We address the perpetual grid exploration (PGE) by a swarm of autonomous, asynchronous, myopic, and luminous robots. We first show that it is impossible for the robots to explore the grid regardless of their number and the number of colors they can take if their visibility range is one. We also show that PGE is impossible with three oblivious robots that have a visibility range of two hops. We then present three optimal algorithms solving the problem. The first algorithm uses four oblivious robots with a visibility range of two, but assumes they agree on a common chirality. For the two other algorithms, no common chirality is assumed. The former uses three robots that have a visibility range of two and a two-color light. The latter uses three oblivious robots under visibility range three.

Low-power wide area networks (LPWANs) are being increasingly used in Internet of Things applications, including smart city and environmental monitoring, as they enable communications from low-power end-devices to distant gateways. LoRaWAN is the most common protocol for LPWANs, and is able to automatically tradeoff throughput and reliability thanks to an algorithm called Adaptive DataRate (ADR). However, the LoRaWAN standard imposes mobile nodes to disable the ADR. In this paper, we propose a protocol called MADERE (for Mobile ADR) that attempts to adapt the LoRaWAN parameters for mobile end-devices. We show that MADERE performs well compared to the few existing algorithms from the literature, with limited overhead.

We consider self-stabilization and its weakened form called pseudo-stabilization. We study conditions under which (pseudo- and self-) stabilizing leader election is solvable in networks subject to frequent topological changes. To model such an high dynamics, we use the dynamic graph (DG) paradigm and study a taxonomy of nine important DG classes. Our results show that self-stabilizing leader election can only be achieved in the classes where all processes are sources. Furthermore, even pseudo-stabilizing leader election cannot be solved in all remaining classes, except in the class where at least one process is a timely source. We illustrate that result by proposing a pseudo-stabilizing leader election algorithm for the latter class. We also show that in this last case, the convergence time of pseudo-stabilizing leader election algorithms cannot be bounded. Nevertheless, we show that our solution is speculative since its convergence time can be bounded when the dynamics is not too erratic, precisely when all processes are timely sources.

We initiate research on self-stabilization in highly dynamic identified message-passing systems where dynamics is modeled using time-varying graphs (TVGs). More precisely, we address the self-stabilizing leader election problem in three wide classes of TVGs: the class TCB (Δ) of TVGs with temporal diameter bounded by Δ, the class TCB (Δ) of TVGs with temporal diameter quasi-bounded by Δ, and the class TCR of TVGs with recurrent connectivity only, where TCB (Δ) ⊆ TCB (Δ) ⊆ TCR. We first study conditions under which our problem can be solved. Precisely, we introduce the notion of size-ambiguity to show that the assumption on the knowledge of the number n of processes is central. Our results reveal that, despite the existence of unique process identifiers, any deterministic self-stabilizing leader election algorithm working in the TVG class TCB (Δ) or TCR cannot be size-ambiguous, justifying why our solutions for those classes assume the exact knowledge of n. We then present three self-stabilizing leader election algorithms for the TVG classes TCB (Δ), TCB(Δ), and TCR, respectively.

We study (deterministic) leader election in unidirectional rings of homonym processes that have no a priori knowledge on the number of processes. In this context, we show that there is no algorithm that solves process-terminating leader election for the class of asymmetric labeled rings. In particular, there is no process-terminating leader election algorithm in rings in which at least one label is unique. However, we show that process-terminating leader election is possible for the subclass of asymmetric rings, where multiplicity is bounded. We confirm this positive results by proposing two algorithms, which achieve the classical trade-off between time and space.