Sensor Networks for High-Confidence Cyber-Physical Systems

Technical advances in ubiquitous sensing, embedded computing, and wireless communication are leading to a new generation of engineered systems called cyber-physical systems (CPSs). This field is attracting more and more attention from researchers and practitioners, as well as the governments. Technically, cyber-physical systems are integrations of computation, networking, and physical dynamics, in which embedded devices are massively networked to sense, monitor, and control the physical world. CPS has been regarded as the next computing revolution. This revolution will be featured by the envisioned transform that CPS will make on how we interact with the physical world.

To facilitate unprecedented interactions between human beings and the physical world, sensor networks will become a crucial ingredient of CPS due to the need for coupling geographically distributed computing devices with physical elements. The proliferation of affordable sensor network technologies has significantly contributed to recent progress in CPS. On the other hand, the unique features of CPS (e.g., cyber-physical coupling driven by new demands and applications) give rise to a lot of open challenges for design and deployment of sensor networks in such systems. In particular, high-confidence CPS requires the employed sensor networks to support real-time, dependable, safe, secure, and efficient operations.

In this issue we are focused on latest research results in wireless sensor networks (WSNs) that address key issues related to high-confidence cyber-physical systems and applications. In response to our call for papers, we have received 36 submissions, out of which 15 papers are finally accepted as a result of thorough review process by international experts in respective areas. The selection provides a glimpse of the state-of-the-art research in the field.

In the paper “A game theoretic approach for interuser interference reduction in body sensor networks,” G. Wu et al. present a decentralized interuser interference reduction scheme with noncooperative game for body sensor networks (BSNs). A no-regret learning algorithm for reducing the effect of the interuser interference with low power consumption is proposed. The correctness and effectiveness of the proposed scheme are theoretically proved, and experimental results demonstrate that the effect of interuser interference can be reduced effectively with low power consumption.

The paper “Low-complexity, distributed characterization of interferers in wireless networks” by V. Kapnadak et al. consider a large-scale wireless network that uses sensors along its edge to estimate the characteristics of interference from neighboring networks or devices. The authors propose and justify a low-complexity threshold design technique in which the sensors use nonidentical thresholds to generate their bits. This technique produces a dithering effect that provides better performance than previous techniques that use different nonidentical thresholds or the case in which all the sensor motes use an identical nonoptimal threshold.

The energy efficiency optimization of the binary power control scheme for MIMO-OFDM wireless communication systems is formulated by Y. Wang et al. in the paper “Modeling and performance analysis of energy efficiency binary power control in MIMO-OFDM wireless communication systems,” wherein a global optimization solution of power allocation is also derived. Furthermore, a new energy efficiency binary power control algorithm is designed to improve the energy efficiency of MIMO-OFDM wireless communication systems.

In the survey paper “A survey of adaptive and real-time protocols based on IEEE 802.15.4,” F. Xia et al. discuss the negative aspects of IEEE 802.15.4 MAC in contention access period, contention-free period, and the overall cross-period, respectively, in terms of adaptive and real-time guarantees. They then give an overview on some interesting mechanisms used in existing adaptive and real-time protocols in compliance with IEEE 802.15.4.

Underwater acoustic sensor networks (UASNs) are playing a key role in ocean applications. The paper “A reliable and efficient MAC protocol for underwater acoustic sensor networks” by J. Xiong et al. proposes a MAC protocol called RAS, a priority scheduling approach for multihop UASNs, which is more efficient in throughput and delay performance. Furthermore, a reliable RAS called RRAS that obtains a tradeoff between the reliability and the efficiency is also suggested.

Design of MAC protocols supporting multimedia traffic QoS (Quality of Service) is challenging. In the paper “A scalable MAC protocol supporting simple multimedia traffic QoS in WSNs,” J. On et al. propose a scalable MAC protocol that guarantees multimedia traffic, still images, and scalar sensor data QoS in multihop WSNs. The proposed MAC protocol outperforms the IEEE 802.11e EDCF and the IEEE 802.15.4 MAC protocol in terms of the end-to-end delay and stable transmission of multimedia streaming data.

The paper “Quadratic programming for TDMA scheduling in wireless sensor networks” is concerned with developing a novel protocol to achieve energy-efficient and reliable multihop data transfer in WSNs satisfying given latency requirements. The authors present a novel multihop aperiodic scheduling (MAS) algorithm that guarantees energy-efficient data collection by WSNs under delay constraints.

In the paper “Link prediction and route selection based on channel state detection in UASNs,” J. Chen et al. propose a model to predict link interruption and route interruption in UASNs by the historical link information and channel state obtained by periodic detection. A method of decomposing and recomposing routes hop by hop in order to optimize route reselection is also presented. Moreover, the authors present a back-up route maintenance scheme to keep back-up routes with fresh information.

The paper “SEF: a secure, efficient, and flexible range query scheme in two-tiered sensor networks” considers large-scale WSNs following the two-tiered architecture. The authors present a novel scheme called SEF for secure range queries. To preserve privacy, SEF employs the order preserving symmetric encryption which not only supports efficient range queries but also maintains a strong security standard. To preserve authenticity and integrity of query results, the authors propose a novel data structure called Authenticity & Integrity tree.

In the context of a body area network (BAN), the confidentiality and integrity of the sensitive health information is particularly important. In the paper “A biometric key establishment protocol for body area networks,” L. Yao et al. present an electrocardiogram- (ECG-) signal-based key establishment protocol to secure the communication between every sensor and the control unit before the physiological data is transferred to external networks for remote analysis or diagnosis.

In mission-critical CPS, dependability is an important requirement at all layers of the system architecture. In the paper “Anonymous aggregator election and data aggregation in wireless sensor networks,” T. Holczer and L. Buttyán propose protocols that increase the dependability of WSNs. More specifically, the authors propose two private aggregator node election protocols, a private data aggregation protocol, and a corresponding private query protocol for sensor networks that allow for secure in-network data aggregation by making it difficult for an adversary to identify and then physically disable the designated aggregator nodes.

In the paper “A mobile-beacon-assisted sensor network localization based on RSS and connectivity observations,” G. Teng et al. propose a distributed mobile-beacon-assisted localization scheme based on received signal strength (RSS) and connectivity observations (named MRC) with a specific trajectory in static WSNs. To meet the requirements of real applications in practice, the authors develop two improved approaches based on MRC to consider irregular radio scenario in noisy environments.

In the paper “Total least squares method for robust source localization in sensor networks using TDOA measurements,” the TDOA-based source localization problem in sensor networks is considered with sensor node location uncertainty. A total least squares (TLSs) algorithm is developed by a linear closed-form solution for this problem, in which the uncertainty of the sensor location is formulated as a perturbation.

Smart phones have become useful tools to implement high-confidence CPS. Context sharing systems in mobile environment attract attention with the popularization of social media. In the paper “Bayesian network-based high-level context recognition for mobile context sharing in cyber-physical system”, H.-S. Park et al. propose a mobile context sharing system that can recognize high-level contexts automatically by using Bayesian networks based on mobile logs. They have developed a ContextViewer application which consists of a phonebook and a map browser to show the feasibility of the system.

The paper “Distributed algorithm for traffic data collection and data quality analysis based on wireless sensor networks” by N. Ding et al. deals with urban traffic data collection. The authors propose a distributed algorithm to collect the traffic data based on sensor networks and improve the reliability of data by quality analysis. The performance of this algorithm is analyzed with a number of simulations based on data set obtained in urban roadway.