On Heterogeneous Neighbor Discovery in Wireless Sensor Networks

Neighbor discovery plays a crucial role in the formation of wireless sensor networks and mobile networks where the power of sensors (or mobile devices) is constrained. Due to the difficulty of clock synchronization, many asynchronous protocols based on wake-up scheduling have been developed over the years in order to enable timely neighbor discovery between neighboring sensors while saving energy. However, existing protocols are not fine-grained enough to support all heterogeneous battery duty cycles, which can lead to a more rapid deterioration of long-term battery health for those without support. Existing research can be broadly divided into two categories according to their neighbor-discovery techniques---the quorum based protocols and the co-primality based protocols.In this paper, we propose two neighbor discovery protocols, called Hedis and Todis, that optimize the duty cycle granularity of quorum and co-primality based protocols respectively, by enabling the finest-grained control of heterogeneous duty cycles. We compare the two optimal protocols via analytical and simulation results, which show that although the optimal co-primality based protocol (Todis) is simpler in its design, the optimal quorum based protocol (Hedis) has a better performance since it has a lower relative error rate and smaller discovery delay, while still allowing the sensor nodes to wake up at a more infrequent rate.Comment: Accepted by IEEE INFOCOM 201

Pushing the Limits of Wireless Sensor Networks - WSNs 20,000 Leagues Under the Sea

In recent years, research in wireless sensor networks (WSNs) has made significant strides, facilitating a variety of applications in the Internet of Things, health, environmental monitoring, and military. Advances in wireless routing and delay tolerance design allow WSNs to achieve data acquisition in networking scenarios with intermittent link and time varying bandwidth. Creative power saving schemes were also developed to allow WSN nodes periodically power down. These advances allow researchers to deploy WSNs in a variety of challenging environments that have limited communication bandwidth with harsh channel dynamics, long delay, and high deployment costs. One such environment is under the ocean, where unconventional types of propagation medium such as acoustics and optics are the only viable types of communication medium.This dissertation describes the design, implementation, and various other aspects of an underwater WSN system using software defined networking (SDN) principles that can be deployed on the ocean floor for purposes ranging from ocean exploration and oil drilling needs to search and rescue missions and military interests. The system consists of a flock of Autonomous Underwater Vehicles (AUVs) acting as mobile WS nodes and primarily relies on a centralized SDN controller doubling as the information hub and recharging station for the AUVs. We address systematic issues related to AUV deployment and networking, including power consumption, data transfer, and channel contention. To limit power consumption, we design two neighbor discovery methods that allow AUVs to turn off their radios and thus save power. For data transfer among nodes and channel contention, we explore the idea of delay-tolerant networking (DTN) and study various acoustic media access control schemes. We also develop a new underwater acoustic MAC protocol that maximizes throughput in good channel conditions and data transfer reliability in bad channel conditions. Simulations and experiments show that our protocol greatly outperforms existing underwater acoustic protocols in both speed and reliability. Along the process, we create and expand a public testbed allowing researchers to run underwater networking experiments in a water tank, in an emulator, and even in the open water for more realistic settings

Carrier recombination spatial transfer by reduced potential barrier causes blue/red switchable luminescence in C8 carbon quantum dots/organic hybrid light-emitting devices

The underlying mechanism behind the blue/red color-switchable luminescence in the C8 carbon quantum dots (CQDs)/organic hybrid light-emitting devices (LEDs) is investigated. The study shows that the increasing bias alters the energy-level spatial distribution and reduces the carrier potential barrier at the CQDs/organic layer interface, resulting in transition of the carrier transport mechanism from quantum tunneling to direct injection. This causes spatial shift of carrier recombination from the organic layer to the CQDs layer with resultant transition of electroluminescence from blue to red. By contrast, the pure CQDs-based LED exhibits green–red electroluminescence stemming from recombination of injected carriers in the CQDs

Differences in phonetic discrimination stem from differences in psychoacoustic abilities in learning the sounds of a second language: Evidence from ERP research

<div><p>The scientific community has been divided as to the origin of individual differences in perceiving the sounds of a second language (L2). There are two alternative explanations: a general psychoacoustic origin vs. a speech-specific one. A previous study showed that such individual variability is linked to the perceivers’ speech-specific capabilities, rather than the perceivers’ psychoacoustic abilities. However, we assume that the selection of participants and parameters of sound stimuli might not appropriate. Therefore, we adjusted the sound stimuli and recorded event-related potentials (ERPs) from two groups of early, proficient Cantonese (L1)-Mandarin (L2) bilinguals who differed in their mastery of the Mandarin (L2) phonetic contrast /in-ing/, to explore whether the individual differences in perceiving L2 stem from participants’ ability to discriminate various pure tones (frequency, duration and pattern). To precisely measure the participants’ acoustic discrimination, mismatch negativity (MMN) elicited by the oddball paradigm was recorded in the experiment. The results showed that significant differences between good perceivers (GPs) and poor perceivers (PPs) were found in the three general acoustic conditions (frequency, duration and pattern), and the MMN amplitude for GP was significantly larger than for PP. Therefore, our results support a general psychoacoustic origin of individual variability in L2 phonetic mastery.</p></div

MMN obtained for the GP and PP groups in the duration condition at the Fz and LM electrode.

<p>MMN obtained for the GP and PP groups in the duration condition at the Fz and LM electrode.</p

The t test of the MMN mean amplitude for the duration conditions at Fz.

<p>The t test of the MMN mean amplitude for the duration conditions at Fz.</p

MMN obtained for the GP and PP groups in the pattern condition at the Fz and LM electrode.

<p>Fig 3(a) shows the MMN obtained for the GP and PP groups in the pattern1 condition at the Fz and LM electrode. Fig 3(b) shows the MMN obtained for the GP and PP groups in the pattern2 condition at the Fz and LM electrode.</p

The t test of the MMN mean amplitude for the frequency conditions at Fz.

<p>The t test of the MMN mean amplitude for the frequency conditions at Fz.</p

MMN obtained for the GP and PP groups in the frequency condition at the Fz and LM electrode.

<p>MMN obtained for the GP and PP groups in the frequency condition at the Fz and LM electrode.</p

A SDN-controlled underwater MAC and routing testbed

© 2016 IEEE. Efficient data communication among autonomous under-water vehicles (AUVs) is difficult. Challenges include the long propagation delays arising with acoustic communication solutions, and line-of-sight requirements for optical transceivers. Existing multi-hop routing approaches are not always appropriate due to node mobility. This work presents a centralized approach to network control, exploiting the observation that AUV networks will have a bounded number of nodes. The paper describes a SDN realization of AUV networking, and documents the implementation of a small-scale replica of the system in our testbed, which can be accessed remotely via a web page and SSH. We then demonstrate the functionality of our implementation by evaluating the performances of two existing MAC protocols namely Slotted FAMA [11] and UW-Aloha [13], in a multi-hop, underwater scenario