Despite national plans to deploy smart meters in small and medium businesses in the UK, there is little knowledge of occupant energy use in offices. The objectives of the study were to investigate the effect of individual feedback on energy use at the workdesk, and to test the relationship between individual determinants, energy use and energy reduction. A field trial is presented, which monitored occupant energy use and provided individual feedback to 83 office workers in a university. The trial comprised pre- and post-intervention surveys, energy measurement and provision of feedback for 18 weeks post-baseline, and two participant focus groups. The main findings were: statistically significant energy reduction was found, but not for the entire measurement period; engagement with feedback diminished over time; no measured individual variables were related to energy reduction and only attitudes to energy conservation were related to energy use; an absence of motivation to undertake energy reduction actions was in evidence. The implications for energy use in offices are considered, including the need for motivations beyond energy reduction to be harnessed to realise the clear potential for reduced energy use at workdesks. © 2013 The Authors

In an effort to find low-cost alternatives for components currently used in dense wavelength division multiplexing, optical ring resonators fabricated on silicon on insulator are currently being investigated. Their performance can be further enhanced if they are polarization independent. Herein we use rib waveguides to control the polarization properties of the devices and hence produce polarization-independent racetrack ring resonators. Transverse electric and transverse magnetic resonant peaks are measured to within 2 pm of one another over four cycles of the free spectral range. The racetrack resonators also exhibit measured An optical ring resonator is a versatile device that can then be utilized to create many different optical devices, including filters, 1,2 switches, 3,4 and add-drop multiplexers 5 for use in dense wavelength division multiplexing systems. In high index media such as silicon on insulator, (SOI), most ring resonator devices realized thus far are made using strip, or photonic wire waveguides.6,7 This is to allow for the small bend radii necessary to minimize the loss associated with devices and hence to produce a large free spectral range (FSR). However, the use of strip waveguides makes it much more difficult to control the polarization properties of the resultant devices. In this work we take an alternative approach, designing optical racetrack resonators based upon rib waveguides, to allow us to optimize control of the polarization properties and therefore realize a polarizationindependent ring resonator. While a polarization-independent ring resonator has been demonstrated in the low index contrast material of silicon oxynitride, our devices are fabricated in single-crystal SOI. The design and fabrication is discussed first, followed by presentation and discussion of experimental results.In order to design a polarization-independent ring resonator, the first step was to investigate the polarization characteristics of the rib waveguide due to its geometry. The BEAMPROP 8 simulation package was used to determine the dimensions necessary to create such a device. The initial height and width were set to 1.35 and 1 µm, respectively. These dimensions were chosen in order to maintain as large a device as possible (within the constraints of the rib height) for ease of coupling light to the device. Using BEAMPROP, the effective indices of the fundamental TE and TM waveguide modes were monitored as the etch depth was varied. Figure 1(a) shows a plot of the effective index as a function of etch depth for both polarizations. The etch depth at which the two curves cross indicates that both TE and TM polarizations have the same effective index and therefore the waveguide is polarization independent in terms of propagation constant.Next it was necessary to design a polarizationindependent directional coupler. Figure 1(b) shows a typical result of modeling a directional coupler using BEAMPROP. For the purposes of the modeling, the left arm of the coupler was excited with an optical field.

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Dynamic spectrum access (

Recent advancements in radio frequency machine learning (RFML) have demonstrated the use of raw in-phase and quadrature (IQ) samples for multiple spectrum sensing tasks. Yet, deep learning techniques have been shown, in other applications, to be vulnerable to adversarial machine learning (ML) techniques, which seek to craft small perturbations that are added to the input to cause a misclassification. The current work differentiates the threats that adversarial ML poses to RFML systems based on where the attack is executed from: direct access to classifier input, synchronously transmitted over the air (OTA), or asynchronously transmitted from a separate device. Additionally, the current work develops a methodology for evaluating adversarial success in the context of wireless communications, where the primary metric of interest is bit error rate and not human perception, as is the case in image recognition. The methodology is demonstrated using the well known Fast Gradient Sign Method to evaluate the vulnerabilities of raw IQ based Automatic Modulation Classification and concludes RFML is vulnerable to adversarial examples, even in OTA attacks. However, RFML domain specific receiver effects, which would be encountered in an OTA attack, can present significant impairments to adversarial evasion.

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Specific Emitter Identification is the association of a received signal to a unique emitter, and is made possible by the naturally occurring and unintentional characteristics an emitter imparts onto each transmission, known as its radio frequency fingerprint. This work presents an approach for identifying emitters using Convolutional Neural Networks to estimate the IQ imbalance parameters of each emitter, using only raw IQ data as input. Because an emitter's IQ imbalance parameters will not change as it changes modulation schemes, the proposed approach has the ability to track emitters, even as they change modulation scheme. The performance of the developed approach is evaluated using simulated quadrature amplitude modulation and phaseshift keying signals, and the impact of signal-to-noise ratio, imbalance value, and modulation scheme are considered. Further, the developed approach is shown to outperform a comparable feature-based approach, while making fewer assumptions and using less data.