172 research outputs found
A Mixed-ADC Receiver Architecture for Massive MIMO Systems
Motivated by the demand for energy-efficient communication solutions in the
next generation cellular network, a mixed-ADC receiver architecture for massive
multiple input multiple output (MIMO) systems is proposed, which differs from
previous works in that herein one-bit analog-to-digital converters (ADCs)
partially replace the conventionally assumed high-resolution ADCs. The
information-theoretic tool of generalized mutual information (GMI) is exploited
to analyze the achievable data rates of the proposed system architecture and an
array of analytical results of engineering interest are obtained. For
deterministic single input multiple output (SIMO) channels, a closed-form
expression of the GMI is derived, based on which the linear combiner is
optimized. Then, the asymptotic behaviors of the GMI in both low and high SNR
regimes are explored, and the analytical results suggest a plausible ADC
assignment scheme. Finally, the analytical framework is applied to the
multi-user access scenario, and the corresponding numerical results demonstrate
that the mixed system architecture with a relatively small number of
high-resolution ADCs is able to achieve a large fraction of the channel
capacity without output quantization.Comment: 5 pages, 5 figures, to appear in IEEE Information Theory Workshop
(ITW2015
Analyzing user reviews of messaging Apps for competitive analysis
Dissertation presented as the partial requirement for obtaining a Master's degree in Data Science and Advanced Analytics, specialization in Data ScienceThe rise of various messaging apps has resulted in intensively fierce competition, and the era of Web 2.0 enables business managers to gain competitive intelligence from user-generated content (UGC). Text-mining UGC for competitive intelligence has been drawing great interest of researchers. However, relevant studies mostly focus on industries such as hospitality and products, and few studies applied such techniques to effectively perform competitive analysis for messaging apps. Here, we conducted a competitive analysis based on topic modeling and sentiment analysis by text-mining 27,479 user reviews of four iOS messaging apps, namely Messenger, WhatsApp, Signal and Telegram. The results show that the performance of topic modeling and sentiment analysis is encouraging, and that a combination of the extracted app aspect-based topics and the adjusted sentiment scores can effectively reveal meaningful competitive insights into user concerns, competitive strengths and weaknesses as well as changes of user sentiments over time. We anticipate that this study will not only advance the existing literature on competitive analysis using text mining techniques for messaging apps but also help existing players and new entrants in the market to sharpen their competitive edge by better understanding their user needs and the industry trends
The investigation of electromagnetic radial force and associated vibration in permanent magnet synchronous machines
The rising public awareness of climate change and urban air pollution has been one
of the key drivers for transport electrification. Such trend drastically accelerates the
quest for high-power-and-torque-density electric drive systems. The rare-earth permanent
magnet synchronous machine, with its excellent steady-state and dynamic
characteristics, has been the ideal candidate for these applications. Specifically, the
fractional-slot and concentrated-winding configuration is widely adopted due to its
distinctive merits such as short end winding, low torque pulsation, and high efficiency.
The vibration and the associated acoustic noise become one of the main
parasitic issues of high-performance permanent magnet synchronous drives. These
undesirable features mainly arise from mechanical connection failure, imperfect assembly,
torque pulsation, and electromagnetic radial and axial force density waves.
The high-power-and-torque-density requirement will only be ultimately fulfilled by
the reduction of both electromagnetic active material and passive support structure.
This results in inflated electromagnetic force density inside the electric machine.
Besides, the sti.ness of the machine parts can be compromised and the resultant
natural frequencies are significantly brought down. Therefore, the vibration and
acoustic noise that are associated with the electromagnetic radial and axial force
density waves become a burden for large deployment of these drives.
This study is mainly dedicated to the investigation of the electromagnetic radial
forced density and its associated vibration and acoustic noise in radial-flux permanent
magnet synchronous machines. These machines are usually powered by voltage
source inverter with pulse width modulation techniques and various control strategies.
Consequently, the vibration problem not only lies on the permanent magnet
synchronous machine but also highly relates to its drive and controller. Generally,
the electromagnetic radial force density and its relevant vibration can be divided
into low-frequency and high-frequency components based on their origins. The
low-frequency electromagnetic radial force density waves stem from the magnetic
field components by the permanent magnets and armature reaction of fundamental
and phase-belt current harmonic components, while the high-frequency ones are
introduced by the interactions between the main low-frequency and sideband highfrequency
magnetic field components.
Both permanent magnets and armature reaction current are the main sources of
magnetic field in electric machines. Various drive-level modeling techniques are first reviewed, explored, and developed to evaluate the current harmonic components
of the permanent magnet synchronous machine drive. Meanwhile, a simple
yet e.ective analytical model is derived to promptly estimate the sideband current
harmonic components in the drive with both sinusoidal and space-vector pulse
width modulation techniques. An improved analytical method is also proposed to
predict the magnetic field from permanent magnets in interior permanent magnet
synchronous machines. Moreover, a universal permeance model is analytically developed
to obtain the corresponding armature-reaction magnetic field components.
With the permanent magnet and armature-reaction magnetic field components, the
main electromagnetic radial force density components can be identified and estimated
based on Maxwell stress tensor theory.
The stator tooth structure has large impacts on both electromagnetic radial force
density components and mechanical vibration behaviors. The stator tooth modulation
e.ect has been comprehensively demonstrated and explained by both finite
element analysis and experimental results. Analytical models of such e.ect are developed
for prompt evaluation and insightful revelation. Based on the proposed
models, multi-physics approaches are proposed to accurately predict low-frequency
and high-frequency electromagnetic radial vibration. Such method is quite versatile
and applicable for both integral-slot and fractional-slot concentrated-winding
permanent magnet synchronous machines. Comprehensive experimental results are
provided to underpin the validity of the proposed models and methods.
This study commences on the derivations of the drive parameters such as torque angle,
modulation index, and current harmonic components from circuit perspective
and further progresses to evaluate and decouple the air-gap magnetic field components
from field perspective. It carries on to dwell on the analytical estimations of
the main critical electromagnetic radial force density components and stator tooth
modulation e.ect. Based on the stator mechanical structure, the corresponding electromagnetic
radial vibration and acoustic noise can be accurately predicted. Various
analytical models have been developed throughout this study to provide a systematic
tool for quick and e.ective investigation of electromagnetic radial force density,
the associated vibration and acoustic noise in permanent magnet synchronous machine
drive. They have all been rigorously validated by finite element analysis and
experimental results. Besides, this study reveals not only a universal approach for
electromagnetic radial vibration analysis but also insightful correlations from both
machine and drive perspectives
An Improved Sideband Current Harmonic Model of Interior PMSM Drive by Considering Magnetic Saturation and Cross-Coupling Effects
The sideband current harmonics, as parasitic characteristics in permanent-magnet synchronous machine (PMSM) drives with space vector pulsewidth modulation technique, will increase the corresponding electromagnetic loss, torque ripple, vibration, and acoustic noises. Therefore, fast yet accurate evaluation of the resultant sideband current harmonic components is of particular importance during the design stage of the drive system. However, the inevitable magnetic saturation and cross-coupling effects in interior PMSM drives would have a significant impact on the current components, while the existing analytical sideband current harmonic model neglects those effects. This paper introduces a significant improvement on the analytical model by taking into account these effects with corresponding nonlinear factors. Experimental results are carried out to underpin the accuracy improvements of the predictions from the proposed model over the existing analytical one. The proposed model can offer a very detailed and insightful revelation of impacts of the magnetic saturation and cross-coupling effects on the corresponding sideband current harmonics
Analytical investigation of sideband electromagnetic vibration in integral-slot PMSM drive with SVPWM technique
This paper provides a comprehensive investigation
into the electromagnetic vibration associated with the sideband
harmonic components introduced by space vector pulse
width modulation applied in integral-slot permanent magnet
synchronous machine drives. The critical permanent magnet,
armature reaction, and sideband magnetic field components,
which are the primary causes for sideband electromagnetic
vibration in integral-slot permanent magnet synchronous machines,
are identified. The analytical derivations of the magnetic
field components are carried out, and amplitudes and
frequencies of the resultant sideband radial electromagnetic force
components are obtained. Furthermore, the proposed models
of the sideband radial electromagnetic force components are
incorporated into the vibration model to analytically evaluate
the corresponding sideband electromagnetic vibrations of the
machine. Experimental tests on an integral-slot permanent magnet
synchronous machine drive are comprehensively performed
to confirm the validity and accuracy of the analytical models.
Not only can the validated analytical models offer insightful
details in understanding the impacts of the key factors, such
as operation conditions, machine geometry, electromagnetic and
power converter parameters, on the sideband electromagnetic
vibration, but also can be readily extended to assess and reduce
noise in integral-slot permanent magnet synchronous machine drives
An Uplink Interference Analysis for Massive MIMO Systems with MRC and ZF Receivers
This paper considers an uplink cellular system, in which each base station
(BS) is equipped with a large number of antennas to serve multiple
single-antenna user equipments (UEs) simultaneously. Uplink training with pilot
reusing is adopted to acquire the channel state information (CSI) and maximum
ratio combining (MRC) or zero forcing (ZF) reception is used for handling
multiuser interference. Leveraging stochastic geometry to model the spatial
distribution of UEs, we analyze the statistical distributions of the
interferences experienced by a typical uplink: intra-cell interference,
inter-cell interference and interference due to pilot contamination.
For a practical but still large number of BS antennas, a key observation for
MRC reception is that it is the intra-cell interference that accounts for the
dominant portion of the total interference. In addition, the interference due
to pilot contamination tends to have a much wider distribution range than the
inter-cell interference when shadowing is strong, although their mean powers
are roughly equal. For ZF reception, on the other hand, we observe a
significant reduction of the intra-cell interference compared to MRC reception,
while the inter-cell interference and the interference due to pilot
contamination remains almost the same, thus demonstrating a substantial
superiority over MRC reception.Comment: 7 pages, 4 figures, accepted by IEEE Wireless Communications and
Networking Conference (WCNC) 201
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