AirSync: Enabling Distributed Multiuser MIMO with Full Spatial Multiplexing

The enormous success of advanced wireless devices is pushing the demand for higher wireless data rates. Denser spectrum reuse through the deployment of more access points per square mile has the potential to successfully meet the increasing demand for more bandwidth. In theory, the best approach to density increase is via distributed multiuser MIMO, where several access points are connected to a central server and operate as a large distributed multi-antenna access point, ensuring that all transmitted signal power serves the purpose of data transmission, rather than creating "interference." In practice, while enterprise networks offer a natural setup in which distributed MIMO might be possible, there are serious implementation difficulties, the primary one being the need to eliminate phase and timing offsets between the jointly coordinated access points. In this paper we propose AirSync, a novel scheme which provides not only time but also phase synchronization, thus enabling distributed MIMO with full spatial multiplexing gains. AirSync locks the phase of all access points using a common reference broadcasted over the air in conjunction with a Kalman filter which closely tracks the phase drift. We have implemented AirSync as a digital circuit in the FPGA of the WARP radio platform. Our experimental testbed, comprised of two access points and two clients, shows that AirSync is able to achieve phase synchronization within a few degrees, and allows the system to nearly achieve the theoretical optimal multiplexing gain. We also discuss MAC and higher layer aspects of a practical deployment. To the best of our knowledge, AirSync offers the first ever realization of the full multiuser MIMO gain, namely the ability to increase the number of wireless clients linearly with the number of jointly coordinated access points, without reducing the per client rate.Comment: Submitted to Transactions on Networkin

Development and evaluation of detection methods of PCBs in food samples

Polychlorinated biphenyls (PCBs) are industrial compounds which are known to be among the most persistent and widely distributed pollutants in the global ecosystem. Since they are lipophilic, they tend to bioaccumulate in the fatty tissues of living organisms, including humans. Owing to the chemical and physical properties of PCBs, the analysis by conventional methods is difficult and expensive. Therefore simple methods for the detection of PCBs in environmental, industrial and food samples are required. The Ph.D. thesis involved the study, design and construction of electrochemical bilayer lipid membrane-based biosensors for rapid detection of compounds of biomedical, environmental and industrial interest such as PCBs. This work describes a novel electrochemical biosensor based on a supported polymerized lipid film with incorporated Sheep anti-PCB antibody for the rapid detection of aroclor 1242, at the levels of 10-9 M concentrations, in flowing solution streams. The antibody was incorporated into the lipid film during polymerization. Injections of Aroclor 1242 antigen solutions were made into flowing streams of a carrier electrolyte solution. Experiments were done in a stopped-flow mode using lipid mixtures containing 15% (w/w) dipalmitoylphosphatidic acid (DPPA) to provide only a single transient current signal with a magnitude related to the antigen concentration. An immunosensor based on the BLM transduction scheme should be regenerable and capable of multiple analyses. Thus, lipid films containing 35% DPPA were used to examine regeneration of the active sites of antibody after complex formation by washing with the carrier electrolyte solution. Repetitive cycles of injection of antigen have shown that the maximum number of cycles is about 5. The mechanism of signal generation was investigated by physicochemical methods of IR, Raman spectrometry and Scanning Electron Microscopy. The device was tested/ evaluated in real samples of vegetables. The investigation of the effect of potent interferences included a wide range of compounds usually found in foods. The results showed no interferences from these compounds in concentration levels usually found in real samples. The analyses that have been concluded in order to define the PCBs in the foods as well as the comparison of these results against the results of other established methods have proved that the biosensor used provides reliable results and it can therefore constitute a valuable tool for future applications in the field of Environmental Chemistry

Open data from the first and second observing runs of Advanced LIGO and Advanced Virgo

Advanced LIGO and Advanced Virgo are monitoring the sky and collecting gravitational-wave strain data with sufficient sensitivity to detect signals routinely. In this paper we describe the data recorded by these instruments during their first and second observing runs. The main data products are gravitational-wave strain time series sampled at 16384 Hz. The datasets that include this strain measurement can be freely accessed through the Gravitational Wave Open Science Center at http://gw-openscience.org, together with data-quality information essential for the analysis of LIGO and Virgo data, documentation, tutorials, and supporting software

Search for intermediate-mass black hole binaries in the third observing run of Advanced LIGO and Advanced Virgo

International audienceIntermediate-mass black holes (IMBHs) span the approximate mass range 100−105 M⊙, between black holes (BHs) that formed by stellar collapse and the supermassive BHs at the centers of galaxies. Mergers of IMBH binaries are the most energetic gravitational-wave sources accessible by the terrestrial detector network. Searches of the first two observing runs of Advanced LIGO and Advanced Virgo did not yield any significant IMBH binary signals. In the third observing run (O3), the increased network sensitivity enabled the detection of GW190521, a signal consistent with a binary merger of mass ∼150 M⊙ providing direct evidence of IMBH formation. Here, we report on a dedicated search of O3 data for further IMBH binary mergers, combining both modeled (matched filter) and model-independent search methods. We find some marginal candidates, but none are sufficiently significant to indicate detection of further IMBH mergers. We quantify the sensitivity of the individual search methods and of the combined search using a suite of IMBH binary signals obtained via numerical relativity, including the effects of spins misaligned with the binary orbital axis, and present the resulting upper limits on astrophysical merger rates. Our most stringent limit is for equal mass and aligned spin BH binary of total mass 200 M⊙ and effective aligned spin 0.8 at 0.056 Gpc−3 yr−1 (90% confidence), a factor of 3.5 more constraining than previous LIGO-Virgo limits. We also update the estimated rate of mergers similar to GW190521 to 0.08 Gpc−3 yr−1.Key words: gravitational waves / stars: black holes / black hole physicsCorresponding author: W. Del Pozzo, e-mail: [email protected]† Deceased, August 2020