Multi-channel wireless sensor networks : protocols, design and evaluation

Pervasive systems, which are described as networked embedded systems integrated with everyday environments, are considered to have the potential to change our daily lives by creating smart surroundings and by their ubiquity, just as the Internet. In the last decade, “Wireless Sensor Networks” have appeared as one of the real-world examples of pervasive systems by combining automated sensing, embedded computing and wireless networking into tiny embedded devices. A wireless sensor network typically comprises a large number of spatially distributed, tiny, battery-operated, embedded sensor devices that are networked to cooperatively collect, process, and deliver data about a phenomenon that is of interest to the users. Traditionally, wireless sensor networks have been used for monitoring applications based on low-rate data collection with low periods of operation. Current wireless sensor networks are considered to support more complex operations ranging from target tracking to health care which require efficient and timely collection of large amounts of data. Considering the low-bandwidth, low-power operation of the radios on the sensor devices, interference and contention over the wireless medium and the energy-efficiency requirements due to the battery-operated devices, fulfilling the mentioned data-collection requirements in complex applications becomes a challenging task. This thesis focuses on the efficient delivery of large amounts of data in bandwidth-limited wireless sensor networks by making use of the multi-channel capability of the sensor radios and by using optimal routing topologies. We start with experimenting the operation of the sensor radios to characterize the behavior of multi-channel communication. We propose a set of algorithms to increase the throughput and timely delivery of the data and analyze the bounds on the data collection capacity of the wireless sensor networks. The main contributions of the thesis are listed as follows: • Contribution 1 Characteristics, challenges and the use of multi-channel communication in wireless ad hoc networks and wireless sensor networks: We review the state of the art channel assignment protocols in wireless multi-hop networks, particularly in wireless ad hoc networks and wireless sensor networks. We classify the existing solutions according to the number of transceivers required per node and according to the dynamics of the channel assignment. Since the channel assignment methods designed for general wireless ad hoc networks may not be directly applicable to wireless sensor networks, we give brief comparisons of them and discuss the additional challenges and requirements for wireless sensor networks. • Contribution 2 Characterization of multi-channel interference: The assumption of perfectly orthogonal, interference-free channels, which is adopted in most of the multi-channel communication studies, may fail in practice. Radio signals are not limited to their allocated frequency band, but cause interference in adjacent bands as well — how much depends on the filtering characteristics of the transceivers. We conduct an extensive set of experiments, using NrF905 radio, to investigate the properties of multi-channel communication in wireless sensor networks. Based on these experi-