We study the barrier coverage problem using relocatable sensor nodes. We assume each sensor can sense an intruder or event inside its sensing range. Sensors are initially located at arbitrary positions on the barrier and can move along the barrier. The goal is to find final positions for sensors so that the entire barrier is covered. In recent years, the problem has been studied extensively in the centralized setting. In this paper, we study a barrier coverage problem in the distributed and discrete setting. We assume that we have n identical sensors located at grid positions on the barrier, and that each sensor repeatedly executes a Look-Compute-Move cycle: based on what it sees in its vicinity, it makes a decision on where to move, and moves to its next position. We make two strong but realistic restrictions on the capabilities of sensors: they have a constant visibility range and can move only a constant distance in every cycle. In this model, we give the first two distributed algorithms that achieve barrier coverage for a line segment barrier when there are enough nodes in the network to cover the entire barrier. Our algorithms are An abbreviated version of this paper is published synchronous, and local in the sense that sensors make their decisions independently based only on what they see within their constant visibility range. One of our algorithms is oblivious whereas the other uses two bits of memory at each sensor to store the type of move made in the previous step. We show that our oblivious algorithm terminates within Θ(n 2 ) steps with the barrier fully covered, while the constant-memory algorithm is shown to take Θ(n) steps to terminate in the worst case. Since any algorithm in which a sensor can only move a constant distance in one step requires Ω(n) steps on some inputs, our second algorithm is asymptotically optimal.

Assume that n sensors with identical range r = f (n)

Future vehicular systems will be able to cooperate in order to perform many functions in a more effective and efficient way. However, achieving predictable and safe coordination of vehicles that autonomously cooperate in open and uncertain environments is a challenging task. Traditional solutions for achieving safety either impose restrictions on performance or require costly resources to deal with the worst case situations. In this paper, we describe a generic architectural pattern that addresses this problem. We consider that cooperative functions can be executed with multiple levels of service, and we rely on a safety kernel to manage the service level in run-time. A set of safety rules defined in design-time determine conditions under which the cooperative function can be performed safely in each level of service. The paper provides details of our implementation of this safety kernel, covering both hardware and software aspects. It also presents an example application of the proposed solutions in the development of a demonstrator using scaled vehicles.

No abstract

Abstract. Given a set P of n points in the plane, we solve the problems of constructing a geometric planar graph spanning P 1) of minimum degree 2, and 2) which is 2-edge connected, respectively, and has max edge length bounded by a factor of 2 times the optimal; we also show that the factor 2 is best possible given appropriate connectivity conditions on the set P, respectively. First, we construct in O(n log n) time a geometric planar graph of minimum degree 2 and max edge length bounded by 2 times the optimal. This is then used to construct in O(n log n) time a 2-edge connected geometric planar graph spanning P with max edge length bounded by √ 5 times the optimal, assuming that the set P forms a connected Unit Disk Graph. Second, we prove that 2 times the optimal is always sufficient if the set of points forms a 2 edge connected Unit Disk Graph and give an algorithm that runs in O(n 2 ) time. We also show that for k ∈ O( √ n), there exists a set P of n points in the plane such that even though the Unit Disk Graph spanning P is kvertex connected, there is no 2-edge connected geometric planar graph spanning P even if the length of its edges is allowed to be up to 17/16.

Abstract. Assume that n directional antennae located at distinct points in the plane are rotating at constant identical speeds. They all have identical range and sensor angle (or field of view). We propose and study the Rotating Antennae Coverage Problem, a new problem concerning rotating sensors for the uninterrupted coverage of a region in the plane. More specifically, what is the initial orientation of the sensors, minimum angle, and range required so that a given (infinite or finite) line or planar domain is covered by the rotating sensors at all times? We give algorithms for determining the initial orientation of the sensors and analyze the resulting angle/range tradeoffs for ensuring continuous coverage of a given region or line in the plane with identical rotating sensors of given transmission angle and range. We also investigate other variants of the problem whereby for a given parameter T (representing time) there is no point in the domain that is left unattended by some sensor for a period of time longer than T . Despite the apparent simplicity of the problem several of the algorithms proposed are intricate and elegant. We have also implemented our algorithms in C++ and the code can be downloaded on the web.

No abstract

We consider the design of a disagreement correction protocol in multi-vehicle systems. Vehicles broadcast in real-time vital information such as position, direction, speed, acceleration, intention, etc. This information is then used to identify the risks and adapt their trajectory to maintain the highest performance without compromising the safety. To minimize the risk due to the use of inconsistent information, all cooperating vehicles must agree whether to use the exchanged information to operate in a cooperative mode or use the only local information to operate in an autonomous mode. However, since wireless communications are prone to failures, it is impossible to deterministically reach an agreement. Therefore, any protocol will exhibit necessary disagreement periods. In this paper, we investigate whether vehicles can still cooperate despite communication failures even in the scenario where communication is suddenly not available. We present a deterministic protocol that allows all participants to either operate a cooperative mode when vehicles can exchange all the information in a timely manner or operate in autonomous mode when messages are lost. We show formally that the disagreement time is bounded by the time that the communication channel requires to deliver messages and validate our protocol using NS-3 simulations. We explain how the proposed solution can be used in vehicular platooning to attain high performance and still guarantee high safety standards despite communication failures.