Intersymbol and Intercarrier Interference in OFDM Transmissions through Highly Dispersive Channels

This work quantifies, for the first time, intersymbol and intercarrier interferences induced by very dispersive channels in OFDM systems. The resulting achievable data rate for \wam{suboptimal} OFDM transmissions is derived based on the computation of signal-to-interference-plus-noise ratio for arbitrary length finite duration channel impulse responses. Simulation results point to significant differences between data rates obtained via conventional formulations, for which interferences are supposed to be limited to two or three blocks, versus the data rates considering the actual channel dispersion

Early changes in rat diaphragm biology with mechanical ventilation

To better characterize the effects of 24-hour mechanical ventilation on diaphragm, the expression of myogenic transcription factors, myosin heavy chains, and sarcoplasmic/endoplasmic reticulum calcium-ATPase pumps was examined in rats. In the diaphragm of mechanically ventilated animals, the mRNA of MyoD, myosin heavy chain-2a and -2b, and sarcoplasmic/endoplasmic reticulum calcium-ATPase-1a decreased, whereas myogenin mRNA increased. In the diaphragm of anesthetized and spontaneously breathing rats, only the mRNA of MyoD and myosin heavy chain-2a decreased. MyoD and myogenin protein expression followed the changes at the mRNA, whereas the myosin heavy chain isoforms did not change. Parallel experiments involving the gastrocnemius were performed to assess the relative contribution of muscle shortening versus immobilization-induced deconditioning on muscle regulatory factor expression. Passive shortening produced no additional effects compared with immobilization-induced deconditioning. The overall changes followed a remarkably similar pattern except for MyoD protein expression, which increased in the gastrocnemius and decreased in the diaphragm while its mRNA diminished in both muscles. The early alterations in the expression of muscle protein and regulatory factors may serve as underlying molecular basis for the impaired diaphragm function seen after 24 hours of mechanical ventilation. Whether immobilization-induced deconditioning and/or passive shortening play a role in these alterations could not be fully unraveled

Compact, simple and robust cross polarized wave generation source of few-cycle, high-contrast pulses for seeding petawatt-class laser systems

International audienceA compact and robust, dual-crystal cross polarized wave generation setup combined with a hollow waveguide filter is implemented to deliver few-cycle, high-contrast laser pulses sourced from a commercial multipass Ti:Sa amplifier. The initial 25-fs pulses with a temporal contrast of 108 are shortened to 10 fs with an improved contrast of at least 10^10. The single nonlinear stage for spectral broadening and contrast enhancement of a commercial amplifier serves as an ideal injector for petawatt-class laser systems

Temporal cleaning of a high energy fiber-based ultrafast laser using cross-polarized wave generation

International audienceWe report the use of cross-polarized wave generation to perform both pulse shortening and temporal cleaning of a high-energy ytterbium-doped fiber-based femtosecond laser system. The nonlinear processes allow both a highly efficient nonlinear conversion of 20% and a large compression ratio of 3.5, with inherently improved coherent and incoherent contrasts. This results in the generation of 37 μJ, 115 fs pulses at a repetition rate of 100 kHz with high temporal quality

Higher Education and Reentry: The Gifts They Bring

This study explores the lived experiences of people with criminal justice histories as they attend and contemplate enrolling in college. The report highlights the journeys of these students and considers a number of important questions: What does it take for people with criminal justice histories to successfully transform the trajectory of their lives? What are the obstacles they face? What affirmative steps can we take to make our public and private colleges and universities more welcoming to this growing population of students

Symbol-asynchronous transmission in multibeam satellite user down-link : rate regions for novel superposition coding schemes

We consider the forward link of a multibeam satellite system with high spectral reuse and the novel low-complexity transmission and detection strategies from [1]. More specifically, we study the impact of a time offset between the antenna beams that cooperate to simultaneously serve a given user. Assuming Gaussian signaling, we provide closed-form expressions for the achievable rate region. It is demonstrated that, in the absence of timing information at the gateway, this region is not affected by a time offset. Our numerical results further show that, in case timing is known at the gateway, an offset of half a symbol period at both user terminals is optimal in terms of spectral efficiency.Grant numbers : Satellite Network of Experts IV. © 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

Millimeter wave wireless system based on point to multipoint transmissions

The continuously growing traffic demand has motivated the exploration of underutilized millimeter wave frequency spectrum for future mobile broadband communication networks. Research activities focus mainly on the use of the V-band (59 - 64 GHz) and E-band (71 - 76 & 81 - 84 GHz) to offer multi-gigabit point to point transmissions. This paper describes an innovative W-band (92-95 GHz) point to multipoint wireless network for high capacity access and backhaul applications. Point to multipoint wireless networks suffer from limited RF power available. The proposed network is based on a high power, wide band traveling wave tube of new generation and an affordable high performance transceiver. These new devices enable a new transmission paradigm and overcome the relevant technological challenges imposed by the high atmosphere attenuation and the presently lack of power amplification required to provide adequate coverage at millimeter waves

TWEETHER project for W-band wireless networks

The European Horizon 2020 project TWEETHER aims to make a breakthrough in wireless networks to overcome the congestion of the actual mobile networks and foster the new 5G networks. A European Consortium including four universities and five companies from four European countries is devoting a relevant effort to realize novel terminals and transmission hubs to operate in the W-band (93 – 95 GHz). This paper will describe the advancement of the project

Coherent beam combining with an ultrafast multicore Yb-doped fiber amplifier

International audienceActive coherent beam combination using a 7-non-coupled core,polarization maintaining, air-clad, Yb-doped fiber is demonstrated as amonolithic and compact power-scaling concept for ultrafast fiber lasers. Amicrolens array matched to the multicore fiber and an active phasecontroller composed of a spatial light modulator applying a stochasticparallel gradient descent algorithm are utilized to perform coherentcombining in the tiled aperture geometry. The mitigation of nonlineareffects at a pulse energy of 8.9 μJ and duration of 860 fs is experimentallyverified at a repetition rate of 100 kHz. The experimental combiningefficiency results in a far field central lobe carrying 49% of the total power,compared to an ideal value of 76%. This efficiency is primarily limited bygroup delay differences between cores which is identified as the maindrawback of the system. Minimizing these group delay issues, e.g. by usingshort and straight rod-type multicore fibers, should allow a practical powerscaling solution for femtosecond fiber systems