Wireless Sensor Networks for Condition Based Maintenance: Security and Reliability

Abstract

In this thesis we present the requirements needed for a Condition Based Main- tenance (CBM) solution by using Wireless Sensor Networks(WSN). The sensor network needs to be secure and reliable to be implemented in a CBM solution, hence we have chosen the popular ZigBee protocol to see how it fulfill the reliability requirements of transmission delay, lost packets and battery consumption. The security requirements is based on the CIA(confidentiality, integrity, availability) triad for security objectives, and in this thesis we will give a general overview of the security mechanisms used in ZigBee to achieve these requirements. Also a brief overview of threats a WSN faces is also presented. Practical experiments for testing delay, battery consumption and environ- mental interference from magnetic fields has been conducted using XBee units from Digi International. These tests shows that the transmisson delay is within acceptable levels, and the battery consumption for sensors allows them to run for several years. Another contender for use in industrial processes is WirelessHART by HART Communication foundation. Like ZigBee, WirelessHART is based on the IEEE 802.15.4 standard for wireless personal area networks. However WirelessHART has a dfferent specification for the data-link layer than ZigBee and offers funda- mental differences like Time Division Multiple Access and Frequency Hopping Spread Spectrum while ZigBee uses Carrier Sense Multiple Access and Direct Sequence Spread Spectrum.