157 research outputs found
Spectral Efficiency of Mixed-ADC Massive MIMO
We study the spectral efficiency (SE) of a mixed-ADC massive MIMO system in
which K single-antenna users communicate with a base station (BS) equipped with
M antennas connected to N high-resolution ADCs and M-N one-bit ADCs. This
architecture has been proposed as an approach for realizing massive MIMO
systems with reasonable power consumption. First, we investigate the
effectiveness of mixed-ADC architectures in overcoming the channel estimation
error caused by coarse quantization. For the channel estimation phase, we study
to what extent one can combat the SE loss by exploiting just N << M pairs of
high-resolution ADCs. We extend the round-robin training scheme for mixed-ADC
systems to include both high-resolution and one-bit quantized observations.
Then, we analyze the impact of the resulting channel estimation error in the
data detection phase. We consider random high-resolution ADC assignment and
also analyze a simple antenna selection scheme to increase the SE. Analytical
expressions are derived for the SE for maximum ratio combining (MRC) and
numerical results are presented for zero-forcing (ZF) detection. Performance
comparisons are made against systems with uniform ADC resolution and against
mixed-ADC systems without round-robin training to illustrate under what
conditions each approach provides the greatest benefit.Comment: To appear in IEEE Transactions on Signal Processin
A Comparison of Hybrid Beamforming and Digital Beamforming with Low-Resolution ADCs for Multiple Users and Imperfect CSI
For 5G it will be important to leverage the available millimeter wave
spectrum. To achieve an approximately omni- directional coverage with a similar
effective antenna aperture compared to state of the art cellular systems, an
antenna array is required at both the mobile and basestation. Due to the large
bandwidth and inefficient amplifiers available in CMOS for mmWave, the analog
front-end of the receiver with a large number of antennas becomes especially
power hungry. Two main solutions exist to reduce the power consumption: hybrid
beam forming and digital beam forming with low resolution Analog to Digital
Converters (ADCs). In this work we compare the spectral and energy efficiency
of both systems under practical system constraints. We consider the effects of
channel estimation, transmitter impairments and multiple simultaneous users.
Our power consumption model considers components reported in literature at 60
GHz. In contrast to many other works we also consider the correlation of the
quantization error, and generalize the modeling of it to non-uniform quantizers
and different quantizers at each antenna. The result shows that as the SNR gets
larger the ADC resolution achieving the optimal energy efficiency gets also
larger. The energy efficiency peaks for 5 bit resolution at high SNR, since due
to other limiting factors the achievable rate almost saturates at this
resolution. We also show that in the multi-user scenario digital beamforming is
in any case more energy efficient than hybrid beamforming. In addition we show
that if different ADC resolutions are used we can achieve any desired
trade-offs between power consumption and rate close to those achieved with only
one ADC resolution.Comment: Submitted to JSTSP. arXiv admin note: text overlap with
arXiv:1610.0290
On the Effect of Mutual Coupling in One-Bit Spatial Sigma-Delta Massive MIMO Systems
The one-bit spatial Sigma-Delta concept has recently been proposed as an
approach for achieving low distortion and low power consumption for massive
multi-input multi-output systems. The approach exploits users located in known
angular sectors or spatial oversampling to shape the quantization noise away
from desired directions of arrival. While reducing the antenna spacing
alleviates the adverse impact of quantization noise, it can potentially
deteriorate the performance of the massive array due to excessive mutual
coupling. In this paper, we analyze the impact of mutual coupling on the uplink
spectral efficiency of a spatial one-bit Sigma-Delta massive MIMO architecture,
and compare the resulting performance degradation to standard one-bit
quantization as well as the ideal case with infinite precision. Our simulations
show that the one-bit Sigma-Delta array is particularly advantageous in
space-constrained scenarios, can still provide significant gains even in the
presence of mutual coupling when the antennas are closely spaced.Comment: Presented in SPAWC 202
Comparison of environmental health status in primary schools in different districts of Isfahan city in 2008-2009
Introduction. Students spend at least 20% of their time in schools. Training, educating and the personality of these students depends on appropriate educational methods, proper physical space, and also favorable mental environment. Students are considered as a major human resources of any society and dealing with their health and promoting educational environment health is in fact a kind of investment for future. In this study we examined the status of environmental health status in primary school of different districts of Isfahan.
Materials and methods. This study was a descriptive-analytical study. The number of studied samples was 77 schools in Isfahan which were selected by regular randomized method. The tool used to gather data was a environmental health inquiry form for school environments, and consisted of two parts: the first part included common school specifications and the second part involved items dealing with desirability of various parts of schools.The above forms were filled
out in 3 months by specialists in public health, evaluating the schools and interviewing the principals. Then, they were analyzed and a comparison was made between the results from various districts.
Results. 76.6% of schools complied with the standards and 80.5% of classrooms were in desired conditions. Regarding the standards for building and classrooms, there was no significant difference between various districts. Hygiene services (water closets and basin) and drinking water were at desired level and there was no significant difference between various districts in this regard, however the district 1 was in undesired condition. Regarding collecting and disposing of rubbishes and trashes, 79% of schools were in desired condition and 49% of them had hygienic tuck-shops according to standards, but there was no significant difference between various districts.
Conclusion. The study showed that the status of environment health is at desired level in primary schools in Isfahan, but the health of tuck-shops should improve in schools and it needs more
attention and interest from authorities of Ministry of Education and Ministry of Health and dedicating proper budgets to solve their health problems
CFD Assessment of Aerodynamic Degradation of a Subsonic Transport Due to Airframe Damage
A computational study is presented to assess the utility of two NASA unstructured Navier-Stokes flow solvers for capturing the degradation in static stability and aerodynamic performance of a NASA General Transport Model (GTM) due to airframe damage. The approach is to correlate computational results with a substantial subset of experimental data for the GTM undergoing progressive losses to the wing, vertical tail, and horizontal tail components. The ultimate goal is to advance the probability of inserting computational data into the creation of advanced flight simulation models of damaged subsonic aircraft in order to improve pilot training. Results presented in this paper demonstrate good correlations with slope-derived quantities, such as pitch static margin and static directional stability, and incremental rolling moment due to wing damage. This study further demonstrates that high fidelity Navier-Stokes flow solvers could augment flight simulation models with additional aerodynamic data for various airframe damage scenarios
Towards Full Aircraft Airframe Noise Prediction: Detached Eddy Simulations
Results from a computational study on the aeroacoustic characteristics of an 18%-scale, semi-span Gulf-stream aircraft model are presented in this paper. NASA's FUN3D unstructured compressible Navier-Stokes solver was used to perform steady and unsteady simulations of the flow field associated with this high-fidelity aircraft model. Solutions were obtained for free-air at a Mach number of 0.2 with the flap deflected at 39 deg, with the main gear off and on (the two baseline configurations). Initially, the study focused on accurately predicting the prominent noise sources at both flap tips for the baseline configuration with deployed flap only. Building upon the experience gained from this initial effort, subsequent work involved the full landing configuration with both flap and main landing gear deployed. For the unsteady computations, we capitalized on the Detached Eddy Simulation capability of FUN3D to capture the complex time-dependent flow features associated with the flap and main gear. To resolve the noise sources over a broad frequency range, the tailored grid was very dense near the flap inboard and outboard tips and the region surrounding the gear. Extensive comparison of the computed steady and unsteady surface pressures with wind tunnel measurements showed good agreement for the global aerodynamic characteristics and the local flow field at the flap inboard tip. However, the computed pressure coefficients indicated that a zone of separated flow that forms in the vicinity of the outboard tip is larger in extent along the flap span and chord than measurements suggest. Computed farfield acoustic characteristics from a FW-H integral approach that used the simulated pressures on the model solid surface were in excellent agreement with corresponding measurements
Plasmonic nickel nanoantennas
7 páginas, 6 figuras.-- El pdf del artículo es la versión post-print.-- et al.The fundamental optical properties of pure nickel nanostructures are studied by far-field extinction spectroscopy and optical near-field microscopy, providing direct experimental evidence of the existence of particle plasmon resonances predicted by theory. Experimental and calculated near-field maps allow for unambiguous identification of dipolar plasmon modes. By comparing calculated near-field and far-field spectra, dramatic shifts are found between the near-field and far-field plasmon resonances, which are much stronger than in gold nanoantennas. Based on a simple damped harmonic oscillator model to describe plasmonic resonances, it is possible to explain these shifts as due to plasmon damping.Supported by the European FP7 project ‘Nanoantenna’ (FP7-HEALTH-F5-2009-241818-NANOANTENNA) and the National Project MAT2009 –08398 from the Spanish Ministerio de Ciencia
e Innovacion. J.A. acknowledges fi nancial help by the Department of Industry of the Basque Government through the ETORTEK program NANOPHOT. P.V. acknowledges funding from the Basque Government under Programs No. PI2009–17 as well as the Spanish Ministry of Science and Education under Project No. MAT2009–07980. Z. P. acknowledges support from Swedish Foundation for
Strategic Research through RMA08–0109 “Functional Electromagnetic Metamaterials” program. J. N. acknowledges funding from the Generalitat de Catalunya and the Spanish Ministry of Science
and Education through No. 2009-SGR-1292 and No. MAT2010–20616-C02 projects. A.D. acknowledges support from the Swedish Research Council.Peer reviewe
Construction hazard prevention: The need to integrate process knowledge into product design
Social network analysis was used to model information exchange networks in construction case studies in the United States of America and Australia/New Zealand. For each case, the quality of work safety and health (WHS) risk control outcomes was measured. This measurement was based on an established "hierarchy of control" in which risk controls are classified in descending order of effectiveness. The construction contractors' degree centrality was examined as a proxy measure of the constructors' influence in decision making during the pre-construction stages of the project. Network metrics were compared for cases in which the risk control scores were higher and lower than average. The results showed a significant difference in constructors' degree centrality for cases with high and low risk control efficacy scores. Constructors had significantly higher degree centrality in cases with high compared to low quality OSH risk control outcomes. The results provide preliminary evidence that integrating construction process knowledge into pre-construction decision-making produces better OSH outcomes. The research also highlights the potential usefulness of social network analysis and network metrics in OSH performance measurement and benchmarking
The role of porcine reproductive and respiratory syndrome (PRRS) virus structural and non-structural proteins in virus pathogenesis
Porcine reproductive and respiratory syndrome (PRRS) is an economically devastating viral
disease affecting the swine industry worldwide. The etiological agent, PRRS virus (PRRSV),
possesses a RNA viral genome with nine open reading frames (ORFs). The ORF1a and ORF1b
replicase-associated genes encode the polyproteins pp1a and pp1ab, respectively. The pp1a is
processed in nine non-structural proteins (nsps): nsp1a, nsp1b, and nsp2 to nsp8. Proteolytic
cleavage of pp1ab generates products nsp9 to nsp12. The proteolytic pp1a cleavage products
process and cleave pp1a and pp1ab into nsp products. The nsp9 to nsp12 are involved in virus
genome transcription and replication. The 30 end of the viral genome encodes four minor
and three major structural proteins. The GP2a, GP3 and GP4 (encoded by ORF2a, 3 and 4), are
glycosylated membrane associated minor structural proteins. The fourth minor structural
protein, the E protein (encoded by ORF2b), is an unglycosylated membrane associated protein.
The viral envelope contains two major structural proteins: a glycosylated major envelope
protein GP5 (encoded by ORF5) and an unglycosylated membrane M protein (encoded by
ORF6). The third major structural protein is the nucleocapsid N protein (encoded by ORF7). All
PRRSV non-structural and structural proteins are essential for virus replication, and PRRSV
infectivity is relatively intolerant to subtle changes within the structural proteins. PRRSV
virulence is multigenic and resides in both the non-structural and structural viral proteins. This
review discusses the molecular characteristics, biological and immunological functions of the
PRRSV structural and nsps and their involvement in the virus pathogenesis
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