Fusion-based surveillance WSN deployment using Dempster–Shafer theory

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Abstract

In mission-critical Wireless Sensor Networks surveillance applications, a high detection rate coupled with a low false alarm rate is essential. Additionally, fusion methods can be employed with the hope that aggregation of uncertain information from multiple sensors enhances the quality of surveillance provided by the network. This paper investigates the following fundamental problem: what is the best way to deploy a finite number of unreliable sensors characterized by uncertain readings in order to satisfy the user detection requirements. Unlike prior efforts that rely on simple fusion schemes, we use the Dempster–Shafer theory to define a generic evidence fusion scheme that captures several characteristics of real-world applications. The fusion-based uncertainty-aware sensor networks deployment problem is formulated as a binary non-linear and non-convex optimization problem that is NP-hard, and an efficient heuristic using genetic algorithms is investigated. The effectiveness and efficiency of the proposed approach are evaluated using both simulations and experiments. The obtained results demonstrate the appropriateness of the evidence fusion model that considers in a meaningful way the information on the quality of sensors decisions as well as the reliability of these sensors along with their uncertain and imprecise decisions. Also, the proposed approach outperforms state-of-the-art deployment strategies.

Introduction

A Wireless Sensor Network (WSN) is a network of wirelessly connected small-scale, low-power, low-cost devices called sensor nodes (or sensors). These tiny sensors are equipped with sensing, computation, storage, communication, and power.

Critical applications such as military target detection impose stringent requirements for event detection accuracy such as a low false alarm rate coupled with a high detection rate. To detect a target, the sensors have to make local observations of their surrounding environment and collaborate to produce a global decision that reflects the status of the Region of Interest (RoI). It is well known that collaboration among sensors improve the sensing quality by jointly considering noisy measurements of multiple unreliable sensors. For example, He et al. (2006) show that the false alarm rate of a real-world Mica2 WSN can be reduced from 60% (when sensors decide independently) to near zero by adopting a fusion scheme.

The deployment is a mandatory and critical step in the process of developing WSNs solutions for real-life applications. Even if many optimizations can be done once the WSN is deployed to enhance its performance, we believe that the most important optimization steps are those performed at the design step in order to build the best possible topology that meets specific user requirements.

Deploying WSNs into the real-world could be a very challenging task. Actually, in addition to the intrinsic properties of WSNs, many challenges stem from the close interactions between the WSN and the physical environment. Examples of such challenges include:

  • How to consider uncertainty related to sensors readings?

  • How to consider sensor reliability?

  • How to combine sensory data from multiple sensors that can vary in their reliability?

  • How to consider harsh deployment environments?

By considering such fundamental challenges in the early design steps of the WSN, one can avoid unpleasant surprises and save effort, time, and money. In an attempt to handle the challenges above, the present paper brings the following contributions:

  • 1.

    A formal definition of an evidence-based sensing model is provided on the basis of Dempster–Shafer theory (Smets and Kennes, 1994). The proposed model captures several characteristics of real-world applications.

  • 2.

    To build belief functions from raw sensing data, a two-step method is described.

  • 3.

    The fusion-based uncertainty-aware sensor networks deployment (denoted by FUSD) problem is formulated as a binary non-linear and non-convex optimization problem. Several characteristics of real-world applications including sensor׳s spatial distribution, uncertain sensor measurements, challenging environments, and sensor reliability can be captured in this framework.

  • 4.

    An efficient heuristic for the FUSD problem is developed. The effectiveness and efficiency of the proposed approach are validated through extensive experiments carried out on both synthetic dataset, data traces collected from a military vehicle detection experiment, as well as a lab testbed.

The remainder of this paper is organized as follows. Section 2 reviews related work. The background of the present work is described in Section 3. Section 4 defines our evidence fusion model. In Section 5, the FUSD problem is formalized. Section 6 addresses our sensor placement algorithm. The evaluation of our proposed approach via numerical experiments and trace-driven simulations is presented in Section 7. Section 8 discusses the results obtained by deploying an experimental testbed for motion detection. In Section 9, some possible extensions are presented. Section 10 concludes the paper and discusses some future directions for our work.

Section snippets

Related work

In our previous work (Senouci et al., 2015), we have investigated the belief functions theory (Smets and Kennes, 1994) to design a unified approach for the uncertainty-aware WSNs deterministic deployment. However, the devised approach considers only the rate of coverage and ignores completely the issue of false alarm. Hence, generated topologies do not guarantee the false alarm rate. In contrast to our previous work (Senouci et al., 2015), in this work we consider both false alarm and detection

Preliminaries

In this section, we describe the background of our work, which includes an overview of the Transferable Belief Model (TBM) (Smets and Kennes, 1994), a subjective interpretation of the Dempster–Shafer theory (Shafer, 1976).

The TBM is a model for representing the quantified beliefs held by an agent at a given time on a given frame of discernment. It involves the same concepts as those considered by the Bayesian model, except it does not rely on probabilistic quantification, but on a more general

Evidence fusion model

In this section, we describe our first contribution, which includes a formal definition of the evidence-based sensing model and a description of how to build evidence from raw sensing data.

Sensor placement problem

The previous section formalizes the evidence-based sensing model and describes how to build evidence from raw sensing data. In this section, we describe our second contribution that includes a formal definition of the fusion-based uncertainty-aware sensor networks deployment (FUSD) problem.

Sensor placement algorithm

The two combinatorial non-linear and non-convex optimization problems formalized in Section 5 are NP-hard (Ke et al., 2007). A non-linear programming solver can be applied to both FUSD problems as done in Chang et al. (2011) where the authors used the CSA solver (Wah et al., 2007). The limitations of this technique are as follows: first, only a local optimum is obtained, and second, there is a limitation on the number of constraints and hence the size of the RoI that can be handled.

In the

Simulation results

To evaluate the effectiveness and efficiency of the proposed approach, both simulations and experiments have been conducted. In this section, we present the numerical results and the trace-driven simulations.

Testbed deployment

To further quantify the real benefit of our approach, we develop ArduiNet, a real WSN testbed for motion detection comprising more than 30 sensor nodes. Our testbed is based on the Arduino (1991) platform, which is an open-source fast prototyping platform based on flexible, easy-to-use hardware and software.

Discussion

Our proposed approach can be extended in several ways. In this section, we discuss how correction mechanisms for weakening or reinforcing belief functions (Smets and Kennes, 1994, Elouedi et al., 2004, Mercier et al., 2006) can be included in our framework in order to handle deployment-related issues such as sensor reliability and challenging environments.

Conclusion

In the present work, a unified approach for robust deployment of fusion-based WSNs is proposed. Our approach is based on the Dempster–Shafer theory that captures several characteristics of real-world applications and allows an efficient management of the uncertainty related to sensor readings. This distinguishes our effort from existing sensor deployment approaches that are either based on ideal detection models or rely on simple fusion schemes. The effectiveness and efficiency of the proposed

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