Sensor Networks and Applications 

About: Sensor Networks and Applications is an academic conference. The conference publishes majorly in the area(s): Wireless sensor network & Key distribution in wireless sensor networks. Over the lifetime, 49 publications have been published by the conference receiving 4488 citations.

The coverage problem in a wireless sensor network

Abstract: One fundamental issue in sensor networks is the coverage problem, which reflects how well a sensor network is monitored or tracked by sensors. In this paper, we formulate this problem as a decision problem, whose goal is to determine whether every point in the service area of the sensor network is covered by at least k sensors, where k is a predefined value. The sensing ranges of sensors can be unit disks or non-unit disks. We present polynomial-time algorithms, in terms of the number of sensors, that can be easily translated to distributed protocols. The result is a generalization of some earlier results where only k=1 is assumed. Applications of the result include: (i) positioning applications, (ii) situations which require stronger environmental monitoring capability, and (iii) scenarios which impose more stringent fault-tolerant capability.

Lightweight time synchronization for sensor networks

Abstract: This paper presents lightweight tree-based synchronization (LTS) methods for sensor networks. First, a single-hop, pair-wise synchronization scheme is analyzed. This scheme requires the exchange of only three messages and has Gaussian error properties. The single-hop approach is extended to a centralized multi-hop synchronization method. Multi-hop synchronization consists of pair-wise synchronizations performed along the edges of a spanning tree. Multi-hop synchronization requires only n-1 pair-wise synchronizations for a network of n nodes. In addition, we show that the communication complexity and accuracy of multi-hop synchronization is a function of the construction and depth of the spanning tree; several spanning-tree construction algorithms are described. Further, the required refresh rate of multi-hop synchronization is shown as a function of clock drift and the accuracy of single-hop synchronization. Finally, a distributed multi-hop synchronization is presented where nodes keep track of their own clock drift and their synchronization accuracy. In this scheme, nodes initialize their own resynchronization as needed.

Using proximity and quantized RSS for sensor localization in wireless networks

Abstract: For wireless sensor networks, received signal strength (RSS) and proximity (also known as connectivity) measurements have been proposed as simple and inexpensive means to estimate range between devices and sensor location. While RSS measurements are recognized to suffer from errors due to the random nature of the fading channel, proximity measurements, ie., knowing only whether or not two devices are in communication range, are often discussed without considering that they are affected by the same fading channel. Proximity measurements are actually just a binary quantization of RSS measurements. We use the Cramer-Rao bound (CRB) to compare the minimal attainable variances of unbiased sensor location estimators for the cases of RSS and proximity measurements. For completeness, we also present the CRB for sensor localization with systems using K-level quantized RSS (QRSS) measurements, of which proximity measurements are the special case: K=2. Examples are presented for the case of one unknown-location sensor, and for the case of a 5 by 5 grid of sensors. These examples show that lower bounds for standard deviation in proximity-based systems are, as a rule of thumb, about 50% higher than the bounds for RSS-based systems. Furthermore, results are presented which show how many bits of quantization are necessary for a QRSS-based system to nearly achieve the bounds of an unquantized RSS system.

Efficient code distribution in wireless sensor networks

Abstract: The need to reprogramme a wireless sensor network may arise from changing application requirements, bug fixes, or during the application development cycle. Once deployed, it will be impractical at best to reach each individual node. Thus, a scheme is required to wirelessly reprogramme the nodes. We present an energy-efficient code distribution scheme to wirelessly update the code running in a sensor network. Energy is saved by distributing only the changes to the currently running code. The new code image is built using an edit script of commands that are easy to process by the nodes. A small change to the programme code can cause many changes to the binary code because the addresses of functions and data change. A naive approach to building the edit script string would result in a large script. We describe a number of optimisations and present experimental results showing that these significantly reduce the edit script size.

Analyzing and modeling encryption overhead for sensor network nodes

Abstract: Recent research in sensor networks has raised security issues for small embedded devices. Security concerns are motivated by the deployment of a large number of sensory devices in the field. Limitations in processing power, battery life, communication bandwidth and memory constrain the applicability of existing cryptography standards for small embedded devices. A mismatch between wide arithmetic for security (32 bit word operations) and embedded data bus widths (often only 8 or 16 bits) combined with lack of certain operations (e.g., multiply) in the ISA present other challenges.This paper offers two contributions. First, a survey investigating the computational requirements for a number of popular cryptographic algorithms and embedded architectures is presented. The objective of this work is to cover a wide class of commonly used encryption algorithms and to determine the impact of embedded architectures on their performance. This will help designers predict a system's performance for cryptographic tasks. Second, methods to derive the computational overhead of embedded architectures in general for encryption algorithms are developed. This allows one to project computational limitations and determine the threshold of feasible encryption schemes under a set of the constraints for an embedded architecture.Experimental measurements indicate uniform cryptographic cost for each encryption class and each architecture class and negligible impact of caches. RC4 is shown to outperform RC5 for the Motes Atmega platform contrary to the choice of RC5 for the Motes project, a choice driven in large by memory constraints. The analytical model allows to assess the impact of arbitrary embedded architectures as a multi-variant function for each encryption scheme. Overall, our results are not only valuable to assess the feasibility of encryption schemes for existing embedded architectures, they also extend to assess the feasibility of encryption methods for new algorithms and architectures for sensor systems.