Low-cost group rekeying for unattended wireless sensor networks

Wireless sensor networks (WSNs) are made up of large groups of nodes that perform distributed monitoring services. Since sensor measurements are often sensitive data acquired in hostile environments, securing WSN becomes mandatory. However, WSNs consists of low-end devices and frequently preclude the presence of a centralized security manager. Therefore, achieving security is even more challenging. State-of-the-art proposals rely on: (1) attended and centralized security systems; or (2) establishing initial keys without taking into account how to efficiently manage rekeying. In this paper we present a scalable group key management proposal for unattended WSNs that is designed to reduce the rekeying cost when the group membership changes.     

Optimal deterministic timeouts for reliable scalable multicast

Reliable multicast protocols suffer from the problem of feedback implosion. To avoid this problem, the number of receivers sending feedback in case of loss must be small. However, losses experienced by different receivers are strongly correlated, since receivers share common resources in the multicast tree. One approach to feedback implosion avoidance relies on delaying feedback at the receivers. We present deterministic timeouts for reliable multicast (DTRM), a distributed algorithm to compute optimal deterministic timeouts for each receiver in a multicast tree as a function of the tree topology and the sender-to-receiver round-trip delays. DTRM has several desirable properties. First, feedback implosion is provably avoided for a single loss anywhere in the tree, provided delay jitter is bounded. Second, the computation of the timeouts can be entirely distributed; receivers and intermediate nodes only rely on local topology information. Third, the timeouts computed by DTRM are optimal with respect to the maximum response time     

Predistribution and local collaboration-based group rekeying for wireless sensor networks

When a sensor network is deployed in a hostile environment, an adversary may launch such attacks as eavesdropping the communications and compromising sensor nodes. Using the compromised nodes, he may inject false sensing reports or modify the reports sent by other nodes. To defend against these attacks, researchers have proposed symmetric group key-based schemes. In these schemes, however, if a large number of nodes are compromised, many (sub)group keys will be revealed. This greatly endangers the filtering schemes, making them very ineffective or even useless. To address this problem, we propose a family of predistribution and local collaboration-based group rekeying (PCGR) schemes, which update the compromised group keys to prevent the compromised nodes from understanding the communications between noncompromised nodes or injecting false data. These schemes are designed based on a simple while controversial idea – preload future group keys into sensor nodes before their deployment. To protect the preloaded keys from being disclosed by compromised nodes, we propose a novel technique that requires neighboring nodes to collaborate to derive the future group keys. To the best of our knowledge, our schemes are the first set of distributed group rekeying schemes for sensor networks without involving online key servers. Extensive analysis and simulations are conducted to evaluate the proposed schemes, and the results show that the proposed schemes can achieve a good level of security, outperform several previous group rekeying schemes, and significantly improve the effectiveness of false data filtering.     

Protocol design for mobile radio group communications oversatellite

A protocol design for a mobile radio service supporting half-duplex push-to-talk voice communications over mobile satellite systems is presented. The service enables a closed group of mobile radio users to communicate among themselves, so that a transmission from any user is received by all. A key issue is the efficient utilization of satellite channels. Demand-assignment multiple access (DAMA) is employed to allocate channels only to those user groups in active sessions of conversations. Owing to the unique characteristics of the half-duplex point-to-multipoint group communications, a new DAMA protocol is proposed for this service. Within a channel assigned to a user group, access contentions exacerbated by very long round-trip delay can occur. A signaling protocol is devised to arbitrate access contentions so as to improve the utilization of the assigned channel. The proposed access control protocol offers 65% or 18% improvement in throughput capacity compared to manual carrier-sensed access without and with collision detection, respectively     

On optimal batch rekeying for secure group communications in wireless networks

Advances in wireless communications and mobile computing have led to the emergence of group communications and applications over wireless. In many of these group interactions, new members can join and current members can leave at any time, and existing members must communicate securely to achieve application-specific missions or network-specific functionality. Since wireless networks are resource-constrained, a key challenge is to provide secure and efficient group communication mechanisms that satisfy application requirements while minimizing the communication cost. Instead of individual rekeying, i.e., performing a rekey operation right after each join or leave request, periodic batch rekeying has been proposed to alleviate rekeying overhead in resource-constrained wireless networks. In this paper, we propose an analytical model to address the issue of how often batch rekeying should be performed. We propose threshold-based batch rekeying schemes and demonstrate that an optimal rekey interval exists for each scheme. We further compare these schemes to identify the best scheme that can minimize the communication cost of rekeying while satisfying application requirements when given a set of parameter values characterizing the operational and environmental conditions of the system. In a highly dynamic wireless environment in which the system parameter values change at runtime, our work may be used to adapt the rekeying interval accordingly.     

Multiring techniques for scalable battlespace group communications

Network-centric warfare must leverage off a common network to support different purposes. While group communications based on a single virtual ring overlay may satisfy the most important requirements for survivability and security, scalability may for cc redesign because a single ring generally has higher delay and delay jitter. In order to provide scalability as the number of group members grows, large single rings may be broken into, smaller multirings interconnected together. Thus, comparing the characteristics of different multiring techniques provides insight into which battlespace applications may be supported via virtual rings. In this article we consider different approaches to providing scalable battlespace group communications using multi-ring techniques, classifying the techniques according to the primary military requirements of QoS, security, and survivability. Some important design issues of multiring techniques, such as the number of ring levels and number of rings per level, are dependent on, application QoS requirements and the underlying network infrastructure in terms of topology (dense vs. sparse) and link bandwidths (bottleneck capacities). Through our survey, we conclude that while no existing multiring scheme provides the single solution to battlespace group communications, some aspects of existing multiring schemes do match specific scenarios and provide us useful insights for designing new schemes for battlespace group communication. To our knowledge, this is the first article to survey and categorize multiring algorithms.     

Energy scalable system design

We introduce the notion of energy-scalable system-design. The principal idea is to maximize computational quality for a given energy constraint at all levels of the system hierarchy. The desirable energy-quality (E-Q) characteristics of systems are discussed. E-Q behavior of algorithms is considered and transforms that significantly improve scalability are analyzed using three distinct categories of commonly used signal-processing algorithms on the StrongARM SA-1100 processor as examples (viz., filtering, frequency domain transforms and classification). Scalability hooks in hardware are analyzed using similar examples on the Pentium III processor and a scalable programming methodology is proposed. Design techniques for true energy scalable hardware are also demonstrated using filtering as an example     

Model design for scalable two-dimensional model-based video coding

Scalable and very low bit rate video coding is vital for audio-visual conversational services over narrow bandwidth channels. A novel model design scheme is proposed in order to make the points of an object model represent the motion more accurately, which will in turn enable better compression. Experimental results demonstrate the performance of the proposed scheme.     

Control plane design for reliable optical networks

The application of an IP-based control plane to optical networks has opened up new opportunities and challenges for network designers. Although much work has been done on standardization of protocols for IP networks, the applicability of these protocols to controlling optical networks and the overall reliability of optical networks needs further investigation. This article provides a detailed discussion of a number of subtle protocol design and implementation issues that were not addressed in early standardization efforts or published papers     

Die cracking and reliable die design for flip-chip assemblies

Die cracking during underfill cure or thermal cycling is a cause for concern in flip-chip assemblies. In this work, an integrated process-reliability modeling methodology has been developed to determine the stresses at the backside of the die during underfill cure and subsequent thermal cycling. The predicted die stresses have been compared with experimental data, and excellent agreement is seen between the theoretical predictions and the experimental data. The modeling methodology has been used to understand the effect of material and geometry parameters such as substrate thickness, die thickness, standoff height, interconnect pitch, underfill modulus and coefficient of thermal expansion (CTE), and solder mask CTE on die stresses and thus die cracking. Based on underfill-cure and thermal cycling models for specific cases, the critical flaw size to induce catastrophic die cracking has been calculated using linear-elastic fracture mechanics. Design recommendations, including die thinning and polishing, have been made to reduce the tensile stresses on the backside of the die and thus die cracking     

一种电台中FPGA的可靠初始化逻辑设计

在机载通信领域,由于飞机体积、重量及功耗等要求,往往需要在一个独立电台设备上实现多种通信模式,同时受限于电台的成本、功耗等因素,通常各种通信模式功能依靠FPGA的动态加载来实现。实际工程中发现,当FPGA动态加载时,由于各版本的加载时间、复位管理、时钟管理、接口时序等不一致,非常容易出现偶发的加载后功能异常,此类问题现象随机,极难定位,很容易耗费大量的人力、物力及时间。为解决上述矛盾,提出一种适合在电台中使用的FPGA初始化逻辑设计,保证不同版本的FPGA加载后能稳定工作,提升电台工作的可靠性与稳定性。实践表明,该方法简单、可靠,具有非常强的工程推广意义。     

A scalable substrate noise coupling model for design ofmixed-signal IC's

This paper describes a design-oriented scalable macromodel for substrate noise coupling in heavily-doped substrates. The model requires only four parameters which can be readily extracted from a small number of device simulations or measurements. Once these parameters have been determined, the model can be used in design for any spacing between the injection and sensing contacts and for different contact geometries. The scalability of the model with separation and width provides insight into substrate coupling and optimization issues prior to and during the layout phase. The model is validated with measurements from test structures fabricated in a 0.5 μm CMOS process. Applications of the model to circuit design are demonstrated with simulation results     

An adaptable and scalable group access control scheme for managing wireless sensor networks

Access control is a prime technology to prevent unauthorized access to private information, which is one of the essential issues appearing in secure group communication (SGC) of wireless sensor networks (WSNs). Many studies have made good progress on access control; however, their methods are inadequate to cope with this new issue for SGC-based WSNs since of their inflexibility, inefficiency, insecurity, or small-scale.     

一种无线代码可靠更新系统的研究与设计

传感节点投入运行后,遇到软件错误或功能升级都需要更新节点的程序,但是传统的现场烧写方式比较繁琐。为了解决该问题,以ARM Cortex M0+内核的MKW01Z128无线射频芯片为基础,设计了一套成本低、实时性好、可靠性高的无线代码更新系统。该系统采用串口和无线射频相结合的通信技术,对片上FLASH进行合理划分,设计了Bootloader对传感节点程序进行代码更新,同时增加了通信帧格式和丢帧重传机制来确保数据传输的可靠性。对更新系统的性能进行了测试,测试结果表明该系统能可靠地实现空旷环境下200 m内的无线代码更新,具有较好的应用前景。     

Modeling and analysis of intrusion detection integrated with batch rekeying for dynamic group communication systems in mobile ad hoc networks

We investigate performance characteristics of secure group communication systems (GCSs) in mobile ad hoc networks that employ intrusion detection techniques for dealing with insider attacks tightly coupled with rekeying techniques for dealing with outsider attacks. The objective is to identify optimal settings including the best intrusion detection interval and the best batch rekey interval under which the system lifetime (mean time to security failure) is maximized while satisfying performance requirements. We develop a mathematical model based on stochastic Petri net to analyze tradeoffs between security and performance properties, when given a set of parameter values characterizing operational and environmental conditions of a GCS instrumented with intrusion detection tightly coupled with batch rekeying. We compare our design with a baseline system using intrusion detection integrated with individual rekeying to demonstrate the effectiveness.     

Automatic scalable face model design for 2D model-based video coding

Scalable low bit-rate video coding is vital for the transmission of video signals over wireless channels. A scalable model-based video coding scheme is proposed in this paper to achieve this. This paper mainly addresses automatic scalable face model design. Firstly, a robust and adaptive face segmentation method is proposed, which is based on piecewise skin-colour distributions. 43 million skin pixels from 900 images are used to train the skin-colour model, which can identify skin-colour pixels reliably under different lighting conditions. Next, reliable algorithms are proposed for detecting the eyes, mouth and chin that are used to verify the face candidatures. Then, based on the detected facial features and human face muscular distributions, a heuristic scalable face model is designed to represent the rigid and non-rigid motion of head and facial features. A novel motion estimation algorithm is proposed to estimate the object model motion hierarchically. Experimental results are provided to illustrate the performance of the proposed algorithms for facial feature detection and the accuracy of the designed scalable face model for representing face motion.     

New advances of high-level synthesis for efficient and reliable hardware design

The spectacular CMOS technology scaling will continue to evolve and dominate the semiconductor industry. This will lead to tens of billions of transistors integrated on a single chip by the year 2020. However, one significant problem is that the design productivity for complex designs has been lagging behind. In addition to several proposed techniques for dealing with the widening productivity gap, e.g., IP reuse and integration, virtual platform modeling, formal verification and others, high-level synthesis (HLS) has been touted as an important solution as it can significantly reduce the number of man-hours required for a design by raising the level of design abstraction. However, existing HLS solutions have limitations, and studies show that the design quality of HLS can be inferior compared to that of manual RTL design. In this paper, we will present a set of new techniques developed recently to drastically improve HLS solutions, which not only improve the traditional design metrics such as circuit performance and energy efficiency but also emerging metrics such as hardware security and robustness. We will also discuss how HLS can collaborate with other techniques to provide a holistic design methodology that can enable the delivery of high-quality designs with much less design cost and much faster time-to-market.