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91.
Multi-radio diversity in wireless networks 总被引:1,自引:0,他引:1
This paper describes the Multi-Radio Diversity (MRD) wireless system, which uses path diversity to improve loss resilience in wireless local area networks (WLANs). MRD
coordinates wireless receptions among multiple radios to improve loss resilience in the face of path-dependent frame corruption
over the radio. MRD incorporates two techniques to recover from bit errors and lower the loss rates observed by higher layers,
without consuming much extra bandwidth. The first technique is frame combining, in which multiple, possibly erroneous, copies of a given frame are combined together in an attempt to recover the frame
without retransmission. The second technique is a low-overhead retransmission scheme called request-for-acknowledgment (RFA), which operates above the link layer and below the network layer to attempt to recover from frame combining failures. We
present an analysis that determines how the parameters for these algorithms should be chosen.
We have designed and implemented MRD as a fully functional WLAN infrastructure based on 802.11a. We evaluate the MRD system
under several different physical configurations, using both UDP and TCP, and measured throughput gains up to 3× over single
radio communication schemes employing 802.11’s autorate adaptation scheme.
Computer and Communication Sciences, EPFL, Switzerland.
Allen Miu received his Ph.D. degree at the Massachusetts Institute of Technology in 2006 and is currently a wireless systems architect
at Ruckus Wireless, Inc. He received his S.M. in Computer Science from MIT and a B.Sc. with highest honors in Electrical Engineering
and Computer Science from the University of California at Berkeley. He previously worked on the Cricket Indoor Location System
and was a research intern at Microsoft Research, Redmond in 2000 and Hewlett-Packard Laboratories, Palo Alto in 2002. His
research interests include wireless networks, location systems, mobile computing, and embedded systems.
Hari Balakrishnan is an Associate Professor in the EECS Department and a member of the Computer Science and Artificial Intelligence Laboratory
(CSAIL) at MIT. His research interests is in the area of networked computer systems. In addition to many widely cited papers,
several systems developed as part of his research are available in the public domain. He received a Ph.D. in Computer Science
from the University of California at Berkeley in 1998 and a B.Tech. from the Indian Institute of Technology (Madras) in 1993.
His honors include an Alfred P. Sloan Research Fellowship (2002), an NSF CAREER Award (2000), the ACM doctoral dissertation
award for his work on reliable data transport over wireless networks (1998), and seven award-winning papers at various top
conferences and journals, including the IEEE Communication Society’s William R. Bennett Prize (2004). He has also received
awards for excellence in teaching and research at MIT (Spira, Junior Bose, and Harold Edgerton faculty achievement awards).
C. Emre Koksal received his B.S. degree in Electrical Engineering from the Middle East Technical University, Ankara in 1996. He received
his S.M. and Ph.D. degrees from MIT in Electrical Engineering and Computer Science in 1998 and 2002 respectively. He was a
postdoctoral fellow in the Networks and Mobile Systems Group in the Computer Science and Artificial Intelligence Laboratory
at MIT until 2003. Since then he has been a senior researcher jointly in the Laboratory for Computer Communications and the
Laboratory for Information Theory at EPFL, Switzerland. His general areas of interest are wireless communications, computer
networks, information theory, stochastic processes and financial economics. He also has a certificate on Financial Technology
from the Sloan School of Management at MIT. 相似文献
92.
D Mangapathi Rao M Muralidhar T Somaiah V Hari Babu 《Bulletin of Materials Science》1991,14(2):199-206
Influence of sintering time and quenching in Bi2 −x
Pb
x
Ca2Sr2Cu3O
y
(x=0.0, 0.1, 0.2, 0.25, 0.3 and 0.4) samples have been studied by resistance and XRD measurements. In samples sintered at 850°C
for 4 days,T
c(0) increases with Pb concentration.T
c(0) increased from 81 K forx=0.0 to 109 K inx=0.30 sample and then decreased. Increasing the sintering time to 10 days decreased theT
c Quenching further decreased theT
c(0). From X-ray diffraction patterns, the intensity peaks of low and highT
c phases have been measured. The addition of Pb promotes highT
c-phase. Sintering time, slow cooling and rapid quenching studies show that there is an optimum sintering time and cooling
rate to produce a highT
c-phase. 相似文献
93.
Stability of any power system is a major issue for secure operation of the system. The stability of power system is concerned with the behavior of synchronous generators following disturbances. Transmission system in competitive market refers to over loading of transmission lines or transformers due to market settlement. Thus there is a need of enhancing transmission capability of the network. FACTS controllers have the capability of controlling power flow by means of controlling line parameters, voltage injection at some of the angle. In the proposed work optimal location for installation of FACTS device is obtained using NN and the amount of voltage and angle to be injected in the system using UPFC is calculated using Bees algorithm. The method is tested on IEEE 26 bus system but it is general in nature and can be applied to any power system. The results exhibit the performance of the method in maintaining the system stability and АТС enhancement. 相似文献
94.
Shukdev Pandey Devendra Kumar Om Parkash Lakshman Pandey 《Integrated ferroelectrics》2017,183(1):141-162
Complex immittance (Impedance Z, Modulus M, Admittance Y, Permittivity ?) spectra for some equivalent circuit models involving resistances, capacitances and constant phase angle elements (CPE) are calculated for different ratios of the parameters. A comparison of experimentally obtained complex immittance plots with these diagrams greatly facilitates the search for the most appropriate equivalent circuit representing the electrical properties of electronic ceramics. An equivalent circuit for Ba1-xSrxTiO3 (x = 0.35) ceramic system is developed by using these simulated plots. 相似文献
95.
Rajesh Kumar Gayatri Sahu Shailendra K. Saxena Hari M. Rai Pankaj R. Sagdeo 《SILICON》2014,6(2):117-121
A qualitative evolution of an asymmetric Raman line-shape function from a Lorentzian line-shape is discussed here for application in low dimensional semiconductors. The step-by-step evolution reported here is based on the phonon confinement model which is successfully used in literature to explain the asymmetric Raman line-shape from semiconductor nanostructures. Physical significance of different terms in the theoretical asymmetric Raman line-shape has been explained here. Better understanding of theoretical reasoning behind each term allows one to use the theoretical Raman line-shape without going into the details of theory from first principle. This will enable one to empirically derive a theoretical Raman line-shape function for any material if information about its phonon dispersion relation, size dependence, etc., is known. 相似文献
96.
The photoluminescence (PL) properties of singly doped (Dy3+) and codoped (Dy3+, Eu3+) fluoroaluminoborate glasses, with an emphasis on the white light generation, are studied. The γ-irradiation led to the formation of defects in Dy3+-doped glasses and photoreduction of Eu3+ to Eu2+ in codoped (Dy3+, Eu3+) glasses. The electron paramagnetic resonance spectra confirm the presence of divalent europium ions and defects in Dy3+, Dy3+–Eu3+-doped glasses. The FTIR spectra mainly establish the compaction of glass network due to γ-irradiation. From the PL spectra, the intensity ratio of Dy3+ emission bands yellow to blue (4F9/2–6H13/2/4F9/2–6H15/2) defines the site symmetry, covalency, and feasibility of extracting white light. The existence of an energy transfer (ET) from Dy3+ to Eu3+ ions are established due to the decrease in intensity of Dy3+ peaks with an increase of Eu2O3 content. Moreover, the non-exponential nature of decay curves was well fitted with the generalization of Yokota–Tanimoto model for electric dipole-quadrupole (S = 8) interaction that is responsible for ET process from sensitizer (Dy3+) to activator (Eu3+). 相似文献
97.
K. Hari Gopi S. Gouse Peera S. D. Bhat P. Sridhar S. Pitchumani 《Bulletin of Materials Science》2014,37(4):877-881
Hydroxyl ion (OH?) conducting anion exchange membranes based on modified poly (phenylene oxide) are fabricated for their application in alkaline polymer electrolyte fuel cells (APEFCs). In the present study, chloromethylation of poly(phenylene oxide) (PPO) is performed by aryl substitution rather than benzyl substitution and homogeneously quaternized to form an anion exchange membrane (AEM). 1H NMR and FT-IR studies reveal successful incorporation of the above groups in the polymer backbone. The membrane is characterized for its ion exchange capacity and water uptake. The membrane formed by these processes show good ionic conductivity and when used in fuel cell exhibited an enhanced performance in comparison with the state-of-the-art commercial AHA membrane. A peak power density of 111 mW/cm2 at a load current density of 250 mA/cm2 is obtained for PPO based membrane in APEFCs at 30 °C. 相似文献
98.
99.
L S Vaidhyanathan A M Niraimathi P Majumdar G Rangarajan M Muralidhar D Mangapathi Rao M Nagabhushanam V Hari Babu 《Bulletin of Materials Science》1991,14(4):913-919
Bi2−x
Pb
x
Sr2Ca2Cu3O
y
superconducting samples with 0<x<0·3 have been synthesized and characterized using X-ray powder diffraction.T
c
and superconducting volume fraction have been measured using a.c. magnetic susceptibility, d.c. electrical resistivity as
well as X-band microwave surface resistance in the normal state. The data indicate the growth of the highT
c
(2223) phase with corresponding reduction of the lowT
c
(2122) phase with increasingx, up to 0·25. Beyond this value ofx there is a slight deterioration of the superconducting behaviour. 相似文献
100.
A detailed chemical kinetic mechanism describing the thermal and catalytic cracking of methylcyclohexane over a 12CaO.7Al2O3 catalyst is presented. The model is based on balanced equations for both molecular and radical species describing an experimental fixed‐bed reactor system. The mechanistic model is based on overall first‐order decomposition kinetics, which satisfactorily describes experimental data. The simulated product distributions show a reasonably good agreement with the experimental results and confirm the hypothesis that the catalyst does not affect the pyrolysis mechanism and only increases the rate of the initiation steps. 相似文献