Tsinghua Science and Technology最新文献

The coverability of Wireless Sensor Networks (WSNs) is essentially a Quality of Service (QoS) problem that measures how well the monitored area is covered by one or more sensor nodes. The coverability of WSNs was examined by combining existing computational geometry techniques such as the Voronoi diagram and Delaunay triangulation with graph theoretical algorithmic techniques. Three new evaluation algorithms, known as CRM (Comprehensive Risk Minimization), TWS (Threshold Weight Shortest path), and CSM (Comprehensive Support Maximization), were introduced to better measure the coverability. The experimental results show that the CRM and CSM algorithms perform better than the MAM (MAximize Minimum weight) and MIM (MInimize Maximum weight) algorithms, respectively. In addition, the TWS algorithm can provide a lower bound detection possibility that accurately reflects the coverability of the wireless sensor nodes. Both theoretical and experimental analyses show that the proposed CRM, TWS, and CSM algorithms have O(n²) complexity.

Smart grid is envisioned as a critical application of cyber-physical systems and of the internet of things. In the smart grid, smart meters equipped with wireless sensors can upload meter readings (data) to smart grid control and schedule centers via the advanced metering infrastructure to improve power delivery efficiency. However, data gathered in short intervals, such as 15 minutes, will expose customers' detailed daily activities (for example, when they get up and when they use oven) using nonintrusive appliance load monitoring. Thus, data must be hidden to protect customers' privacy. However, data accountability is still required for emergency responses or to trace back suspected intrusions, even though the data is anonymous. In addition to desired security requirements, this imposes two extra tasks: Sensors in smart meters usually have resource constraints; thus, the desired security protocols have to remain lightweight in terms of computation and storage cost. Furthermore, scalability and flexibility are required since there exist vast meters. This paper presents a lightweight Privacy-aware yet Accountable Secure Scheme called PASS which guarantees privacy-aware accountability yet tackles the above challenges in the smart grid. A formal security analysis justifies that PASS can attain the security goals, while a performance analysis verifies that PASS requires few computations, and is scalable and flexible.

Current highway tunnel lighting control systems are often manually controlled, resulting in significant energy waste. This article designs a fuzzy control algorithm for tunnel lighting energy control systems. The system uses LED (Light Emitting Diode) lighting, so the fuzzy control algorithm is designed for LED lights. The traffic and the natural illumination level are used as parameters in the intelligent lighting control algorithm. This system has been deployed in the Lengshui tunnel on the 49th provincial highway of Zhejiang province and operated for more than six months. The performance results show that the energy conservation system provides sufficient lighting levels for traffic safety with significant energy conservation.

Previous research on security of network coding focused on the protection of data dissemination procedures and the detection of malicious activities such as pollution attacks. The capabilities of network coding to detect other attacks have not been fully explored. In this paper, we propose a new mechanism based on physical layer network coding to detect wormhole attacks. When two signal sequences collide at the receiver, the starting point of the collision is determined by the distances between the receiver and the senders. Therefore, by comparing the starting points of the collisions at two receivers, we can estimate the distance between them and detect fake neighbor connections via wormholes. While the basic idea is clear, we have proposed several schemes at both physical and network layers to transform the idea into a practical approach. Simulations using BPSK modulation at the physical layer show that the wireless nodes can effectively detect fake neighbor connections without the adoption of special hardware or time synchronization.

A critical aspect of applications with Wireless Sensor Networks (WSNs) is network lifetime. Power-constrained WSNs are usable as long as they can communicate sense data to a processing node. Poor communication links and hazardous environments make the WSNs unreliable. Existing schemes assume that the state of a sensor covering targets is binary: success (covers the targets) or failure (cannot cover the targets). However, in real WSNs, a sensor covers targets with a certain probability. To improve WSNs' reliability, we should consider that a sensor covers targets with users' satisfied probability. To solve this problem, this paper first introduces a failure probability into the target coverage problem to improve and control the system reliability. Furthermore, we model the solution as the α-Reliable Maximum Sensor Covers (α-RMSC) problem and design a heuristic greedy algorithm that efficiently computes the maximal number of α-Reliable sensor covers. To efficiently extend the WSNs lifetime with users' pre-defined failure probability requirements, only the sensors from the current active sensor cover are responsible for monitoring all targets, while all other sensors are in a low-energy sleep mode. Simulation results validate the performance of this algorithm, in which users can precisely control the system reliability without sacrificing much energy consumption.

A state-of-the-art sensorweb is a global observation system for varied sensory phenomena from the physical world and the cyber world. This paper presents the architecture, design, and application of a sensorweb service portal called the LiveWeb. This portal has been published on the Internet and is used by researchers, students, and also other communities. This system has been used to represent and monitor real-time physical sensor data and cyber activities from ubiquitous sources. LiveWeb meets its goal of providing an efficient and robust sensor information oriented web service, enabled with real-time data representation and notification. Living in the current world with the immense magnitude of information, it is important to keep different communities updated and informed with their context specific data. There are search engines available in the Internet to find relatively static items, but not to observe the events in real-time. In addition, mostly the sensed data and events have meaning only when accompanied with corresponding geographic information. LiveWeb is an effective and efficient sensorweb service, that tries to fulfill the aforementioned requirements. The LiveWeb system consists of three main components: (a) special features of a PHP web application, (b) a Java background processing program, and (c) a database. It is a robust system and is currently running efficiently under the environment of Ubuntu 6.10, Apache 2.0, PHP 5.0, JAVA 1.60, and MySQL 1.6.

We propose a localized address autoconfiguration (LaConf) scheme for wireless ad hoc networks. Address allocation information is maintained on the network border nodes, called addressing agents (AAs), which are locally identified by a geographic routing protocol GFG (Greedy-FACE-Greedy). When a node joins the network, it acquires an address from a neighboring AA (if any exists) by local communication or from the head AA (a geographic extreme AA) by GFG-based multi-hop communication. A Geographic Hash Table (GHT) is adopted for duplicate address detection. Each address is hashed to a unique location in the network field, and the associated assignment information is stored along the face perimeter enclosing that location (in the planar graph). When a node receives an address assignment, it consults with the perimeter nodes around the hash location of the assigned address about any conflicts. AAs detect network partitions and merger locally according to neighborhood change and trigger AA re-selection and network re-configuration (if necessary). We propose to apply a Connected Dominating Set (CDS) to improve the performance. We also evaluate LaConf through simulation using different planar graphs.

This paper proposes a multi-axis projection (MAP) based giant component formation strategy via the Maximal Independent Set (MIS) in a random unit-disk graph. We focus on the problem of virtual backbone construction in wireless ad hoc and sensor networks, where the coverage areas of the nodes are disks with identical radii. In the simulation, we show that the MAP-based giant component has the ability to connect most nodes and serves as a backbone in the network. The algorithm is localized and may play an important role in efficiently constructing a virtual backbone for ad hoc and sensor networks.

Mobile Cloud Computing usually consists of front-end users who possess mobile devices and back-end cloud servers. This paradigm empowers users to pervasively access a large volume of storage resources with portable devices in a distributed and cooperative manner. During the period between uploading and downloading files (data), the privacy and integrity of files need to be guaranteed. To this end, a family of schemes are proposed for different situations. All schemes are lightweight in terms of computational overhead, resilient to storage compromise on mobile devices, and do not assume that trusted cloud servers are present. Corresponding algorithms are proposed in detail for guiding off-the-shelf implementation. The evaluation of security and performance is also extensively analyzed, justifying the applicability of the proposed schemes.