Scalar Sensor Research Articles

Achieving full-view coverage in camera sensor networks

Camera sensors are different from traditional scalar sensors, as cameras at different positions can form very different views of the object. However, traditional coverage model does not consider this intrinsic property of camera sensors. To address this issue, a novel model called full-view coverage is proposed. It uses the angle between the object's facing direction and the camera's viewing direction to measure the quality of coverage. An object is full-view covered if there is always a camera to cover it no matter which direction it faces and the camera's viewing direction is sufficiently close to the object's facing direction. An efficient method is proposed for full-view coverage detection in any given camera sensor networks, and a sufficient condition on the sensor density needed for full-view coverage in a random uniform deployment is derived. In addition, the article shows a necessary and sufficient condition on the sensor density for full-view coverage in a triangular lattice-based deployment. Based on the full-view coverage model, the article further studies the barrier coverage problem. Existing weak and strong barrier coverage models are extended by considering direction issues in camera sensor networks. With these new models, weak/strong barrier coverage verification problems are introduced, and new detection methods are proposed and evaluated.

Adaptive Monitoring Relevance in Camera Networks for Critical Surveillance Applications

Camera networks have been considered for a large set of visual monitoring applications. For some of them, cameras may be continuously monitoring scenes or groups of targets, but some events may trigger a critical level of visual monitoring, as in public security, industrial automation, and response to natural disasters. In such way, some critical events as a bomb explosion, a volcanic eruption, forest wildfire, or a car accident must be captured with high relevance, potentially helping when identifying responsibilities and during rescue operations. New relevance levels, which can be reflected in higher quality of transmitted images or video streams or even higher priority during transmission over the network must be quickly assigned to cameras that can view the critical events. In this work we propose a methodology to dynamically assign relevancies to cameras that view the area of critical events, employing scalar sensors and a decentralized decision mechanism. The resulting multimodal camera network can considerably enhance the critical surveillance in different monitoring applications. We propose some optimizations that exploit the monitoring relevance in such scenarios.

Modeling and Verification of a Heterogeneous Sky Surveillance Visual Sensor Network

A visual sensor network (VSN) is a distributed system of a large number of camera nodes and has useful applications in many areas. The primary difference between a VSN and an ordinary scalar sensor network is the nature and volume of the information. In contrast to scalar sensor networks, a VSN generates two-dimensional data in the form of images. In this paper, we design a heterogeneous VSN to reduce the implementation cost required for the surveillance of a given area between two altitude limits. The VSN is designed by combining three sub-VSNs, which results in a heterogeneous VSN. Measurements are performed to verify full coverage and minimum achieved object image resolution at the lower and higher altitudes, respectively, for each sub-VSN. Verification of the sub-VSNs also verifies the full coverage of the heterogeneous VSN, between the given altitudes limits. Results show that the heterogeneous VSN is very effective to decrease the implementation cost required for the coverage of a given area. More than 70% decrease in cost is achieved by using a heterogeneous VSN to cover a given area, in comparison to homogeneous VSN.

Differential Forms for Target Tracking and Aggregate Queries in Distributed Networks

Consider mobile targets in a plane and their movements being monitored by a network such as a field of sensors. We develop distributed algorithms for in-network tracking and range queries for aggregated data (for example, returning the number of targets within any user given region). Our scheme stores the target detection information locally in the network and answers a query by examining the perimeter of the given range. The cost of updating data about mobile targets is proportional to the target displacement. The key insight is to maintain in the sensor network a function with respect to the target detection data on the graph edges that is a differential form such that the integral of this form along any closed curve C gives the integral within the region bounded by C. The differential form has great flexibility, making it appropriate for tracking mobile targets. The basic range query can be used to find a nearby target or any given identifiable target with cost O(d), where d is the distance to the target in question. Dynamic insertion, deletion, coverage holes, and mobility of sensor nodes can be handled with only local operations, making the scheme suitable for a highly dynamic network. It is extremely robust and capable of tolerating errors in sensing and target localization. Targets do not need to be identified for the tracking, thus user privacy can be preserved. In this paper, we only elaborate the advantages of differential forms in tracking of mobile targets. Similar routines can be applied for organizing many other types of information--for example, streaming scalar sensor data (such as temperature data field)--to support efficient range queries. We demonstrate through analysis and simulations that this scheme compares favorably to existing schemes that use location services for answering aggregate range queries of target detection data.

Routing Protocols for Wireless Multimedia Sensor Network: A Survey

Multimedia applications have become an essential part of our daily lives, and their use is flourishing day by day. The area of wireless sensor network is not an exception where the multimedia sensors are attracting the attention of the researchers increasingly, and it has shifted the focus from traditional scalar sensors to sensors equipped with multimedia devices. The multimedia sensors have the ability to capture video, image, audio, and scalar sensor data and deliver the multimedia content through sensors network. Due to the resource constraints nature of WSN introducing multimedia will add more challenges, so the protocols designed for multimedia wireless sensor network should be aware of the resource constraints nature of WSN and multimedia transmission requirement. This paper discusses the design challenges of routing protocols proposed for WMSN. A survey and comprehensive discussion are given for proposed protocols of WMSN followed by their limitations and features.

Quadrupole 구조를 가진 Tonpilz형 수중 음향 벡터 센서를 이용한 입사각 추정

압전 세라믹을 이용한 전형적인 Tonpilz형 수중 음향센서는 외부에서 들어오는 음향 신호를 이에 상응하는 전압으로 변환해 스칼라 양인 음압의 크기만 측정할 뿐 외부에서 들어오는 신호의 방향은 파악할 수 없는 한계가 있다. 이와 같은 문제점을 해결하고자 본 논문에서는 Tonpilz형 트랜스듀서를 이용해 단일 센서만으로도 음압의 크기와 방위각 방향을 동시에 분석해 낼 수 있는 새로운 벡터 센서 구조를 제안하고, 제안된 구조의 타당성을 수식 및 유한요소해석을 통해 검증하였다. Typical Tonpilz type underwater acoustic transducers making use of piezoelectric ceramics detect the magnitude of an acoustic pressure, a scalar quantity, and convert this pressure into a proportional output voltage. The scalar sensor has no directional sensitivity. In this paper, we have proposed a new vector sensor based on the Tonpilz transducer structure, which is sensitive to both the magnitude and the azimuthal direction of an acoustic wave. Validity of this new design has been confirmed with analytic equations and finite element analyses.

Nanostructured thin manganite films in megagauss magnetic field

We report on the use of the colossal magnetoresistance (CMR) effect in manganites for the measurement of pulsed magnetic fields up to the megagauss limit. To increase the application range in a magnetic field, we fabricated nanostructured La-Sr-Mn-O films consisting of nanocrystallites cummulated into clusters separated by highly amorphous inter-cluster boundaries. We demonstrate that the CMR effect does not saturate in these films at 77 K up to 91.4 T. Moreover, the magnetoresistance behavior at 290 K shows that nanostructured manganite films are promising candidates for the development of magnetic field scalar sensors operating in wide field and temperature ranges.

A collaborative node management scheme for energy-efficient monitoring in wireless multimedia sensor networks

Clustering in sensor networks provides energy conservation, network scalability, topology stability, reducing overhead and also allows data aggregation and cooperation in data sensing and processing. Wireless Multimedia Sensor Networks are characterized for directional sensing, the Field of View (FoV), in contrast to scalar sensors in which the sensing area usually is more uniform. In this paper, we first group multimedia sensor nodes in clusters with a novel cluster formation approach that associates nodes based on their common sensing area. The proposed cluster formation algorithm, called Multi-Cluster Membership (MCM), establishes clusters with nodes that their FoVs overlap at least in a minimum threshold area. The name of Multi-Cluster Membership comes from the fact that a node may belong to multiple clusters, if its FoV intersects more than one cluster-head and satisfies the threshold area. Comparing with Single-Cluster Membership (SCM) schemes, in which each node belongs to exactly one cluster, because of the capability of coordination between intersected clusters, MCM is more efficient in terms of energy conservation in sensing and processing subsystems at the cost of adding complexity in the node/cluster coordination. The main imposed difficulty by MCM, is the coordination of nodes and clusters for collaborative monitoring; SCMs usually assign tasks in a round-robin manner. Then, as second contribution, we define a node selection and scheduling algorithm for monitoring the environment that introduces intra and inter-cluster coordination and collaboration, showing how the network lifetime is prolonged with high lifetime prolongation factors particularly in dense deployments.

Distributed Collaborative Camera Actuation Scheme Based on Sensing-Region Management for Wireless Multimedia Sensor Networks

Considering the high energy consumption of image acquisition, computation, and transmission in wireless multimedia sensor networks (WMSNs), two-tier network structure is usually used to lighten the energy consumption burden on camera sensors. Thus, a camera sensor can only be actuated when an event is detected by scalar sensors within its field of view (FoV). In this paper, we study the event-driven camera actuation problem and propose a distributed collaborative camera actuation scheme based on sensing-region management (DCCA-SM). The basic idea of this scheme is to divide the whole sensing field into many sensing regions which are covered by different sets of camera sensors. During the running of the network, by forming a cluster of the scalar sensors in each sensing region, the events occurring in each sensing region can be managed by the scalar cluster head. Therefore, by hearing from the scalar cluster heads, each camera sensor can know the exact coverage overlaps without changing information with the neighboring camera sensors. Meanwhile, sensing-region management avoids repeatedly event reporting from scalar sensors. In order to show the performance of the DCCA-SM, a simulation has been conducted. The comparative performance evaluations demonstrate effectiveness and energy efficiency of the proposed scheme.

Coverage estimation for crowded targets in visual sensor networks

Coverage estimation is one of the fundamental problems in sensor networks. Coverage estimation in visual sensor networks (VSNs) is more challenging than in conventional 1-D (omnidirectional) scalar sensor networks (SSNs) because of the directional sensing nature of cameras and the existence of visual occlusion in crowded environments. This article represents a first attempt toward a closed-form solution for the visual coverage estimation problem in the presence of occlusions. We investigate a new target detection model, referred to as the certainty-based target detection (as compared to the traditional uncertainty-based target detection ) to facilitate the formulation of the visual coverage problem. We then derive the closed-form solution for the estimation of the visual coverage probability based on this new target detection model that takes visual occlusions into account. According to the coverage estimation model, we further propose an estimate of the minimum sensor density that suffices to ensure a visual K-coverage in a crowded sensing field. Simulation is conducted which shows extreme consistency with results from theoretical formulation, especially when the boundary effect is considered. Thus, the closed-form solution for visual coverage estimation is effective when applied to real scenarios, such as efficient sensor deployment and optimal sleep scheduling.

A real-time dynamic key management for hierarchical wireless multimedia sensor network

With the recent fast growth in the electronics industry and potential customers, communication managements in interactive Wireless Multimedia Sensor Networks (WMSNs) are increasingly ubiquitous, such as retrieving images, audio streams, video streams, and scalar sensor data, etc. However, due to restricted resources and operation in a hostile environment, WMSNs are usually subjected to numerous threats and vulnerable to various attacks. In this paper, we present a Real-time Dynamic Key Management (RDKM), a splay tree-based rekey management, which can efficiently enhance the network security and survivability in the LEACH-like protocol. Compared to other LEACH-like security solutions, our work offers some salient advantages. First, it establishes a real-time rekey mechanism based on the access-triggered splay tree architecture. In the mechanism, the keys will be changed during messages exchanging phase. To the best of our knowledge, RDKM is the first real-time key management for security in WMSNs. Second, it designs and realizes the rekey mechanism based on the splay tree, which can provide dynamic architecture to generate new keys and make the dynamic key management feasible without any overhead. The novel mechanism can efficiently protect the network against attacks from eavesdropping or captured nodes compromise and address challenging security issues of runtime in WMSNs. Experimental analysis shows that our solution has high security levels as well as good performance.

A Discrete Wavelet Transform (DWT)-Based Energy-Efficient Selective Retransmission Mechanism for Wireless Image Sensor Networks

Source nodes in wireless image sensor networks transmit much more information than traditional scalar sensor networks, thereby demanding more energy of intermediate relaying nodes and putting energy efficiency as a key design issue. Intermediate nodes are usually interconnected by error-prone links where bit-errors are common, potentially degrading the application monitoring quality. When reliability is assured by retransmission mechanisms, higher packet error rates do not affect the application quality but result in additional energy consumption due to packet retransmission, even though many monitoring applications can tolerate some loss in the quality of the received image. DWT coding can decompose an image in data subbands, each one with different relevancies for the reconstruction of the original image at the receiver side. We propose an energy-efficient selective hop-by-hop retransmission mechanism where the reliability level of each packet is a function of the relevance of the payload data, according to the resulting subbands and the number of times a 2D DWT is applied over the images captured by the sensors’ cameras. In so doing, some lost packets are not retransmitted, saving energy of intermediate nodes with low impact to the quality of the reconstructed images. In order to estimate the benefits of this tradeoff between energy consumption and image quality, we designed a comprehensive energy consumption model and applied it in extensive mathematic simulations, providing substantial information about the mean performance of the proposed approach when compared with a fully-reliable transmission mechanism.

Environment-Aware CMT for Efficient Video Delivery in Wireless Multimedia Sensor Networks

Wireless Multimedia Sensor Networks (WMSNs) have gained significant attention with capabilities of retrieving video and audio streams, still images, and scalar sensor data but with challenge of high data loss. As more and more wireless devices are equipped with multiple network interfaces, multimedia delivery over multipath has been cognized as a more promising approach in wireless transmission. In this paper, based on the Concurrent Multipath Transfer (CMT) extension for Stream Control Transport Protocol (SCTP), we propose a novel environment-aware CMT (e-CMT) to overcome the high data loss challenge, as well as “a hot potato” congestion problem in wireless transmission. The e-CMT provides environment-aware cognitive ability for efficient video delivery with three modules, which are Path Quality-aware Model (PQM) that devotes to estimate path quality and select candidate path using for retransmission, Adaptive Retransmission Trigger (ART) that contributes to cognize packet loss and trigger efficient retransmission behaviors, and Congestion-avoid Data Distributor (CDD) that serves to enable Partial-Reliable retransmission to mitigate congestion condition. We design a close realistic topology to present how the e-CMT outperforms the original CMT for efficient video delivery over multihomed WMSNs.

A Qos Based Mac Protocol for Wireless Multimedia Sensor Network

Wireless Multimedia Sensor Networks (WMSNs) have emerged and shifted the focus from the typical scalar wireless sensor networks to networks with multimedia devices that are capable to retrieve video, audio, images, as well as scalar sensor data. WMSNs are able to deliver multimedia content due to the availability of inexpensive CMOS cameras and microphones coupled with the significant progress in distributed signal processing and multimedia source coding techniques. MAC in WMSNs is essential to coordinate the channel access among competing devices. Therefore, a proposal of MAC layer protocol for WMSNs should satisfy the following feature like Maximize network throughput, Enhance transmission reliability, and Minimize control overhead, be energy-efficient, Guarantee a certain level of QoS In this project, using NS2 simulation tool, we have proposed a new QoS-based sensory MAC protocol, which not only adapts to application oriented QoS, but also attempts to conserve energy without violating QoS-constraints.

The representation of a broadband vector field

Compared to a scalar pressure sensor, a vector sensor can provide a higher signal-to-noise ratio (SNR) signal and more detailed information on the sound field. Study on vector sensors and their applications have become a hot topic. Research on the representation of a vector field is highly relevant for extending the scope of vector sensor technology. This paper discusses the range-frequency distribution of the vector field due to a broadband acoustic source moving in a shallow-water waveguide as the self noise of a surface ship, and the vector extension of the waveguide impulse response measured over a limited frequency range using an active source of known waveform. From theory analysis and numerical simulation, the range-frequency representation of a vector field exhibits an interference structure qualitatively similar to that of the corresponding pressure field but, being quantitatively different, provides additional information on the waveguide, especially through the vertical component. For the range-frequency representation, physical quantities that can better exhibit the interference characteristics of the waveguide are the products of pressure and particle velocity and of the pressure and pressure gradient. An image processing method to effectively detect and isolate the individual striations from an interference structure was reviewed briefly. The representation of the vector impulse response was discussed according to two different measurement systems, also known as particle velocity and pressure gradient. The vector impulse response representation can not only provide additional information from pressure only but even more than that of the range-frequency representation.

Capacity and statistics of measured underwater acoustic particle velocity channels

Acoustic particle velocity channels can be used for communication in underwater systems [A. Abdi and H. Guo, IEEE Trans. Wireless Communi. 8, 3326-3329, (2009)]. In this paper, the information (Shannon) capacity of underwater acoustic particle velocity channels is studied using measured data. More specifically, the maximum achievable data rates of a compact vector sensor communication receiver and another communication receiver with spatially separated scalar sensors are compared. Some statistics of particle velocity channels such as amplitude distribution and power delay profile are investigated using measured data and proper models are suggested as well. The results are useful for design and simulation of vector sensor underwater communication systems in particle velocity channels.The work is supported in part by the National Science Foundation (NSF), Grant CCF-0830190.

Design and implementation of a QoS-aware MAC protocol for Wireless Multimedia Sensor Networks

Wireless Multimedia Sensor Networks (WMSNs) have entered the class of Wireless Sensor Networks (WSNs) to meet the multimedia requirements of new emerging applications, such as surveillance and telepresence. Combining the traditional scalar sensors used in WSN nodes with tiny cameras and microphones, WMSNs commonly carry heterogeneous traffic with different Quality of Service (QoS) requirements. In order to deliver heterogeneous traffic with different requirements in highly resource constrained sensor networks, QoS provisioning and service differentiation become unavoidable. In this paper first we discuss the QoS-provisioning in sensor networks and evaluate the efficiency of existing QoS-aware MAC protocols. As a result of this evaluation, next we design and implement a QoS-aware MAC protocol for WMSNs, Diff-MAC, which integrates different methods to meet the requirements of QoS provisioning to deliver heterogeneous traffic and provides a fair all-in-one QoS-aware MAC protocol. Diff-MAC aims to increase the utilization of the channel with effective service differentiation mechanisms while providing fair and fast delivery of the data. Performance evaluation results of Diff-MAC, obtained through extensive simulations, show significant improvements, in terms of latency, data delivery and energy efficiency, compared to two other existing protocols. Implementation of Diff-MAC on Imote2 platform also reveals that the protocol with moderate complexity can be easily implemented on the resource constrained motes.

Tonpilz type underwater vector sensor with directional sensitivity to acoustic waves.

Typical Tonpilz-type underwater acoustic transducers making use of piezoceramics detect the magnitude of an acoustic pressure, a scalar quantity, and convert this pressure into a proportional output voltage. The scalar sensor has no directional sensitivity. In this paper, a new Tonpilz transducer structure is proposed to measure both the magnitude and the direction of an incoming acoustic wave with a single transducer unit, which is accordingly referred to as a vector sensor. The piezoceramic stack clamped between the head mass and the tail mass of a Tonpilz transducer is divided into four radial segments, each segment polarized alternately to its neighboring one. An acoustic pressure wave coming from outside causes positive or negative signed electric voltage signals in the piezoceramic segments in accordance with their polarization directions as well as a certain amount of time delay between the electric signals. Proper manipulation of the electric signals, i.e., pairing the segments and either adding or subtracting the signals of the paired segments, can provide the relationship between the signals and the magnitude and direction of the acoustic wave. Feasibility of this structure is confirmed through 3-D simulations of the receiving properties of the transducer with the finite element method.

Analysis of SNR for acoustic vector sensor linear array in volume and surface-generated noise fields

Acoustic vector sensor consists of pressure and particle velocity sensors, which measure the three-dimensional acoustic particle velocity, as well as the pressure at one location at the same time. By preserving the amplitude and phase information of the pressure and particle velocity, they possess a number of advantages over traditional scalar sensors. Signal-to-noise ratio (SNR) gain (which is often called array gain) is one of such advantages and is always interested by all of us. But it is not unchangeable if the spatial correlation of the noise field varies. Much more important, it is difficult to be given if the noise becomes complex. In this paper, spatial correlation of the vector field of isotropic volume-noise and surface-generated noise has been introduced briefly. Based on the results, the combined SNR output of a vector linear array is investigated and the maximum gain is given in the specified noise. Computer simulation shows that the output of one array in the same noise is not the same in different gestures. And then we find the best gesture through SNR calculation and obtain the biggest gain, which has important meaning to guide how to deploy an array in practice. We also should use the array with respect to the characteristics of the real ambient noise, especially in anisotropic noise field.

Study on the Dynamic QoS Provisioning Scheme for U-Healthcare over WMSAN

The design of wireless multimedia sensor and actor networks (WMSAN) support emerging information-intensive data such as video and audio streams, images, and scalar sensor data by controlling individual data flows to increase or decrease their bandwidth in response to changes in traffic workload. Potential applications include u-healthcare which is the most exciting technologies today for improving public health condition. This paper presents a dynamic scheme for quality of service (QoS) provisioning for u-healthcare to optimize the network traffic load subject to multiple QoS constraints. Simulation results demonstrate the effectiveness of the proposed scheme for wireless multimedia sensor and actor networks.