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    The Internet of Things (IoT) devices exchange certificates and authorization tokens over the IEEE 802.15.4 radio medium that supports a Maximum Transmission Unit (MTU) of 127 bytes. However, these credentials are significantly larger than the MTU and are therefore sent in a large number of fragments. As IoT devices are resource-constrained and battery-powered, there are considerable computations and communication overheads for fragment processing both on sender and receiver devices, which limit their ability to serve real-time requests. Moreover, the fragment processing operations increase energy consumption by CPUs and radio-transceivers, which results in shorter battery life. In this article, we propose CATComp -a compression-aware authorization protocol for Constrained Application Protocol (CoAP) and Datagram Transport Layer Security (DTLS) that enables IoT devices to exchange smallsized certificates and capability tokens over the IEEE 802.15.4 media. CATComp introduces additional messages in the CoAP and DTLS handshakes that allow communicating devices to negotiate a compression method, which devices use to reduce the credentials’ sizes before sending them over an IEEE 802.15.4 link. The decrease in the size of the security materials minimizes the total number of packet fragments, communication overheads for fragment delivery, fragment processing delays, and energy consumption. As such, devices can respond to requests faster and have longer battery life. We implement a prototype of CATComp on Contiki-enabled RE-Mote IoT devices and provide a performance analysis of CATComp. The experimental results show that communication latency and energy consumption are reduced when CATComp is integrated with CoAP and DTLS. 
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  5. We demonstrate coupling to and control over the broadening and dispersion of a mid-infrared leaky mode, known as the Berreman mode, in samples with different dielectric environments. We fabricate subwavelength films of AlN, a mid-infrared epsilon-near-zero material that supports the Berreman mode, on materials with a weakly negative permittivity, strongly negative permittivity, and positive permittivity. Additionally, we incorporate ultra-thin AlN layers into a GaN/AlN heterostructure, engineering the dielectric environment above and below the AlN. In each of the samples, coupling to the Berreman mode is observed in angle-dependent reflection measurements at wavelengths near the longitudinal optical phonon energy. The measured dispersion of the Berreman mode agrees well with numerical modes. Differences in the dispersion and broadening for the different materials is quantified, including a 13 cm-1red-shift in the energy of the Berreman mode for the heterostructure sample.

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  6. The increasing use of light emitting diodes (LED) and light receptors such as photodiodes and cameras in vehicles motivates the use of visible light communication (VLC) for inter–vehicular networking. However, the mobility of the vehicles presents a fundamental impediment for high throughput and link sustenance in vehicular VLC. While prior work has explored vehicular VLC system design, yet, there is no clear understanding on the amount of motion of vehicles in real world vehicular VLC use–case scenarios. To address this knowledge gap, in this paper, we present a mobility characterization study through extensive experiments in real world driving scenarios. We characterize motion using a constantly illuminated transmitter on a lead vehicle and a multi–camera setup on a following vehicle. The observations from our experiments reveal key insights on the degree of relative motion of a vehicle along its spatial axis and different vehicular motion behaviors. The motion characterization from this work lays a stepping stone to addressing mobility in vehicular VLC. 
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  7. Theoretical models estimate visible light communication (VLC) data capacity to be of the order of Tera-bits-per-second (Tbps). However, practical limitations in receiver designs have limited state-of-the-art VLC prototypes to (multiple) orders of magnitude lower data rates. This paper explores a new architecture to realize ultra-high data rates in visible light communication systems by dramatically improving the Signal-to-Interference-Noise-Ratio (SINR) at the receiver. The key idea is to leverage the fast sampling rates of photodiode receivers and integrate a shutter mechanism that filters noise and interference thus creating a high-speed imaging receiver effect. Through adaptive selection of the exact receiver area over which the transmitted light is detected, the SINR can be dramatically increased yet not compromising the high sampling rate achievable using state-of-the-art photoreceptors. In addition to introducing the new hybrid architecture for high SINR reception, in this paper, we study the feasibility of noise and interference reduction through a proof-of-concept experimentation. 
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