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In mobile wireless networks, the emerging proximity-based applications have led to needs for highly effective and energy-efficient neighbor discovery protocols. However, existing works cannot realize the optimal worst-case latency in symmetric case, and their performances with asymmetric duty cycles can still be improved. In this work, we investigate asynchronous neighbor discovery through a code-based approach, including the symmetric and asymmetric cases. We derive the tight worst-case latency bound in the case of symmetric duty cycle. We design a novel class of symmetric patterns called Diff-Codes, which is optimal when the Diff-Code can be extended from a perfect difference set. We further consider the asymmetric case, and design ADiff-Codes. To evaluate (A)Diff-Codes, we conduct both simulations and testbed experiments. Both simulation and experiment results show that (A)Diff-Codes significantly outperform existing neighbor discovery protocols in both the median case and worst-case. Specifically, in symmetric case, the maximum worst-case improvement is up to 50%; in both symmetric and asymmetric cases, the median case gain is as high as 30%.

An investigation is performed to detect debond in reinforced concrete structures. This study utilizes built-in piezoelectric discs as sensors and actuators in a pitch-catch mode to generate sensor data, which are sensitive to debond in reinforced concrete. A comparison of sensor measurements or signal changes before and after maintenance or inspection can be correlated to debonding. Both experimental and analytical works are performed during the study. Experimental study and test data are presented in this article. The test results clearly indicate that debond between concrete and rebar and yielding in rebar can be detected with built-in piezoelectric sensors and actuators in a pitch-catch mode.

Abstract-In Vehicular Ad Hoc Networks (VANETs), because of the non-existence of end-to-end connections, it is essential that nodes take advantage of connection opportunities to forward messages, to make end-to-end messaging possible. Thus it is crucial to make sure that nodes have incentives to forward messages for others, despite that the routing protocols in VANETs are different from traditional end-to-end routing protocols. In this paper, we study how to stimulate message forwarding in VANETs. Our approach is based on coalitional game theory. In particular, we propose an incentive scheme for VANETs and rigorously show that with our scheme faithfully following the routing protocol is to the best interests of each node. In addition, we extend our scheme to take the limited storage space of each node into consideration. Experiments on testbed trace data verify that our scheme is effective in stimulating cooperation of message forwarding in VANETs.