2,265 research outputs found
Parameterized Verification of Algorithms for Oblivious Robots on a Ring
We study verification problems for autonomous swarms of mobile robots that
self-organize and cooperate to solve global objectives. In particular, we focus
in this paper on the model proposed by Suzuki and Yamashita of anonymous robots
evolving in a discrete space with a finite number of locations (here, a ring).
A large number of algorithms have been proposed working for rings whose size is
not a priori fixed and can be hence considered as a parameter. Handmade
correctness proofs of these algorithms have been shown to be error-prone, and
recent attention had been given to the application of formal methods to
automatically prove those. Our work is the first to study the verification
problem of such algorithms in the parameter-ized case. We show that safety and
reachability problems are undecidable for robots evolving asynchronously. On
the positive side, we show that safety properties are decidable in the
synchronous case, as well as in the asynchronous case for a particular class of
algorithms. Several properties on the protocol can be decided as well. Decision
procedures rely on an encoding in Presburger arithmetics formulae that can be
verified by an SMT-solver. Feasibility of our approach is demonstrated by the
encoding of several case studies
Ring Exploration with Oblivious Myopic Robots
The exploration problem in the discrete universe, using identical oblivious
asynchronous robots without direct communication, has been well investigated.
These robots have sensors that allow them to see their environment and move
accordingly. However, the previous work on this problem assume that robots have
an unlimited visibility, that is, they can see the position of all the other
robots. In this paper, we consider deterministic exploration in an anonymous,
unoriented ring using asynchronous, oblivious, and myopic robots. By myopic, we
mean that the robots have only a limited visibility. We study the computational
limits imposed by such robots and we show that under some conditions the
exploration problem can still be solved. We study the cases where the robots
visibility is limited to 1, 2, and 3 neighboring nodes, respectively.Comment: (2012
Gathering over Meeting Nodes in Infinite Grid
The gathering over meeting nodes problem asks the robots to gather at one of
the pre-defined meeting nodes. The robots are deployed on the nodes of an
anonymous two-dimensional infinite grid which has a subset of nodes marked as
meeting nodes. Robots are identical, autonomous, anonymous and oblivious. They
operate under an asynchronous scheduler. They do not have any agreement on a
global coordinate system. All the initial configurations for which the problem
is deterministically unsolvable have been characterized. A deterministic
distributed algorithm has been proposed to solve the problem for the remaining
configurations. The efficiency of the proposed algorithm is studied in terms of
the number of moves required for gathering. A lower bound concerning the total
number of moves required to solve the gathering problem has been derived
Synchronous Robots vs Asynchronous Lights-Enhanced Robots on Graphs
AbstractIn this paper, we consider the distributed setting of computational mobile entities, called robots, that have to perform tasks without global coordination. Depending on the environment as well as on the robots' capabilities, tasks might be accomplished or not.In particular, we focus on the well-known scenario where the robots reside on the nodes of a graph and operate in Look-Compute-Move cycles. In one cycle, a robot perceives the current configuration in terms of robots positions (Look), decides whether to move toward some edge of the graph (Compute), and in the positive case it performs an instantaneous move along the computed edge (Move).We then compare two basic models: in the first model robots are fully synchronous, while in the second one robots are asynchronous and lights-enhanced, that is, each robot is equipped with a constant number of lights visible to all other robots. The question whether one model is more powerful than the other in terms of computable tasks has been considered in [Das et al., Int.'l Conf. on Distributed Computing Systems, 2012] but for robots moving on the Euclidean plane rather than on a graph.We provide two different tasks, and show that on graphs one task can be solved in the fully synchronous model but not in the asynchronous lights-enhanced model, while for the other task the converse holds. Hence we can assert that the fully synchronous model and the asynchronous lights-enhanced model are incomparable on graphs. This opens challenging directions in order to understand which peculiarities make the models so different
Optimal Rendezvous L-Algorithms for Asynchronous Mobile Robots with External-Lights
We study the Rendezvous problem for two autonomous mobile robots in asynchronous settings with persistent memory called light. It is well known that Rendezvous is impossible in a basic model when robots have no lights, even if the system is semi-synchronous. On the other hand, Rendezvous is possible if robots have lights of various types with a constant number of colors. If robots can observe not only their own lights but also other robots\u27 lights, their lights are called full-light. If robots can only observe the state of other robots\u27 lights, the lights are called external-light. This paper focuses on robots with external-lights in asynchronous settings and a particular class of algorithms called L-algorithms, where an L-algorithm computes a destination based only on the current colors of observable lights. When considering L-algorithms, Rendezvous can be solved by robots with full-lights and three colors in general asynchronous settings (called ASYNC) and the number of colors is optimal under these assumptions. In contrast, there exist no L-algorithms in ASYNC with external-lights regardless of the number of colors.
In this paper, extending the impossibility result, we show that there exist no L-algorithms in so-called LC-1-Bounded ASYNC with external-lights regardless of the number of colors, where LC-1-Bounded ASYNC is a proper subset of ASYNC and other robots can execute at most one Look operation between the Look operation of a robot and its subsequent Compute operation. We also show that LC-1-Bounded ASYNC is the minimal subclass in which no L-algorithms with external-lights exist. That is, Rendezvous can be solved by L-algorithms using external-lights with a finite number of colors in LC-0-Bounded ASYNC (equivalently LC-atomic ASYNC). Furthermore, we show that the algorithms are optimal in the number of colors they use
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