Energy-efficient link assessment in wireless sensor networks

For energy-constrained stationary wireless networks of sensors, selection of links with high quality rate helps to ensure reliable long-term operation. During the implementation of a protocol targeting industrial applications of such systems, it was found that it is advantageous to acquire accurate information about the availability and quality of the RF communication links prior to the network topology formation. "Link assessment" as part of the initialization process, accomplishes this task by assessing a sufficient number of packets exchanged between neighboring nodes. This paper introduces and analyzes two different approaches to link assessment: The first approach is a random non-deterministic scheme that allows for a probabilistic guarantee of collision-free packet exchange. An alternative method is described which employs 'constant-weight codes' and provides a deterministic guarantee of success. In particular, a special class of constant-weight codes, known as optical orthogonal codes, are considered. Since, these codes are cyclically permutable, they make the link assessment process simpler, and therefore they are preferred over other codes. We evaluate the performance of these methods based on their energy consumption, time duration, and implementation complexity.