The Driving Philosophers

We introduce a new synchronization problem in mobile ad-hoc systems: the Driving Philosophers. In this problem, an unbounded number of driving philosophers (processes) access a round-about (set of shared resources organized along a logical ring). The crux of the problem is to ensure, beside traditional mutual exclusion and starvation freedom at each particular resource, gridlock freedom (i.e., cyclic waiting chain amongst processes). The problem captures explicitly the very notion of process mobility and the underlying model does not involve any assumption on the total number of (participating) processes or the use of shared memory, i.e., the model conveys the ad-hoc environment. We present a generic algorithm that solves the problem in a synchronous model. Instances of this algorithm can be fair but not concurrent, or concurrent but not fair. We derive the impossibility of achieving fairness and concurrency at the same time as well as the impossibility of solving the problem in an asynchronous model. We also conjecture the impossibility of solving the problem in an ad-hoc network model with limited-range communication

Optimal Deterministic Protocols for Mobile Robots on a Grid

. A Multi Robot Grid System consists of m robots that operate in a set of n m work locations connected by aisles in a p n \Theta p n grid. From time to time the robots need move along the aisles, in order to visit disjoint sets of locations. The movement of the robots must comply with the following constraints: (1) no two robots can collide at a grid node or traverse an edge at the same time; (2) a robot's sensory capability is limited to detecting the presence of another robot at a neighboring node. We present an efficient deterministic protocol that allows m = \Theta (n) robots to visit their target destinations in O \Gamma p dn \Delta time, where each robot visits at most d n targets in any order. We also prove a lower bound that shows that our protocol is optimal. Prior to this paper, no optimal protocols were known for d ? 1. For d = 1 optimal protocols were known only for m = O \Gamma p n \Delta , while for m = O (n) only a randomized suboptimal protoco..

Optimal deterministic protocols for mobile robots on a grid

A Multi Robot Grid System consists of m robots that operate in a set of n 65 m work locations connected by aisles in a 1an 7 1an grid. From time to time the robots need move along the aisles, in order to visit disjoint sets of locations. The movement of the robots must comply with the following constraints: (1) no two robots can collide at a grid node or traverse an edge at the same time; (2) a robot's sensory capability is limited to detecting the presence of another robot at a neighboring node. We present an efficient deterministic protocol that allows m=\u3b8 (n) robots to visit their target destinations in O ( 1adn) time, where each robot visits at most d 64 n targets in any order. We also prove a lower bound that shows that our protocol is optimal. Prior to this paper, no optimal protocols were known for d > 1. For d=1 optimal protocols were known only for m=O ( 1an), while for m=O (n) only a randomized suboptimal protocol was known