Synchronization of OFDM at low SNR over an AWGN channel

This paper is based on Extended Symbol OFDM (ES-OFDM) where symbols are extended in time. This way ES-OFDM can operate at low SNR. Each doubling of the symbol length improves the SNR performance by 3 dB in case of a coherent receiver. One of the basic questions is how to synchronize to signals far below the noise floor. An algorithm is presented which is based on the transmission of pilot symbols. At the receiver, the received signal is cross correlated with the known pilot symbol and the maximum magnitude is determined. The position of the maximum value within the cross correlation function indicates the time difference between transmitter and receiver. The performance of the algorithm in case of an Additive White Gaussian Noise (AWGN) channel, is assessed based on a theoretical approximation of the probability of correct detection of the time difference. The theoretical approximation matches with simulation results and shows that synchronization can be achieved for low (negative) SNRs

Adaptive OFDM System Design For Cognitive Radio

Recently, Cognitive Radio has been proposed as a promising technology to improve spectrum utilization. A highly flexible OFDM system is considered to be a good candidate for the Cognitive Radio baseband processing where individual carriers can be switched off for frequencies occupied by a licensed user. In order to support such an adaptive OFDM system, we propose a Multiprocessor System-on-Chip (MPSoC) architecture which can be dynamically reconfigured. However, the complexity and flexibility of the baseband processing makes the MPSoC design a difficult task. This paper presents a design technology for mapping flexible OFDM baseband for Cognitive Radio on a multiprocessor System-on-Chip (MPSoC)

Nature of Ar bonding to small Co_n^+ clusters and its effect on the structure determination by far-infrared absorption spectroscopy

Far-infrared vibrational spectroscopy by multiple photon dissociation has proven to be a very useful technique for the structural fingerprinting of small metal clusters. Contrary to previous studies on cationic V, Nb and Ta clusters, measured vibrational spectra of small cationic cobalt clusters show a strong dependence on the number of adsorbed Ar probe atoms, which increases with decreasing cluster size. Focusing on the series Co_4^+ to Co_8^+ we therefore use density-functional theory to analyze the nature of the Ar-Co_n^+ bond and its role for the vibrational spectra. In a first step, energetically low-lying isomer structures are identified through first-principles basin-hopping sampling runs and their vibrational spectra computed for a varying number of adsorbed Ar atoms. A comparison of these fingerprints with the experimental data enables in some cases a unique assignment of the cluster structure. Independent of the specific low-lying isomer, we obtain a pronounced increase of the Ar binding energy for the smallest cluster sizes, which correlates nicely with the observed increased influence of the Ar probe atoms on the IR spectra. Further analysis of the electronic structure motivates a simple electrostatic picture that not only explains this binding energy trend, but also why the influence of the rare-gas atom is much stronger than in the previously studied systems.Comment: 12 pages including 10 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm

Near field phased array DOA and range estimation of UHF RFID tags

This paper presents a near field localization system based on a phased array for UHF RFID tags. To estimate angle and range the system uses a two-dimensional MUSIC algorithm. A four channel phased array is used to experimentally verify the estimation of angle and range for an EPC gen2 tag. The system is calibrated for phase offsets introduced by hardware as simulations show the sensitivity to these offsets. Experiments with this calibrated receiver array give inaccurate ranging estimates. A solution is to calibrate the system for every angle, allowing meaningful range estimates. Experiments in a different environment show a reduced result, indicating the need for extensive calibration

The Chameleon Architecture for Streaming DSP Applications

We focus on architectures for streaming DSP applications such as wireless baseband processing and image processing. We aim at a single generic architecture that is capable of dealing with different DSP applications. This architecture has to be energy efficient and fault tolerant. We introduce a heterogeneous tiled architecture and present the details of a domain-specific reconfigurable tile processor called Montium. This reconfigurable processor has a small footprint (1.8 mm$^2$ in a 130 nm process), is power efficient and exploits the locality of reference principle. Reconfiguring the device is very fast, for example, loading the coefficients for a 200 tap FIR filter is done within 80 clock cycles. The tiles on the tiled architecture are connected to a Network-on-Chip (NoC) via a network interface (NI). Two NoCs have been developed: a packet-switched and a circuit-switched version. Both provide two types of services: guaranteed throughput (GT) and best effort (BE). For both NoCs estimates of power consumption are presented. The NI synchronizes data transfers, configures and starts/stops the tile processor. For dynamically mapping applications onto the tiled architecture, we introduce a run-time mapping tool

A CMOS spectrum analyzer frontend for cognitive radio achieving +25dBm IIP3 and −169 dBm/Hz DANL

A dual RF-receiver preceded by discrete-step attenuators is implemented in 65nm CMOS and operates from 0.3– 1.0 GHz. The noise of the receivers is reduced by cross-correlating the two receiver outputs in the digital baseband, allowing attenuation of the RF input signal to increase linearity. With this technique a displayed average noise level below -169 dBm/Hz is obtained with +25 dBm IIP3, giving a spurious-free dynamic range of 89 dB in 1 MHz resolution bandwidth

Multiple packets of neutral molecules revolving for over a mile

The level of control that one has over neutral molecules in beams dictates their possible applications. Here we experimentally demonstrate that state-selected, neutral molecules can be kept together in a few mm long packet for a distance of over one mile. This is accomplished in a circular arrangement of 40 straight electrostatic hexapoles through which the molecules propagate over 1000 times. Up to 19 packets of molecules have simultaneously been stored in this ring structure. This brings the realization of a molecular low-energy collider within reach

One-note samba: the biogeographical history of the relict Brazilian butterfly Elkalyce cogina

[Aim] Biogeographically puzzling taxa represent an opportunity to understand the processes that have shaped current species distributions. The systematic placement and biogeographical history of Elkalyce cogina, a small lycaenid butterfly endemic to Brazil and neighbouring Argentina, are long-standing puzzles. We use molecular tools and novel biogeographical and life history data to clarify the taxonomy and distribution of this butterfly.[Location] South America, with emphasis on the Atlantic Rain Forest and Cerrado biomes (Brazil and Argentina).[Methods] We gathered a data set of 71 Polyommatini (Lycaenidae) samples, including representatives of all described subtribes and/or sections. Among these, we contributed new sequences for E. cogina and four additional relevant taxa in the target subtribes Everina, Lycaenopsina and Polyommatina. We inferred a molecular phylogeny based on three mitochondrial genes and four nuclear markers to assess the systematic position and time of divergence of E. cogina. Ancestral geographical ranges were estimated with the R package BioGeoBEARS. To investigate heterogeneity in clade diversification rates, we used Bayesian analysis of macroevolutionary mixtures (bamm).[Results] Our results confirm the hypothesis that E. cogina belongs to the subtribe Everina and not Lycaenopsina, but unexpectedly recovered it as the sister group to the rest of Everina, with an estimated divergence time of approximately 10 Ma. Ancestral geographical range reconstruction points to an old colonization from Asia, the centre of diversity for the Everina, to the New World. The Neotropical Polyommatina lineage diversified to produce almost 100 species in multiple genera, whereas the E. cogina lineage did not diversify at all. Such lack of diversification is unique among the seven Everina/Polyommatina lineages that colonized the New World. We also show that the larvae of E. cogina feed on Fabaceae, supporting the identification of this host-plant family as the ancestral state for the whole group.[Main conclusions] The age and biogeographical reconstruction of the Elkalyce lineage are similar to those of the Neotropical lineage of Polyommatina and suggest that both travelled via the route proposed by Vladimir Nabokov (Asia-Beringia-North America-South America). This coincidence suggests that the climatic conditions at c. 10 Ma favoured dispersal from Asia to the Neotropics and that later events may have erased traces of these butterfly lineages in North America.Funding was provided by the Spanish Ministerio de Economía y Competitividad (project CGL2013-48277-P). G.T. is supported by the grant BP-A00275 (AGAUR-Generalitat de Catalunya), Marie Curie Actions FP7-PEOPLE-2013-IOF (project 622716) and the grant 1.50.1617.2013 at Saint Petersburg State University; L.A.K. was supported by CAPES (3200-14-0); A.V.L.F. thanks ICMBio for research permits (SISBIO no. 10802-5), CNPq (fellowship 302585/2011-7 and grant 564954/2010-1), RedeLep-SISBIOTA-Brasil/CNPq (563332/2010-7), the National Science Foundation (DEB-1256742), BR-BoL (MCT/CNPq/FNDCT 50/2010) and FAPESP (grant 2012/50260-6 and BIOTA-FAPESP Programs 2011/50225-3 and 2013/50297-0).Peer Reviewe

Correcting Knowledge Base Assertions

The usefulness and usability of knowledge bases (KBs) is often limited by quality issues. One common issue is the presence of erroneous assertions, often caused by lexical or semantic confusion. We study the problem of correcting such assertions, and present a general correction framework which combines lexical matching, semantic embedding, soft constraint mining and semantic consistency checking. The framework is evaluated using DBpedia and an enterprise medical KB