Controlled Interference Generation for Wireless Coexistence Research

In recent years, we have witnessed a proliferation of wireless technologies and devices operating in the unlicensed bands. The resulting escalation of wireless demand has put enor-mous pressure on available spectrum. This raises a unique set of communication challenges, notably co-existence, Cross Technology Interference (CTI), and fairness amidst high un-certainty and scarcity of interference-free channels. Conse-quently, there is a strong need for understanding and debug-ging the performance of existing wireless protocols and sys-tems under various patterns of interference. Therefore, we need to augment testbeds with tools that can enable repeat-able generation of realistic interference patterns. This would primarily facilitate wireless coexistence research experimen-tation. The heterogeneity of the existing wireless devices and protocols operating in the unlicensed bands makes in-terference hard to model. Meanwhile, researchers working on wireless coexistence generally use interference generated from various radio appliances. The lack of a systematic way of controlling these appliances makes it inconvenient to run experiments, particularly in remote testbeds. In this pa-per, we present a Controlled Interference Generator (CIG) framework for wireless networks. In the design of CIG, we consider a unified approach that incorporates a careful se-lection of interferer technologies (implemented in software), to expose networks to realistic interference patterns. We validate the resemblance of interference generated by CIG and interference from represented RF devices, by showing the accuracy in temporal and spectral domains

Observational characteristics of early star formation

The formation of low mass stars has been modelled in detail for several decades and in the last 30 years infrared and submillimetre telescopes have observed protostellar sources and discovered faint, embedded protostars, outflows, jets and discs. The first hydrostatic core (FHSC), the first stable pressure–supported object to form during the star formation process, was first predicted in 1969 but has not been definitively observed. Specific criteria are required to distinguish it from other faint pre– and protostellar objects observationally. In this thesis, we develop synthetic observations of the early stages of star formation to help determine how to identify the FHSC in nature. We present synthetic spectral energy distributions (SEDs) from 3-D radiation hydrodynamical simulations of collapsing pre–stellar cores for a variety of initial conditions. Variations in the initial rotation rate, radius and mass lead to differences in the location of the SED peak and far–infrared flux. We then attempt to fit the SEDs of 15 candidate FHSCs with model SEDs. This showed that the SED can provide an insight into the nature of these sources and enable sources that are probably more evolved to be ruled out. Next, we produced spectral line observations for CO, HCO+, CS and SO, calculated from radiation (magneto)hydrodynamical models, chemical modelling and Monte Carlo radiative transfer. Many common molecules are strongly depleted except for in the inner few 10s of AU , after the formation of the FHSC. HCO+ (1−0) and SO (87−76) spectra show variations which may allow a candidate FHSC to be distinguished from a more evolved object. It may also be possible to detect the rotation of the outflow in CO (4 − 3) and (3 − 2) lines for nearby (∼ 150 pc) sources. Lastly, we applied the chemical model to a large–scale simulation of cluster formation. This showed, again, that the abundances of most species are depleted with respect to abundances in the interstellar medium and are only released into the gas phase in small scale regions where protostars are forming. This work also highlighted the importance of considering the initial conditions carefully because the physical history has a substantial effect on the calculated abundances in the outer, low density regions.European Commissio

SPICA:revealing the hearts of galaxies and forming planetary systems : approach and US contributions

How did the diversity of galaxies we see in the modern Universe come to be? When and where did stars within them forge the heavy elements that give rise to the complex chemistry of life? How do planetary systems, the Universe's home for life, emerge from interstellar material? Answering these questions requires techniques that penetrate dust to reveal the detailed contents and processes in obscured regions. The ESA-JAXA Space Infrared Telescope for Cosmology and Astrophysics (SPICA) mission is designed for this, with a focus on sensitive spectroscopy in the 12 to 230 micron range. SPICA offers massive sensitivity improvements with its 2.5-meter primary mirror actively cooled to below 8 K. SPICA one of 3 candidates for the ESA's Cosmic Visions M5 mission, and JAXA has is committed to their portion of the collaboration. ESA will provide the silicon-carbide telescope, science instrument assembly, satellite integration and testing, and the spacecraft bus. JAXA will provide the passive and active cooling system (supporting the

The Apertif Surveys:The First Six Months

Apertif is a new phased-array feed for the Westerbork Synthesis Radio Telescope (WSRT), greatly increasing its field of view and turning it into a natural survey instrument. In July 2019, the Apertif legacy surveys commenced; these are a time-domain survey and a two-tiered imaging survey, with a shallow and medium-deep component. The time-domain survey searches for new (millisecond) pulsars and fast radio bursts (FRBs). The imaging surveys provide neutral hydrogen (HI), radio continuum and polarization data products. With a bandwidth of 300 MHz, Apertif can detect HI out to a redshift of 0.26. The key science goals to be accomplished by Apertif include localization of FRBs (including real-time public alerts), the role of environment and interaction on galaxy properties and gas removal, finding the smallest galaxies, connecting cold gas to AGN, understanding the faint radio population, and studying magnetic fields in galaxies. After a proprietary period, survey data products will be publicly available through the Apertif Long Term Archive (ALTA, https://alta.astron.nl). I will review the progress of the surveys and present the first results from the Apertif surveys, including highlighting the currently available public data