1,039 research outputs found
Designing Power-Efficient Modulation Formats for Noncoherent Optical Systems
We optimize modulation formats for the additive white Gaussian noise channel
with a nonnegative input constraint, also known as the intensity-modulated
direct detection channel, with and without confining them to a lattice
structure. Our optimization criteria are the average electrical and optical
power. The nonnegativity input signal constraint is translated into a conical
constraint in signal space, and modulation formats are designed by sphere
packing inside this cone. Some remarkably dense packings are found, which yield
more power-efficient modulation formats than previously known. For example, at
a spectral efficiency of 1 bit/s/Hz, the obtained modulation format offers a
0.86 dB average electrical power gain and 0.43 dB average optical power gain
over the previously best known modulation formats to achieve a symbol error
rate of 10^-6. This modulation turns out to have a lattice-based structure. At
a spectral efficiency of 3/2 bits/s/Hz and to achieve a symbol error rate of
10^-6, the modulation format obtained for optimizing the average electrical
power offers a 0.58 dB average electrical power gain over the best
lattice-based modulation and 2.55 dB gain over the best previously known
format. However, the modulation format optimized for average optical power
offers a 0.46 dB average optical power gain over the best lattice-based
modulation and 1.35 dB gain over the best previously known format.Comment: Submitted to Globecom 201
Application of Expurgated PPM to Indoor Visible Light Communications - Part I: Single-User Systems
Visible light communications (VLC) in indoor environments suffer from the
limited bandwidth of LEDs as well as from the inter-symbol interference (ISI)
imposed by multipath. In this work, transmission schemes to improve the
performance of indoor optical wireless communication (OWC) systems are
introduced. Expurgated pulse-position modulation (EPPM) is proposed for this
application since it can provide a wide range of peak to average power ratios
(PAPR) needed for dimming of the indoor illumination. A correlation decoder
used at the receiver is shown to be optimal for indoor VLC systems, which are
shot noise and background-light limited. Interleaving applied on EPPM in order
to decrease the ISI effect in dispersive VLC channels can significantly
decrease the error probability. The proposed interleaving technique makes EPPM
a better modulation option compared to PPM for VLC systems or any other
dispersive OWC system. An overlapped EPPM pulse technique is proposed to
increase the transmission rate when bandwidth-limited white LEDs are used as
sources.Comment: Journal of Lightwave Technolog
High-Speed Visible Light Indoor Networks Based on Optical Orthogonal Codes and Combinatorial Designs
Interconnecting devices in an indoor environment using the illumination
system and white light emitting diodes (LED) requires adaptive networking
techniques that can provide network access for multiple users. Two techniques
based on multilevel signaling and optical orthogonal codes (OOC) are explored
in this paper in order to provide simultaneous multiple access in an indoor
multiuser network. Balanced incomplete block designs (BIBD) are used to
construct multilevel symbols for M-ary signaling. Using these multilevel
symbols we are able to control the optical peak to average power ratio (PAPR)
in the system, and hereby control the dimming level. In the first technique,
the M-ary data of each user is first encoded using the OOC codeword that is
assigned to that user, and then it is fed into a BIBD encoder to generate a
multilevel signal. The second multiple access method uses sub-sets of a BIBD
code to apply multilevel expurgated pulse-position modulation (MEPPM) to the
data of each user. While the first approach has a larger Hamming distance
between the symbols of each user, the latter can provide higher bit-rates for
users in VLC systems with bandwidth-limited LEDs
Power efficient subcarrier modulation for intensity modulated channels
We compare formats for optical intensity modulation limited by thermal noise with the assumption of having ideal devices. At the same bitrate and bandwidth, a hitherto unknown format turns out to be more power efficient than known formats. This new modulation, which is a hybrid between on-off keying and phase-shift keying, belongs to the subcarrier modulation family. At asymptotically high signal-to-noise ratios, this hybrid scheme has a 1.2 dB average electrical power gain and 0.6 dB average optical power gain compared to OOK, while it has a 3.0 dB average electrical power gain and 2.1 dB average optical power gain compared to subcarrier QPSK
Simulation and modeling of the behavior in the four-stroke spark ignition engine by using CFD simulation
Computational fluid dynamics (CFD) is a branch of fluid mechanics that use numerical analysis and data structures to analyze and solves problems that involve fluid flows. CFD have been applied to a wide range of research and engineering problems in many fields of study and industries, including engine and combustion analysis. The objective of this review paper is to analyze the behavior in the four-stroke Spark Ignition (SI) engine by using CFD simulation. To get the require result a few methods have been used to analyze the behavior in the engine such as using CAD geometric model where the solid works software have been prepared. Then, in the CAD geometric model also have ANSYS software to perform analysis in engine module. To predict the behavior of the engine during its working two type of analysis can be performed namely port flow simulation and combustion simulation. So, in first part of this report, the CFD analysis is carried out to analyze the performance parameter, including intake stroke, compression stroke, power stroke and exhaust stroke with hexane fuel combustion. For the results, some details of the engine model and some predicted results including temperature, flow time and pressure profiles. With the existence of CFD simulation it can help many fields of study and industries by predict and analyze the possibility that can be happened in the future. At the same time, serves as a quick and economical way of future engine designs and concepts
Experimental comparison of modulation formats in IM/DD links
We present an experimental comparison of modulation formats
for optical intensity modulated links with direct detection. Specifically, we
compare OOK, QPSK on an electrical subcarrier and a new modulation
format named OOPSK. The OOPSK modulation format is shown to have
better sensitivity than the other modulation formats, in agreement with
theoretical predictions. The impact of propagation in multimode fiber is
also studied and the results show that all modulation formats have similar
sensitivity penalties, with respect to the fibre length
Adaptive modulation schemes for optical wireless communication systems
High-speed wireless optical communication links have become more popular for
personal mobile applications. This is a consequence of the increasing demand
from the personal information service boom. Compared to the radio frequency
domain, optical wireless communication offers much higher speeds and bit rates
per unit power consumption. As stated by the official infrared standard IrDA
optical communication enjoys much lower power consumption than Bluetooth,
with an inherent security feature while in Line of Sight (LOS) applications. There
are also drawbacks such as the infrared radiation cannot penetrate walls as radio
frequencies do and interference from the background contribute to the channel
dispersions.
Focus on the modulation aspects of the optical wireless communication, this
thesis try to improve the channel immunity by utilising optimised modulation to
the channel. Modulation schemes such as on off keying (OOK), pulse amplitude
modulation (PAM) and pulse position modulation (PPM) and pulse position and
amplitude modulation PAPM schemes have been validated. The combined power
and bandwidth requirements suggest that the adaptive modulation schemes can
provide reliability when deployed in a real time channel, resulting in improved
system performance.
As a result, an adaptive modulation technique is proposed. Extensive simulations
of severe noise distraction have been carried out to validate the new scheme. The
simulation results indicate that the new scheme can provide increased immunity
against channel noise fluctuation at a relatively low complexity. The scheme
obtained formed a basis to support reliable mobile optical wireless
communication applications.
The adaptive scheme also takes the real time channel conditions into account,
which is different from existing schemes. Guaranteed system performance can be
secured without compromising power and bandwidth efficiency. This is also a
new approach to realise reliable optical wireless links. Fuzzy logic control
module has been developed to match the adaptive pattern
Building resilient future: information technology and disaster management - a Malaysian perspective
The recent evets of flooding, earthquakes, uncontrolled wildfires, hurricanes, and deadly storms in world has considered a serious threat to mankind and preparing for devastating disasters has never been more critical and urgent. Emergency Events Database suggests that by year 2050 the damages to flood related incidents to coastal cities will cost near to US$1 trillion. Risk from acts of nature cannot be fully prevented but needs to minimize and safe the innocent lives and property by utilizing disaster management technique to mitigate the losses. This paper presents Information Technologies applications in disaster management phases such as Mitigation, Preparedness, Response and Recovery. Geographic Information System, Remote Sensing, mobile technology, drone, and satellite imagery and MOBILISE analytic platform considered as effective and efficient ways of strengthening resilience when disaster strikes and tremendously helpful for coordinating responses and accelerating the recovery of individuals and communities in the aftermath of recent natural disasters
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