abstract][hide abstract] ABSTRACT: Data Intensive Mobile Sensor Networks (DIMSNs) introduce a promising but still under-utilized technology. Meanwhile, there is a growing confidence that certain applications (Killer Apps) have a potential to create a sustained market for this technology. For example, a large team of cooperative mobile robots can be considered as a wireless sensornet composed of a number of mobile nodes most of which are powerconstrained. Such mobile robots can be deployed in conjunction with stationary sensor nodes to acquire and process data for surveillance and tracking, environmental monitoring for highly sensitive areas, or execute search and rescue operations. This example illustrates conceptual attractiveness of the DIMSN systems that generates interesting and appealing research challenges (e.g., intelligent mobile agents, semantically enriched and contextaware wireless services, smart network monitoring infrastructures). However, while providing excellent funding opportunities, those challenges often underestimate the GRAND DETERRENTS that make moves towards practical data-intensive mobile sensornets extremely difficult.
Mobile Data Management, 2006. MDM 2006. 7th International Conference on; 06/2006
[show abstract][hide abstract] ABSTRACT: Due to broadcast nature of wireless radio transmission, security services are of paramount importance to protect information exchanged in a wireless network. However, providing security services increases the computation and hence energy consumption due to cryptographic algorithms. Energy tends to be a very limited resource for wireless devices operating on battery. Thus, energy efficient security services are necessary to operate limited wireless devices securely. In this paper, we propose Tunable Security Model (TSM) to minimize energy consumption while providing security services such that the user's security level requirement is satisfied. From our experiments in IEEE 802.11 wireless networks, it is shown that using TSM can save up to 8% energy for low-level security, and up to 43% energy for high-level security.
Wireless Pervasive Computing, 2006 1st International Symposium on; 02/2006
[show abstract][hide abstract] ABSTRACT: Energy sayings are extremely important in wireless networks where devices operate using battery power. Security in wireless networks is also becoming crucial with the deployment of wireless local area networks in hot spot areas, organizations, hospitals and so on. Security protocols depend on energy consuming operations that occur in the cryptographic primitives used in the protocols. It has been observed that different cryptographic algorithms consume different amounts of energy. Also, the amount of energy consumed can depend on the key size, the number of cryptographic operational rounds, and packet or frame size. At the same time, the strength of a security protocol also depends on the key sizes and ciphers used to build it. We apply these results to protocols in wireless local area networks and study the tradeoffs between the security strengths of these protocols and the amount of energy consumed. For the analysis, we use distributions of packet sizes based on packets collected in home and campus wireless local area networks and measurements of the number of CPU cycles taken for cryptographic computation.
[show abstract][hide abstract] ABSTRACT: Indoor positioning systems that make use of received signal strength based location fingerprints and existing wireless local area network infrastructure have recently been the focus for supporting location-based services in indoor and campus areas. A knowledge and understanding of the properties of the location fingerprint can assist in improving design of algorithms and deployment of position location systems. However, most existing research work ignores the radio signal properties. This paper investigates the properties of the received signal strength reported by IEEE 802.11b wireless network interface cards. Analyses of the data are performed to understand the underlying features of location fingerprints. The performance of an indoor positioning system in terms of its precision is compared using measured data and a Gaussian model to see how closely a Gaussian model may fit the measured data.
Mobile and Ubiquitous Systems: Networking and Services, 2004. MOBIQUITOUS 2004. The First Annual International Conference on; 09/2004
[show abstract][hide abstract] ABSTRACT: Recently, several authentication protocols have been proposed for wireless local area networks (WLANs) to improve security in hotspot public access and corporate networks, and some have been proposed for integrated 3G-WLAN networks. These authentication protocols are based on the extensible authentication protocol and have been directly applied to wireless networks based on their widespread use in wired networks. Depending on the 3G-WLAN architecture and how the WLAN is tied to the 3G network, these protocols could have large latency. Moreover, they do not have mechanisms for authenticating the usage time of a mobile in a WLAN. We first discuss these issues related to existing authentication protocols for a 3G-WLAN integrated network. Then, we propose a new authentication mechanism based on the dual signature concept used in secure electronic transactions that can be used in a loosely coupled architecture. Finally, we present a preliminary evaluation of the energy performance and latency of the existing and proposed protocols.
[show abstract][hide abstract] ABSTRACT: In previous years, positioning systems for indoor areas using the existing wireless local area network infrastructure have been suggested. Such systems make use of location fingerprinting rather than time or direction of arrival techniques for determining the location of mobile stations. While experimental results related to such positioning systems have been presented, there is a lack of analytical models that can be used as a framework for designing and deploying the positioning systems. In this paper, we present an analytical model for analyzing such positioning systems. We develop the framework for analyzing a simple positioning system that employs the Euclidean distance between a sample signal vector and the location fingerprints of an area stored in a database. We analyze the effect of the number of access points that are visible and radio propagation parameters on the performance of the positioning system and provide some preliminary guidelines on its design.
INFOCOM 2004. Twenty-third AnnualJoint Conference of the IEEE Computer and Communications Societies; 04/2004
[show abstract][hide abstract] ABSTRACT: It is well known that the distributed coordination function (DCF) of the IEEE 802.11 MAC protocol is not suitable for supporting multimedia and QoS-sensitive applications because of its inherent lack of QoS support and fairness. Recently, several distributed QoS mechanisms have been proposed which translate user QoS requirements into typically a single parameter of the DCF protocol. In this paper, we compare the pros and cons of the major distributed QoS mechanisms, and propose a new mechanism that provides superior performance and supports two different QoS models. The proposed mechanism is based on deficit round robin scheduling and translates the user throughput requirements into the 802.11 MAC interframe space and backoff interval parameters. We show via simulations that the proposed mechanism provides low variability of throughput and delay and has the advantage of low complexity.
Global Telecommunications Conference, 2003. GLOBECOM '03. IEEE; 01/2004