162,283 research outputs found
Impact of VLC on Light Emission Quality of White LEDs
No full textData set for the published paper:
W. O. Popoola, "Impact of VLC on Light Emission Quality of White LEDs," in Journal of Lightwave Technology, vol. 34, no. 10, pp. 2526-2532, May15, 15 2016. doi: 10.1109/JLT.2016.254211
Data set for: 'Impact of VLC on Light Emission Quality of White LEDs', in Journal of Lightwave Technology, vol. 34, no. 10, pp. 2526-2532, May15, 15 2016
No full textData set for the published paper: W. O. Popoola, "Impact of VLC on Light Emission Quality of White LEDs," in Journal of Lightwave Technology, vol. 34, no. 10, pp. 2526-2532, May15, 15 2016. doi: 10.1109/JLT.2016.254211
Underwater optical wireless communication with subcarrier intensity modulation: an experimental demonstration
No full textThis paper presents an experimental study of an underwater optical wireless communications system (UOWC). The potential of UOWC and how it can operate alongside acoustic based communications in a hybrid system is outlined. The channel characteristics, in terms of the inherent optical properties of water, are described and the impact on data transmission assessed. We present data transmission with a blue laser diode using both on-off keying (OOK) and subcarrier intensity modulation (SIM). These modulation schemes are evaluated in both still and turbulent water, demonstrating the inherent resilience to turbulence of SIM as well as the impact of turbulence on signal transmission. We show a maximum data rate in the range of Gbps, showing the potential for high speed underwater communications links using UOWC
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Enhanced carrierless amplitude and phase modulation for optical communication systems
No full textThis thesis develops and investigates enhanced techniques for carrierless amplitude and phase
modulation (CAP) in optical communication systems. The CAP scheme is studied as the
physical layer modulation technique due to its implementation simplicity and versatility, that
enables its implementation as a single carrier (CAP) or multi-carrier technique (m-CAP).
The effect of timing jitter on the error performance of CAP is first investigated. The
investigation indicates that synchronization is a critical requirement for CAP receiver and as
a result, a novel low-complexity synchronization algorithm is developed with experimental
demonstration for CAP-based visible light communication (VLC) systems. To further reduce
the overall link complexity, a fractionally-spaced equalizer (FSE) is considered to mitigate the
effects of inter-symbol interference (ISI) and timing jitter. The FSE implementation, which
eliminates the need for a separate synchronization block, is shown through simulation and
VLC experimental demonstration to outperform symbol-spaced equalizers (SSE) that are
reported in literature for CAP-based VLC systems.
Furthermore, in this thesis, spectrally-efficient index modulation techniques are developed for
CAP. The proposed techniques can be divided into two broad groups, namely spatial index CAP
(S-CAP) and subband index CAP (SI-CAP). The proposed spatial index techniques leverage
the fact that in VLC, multiple optical sources are often required. The spatial CAP (S-CAP)
transmits CAP signal through one of Nt available LEDs. It is developed to reduce equalization
requirement and improve the spectral efficiency of the conventional CAP. In addition to the bits
transmitted through the CAP symbol, the S-CAP encodes additional bits on the indexing/spatial
location of the LEDs. The generalised S-CAP (GS-CAP) is further developed to relax the
S-CAP limitation of using a single LED per symbol duration. In addition to the S-CAP scheme,
multiple-input multiple-output (MIMO) techniques of repetitive-coded CAP (RC-CAP) and
spatial multiplexing CAP (SMux-CAP) are investigated for CAP. Low-complexity detectors
are also developed for the MIMO schemes. A key challenge of the MIMO schemes is that they
suffer power penalty when channel gains are similar, which occur when the optical sources are
closely located. The use of multiple receivers and power factor imbalance (PFI) techniques
are proposed to mitigate this power penalty. The techniques result in significant improvement
in the power efficiency of the MIMO schemes and ensure that the spectral efficiency gain is
obtained with little power penalty.
Finally, subband index CAP (SI-CAP) is developed to improve the spectral efficiency of
m-CAP and reduce its peak-to-average power ratio (PAPR). The SI-CAP encodes additional
information bits on the selection of ‘active’ subbands of m-CAP and only modulate data
symbols on these ‘active’ subbands. The error performance of the proposed SI-CAP is
evaluated analytically and verified with computer-based simulations. The SI-CAP technique is
also experimented for both VLC and step-index plastic optical fibre (SI-POF) communication
links. The experimental results show that for a fixed power efficiency, SI-CAP achieves higher
data rate compared tom-CAP. For example, at a representative bit error rate (BER) of 10-5, the
SI-CAP achieves a data rate and power efficiency gain of 26:5 Mb/s and 2:5 dB, respectively
when compared to m-CAP. In addition, an enhanced SI-CAP (eSI-CAP) is developed to
address the complexity that arises in SI-CAP at higher modulation order. The results of the
experimental demonstrations in VLC and 10 m SI-POF link shows that when compared with
m-CAP, eSI-CAP consistently yields a data rate improvement of between 7% and 13% for
varying values of the SNR
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Study of MIMO techniques for optical wireless communications
No full textWith its huge spectral resource, optical wireless communication (OWC) has emerged as a
promising complementary technology to the radio frequency (RF) communication systems.
OWC provides data communications for a variety of user applications and it can be deployed
using simple, low-cost, low-power and energy-efficient component. In order to enhance
capacity, reliability and/or coverage of OWC, multiple-input-multiple-output (MIMO) systems
are employed to exploit additional degrees of freedom, such as the location and angular
orientation of optical sources and detectors. However, the implementation of MIMO systems is
faced with challenges such as the strong correlation and multipath propagation in indoor OWC
channels, system synchronisation, as well as inter-channel interference (ICI) due to multiple
parallel data transmission. This dissertation investigates MIMO OWC systems which utilises
transmission techniques with reduced complexity. A detailed study and performance evaluation
of the techniques in terms of capacity, spectral efficiency and error rates is conducted through
theoretical analysis, simulation and experiments. The system performance is investigated
under different constraints imposed by impairments such as interference, synchronization and
channel correlation.
Optical spatial modulation (OSM) is studied as a low complexity technique using multiple
light sources to enhance system capacity. A generalised framework for implementing OSM
with energy efficient pulse position modulation scheme is devised. This framework supports
other variants of OSM, and it can be adapted to satisfy varying system requirement such
as spectral and energy efficiencies. The performance of the OWC system is investigated in
indoor line-of-sight (LOS) propagation. The error performance of the system is analysed
theoretically and matched by simulation results. Also, the system performance is evaluated
with experiments to demonstrate feasibility. Furthermore, the performance of OSM MIMO
techniques in the realistic indoor scenario is considered by taking into account the multiple
reflections of the transmitted signal from room surfaces. This is motivated by the recent drive
towards high-speed Gigabits per second (Gbps) data communication, where the inter-symbol
interference (ISI) caused by the multipath propagation may pose a major bottleneck. A model
of the multipath-induced ISI is presented to account for signal spreading and then applied to
formulate the error performance analysis. The impact of multipath-induced power penalty and
delay spread on system performance is demonstrated using their spatial distributions across the
coverage area. Additionally, the impact of timing synchronization problems on the error performance of
different variants of the OSM MIMO techniques is investigated. While most works related
to SM have assumed a perfect synchronization among the multiple transmitter and receiver
elements, such assumption pose a challenge in practical deployment. Hence, the need to
examine the impact of synchronisation error that can result from clock jitters and variations
in propagation delay. Synchronisation error analyses of OSM schemes are presented, and
the tolerance of each scheme to timing synchronization errors is demonstrated. To further
enhance system capacity, this thesis also explores spatial multiplexing MIMO technique with
orthogonal frequency division multiplexing (OFDM). The central objective is to propose and
apply techniques to address the correlation of the indoor optical wireless channel and the
frequency selectivity due to the limited bandwidth of LEDs. To address these two effects,
a joint coding of paired information symbols was applied in a technique termed pairwise
coding (PWC). This technique is based on rotated symbol constellation and it offers significant
performance improvement. The error performance of the proposed system is evaluated through
simulation and experimental demonstration. PWC proved to be effective over varying degrees
of bandwidth limitation and under different channel conditions
BPSK subcarrier intensity modulated free-space optical communications in atmospheric turbulence
No full textFree-space optical communications (FSO) propagated over a clear atmosphere suffers from irradiance fluctuation caused by small but random atmospheric temperature fluctuations. This results in decreased signal-to-noise ratio (SNR) and consequently impaired performance. In this paper, the error performance of the FSO using a subcarrier intensity modulation (SIM) based on a binary phase shift keying (BPSK) scheme in a clear but turbulent atmosphere is presented. To evaluate the system error performance in turbulence regimes from weak to strong, the probability density function (pdf) of the received irradiance after traversing the atmosphere is modelled using the gamma-gamma distribution while the negative exponential distribution is used to model turbulence in the saturation region and beyond. The effect of turbulence induced irradiance fluctuation is mitigated using spatial diversity at the receiver. With reference to the single photodetector case, up to 12 dB gain in the electrical SNR is predicted with two direct detection PIN photodetectors in strong atmospheric turbulence
Larry O. Spencer, Conference Author Presentation
No full textGen. Larry O. Spencer, USAF (Ret.), author of Dark Horse: A Journey from the Horseshoe to the Pentago
Using continuous quality improvement approach as an integral part of students academic achievement in Africa
No full textIn: Adegoke, B. A., Popoola, O., and Babatiunde, O. E. (eds.) Public Examining in Sub-Saharan Africa: Issues, Challenges and Prospects- A book of Readings in Honour of Emeritus Prof. 'Dibu Ojerinde, pp. 148-15
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