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

DESIGN OF RELIABLE AND SUSTAINABLE WIRELESS SENSOR NETWORKS: CHALLENGES, PROTOCOLS AND CASE STUDIES

Integrated with the function of sensing, processing, and wireless communication, wireless sensors are attracting strong interest for a variety of monitoring and control applications. Wireless sensor networks (WSNs) have been deployed for industrial and remote monitoring purposes. As energy shortage is a worldwide problem, more attention has been placed on incorporating energy harvesting devices in WSNs. The main objective of this research is to systematically study the design principles and technical approaches to address three key challenges in designing reliable and sustainable WSNs; namely, communication reliability, operation with extremely low and dynamic power sources, and multi-tier network architecture. Mathematical throughput models, sustainable WSN communication strategies, and multi-tier network architecture are studied in this research to address these challenges, leading to protocols for reliable communication, energy-efficient operation, and network planning for specific application requirements. To account for realistic operating conditions, the study has implemented three distinct WSN testbeds: a WSN attached to the high-speed rotating spindle of a turning lathe, a WSN powered by a microbial fuel cell based energy harvesting system, and a WSN with a multi-tier network architecture. With each testbed, models and protocols are extracted, verified and analyzed. Extensive research has studied low power WSNs and energy harvesting capabilities. Despite these efforts, some important questions have not been well understood. This dissertation addresses the following three dimensions of the challenge. First, for reliable communication protocol design, mathematical throughput or energy efficiency estimation models are essential, yet have not been investigated accounting for specific application environment characteristics and requirements. Second, for WSNs with energy harvesting power sources, most current networking protocols do not work efficiently with the systems considered in this dissertation, such as those powered by extremely low and dynamic energy sources. Third, for multi-tier wireless network system design, routing protocols that are adaptive to real-world network conditions have not been studied. This dissertation focuses on these questions and explores experimentally derived mathematical models for designing protocols to meet specific application requirements. The main contributions of this research are 1) for industrial wireless sensor systems with fast-changing but repetitive mobile conditions, understand the performance and optimal choice of reliable wireless sensor data transmission methods, 2) for ultra-low energy harvesting wireless sensor devices, design an energy neutral communication protocol, and 3) for distributed rural wireless sensor systems, understand the efficiency of realistic routing in a multi-tier wireless network. Altogether, knowledge derived from study of the systems, models, and protocols in this work fuels the establishment of a useful framework for designing future WSNs