Not All Wireless Sensor Networks Are Created Equal: A Comparative Study On Tunnels

Wireless sensor networks (WSNs) are envisioned for a number of application scenarios. Nevertheless, the few in-the-field experiences typically focus on the features of a specific system, and rarely report about the characteristics of the target environment, especially w.r.t. the behavior and performance of low-power wireless communication. The TRITon project, funded by our local administration, aims to improve safety and reduce maintenance costs of road tunnels, using a WSN-based control infrastructure. The access to real tunnels within TRITon gives us the opportunity to experimentally assess the peculiarities of this environment, hitherto not investigated in the WSN field. We report about three deployments: i) an operational road tunnel, enabling us to assess the impact of vehicular traffic; ii) a non-operational tunnel, providing insights into analogous scenarios (e.g., underground mines) without vehicles; iii) a vineyard, serving as a baseline representative of the existing literature. Our setup, replicated in each deployment, uses mainstream WSN hardware, and popular MAC and routing protocols. We analyze and compare the deployments w.r.t. reliability, stability, and asymmetry of links, the accuracy of link quality estimators, and the impact of these aspects on MAC and routing layers. Our analysis shows that a number of criteria commonly used in the design of WSN protocols do not hold in tunnels. Therefore, our results are useful for designing networking solutions operating efficiently in similar environments

Survey of energy efficient tracking and localization techniques in buildings using optical and wireless communication media

This paper presents a survey of beamforming, beamsteering and mobile tracking techniques. The survey was made in the context of the SOWICI project. The aim of this project is to reduce power consumption of data exchanging devices within houses. An optical fiber network is used for data transport to and from rooms whereas wireless transceivers communicate with appliances within the rooms. Using this approach, the aim is to reduce power consumption and exposure to electromagnetic radiation. To realize this, beamforming will be used to only radiate energy in, and receive signals from, the direction of interest. Because appliances within households can move, some of them even relatively fast, the pointing direction of the beam should be steerable. The pointing direction can be deduced from the communication link (beamsteering) or via separate mobile tracking techniques

PACKET ERROR RATE PREDICTIVE MODEL FOR SENSOR RADIOS ON FAST ROTATING STRUCTURES

Wireless sensing technologies have raised widespread interests in the applications for monitoring fast rotating or moving machinery structures in manufacturing environments. Over the past five years, a few wireless sensor systems have been implemented and proven to feasibly work under fast rotation conditions. However, few of these studies evaluated data transmission performance of the wireless communication systems. Although the manufacturing environments are known to be harsh for wireless communication, in many cases, an excellent data throughput is critical for such systems. Conventional statistical methods for studying wireless communication channels are not sufficient in this specific field. This dissertation presents systematic experiments to understand and characterize the behavior of a 2.4 GHz band wireless channel between a fast rotating transmitter and a stationary data receiver. The experiments prove, in manufacturing machines, multipath propagation induced by metallic objects causes high power attenuation of radio signals during transmitter motion, and the consequence, low received signal power, is recognized as the major cause of transmission errors. The dissertation proposes a deterministic packet error rate (PER) predictive model for rotating wireless measuring systems using IEEE 802.15.4 sensor radios. The model consists of three sub-models that predict power attenuation, bit error rate (BER), and PER in three stages for given specifications regarding environment, radio transmission, and rotation. The dissertation provides experimental validation of the sub-models and discusses their limitations and prediction errors. By either experiments or simulations, two data transmission protocols, automatic retransmission request (ARQ) method and online error avoidance algorithm, are proved efficient for a reliable wireless communication of such sensor radios. As the first effort to characterize and model such radio channels, the dissertation provides in-depth understandings of the channels\u27 fast varying behavior, achieves prediction guidance for the channels\u27 communication performance, and introduces prospective transmission protocols for performance enhancement

Transmission Error Analysis and Avoidance for IEEE 802.15.4 Wireless Sensors on Rotating Structures

Wireless sensors are increasingly adopted in manufacturing and vehicular systems for monitoring critical components under continuous operation. Many such components move rapidly and frequently in metallic containments with challenging radio propagation characteristics. For wireless sensors mounted on rotating structures, previous studies identified an eminent increase in packet transmission errors at higher rotation speeds. Such errors were found to occur at specific locations around the rotating spindle\u27s periphery and such locations depended sensitively on sensor location and surrounding geometry. This thesis presents a systematic study of the expected packet error rates due to such errors, and analytically derives the first transmission error rate for a given system. Simulations done on C++ are used to characterize the error region properties. A transmission error avoidance approach based on on-line error pattern inference and packet transmission time control for IEEE 802.15.4 compatible sensor radios is proposed. The transmission avoidance scheme has two phases: error identification phase to determine the error characteristics of the system and the operational phase to avoid errors. Simulation studies showed a 50% error reduction and up to 75% throughput increase for a rotation system with four symmetric 4¼ wide error zones with 100% BER inside the error region and 0% BER outside the error region. Higher throughput gains for higher rate and larger size transmissions were also noticed for this system. Simulations also show that the throughput decreases when the packet size duration is greater than the separation between the error zone

A critical analysis of research potential, challenges and future directives in industrial wireless sensor networks

In recent years, Industrial Wireless Sensor Networks (IWSNs) have emerged as an important research theme with applications spanning a wide range of industries including automation, monitoring, process control, feedback systems and automotive. Wide scope of IWSNs applications ranging from small production units, large oil and gas industries to nuclear fission control, enables a fast-paced research in this field. Though IWSNs offer advantages of low cost, flexibility, scalability, self-healing, easy deployment and reformation, yet they pose certain limitations on available potential and introduce challenges on multiple fronts due to their susceptibility to highly complex and uncertain industrial environments. In this paper a detailed discussion on design objectives, challenges and solutions, for IWSNs, are presented. A careful evaluation of industrial systems, deadlines and possible hazards in industrial atmosphere are discussed. The paper also presents a thorough review of the existing standards and industrial protocols and gives a critical evaluation of potential of these standards and protocols along with a detailed discussion on available hardware platforms, specific industrial energy harvesting techniques and their capabilities. The paper lists main service providers for IWSNs solutions and gives insight of future trends and research gaps in the field of IWSNs

Field Measurements and Guidelines for the Application of Wireless Sensor Networks to the Environment and Security

Frequently, Wireless Sensor Networks (WSN) are designed focusing on applications and omitting transmission problems in these wireless networks. In this paper, we present a measurement campaign that has been carried out using one of the most commonly used WSN platforms, the micaZ from Crossbow©. Based on these measurements, some guidelines to deploy a robust and reliable WSN are provided. The results are focused on security and environmental applications but can also be extrapolated to other scenarios. A main conclusion that can be extracted is that, from the transmission point of view, a dense WSN is one of the best choices to overcome many of the transmission problems such as the existence of a transitional region, redundance, forwarding, obstructions or interference with other systems