David Rodenas-Herraiz

Current Trends in Wireless Mesh Sensor Networks: A Review of Competing Approaches

Finding a complete mesh-based solution for low-rate wireless personal area networks (LR-WPANs) is still an open issue. To cope with this concern, different competing approaches have emerged in the Wireless Mesh Sensor Networks (WMSNs) field in the last few years. They are usually supported by the IEEE 802.15.4 standard, the most commonly adopted LR-WPAN recommendation for point-to-point topologies. In this work, we review the most relevant and up-to-date WMSN solutions that extend the IEEE 802.15.4 standard to multi-hop mesh networks. To conduct this review, we start by identifying the most significant WMSN requirements (i.e., interoperability, robustness, scalability, mobility or energy-efficiency) that reveal the benefits and shortcomings of each proposal. Then, we re-examine thoroughly the group of proposals following different design guidelines which are usually considered by end-users and developers. Among all of the approaches reviewed, we highlight the IEEE 802.15.5 standard, a recent recommendation that, in its LR-WPAN version, fully satisfies the greatest number of WMSN requirements. As a result, IEEE 802.15.5 can be an appropriate solution for a wide-range of applications, unlike the majority of the remaining solutions reviewed, which are usually designed to solve particular problems, for instance in the home, building and industrial sectors. In this sense, a description of IEEE 802.15.5 is also included, paying special attention to its efficient energy-saving mechanisms. Finally, possible improvements of this recommendation are pointed out in order to offer hints for future research.

On the optimization of wireless multimedia sensor networks: A goal programming approach

Network lifetime is a crucial concern for Wireless Multimedia Sensor Networks (WMSNs), particularly due to the energy constraints of their nodes and the significant bitrate required by multimedia applications. This paper deals with this issue, studying how to achieve the maximum network lifetime, and simultaneously satisfying the best aggregate throughput for the multimedia services offered. To this end, we propose a planning model that results in a more accurate solution for an arbitrary network deployment than using the current optimization techniques applied both to WMSNs and traditional Wireless Sensor Networks (WSNs). Our model is based on multi-objective formulation and goal programming, which, to the best of our knowledge, have never been employed in the WSN field. This paper also proposes a load balancing algorithm which ensures a fair traffic load distribution per link during the network operation and matches the values returned by the mathematical planning model for the set lifetime and throughput. Simulation results are presented and further discussed to show the effectiveness of the numerical solutions. Finally, a test-bed deployed in a trial environment validates the theoretical contributions of this work.

On the synchronization of IEEE 802.15.5 wireless mesh sensor networks: Shortcomings and improvements

As part of the recent IEEE 802.15.5 wireless mesh sensor networks (WMSN) standard, Synchronous Energy Saving (SES) is planned to provide energy savings to scheduled communications with strict temporal requirements that, a priori, facilitate the development of delay-sensitive applications. It is accomplished by means of different mechanisms, among which we highlight a straightforward synchronization process. However, the SES synchronization scheme introduces variable delays in the dissemination of information and reduces the lifetime of the nodes and the entire network significantly, thus limiting the full exploitation of SES. This article presents a new synchronization approach, that we call High-PerformanceSynchronization Algorithm for wireless mesh sensor networks (HIPESYN), which is adapted to the IEEE 802.15.5 standard for synchronous communications. HIPESYN supports intensive bandwidth applications in a much better way than with the original design. The proposed algorithm is also thoroughly evaluated and its results carefully discussed.

On the Feasibility of Wireless Multimedia Sensor Networks over IEEE 802.15.5 Mesh Topologies.

Wireless Multimedia Sensor Networks (WMSNs) are a special type of Wireless Sensor Network (WSN) where large amounts of multimedia data are transmitted over networks composed of low power devices. Hierarchical routing protocols typically used in WSNs for multi-path communication tend to overload nodes located within radio communication range of the data collection unit or data sink. The battery life of these nodes is therefore reduced considerably, requiring frequent battery replacement work to extend the operational life of the WSN system. In a wireless sensor network with mesh topology, any node may act as a forwarder node, thereby enabling multiple routing paths toward any other node or collection unit. In addition, mesh topologies have proven advantages, such as data transmission reliability, network robustness against node failures, and potential reduction in energy consumption. This work studies the feasibility of implementing WMSNs in mesh topologies and their limitations by means of exhaustive computer simulation experiments. To this end, a module developed for the Synchronous Energy Saving (SES) mode of the IEEE 802.15.5 mesh standard has been integrated with multimedia tools to thoroughly test video sequences encoded using H.264 in mesh networks.

On the improvement of wireless mesh sensor network performance under hidden terminal problems

Wireless Mesh Sensor Networks (WMSNs) have recently received a great deal of attention in the scientific and developers communities due to the significant advances of this technology in the wireless communication field. The main reason was that competing WMSN approaches that emerged in the last few years provide mesh capabilities ( e . g ., robustness, scalability, multi-hop mesh routing, or energy efficiency, among others) to conventional WSN-based applications, encouraging researchers and end users to adopt new perspectives and solutions. Unfortunately, each one of these approaches lacks some (or many) of the aforementioned mesh capabilities, not assuring, a priori, the feasibility and, especially, the long-term stability of WMSN applications. The IEEE 802.15.5 standard and, in particular, its Asynchronous Energy Saving (ASES) mode was conceived to fill this gap since it integrates, in a single solution, most of these capabilities, guaranteeing, among other benefits, a long network lifetime. However, the ASES mode has no built-in mechanisms to mitigate the negative effects of hidden terminals, which sharply degrades the network performance. This fact leads us to conclude that any current WMSN approach is non-exempt of some problem, which prevents the definitive boost of this technology in the consumer market. Under these circumstances, our contribution to the WMSN field in this paper is a twofold proposal addressed to alleviating the hidden terminal problems in a scenario running under the most relevant design premises of ASES mode. Therefore, we first formulate a multi-objective optimization and then solve it by using Goal Programming. Both mathematical techniques are applied to obtain the best solution that simultaneously minimizes the aggregate message collision time due to hidden terminals and maximizes the network lifetime. Secondly, we propose the design of a MULti-channel TIme-scheduled algorithm for the HIdden Terminal problem avoidance (MULTI-HIT) which appropriately exploits the available bandwidth and accomplishes a straightforward coordination between any sender-receiver pair. Finally, the analysis and simulation experiments are presented and their results carefully discussed, demonstrating the effectiveness of both proposals in the WMSN arena. WMSN approaches offer new perspectives to conventional WSN-based applications.Among WMSN proposals, the ASES mode guarantees the most relevant mesh capabilities.ASES has no mechanisms to mitigate the negative effects of hidden terminals (HT).Under ASES rules, we propose an optimization model and a multi-channel time-slotted algorithm to alleviate the HT problem.An intensive performance evaluation study is discussed to validate our proposals.

On the influence of the hidden and exposed terminal problems on asynchronous IEEE 802.15.5 networks

Hidden and exposed terminal problems are known to negatively impact wireless communications, degrading potential computing services on top. These effects are more significant in Wireless Mesh Sensor Networks (WMSNs), and, particularly, in those based on the IEEE 802.15.5 Low-Rate Wireless Personal Area Network (LR-WPAN mesh) standard, a promising solution for enabling low-power WMSNs. The first contribution of this paper is a quantitative evaluation of these problems under the IEEE 802.15.5 Asynchronous Energy Saving (ASES) mode, which is intended for asynchronous data-collection applications. The results obtained show a sharp deterioration of the network performance. Therefore, this paper also reviews the most relevant approaches that cope with these problems and are compatible with ASES. Finally, a set of these proposals is assessed to find out those more suitable for their potential integration with ASES, which constitutes the second major contribution of the paper. The hidden and exposed effects are assessed on Wireless Mesh Sensor Networks (WMSNs).Performance evaluation reveals a clear negative impact on WMSNs.Different scientific proposals are discussed in order to mitigate these problems.Some of these proposals are stressed and compared according to WMSN premises.Best solutions of our comparative study are shown to the audience.

A handheld diagnostic system for 6LoWPAN networks

The successful deployment of low-power wireless sensor networks (WSNs) in real application environments is a much broader exercise than just the simple instrumentation of the intended monitoring site. Many problems, from node malfunctions to connectivity issues, may arise during commissioning of these networks. These need to be corrected on the spot, often within limited time, to avoid undesired delays in commissioning and yet a fully functional system does not guarantee that no new problems will occur after leaving the site. In this paper we present the first ever (to our knowledge) implementation of a handheld diagnostic system for fast on-site commissioning of low-power IPv6 (6LoWPAN) WSNs as well as troubleshooting of network problems during and after deployment. This system can be used where traditional solutions are insufficient to ascertain the root causes of any problems encountered at no additional complexity in the implementation of the WSN. The embedded diagnosis capability in our system is based on a lightweight decision tree that distills the functioning of communication protocols in use by the network, with a major focus on interoperable IPv6 standards and protocols for low-power WSNs. To show the applicability of our system, we present a set of experiments based on results from a real deployment in a large construction site. Through these experiments, important performance insights are gained that can be used as guidelines for improvement of operation and maintenance of 6LoWPAN networks.

Monitoring A Large Construction Site Using Wireless Sensor Networks

Despite the significant advances made by wireless sensor network research, deployments of such networks in real application environments are fraught with significant difficulties and challenges that include robust topology design, network diagnostics and maintenance. Based on our experience of a six-month-long wireless sensor network deployment in a large construction site, we highlight these challenges and argue the need for new tools and enhancements to current protocols to address these challenges.

Wireless sensor monitoring of Paddington Station Box Corner

This paper presents the real performance of three diaphragm wall panels on the southeast corner of Paddington Station Box during excavation, monitored using a wireless sensor network. In total, 15 LPDT displacement sensors, 12 tilt sensors, 13 relay nodes and a gateway were deployed at three different stages. Each wireless sensor node is programmed with Contiki OS using the in-built IPv6-based network layer (6LoWPAN/RPL) for link-local addressing and routing, and ContikiMAC at the medium access control (MAC) layer for radio duty cycling. Extensive testing and calibration was carried out in the laboratory to ensure that the system functioned as expected. Wireless tilt and displacement sensors were installed to measure the inclination, angular distortion and relative displacement of these corner panels at three different depths. The monitoring data reveal that the corner produced a stiffening effect on the station box, which might result in a breakdown of plane strain conditions. The network performance characteristics (e.g. message reception ratio and network topology status) and challenges are also highlighted and discussed.

Energy neutral operation of vibration energy-harvesting sensor networks for bridge applications.

Structural monitoring of critical bridge structures can greatly benefit from the use of wireless sensor networks (WSNs), however energy harvesting for the operation of the network remains a challenge in this setting. While solar and wind power are possible and credible solutions to energy generation, the need for positioning sensor nodes in shaded and sheltered locations, e.g., under a bridge deck, is also often precluding their adoption in real-world deployments. In some scenarios vibration energy harvesting has been shown as an effective solution, instead.This paper presents a multihop vibration energy-harvesting WSN system for bridge applications. The system relies on an ultra-low power wireless sensor node, driven by a novel vibration based energy-harvesting technology. We use a receiver-initiated routing protocol to enable energy-efficient and reliable connectivity between nodes with different energy charging capabilities. By combining real vibration data with an experimentally validated model of the vibration energy harvester, a hardware model, and the COOJA simulator, we develop a framework to conduct realistic and repeatable experiments to evaluate the system before on-site deployment.Simulation results show that the system is able to maintain energy neutral operation, preserving energy with careful management of sleep and communication times. We also validate the system through a laboratory experiment on real hardware against real vibration data collected from a bridge. Besides providing general guidelines and considerations for the development of vibration energy-harvesting systems for bridge applications, this work highlights the limitations of the energy budget made available by traffic-induced vibrations, which clearly shrink the applicability of vibration energy-harvesting technology for WSNs to low traffic applications.