Listen-and-Talk: Full-duplex Cognitive Radio Networks

In traditional cognitive radio networks, secondary users (SUs) typically access the spectrum of primary users (PUs) by a two-stage "listen-before-talk" (LBT) protocol, i.e., SUs sense the spectrum holes in the first stage before transmit in the second stage. In this paper, we propose a novel "listen-and-talk" (LAT) protocol with the help of the full-duplex (FD) technique that allows SUs to simultaneously sense and access the vacant spectrum. Analysis of sensing performance and SU's throughput are given for the proposed LAT protocol. And we find that due to self-interference caused by FD, increasing transmitting power of SUs does not always benefit to SU's throughput, which implies the existence of a power-throughput tradeoff. Besides, though the LAT protocol suffers from self-interference, it allows longer transmission time, while the performance of the traditional LBT protocol is limited by channel spatial correction and relatively shorter transmission period. To this end, we also present an adaptive scheme to improve SUs' throughput by switching between the LAT and LBT protocols. Numerical results are provided to verify the proposed methods and the theoretical results.Comment: in proceeding of IEEE Globecom 201

Full-duplex MAC Protocol Design and Analysis

The idea of in-band full-duplex (FD) communications revives in recent years owing to the significant progress in the self-interference cancellation and hardware design techniques, offering the potential to double spectral efficiency. The adaptations in upper layers are highly demanded in the design of FD communication systems. In this letter, we propose a novel medium access control (MAC) using FD techniques that allows transmitters to monitor the channel usage while transmitting, and backoff as soon as collision happens. Analytical saturation throughput of the FD-MAC protocol is derived with the consideration of imperfect sensing brought by residual self- interference (RSI) in the PHY layer. Both analytical and simulation results indicate that the normalized saturation throughput of the proposed FD-MAC can significantly outperforms conventional CSMA/CA under various network conditions

Full-Duplex Cognitive Radio: A New Design Paradigm for Enhancing Spectrum Usage

With the rapid growth of demand for ever-increasing data rate, spectrum resources have become more and more scarce. As a promising technique to increase the efficiency of the spectrum utilization, cognitive radio (CR) technique has the great potential to meet such a requirement by allowing un-licensed users to coexist in licensed bands. In conventional CR systems, the spectrum sensing is performed at the beginning of each time slot before the data transmission. This unfortunately results in two major problems: 1) transmission time reduction due to sensing, and 2) sensing accuracy impairment due to data transmission. To tackle these problems, in this paper we present a new design paradigm for future CR by exploring the full-duplex (FD) techniques to achieve the simultaneous spectrum sensing and data transmission. With FD radios equipped at the secondary users (SUs), SUs can simultaneously sense and access the vacant spectrum, and thus, significantly improve sensing performances and meanwhile increase data transmission efficiency. The aim of this article is to transform the promising conceptual framework into the practical wireless network design by addressing a diverse set of challenges such as protocol design and theoretical analysis. Several application scenarios with FD enabled CR are elaborated, and key open research directions and novel algorithms in these systems are discussed

Listen-and-Talk: Protocol Design and Analysis for Full-duplex Cognitive Radio Networks

In traditional cognitive radio networks, secondary users (SUs) typically access the spectrum of primary users (PUs) by a two-stage "listen-before-talk" (LBT) protocol, i.e., SUs sense the spectrum holes in the first stage before transmitting in the second. However, there exist two major problems: 1) transmission time reduction due to sensing, and 2) sensing accuracy impairment due to data transmission. In this paper, we propose a "listen-and-talk" (LAT) protocol with the help of full-duplex (FD) technique that allows SUs to simultaneously sense and access the vacant spectrum. Spectrum utilization performance is carefully analyzed, with the closed-form spectrum waste ratio and collision ratio with the PU provided. Also, regarding the secondary throughput, we report the existence of a tradeoff between the secondary transmit power and throughput. Based on the power-throughput tradeoff, we derive the analytical local optimal transmit power for SUs to achieve both high throughput and satisfying sensing accuracy. Numerical results are given to verify the proposed protocol and the theoretical results

Ceramics from Khalet al-Jam'a (Bethlehem, Palestine): a material hidden for millennia

Introduction: Bethlehem, the ancient city of Palestine, has been known for its religious and historical significance for millennia. A recently excavated site, Khalet al-Jam’a, was unearthed and surveyed by a joint team of the Palestinian MOTA-DACH (Ministry of Tourism and Antiquities - Department of Archaeology and Cultural Heritage) and Sapienza University of Rome in 2013-2016 and abundant materials were recovered. This study is focused on the mineralogical-petrographic and chemical characterization of ceramic material yielded from this site, with the aim to reconstruct the technological level reached by the ancient civilization occupying it during the Early Bronze Age. Optical microscopy (OM), X-ray Powder Diffraction (XRPD) and Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) provided results which can define the nature and provenance of raw materials, as well as technological aspects such as firing conditions and post-burial processes, to finally give a view of the socio-economic status at that time

Investigating the Effects of TBDF Regulations on Multinational Firms\u27 Operation

The far advance in computer and telecommunication technology, and the evolution of Multinational corporations (MNCs) have led to an era of global economy. While MNCs strive for competitive advantage via their global information systems, diverse barriers on transborder data flow (TBDF) work in the opposite direction. Many researchers indicated that TBDF restrictions not only affected the operation of MNCs, but also the management of international information systems. Some others argued that transborder data laws were either found too vague to follow, or unable to seriously hamper some MNCs due to their smooth relationship with local telecommunication authorities at host countries. This paper aims to investigate the context and causes of the discrepancy. The results indicated that vendor’ s support, deregulation of telecommunication restrictions, and the areas in which MNCs operated accounted for the discrepancy and thus alleviated the impact of TBDF regulations on MNCs\u27 operation

Performance of Lightweight Structures During Liquefaction From Recent Earthquakes

Several case histories of lightweight structures performance during liquefaction from recent earthquake are reviewed. The review is focused on performance of lightweight structures in terms of liquefaction-induced vertical settlement, tilting, lateral displacement and their effects on occupancy and functionality of the structures. These case histories were reported during the 1997 Mw 7.4 Caucete- Argentina, 2007 Mw 8.0 Pisco-Peru, 2010 Mw 8.8 Chile, 2010 Mw 7.2 El Mayor-Cucapah, 2010-2011 New Zealand, and 2011 Mw 9.0 Great East Japan earthquakes. The review is performed to identify similarities, discuss conditions, and their effects on foundation and structures. Financial and economic considerations are discussed and compared for housing, i.e., cost of housing versus cost of strengthened foundation and/or improved ground. Some recommendations for residential areas are proposed

Empirical research on the evaluation model and method of sustainability of the open source ecosystem

The development of open source brings new thinking and production modes to software engineering and computer science, and establishes a software development method and ecological environment in which groups participate. Regardless of investors, developers, participants, and managers, they are most concerned about whether the Open Source Ecosystem can be sustainable to ensure that the ecosystem they choose will serve users for a long time. Moreover, the most important quality of the software ecosystem is sustainability, and it is also a research area in Symmetry. Therefore, it is significant to assess the sustainability of the Open Source Ecosystem. However, the current measurement of the sustainability of the Open Source Ecosystem lacks universal measurement indicators, as well as a method and a model. Therefore, this paper constructs an Evaluation Indicators System, which consists of three levels: The target level, the guideline level and the evaluation level, and takes openness, stability, activity, and extensibility as measurement indicators. On this basis, a weight calculation method, based on information contribution values and a Sustainability Assessment Model, is proposed. The models and methods are used to analyze the factors affecting the sustainability of Stack Overflow (SO) ecosystem. Through the analysis, we find that every indicator in the SO ecosystem is partaking in different development trends. The development trend of a single indicator does not represent the sustainable development trend of the whole ecosystem. It is necessary to consider all of the indicators to judge that ecosystem’s sustainability. The research on the sustainability of the Open Source Ecosystem is helpful for judging software health, measuring development efficiency and adjusting organizational structure. It also provides a reference for researchers who study the sustainability of software engineering

Formation of in-volume nanogratings with sub-100 nm periods in glass by femtosecond laser irradiation

We present direct experimental observation of the morphological evolution during the formation of nanogratings with sub-100-nm periods with the increasing number of pulses. Theoretical simulation shows that the constructive interference of the scattering light from original nanoplanes will create an intensity maximum located between the two adjacent nanoplanes, resulting in shortening of the nanograting period by half. The proposed mechanism enables explaining the formation of nanogratings with periods beyond that predicted by the nanoplasmonic model.Comment: 4 pages, 3 figure