Application-level assessment of approaches to coordinate node mobility in wireless sensor and actor networks

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Abstract

Wireless networks of sensor and actor devices require a great deal of coordination to fulfil their objectives. This paper focuses on the dimension of actor–actor coordination, that involves analyzing the data gathered by the sensors and deciding how to act on the environment. Specifically, we tackle the open problem of considering the effects of actors’ mobility on the communications needed for coordination. Firstly, we define three general approaches to bring mobility concerns into coordination, adapting solutions from the field of ad-hoc networking. Then, we assess the strengths and weaknesses of the three approaches through simulations of an autonomous robotic system in a representative application scenario, namely the extinction of forest fires. The results reveal trade-offs among performance, delays in communication, sensitiveness to timing and positioning imprecisions, and energy consumption.

Introduction

Recent technological advances have led to the emergence of Wireless Sensor and Actor Networks (WSANs), in which hundreds or thousands of inexpensive devices (the sensors) observe an environment, and far fewer richer devices (the actors) process the sensed data and make decisions to automatically perform certain actions [2], [11]. A sample such network is depicted in Fig. 1. This paradigm finds application in diverse areas such as battlefield or disaster-area surveillance, smart spaces, maintenance of industrial plants, environmental and structural monitoring, etc.

Sensors usually have low power and limited sensing, computing and wireless communication capabilities, whereas actors feature much better processing capabilities, higher transmission power and longer battery life. This heterogeneity, together with the challenges of the WSAN application domains, demands a great deal of coordination to provide effective sensing and acting. The process of establishing and maintaining data paths between sensors and actors has been termed actor–actor coordination [2], whereas the decisions about what actions to perform, how, when, where and by whom fall within actor–actor coordination.

In this paper, we tackle the open problem of considering the effects of node mobility in actor–actor coordination. Recent pieces of work, such as those of [18], [25], overlooked this question by considering immobile actors, that is, nodes which are not mobile from a networking perspective but contain moving mechanical parts that delimit their action range. In [14], [17] we can read about mobile actors, but the exchange of information relies on the assumption that transmission ranges are big enough to ensure total connectivity. While it is true that the energy required for actions and movements is orders of magnitude higher than that required for communication, it frequently happens that WSANs have to work in adverse transmission conditions, with few actors to cover large areas and/or some actors having no line of sight to the others. In such conditions, it is mandatory to consider that actors have limited transmission ranges, and it may well happen that a node enters or exits the range of others when it moves. In other words, it is mandatory to consider that the connectivity of the network formed by the actors alone depends on their mobility.1

The effects of node mobility have been thoroughly studied with regard to wireless connectivity and network performance metrics in the literature of ad-hoc networking. Leaving sensor devices aside, the actors of a WSAN can be seen as forming a mobile ad-hoc network to exchange information with which to coordinate their activities, with the additional property that their mobility can be controlled. Knowing that, the goal of this paper is to analyze solutions that could be retrieved from ad-hoc networking to advance research in WSAN coordination, introducing realistic conditions for communication among actors. We start out by classifying those solutions (which, by the way, need not have been devised for coordination purposes) into three general approaches to actor–actor coordination in Section 2. Then, we evaluate three instances of these approaches in the context of a representative WSAN application (Section 3), to finally draw conclusions about their relative merits and weaknesses (Section 4).

Section snippets

Approaches to coordinate actors’ mobility

In the following subsections, we introduce three approaches to deal with mobility in actor–actor coordination, adapting existing solutions from the field of ad-hoc networking. To a large extent, these approaches are independent of the protocols employed in the network layer and below, and also independent of the techniques that may implement the intelligence of the application domain (including tasks like mission control, scheduling or disagreement detection, that fall within the scopes of

Assessing instances of the three approaches

In this section, we shall discuss the results of simulating WSANs in the context of extinguishing forest fires, with a team of robots coordinated by three instances of the approaches introduced in Section 2. This setting is representative of the range of applications envisaged for WSANs (see [2]) and is advantageous for providing an intuitive notion of coordination success or failure (in terms of burnt-down area).

Conclusions

In this paper, we have brought out the issues raised by node mobility in the coordination between actors in WSANs, describing three general approaches to tackle the problem: (i) tethered mobility, that takes connectivity as a primary concern; (ii) prediction-supported connectivity, that allows deciding the actors’ movements by application-level concerns, relying on prediction techniques to anticipate disconnections and regain contact; and (iii) knowledge exploitation, that also emphasizes the

Acknowledgements

This work has been supported by the Consellería de Educación e Ordenación Universitaria (Xunta de Galicia) incentives file 2007/000016-0.

References (27)

  • I.F. Akyildiz et al.

    Wireless sensor and actor networks: research challenges

    Ad Hoc Networks

    (2004)
  • Q. Li et al.

    Communication in disconnected ad hoc networks using message relay

    Parallel and Distributed Computing

    (2003)
  • M. López-Nores et al.

    KEPPAN: knowledge exploitation for proactively-planned ad-hoc networks

    Journal of Network and Computer Applications

    (2009)
  • The network simulator – ns-2. Available from:...
  • P. Basu et al.

    Movement control algorithms for realization of fault-tolerant ad hoc robot networks

    IEEE Network

    (2004)
  • A. Bhattacharya, S.K. Das, LeZi-Update: an information-theoretic approach to track mobile users in PCS networks, in:...
  • T. Clausen, P. Jacquet, Optimized Link State Routing Protocol (OLSR). Technical Report RFC 3561,...
  • S. Das et al.

    A localized algorithm for bi-connectivity of connected mobile robots

    Telecommunication Systems

    (2009)
  • F. deRosa et al.

    Disconnection prediction in mobile ad hoc networks for supporting cooperative work

    IEEE Pervasive Computing

    (2005)
  • M.A. Finney, FARSITE: fire area simulator – model development and evaluation. Technical Report RMRS-RP-4, Forest...
  • B.P. Gerkey, M.J. Matarić, A market-based formulation of sensor-actuator network coordination, in: AAAI Spring...
  • D.K. Goldenberg, J. Lin, A.S. Morse, B.E. Rosen, Y.R. Yang, Towards mobility as a network control primitive, in: 5th...
  • M. Haenggi, Mobile sensor-actuator networks: opportunities and challenges, in: 7th IEEE International Workshop on...
  • Cited by (1)

    View full text