Andréa W. Richa

A jamming-resistant MAC protocol for single-hop wireless networks

In this paper we consider the problem of designing a medium access control (MAC) protocol for single-hop wireless networks that is provably robust against adaptive adversarial jamming. The wireless network consists of a set of honest and reliable nodes that are within the transmission range of each other. In addition to these nodes there is an adversary. The adversary may know the protocol and its entire history and use this knowledge to jam the wireless channel at will at any time. It is allowed to jam a (1-epsilon)-fraction of the time steps, for an arbitrary constant epsilon>0, but it has to make a jamming decision before it knows the actions of the nodes at the current step. The nodes cannot distinguish between the adversarial jamming or a collision of two or more messages that are sent at the same time. We demonstrate, for the first time, that there is a local-control MAC protocol requiring only very limited knowledge about the adversary and the network that achieves a constant throughput for the non-jammed time steps under any adversarial strategy above. We also show that our protocol is very energy efficient and that it can be extended to obtain a robust and efficient protocol for leader election and the fair use of the wireless channel.

Stabilization, Safety, and Security of Distributed Systems

Consensus algorithms allow a set of nodes to reach an agreement on a quantity of interest. For instance, a consensus algorithm may be used to allow a network of sensors to determine the average value of samples collected by the different sensors. Similarly, a consensus algorithm can also be used by the nodes to synchronize their clocks. Research on consensus algorithms has a long history, with contributions from different research communities, including distributed computing, control systems, and social science. In this talk, we will discuss two resilient consensus algorithms that can perform correctly despite the following two types of adversities: (i) In wireless networks, transmissions are subject to transmission errors, resulting in packet losses. We will discuss how “average consensus” can be achieved over such lossy links, without explicitly making the links reliable, for instance, via retransmissions. (ii) In a distributed setting, some of the nodes in the network may fail or may be compromised. We will discuss a consensus algorithm that can tolerate “Byzantine” failures in partially connected networks. Low-Congestion Distributed Algorithms

An O(log n) dominating set protocol for wireless ad-hoc networks under the physical interference model

Dealing with interference is one of the primary challenges to solve in the design of protocols for wireless ad-hoc networks. Most of the work in the literature assumes localized or hop-based interference models in which the effect of interference is neglected beyond a certain range from the transmitter. However, interference is a more complex phenomenon that cannot, in general, be captured by localized models, implying that protocols based on such models are not guaranteed to work in practice. This paper is the first to present and rigorously analyze a distributed dominating set protocol for wireless ad-hoc networks with O(1) approximation bound based on the physical interference model, which accounts for interference generated by all nodes in the network. The proposed protocol is fully distributed, randomized, and extensively uses physical carrier sensing to reduce message overhead. It does not need node identifiers or any kind of prior information about the system, and all messages are of constant size (in bits). We prove that, by appropriately choosing the threshold for physical carrier sensing, the protocol stabilizes within a logarithmic number of communication rounds, w.h.p., which is faster than the runtime of any known distributed protocol without prior knowledge about the system under any wireless model that does not abstract away collisions.

A distributed polylogarithmic time algorithm for self-stabilizing skip graphs

Peer-to-peer systems rely on scalable overlay networks that enable efficient routing between its members. Hypercubic topologies facilitate such operations while each node only needs to connect to a small number of other nodes. In contrast to static communication networks, peer-to-peer networks allow nodes to adapt their neighbor set over time in order to react to join and leave events and failures. This paper shows how to maintain such networks in a robust manner. Concretely, we present a distributed and self-stabilizing algorithm that constructs a (variant of the) skip graph in polylogarithmic time from any initial state in which the overlay network is still weakly connected. This is an exponential improvement compared to previously known self-stabilizing algorithms for overlay networks. In addition, individual joins and leaves are handled locally and require little work.

Coping with a Smart Jammer in Wireless Networks: A Stackelberg Game Approach

Jamming defense is an important yet challenging problem. In this paper, we study the jamming defense problem in the presence of a smart jammer, who can quickly learn the transmission power of the user and adaptively adjust its transmission power to maximize the damaging effect. We consider both the single-channel model and the multi-channel model. By modeling the problem as a Stackelberg game, we compute the optimal transmission power for the user to maximize its utility, in the presence of a smart jammer. For the single-channel model, we prove the existence and uniqueness of the Stackelberg Equilibrium (SE) by giving closed-form expressions for the SE strategies of both the user and the player. For the multi-channel model, we prove the existence of the SE. We design algorithms for computing the jammers best response strategy and approximating the users optimal strategy. Finally, we validate our theoretical analysis through extensive simulations.

Dynamic coverage in ad-hoc sensor networks

AbstractAd-hoc networks of sensor nodes are in general semi-permanently deployed. However, the topology of such networks continuously changes over time, due to the power of some sensors wearing out, to new sensors being inserted into the network, or even due to designers moving sensors around during a network re-design phase (for example, in response to a change in the requirements of the network). In this paper, we address the problem of how to dynamically maintain two important measures on the quality of the coverage of a sensor network: the best-case coverage and worst-case coverage distances. We assume that the ratio between upper and lower transmission power of sensors is bounded by a polynomial of n, where n is the number of sensors, and that the motion of mobile sensors can be described as a low-degree polynomial function of time. We maintain a (1+ε)-approximation on the best-case coverage distance and a

Competitive and Fair Medium Access Despite Reactive Jamming

(\sqrt 2 + \varepsilon )

Randomized protocols for low-congestion circuit routing in multistage interconnection networks

-approximation on the worst-case coverage distance of the network, for any fixed ε>0. Our algorithms have amortized or worst-case poly-logarithmic update costs. We are able to efficiently maintain the connectivity of the regions on the plane with respect to the sensor network, by extending the concatenable queue data structure to also serve as a priority queue. In addition, we present an algorithm that finds the shortest maximum support path in time O(nlog n).