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Analysis of Cross-layer Interaction in Multi-rate 802.11 WLANs
ABSTRACT
Recent works in empirical 802.11 wireless LAN performance evaluation have shown that cross-layer interactions in WLANs can be subtle, sometimes leading to unexpected results. Two such instances are: (i) significant throughput degradation resulting from automatic rate fallback (ARF) having difficulty distinguishing collision from channel noise, and (ii) scalable TCP over DCF performance that is able to mitigate the negative performance effect of ARF by curbing multiple access contention even when the number of stations is large. In this paper, we present a framework for analyzing complex crosslayer interactions in 802.11 WLANs, with the aim of providing effective tools for understanding and improving WLAN performance. We focus on cross-layer interactions between ARF, DCF, and TCP, where ARF adjusts coding at the physical layer, DCF mediates link layer multiple access control, and TCP performs end-to-end transport. We advance station-centric Markov chain models of ARF, ARFDCF with and without RTS/CTS, and TCP over DCF that may be viewed as multi-protocol extensions of Bianchi’s IEEE 802.11 model. We show that despite significant increase in complexity the analysis framework leads to tractable and accurate performance predictions. Our results complement empirical and simulation-based findings, demonstrating the versatility and efficacy of station-centric Markov chain analysis for capturing cross-layer WLAN dynamics.
Opportunistic Scheduling with Reliability Guarantees in Cognitive Radio Networks
ABSTRACT
We develop opportunistic scheduling policies for cognitive radio networks that maximize the throughput utility of the secondary (unlicensed) users subject to maximum collision constraints with the primary (licensed) users. We consider a cognitive network with static primary users and potentially mobile secondary users. We use the technique of Lyapunov Optimization to design an online flow control, scheduling, and resource allocation algorithm that meets the desired objectives and provides explicit performance guarantees.
Connectivity-Guaranteed and Obstacle-Adaptive Deployment Schemes for Mobile Sensor Networks
ABSTRACT
Mobile sensors can move and self-deploy into a network. While focusing on the problems of coverage, existing deployment schemes mostly over-simplify the conditions for network connectivity: they either assume that the communication range is large enough for sensors in geometric neighborhoods to obtain each other’s location by local communications, or assume a dense network that remains connected. At the same time, an obstacle-free field or full knowledge of the field layout is often assumed. We present new schemes that are not restricted by these assumptions, and thus adapt to a much wider range of application scenarios. While maximizing sensing coverage, our schemes can achieve connectivity for a network with arbitrary sensor communication/ sensing ranges or node densities, at the cost of a small moving distance; the schemes do not need any knowledge of the field layout, which can be irregular and have obstacles/ holes of arbitrary shape. Simulations results show that the proposed schemes achieve the targeted properties.
Overlapped Carrier-Sense Multiple Access (OCSMA) in Wireless Ad Hoc Networks
ABSTRACT
In wireless ad hoc networks (WANets), multihop routing may result in a radio knowing the content of transmissions of nearby radios. This knowledge can be used to improve spatial reuse in the network, thereby enhancing network throughput. Consider two radios, Alice and Bob, that are neighbors in a WANet not employing spread-spectrum multiple access (SSMA). Suppose that Alice transmits a packet to Bob for which Bob is not the final destination. Later, Bob forwards that packet on to the destination. Any transmission by Bob not intended for Alice usually causes interference that prevents Alice from receiving a packet from any of her neighbors. However, if Bob is transmitting a packet that he had previously received from Alice, then Alice knows the content of the interfering packet, and this knowledge can allow Alice to receive a packet from one of her neighbors during Bob’s transmission. In this paper, we develop a MAC protocol to support this technique in a WANet. We show how the 802.11 MAC protocol can be modified to allow for transmissions to be overlapped by taking advantage of noncausal knowledge of interfering signals. The resulting overlapped CSMA (OCSMA) protocol improves spatial reuse and end-to-end throughput in several scenarios.
An Epidemic Theoretic Framework for Vulnerability Analysis of Broadcast Protocols inWireless Sensor Networks
ABSTRACT
While multi-hop broadcast protocols, such as Trickle, Deluge and MNP, have gained tremendous popularity as a means for fast and convenient propagation of data/code in large scale wireless sensor networks, they can, unfortunately, serve as potential platforms for virus spreading if the security is breached. To understand the vulnerability of such protocols and design defense mechanisms against piggy-backed virus attacks, it is critical to investigate the propagation process of these protocols in terms of their speed and reachability. In this paper, we propose a general framework based on the principles of epidemic theory, for vulnerability analysis of current broadcast protocols in wireless sensor networks. In particular, we develop a common mathematical model for the propagation that incorporates important parameters derived from the communication patterns of the protocol under test. Based on this model, we analyze the propagation rate and the extent of spread of a malware over typical broadcast protocols proposed in the literature. The overall result is an approximate but convenient tool to characterize a broadcast protocol in terms of its vulnerability to malware propagation. We have also performed extensive simulations which have validated our model.
Contention-Aware Performance Analysis of Mobility-Assisted Routing
ABSTRACT
A large body of work has theoretically analyzed the performance of mobility-assisted routing schemes for intermittently connected mobile networks. However, the vast majority of these prior studies have ignored wireless contention. Recent papers have shown through simulations that ignoring contention leads to inaccurate and misleading results, even for sparse networks. In this paper, we analyze the performance of routing schemes under contention. First, we introduce a mathematical framework to model contention. This framework can be used to analyze any routing scheme with any mobility and channel model. Then, we use this framework to compute the expected delays for different representative mobility-assisted routing schemes under random direction, random waypoint and community-based mobility models. Finally, we use these delay expressions to optimize the design of routing schemes while demonstrating that designing and optimizing routing schemes using analytical expressions which ignore contention can lead to suboptimal or even erroneous behavior.
CAR: Context-aware Adaptive Routing for Delay Tolerant Mobile Networks
ABSTRACT
Most of the existing research work in mobile ad hoc networking is based on the assumption that a path exists between the sender and the receiver. On the other hand, applications of decentralised mobile systems are often characterised by network partitions. As a consequence delay tolerant networking research has received considerable attention in the recent years as a means to obviate to the gap between ad hoc network research and real applications. In this paper we present the design, implementation and evaluation of the Context-aware Adaptive Routing (CAR) protocol for delay tolerant unicast communication in intermittently connected mobile ad hoc networks. The protocol is based on the idea of exploiting nodes as carriers of messages among network partitions to achieve delivery. The choice of the best carrier is made using Kalman filter based prediction techniques and utility theory. The large scale performance of the CAR protocol are evaluated using simulations based on a social network founded mobility model, a purely random one and real traces from Dartmouth College.
Using Local Geometry for Tunable Topology Control in Sensor Networks
ABSTRACT
Neighbor-Every-Theta (NET) graphs are such that each node has at least one neighbor in every theta angle sector of its communication range. We show that for , NET graphs are guaranteed to have an edge-connectivity of at least b2 c, even with an irregular communication range. Our main contribution is to show how this family of graphs can achieve tunable topology control based on a single parameter . Since the required condition is purely local and geometric, it allows for distributed topology control. For a static network scenario, a power control algorithm based on the NET condition is developed for obtaining k-connected topologies and shown to be significantly efficient compared to existing schemes. In controlled deployment of a mobile network, control over positions of nodes can be leveraged for constructing NET graphs with desired levels of network connectivity and sensing coverage. To establish this, we develop a potential fields based distributed controller and present simulation results for a large network of robots. Lastly, we extend NET graphs to 3D and provide an efficient algorithm to check for the NET condition at each node. This algorithm can be used for implementing generic topology control algorithms in 3D.
Passive Online Detection of 802.11 Traffic Using Sequential Hypothesis Testing with TCP ACK-Pairs
ABSTRACT
In this paper, we propose two online algorithms to detect 802.11 traffic from packet-header data collected passively at a monitoring point. These algorithms have a number of applications in real-time wireless LAN management, for instance, in detecting unauthorized access points and detecting/predicting performance degradations. Both algorithms use sequential hypothesis tests and exploit fundamental properties of the 802.11 CSMA/CA MAC protocol and the half-duplex nature of wireless channels. They differ in that one requires training sets, while the other does not. We have built a system for online wireless traffic detection using these algorithms and deployed it at a university gateway router. Extensive experiments have demonstrated the effectiveness of our approach: the algorithm that requires training provides rapid detection and is extremely accurate (the detection is mostly within 10 seconds, with very low false-positive and false-negative ratios), the algorithm that does not require training detects 60 percent to 76 percent of the wireless hosts without any false positives, and both algorithms are lightweight, with computation and storage overhead well within the capability of commodity equipment.
BSMR: Byzantine-Resilient Secure Multicast Routing in Multi-hop Wireless Networks
ABSTRACT
In this work we identify vulnerabilities of ondemand multicast routing protocols for multi-hop wireless networks and discuss the challenges encountered in designing mechanisms to defend against them. We propose BSMR, a novel secure multicast routing protocol that withstands insider attacks from colluding adversaries. Our protocol is a software-based solution and does not require additional or specialized hardware. We present simulation results which demonstrate that BSMR effectively mitigates the identified attacks.
Many-to-One Throughput Capacity of IEEE 802.11 Multi-hop Wireless Networks
ABSTRACT
This paper investigates the many-to-one throughput capacity (and by symmetry, one-to-many throughput capacity) of IEEE 802.11 multi-hop networks. It has generally been assumed in prior studies that the many-to-one throughput capacity is upper-bounded by the link capacity L. Throughput capacity L is not achievable under 802.11. This paper introduces the notion of “canonical networks”, which is a class of regularly-structured networks whose capacities can be analyzed more easily than unstructured networks. We show that the throughput capacity of canonical networks under 802.11 has an analytical upper bound of 3L/4 when the source nodes are two or more hops away from the sink; and simulated throughputs of 0.690L (0.740L) when the source nodes are many hops away. We conjecture that 3L/4 is also the upper bound for general networks. When all links have equal length, 2L/3 can be shown to be the upper bound for general networks. Our simulations show that 802.11 networks with random topologies operated with AODV routing can only achieve throughputs far below the upper bounds. Fortunately, by properly selecting routes near the gateway (or by properly positioning the relay nodes leading to the gateway) to fashion after the structure of canonical networks, the throughput can be improved significantly by more than 150%. Indeed, in a dense network, it is worthwhile to deactivate some of the relay nodes near the sink judiciously.
Cooperative Asynchronous Multi-Channel MAC: Design, Analysis, and Implementation
ABSTRACT
Medium access control (MAC) protocols have been studied under different contexts for decades. In decentralized contexts, transmitter-receiver pairs make independent decisions, which are often sub-optimal due to insufficient knowledge about the communication environment. In this paper, we introduce distributed information sharing (DISH), which is a distributed flavor of control-plane cooperation, as a new approach to wireless protocol design. The basic idea is to allow nodes to share control information with each other such that nodes can make more informed decisions in communication. This notion of controlplane cooperation augments the conventional understanding of cooperation, which sits at the data plane as a data relaying mechanism. In a multi-channel network, DISH allows neighboring nodes to notify transmitter-receiver pairs of channel conflicts and deaf terminals to prevent collisions and retransmissions. Based on this, we design a single-radio cooperative asynchronous multi-channel MAC protocol called CAM-MAC. For illustration and evaluation purposes, we choose a specific set of parameters for CAM-MAC. First, our analysis shows that its throughput upper bound is 91% of the system bandwidth and our simulations show that it actually achieves a throughput of 96% of the upper bound. Second, our analysis shows that CAM-MAC can saturate 15 channels at maximum and our simulations show that it saturates 14.2 channels on average, which indicates that, although CAM-MAC uses a control channel, it does not realistically suffer from control channel bottleneck. Third, we compare CAM-MAC with its noncooperative version called UNCOOP, and observe a throughput ratio of 2.81 and 1.70 in single-hop and multi-hop networks, respectively. This demonstrates the value of cooperation. Fourth, we compare CAM-MAC with three recent multi-channel MAC protocols, MMAC [2], SSCH [3] and AMCP [4], and find that CAM-MAC significantly outperforms all of them. Finally, we implement CAM-MAC and UNCOOP on commercial off-theshelf hardware and share lessons learned in the implementation. The experimental results confirm the viability of CAM-MAC and the idea of DISH.
Cost- and Collision-Minimizing Forwarding Schemes for Wireless Sensor Networks: Design, Analysis, and Experimental Validation
ABSTRACT
The paper presents an original integrated MAC and routing scheme for wireless sensor networks. Our design objective is to elect the next hop for data forwarding by jointly minimizing the amount of signaling to complete a contention and maximizing the probability of electing the best candidate node. Toward this aim, we represent the suitability of a node to be the relay by means of locally calculated and generic cost metrics. Based on these costs, we analytically model the access selection problem through dynamic programming techniques, which we use to find the optimal access policy. Hence, we propose a contention-based MAC and forwarding technique, called Cost- and Collision-Minimizing Routing (CCMR). This scheme is then thoroughly validated and characterized through analysis, simulation, and experimental results.
RandomCast: An Energy-Efficient Communication Scheme for Mobile Ad Hoc Networks
ABSTRACT
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 low-power 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.