37 research outputs found
Code Design for Visible Light Communications Under Illumination Constraints
Visible light communication (VLC) uses the same LEDs which are an efficient source of illumination
to transmit information concurrently using optical direct-detection. As a result of modulating
the LED to convey information, there may be a perceived change in the light perception
which besides being annoying, may produce physiological consequences under prolonged exposure.
The aim of this research is to propose code design methodologies for controlling the effects
of light intensity flickering, brightness control, and color shifts due to the modulation, encoding
information bits in organized optical symbol sequences, and improving the coding gain by the use
of the Viterbi algorithm.
In order to mitigate the effect of intensity flickering presented in On-Off Keying modulation,
five codes are designed with two proposed algorithms using finite-state machines (FSMs) for constraining
the runs of zeros or ones. The codes are compared with the codes proposed in the IEEE
802.15.7 standard on VLC (Manchester code, 4B6B code, and the 8B10B code) in terms of flicker
mitigation using the perceived flicker index (PFI) (a mathematical measure of flicker introduced in
this study) and error-rate performance. The designed codes show asymptotic coding gains between
1:25 and 6 dB with a low sacrifice in PFI.
To avoid color shifts in color-shift keying (CSK) modulation, four codes were designed from
optimally CSK constellations and two classes of codes where one class is based on FSMs and
the other on trellis-coded modulation (TCM) according to the desired color perception constraint.
The designed codes show asymptotic coding gains between 1:5 to 3:5 dB with respect to uncoded
transmission.
For brightness control, variable-weight multipulse pulse-position modulation (VW-MPPM) is
introduced as an alternative for increasing the spectral efficiency by the selection of multipulse
pulse-position modulation symbols of diverse weight to attain the desired dimming level. Combining
VM-MPPM symbols with Huffman codes and TCM, two designed codes are compared with
MPPM codes for dimming level of 0:67 and 0:40 showing an asymptotic coding gain of 0:94 and
1:29 dB, respectively.
Finally, we show the trade-offs between coding gain improvement and their effects on light
perception
Heterogeneous integration of optical wireless communications within next generation networks
Unprecedented traffic growth is expected in future wireless networks and new
technologies will be needed to satisfy demand. Optical wireless (OW) communication offers vast unused spectrum and high area spectral efficiency. In this work, optical
cells are envisioned as supplementary access points within heterogeneous RF/OW networks. These networks opportunistically offload traffic to optical cells while utilizing
the RF cell for highly mobile devices and devices that lack a reliable OW connection.
Visible light communication (VLC) is considered as a potential OW technology due
to the increasing adoption of solid state lighting for indoor illumination.
Results of this work focus on a full system view of RF/OW HetNets with three primary areas of analysis. First, the need for network densication beyond current RF
small cell implementations is evaluated. A media independent model is developed
and results are presented that provide motivation for the adoption of hyper dense
small cells as complementary components within multi-tier networks. Next, the relationships between RF and OW constraints and link characterization parameters are
evaluated in order to define methods for fair comparison when user-centric channel
selection criteria are used. RF and OW noise and interference characterization techniques are compared and common OW characterization models are demonstrated
to show errors in excess of 100x when dominant interferers are present. Finally,
dynamic characteristics of hyper dense OW networks are investigated in order to optimize traffic distribution from a network-centric perspective. A Kalman Filter model
is presented to predict device motion for improved channel selection and a novel OW
range expansion technique is presented that dynamically alters coverage regions of
OW cells by 50%.
In addition to analytical results, the dissertation describes two tools that have
been created for evaluation of RF/OW HetNets. A communication and lighting
simulation toolkit has been developed for modeling and evaluation of environments
with VLC-enabled luminaires. The toolkit enhances an iterative site based impulse
response simulator model to utilize GPU acceleration and achieves 10x speedup over
the previous model. A software defined testbed for OW has also been proposed
and applied. The testbed implements a VLC link and a heterogeneous RF/VLC
connection that demonstrates the RF/OW HetNet concept as proof of concept
Efficient Bayesian inference for harmonic models via adaptive posterior factorization
NOTICE: this is the author’s version of a work that was accepted for publication in Neurocomputing. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in NEUROCOMPUTING, [VOL72, ISSUE 1-3, (2008)] DOI10.1016/j.neucom.2007.12.05
Investigation and Implementation of Dicode Pulse Position Modulation Over Indoor Visible Light Communication System
A visible light communication (VLC) system with green technology is available and enables users to use white LEDs for illumination as well as for high data rate transmission over wireless optical links. In addition, LEDs have advantages of low power consumption, high speed with power efficiency and low cost. Therefore, a great deal of research is considered for indoor VLC, as it offers huge bandwidth whilst using a significant modulation technique.
This thesis is concerned with the investigation and implementation of the dicode pulse position modulation (DiPPM) scheme over a VLC link using white LED sources. Novel work is carried out for applying DiPPM over a VLC channel theoretically and experimentally including a comparison with digital PPM (DPPM) in order to examine the system performance. Moreover, a proposal of variable DiPPM (VDiPPM) is presented in this thesis for dimming control.
The indoor VLC channel characteristics have been investigated for two propagation prototypes. Two models have been proposed and developed with DiPPM and DPPM being applied over the VLC channel. A computer simulation for the proposed models for both DiPPM and DPPM systems is performed in order to analyse the receiver sensitivity with the effect of intersymbol interference (ISI). Both systems are operating at 100 Mbps and 1 Gbps for a BER of 10-9. An improvement in sensitivity being achieved by the DiPPM compared to the DPPM VLC system. The system performance has been carried out by Mathcad software. The predicted DiPPM receiver sensitivity outperforms DPPM receiver at by -5.55 dBm and -8.24 dBm, at 1 Gbps data rate, and by -5.53 dBm and -8.22 dBm, at 100 Mbps, without and with guard intervals, respectively. In both cases the optical receiver sensitivity is increased when the ISI is ignored. These results based on the received optical power required by each modulation scheme.
Further work has been done in mathematical evaluation carried out to calculate the optical receiver sensitivity to verify the comparison between the two systems. The original numerical results show that DiPPM VLC system provides a better sensitivity than a DPPM VLC system at a selected BER of 10-9 when referred to the same preamplifier at wavelength of 650 nm and based on the equivalent input noise current generated by the optical front end receiver. The results show that the predicted sensitivity for DPPM is greater than that of DPPM by about 1 dBm when both systems operating at 100 Mbps and 1 Gbps. Also, it is show that the receiver sensitivity is increased when the ISI is limited.
Experimentally, a complete indoor VLC system has been designed and implemented using Quartus II 11.1 software for generating VHDL codes and using FPGA development board (Cyclone IV GX) as main interface real-time transmission unit in this system. The white LEDs chip based transmitter and optical receiver have been constructed and tested. The measurements are performed by using LED white light as an optical transmitter faced to photodiode optical receiver on desk. Due to the LED bandwidth limitation the achieved operating data rate, using high speed LED driver, is 5.5 Mbps at BER of 10-7. The original results for the measurements determined that the average photodiode current produced by using DiPPM and DPPM optical receivers are 8.50 μA and 10.22 μA, respectively. And this in turn indicates that the DiPPM receiver can give a better sensitivity of -17.24 dBm while compared to the DPPM receiver which gives is -16.44 dBm.
The original practical results proved the simulation and theoretical results where higher performance is achieved when a DiPPM scheme is used compared to DPPM scheme over an indoor VLC system
Mobile Ad-Hoc Networks
Being infrastructure-less and without central administration control, wireless ad-hoc networking is playing a more and more important role in extending the coverage of traditional wireless infrastructure (cellular networks, wireless LAN, etc). This book includes state-of-the-art techniques and solutions for wireless ad-hoc networks. It focuses on the following topics in ad-hoc networks: quality-of-service and video communication, routing protocol and cross-layer design. A few interesting problems about security and delay-tolerant networks are also discussed. This book is targeted to provide network engineers and researchers with design guidelines for large scale wireless ad hoc networks
Optical wireless data transfer for rotor detection and diagnostics
A special application of optical wireless data transfer, namely on-line monitoring
and diagnostic of rotors in turbines and engines, has been considered in this thesis. In
this application, to maintain line of sight, i.e. data transfer, between a sensor placed on a
rotating component inside the turbine and a monitoring point placed in a fixed position
outside the turbine, a periodic fast fading channel is generated, which gives the
transceivers more flexibility regarding their mounting location. The communication in
such a channel is affected by the intermittency and variation of the signal power, which
produces a unique channel condition that influences the performance of the optical
transceiver.
To investigate the channel condition and the error rate of the periodic fast fading
channel with signal fluctuation, a model is developed to simulate the optical channel by
considering the variation of signal power as a result of the change in the relative
position of the photodiode with respect to the Lambertian radiation pattern of the LED,
in a simplified linear geometry. The error rate is estimated using the Saddlepoint
approximation on a specific threshold strategy. The results show that the channel can
afford the sensor data transmission and the performance can be improved by modifying
several parameters, such as geometrical distance, transmitter power and load resistor.
Compared to a normal channel, a higher load resistor on the photodiode front end has
the advantage of decreasing the noise level and increasing the data capacity in the fast
fading channel. The analysis of the automatic gain control amplifier indicates that a
higher load resistor needs a lower loop gain and from the model of the Transimpedance
amplifier (TIA), the bandwidth extension from the amplifier is more significant for a
higher resistor.
In addition to the theoretical model, an experimental setup is built to emulate the
channel in practice. The degree of similarity between the experimental setup and the
theoretical model of the channel is estimated from the comparison of the generated communication windows. Since it has been found that differences exist in the duration
of the communication window and the variation of the signal power, scaling factors to
ensure their compatibility have been derived. Transceiver hardware which
implemented the modelled functionality has been developed and a protocol to
establish the communication with the required error rate has been proposed. Using the
hardware implementation, a detection method for both rising and falling edges of the
signal pulses and a threshold strategy have been demonstrated. The device power
consumption is also estimated.
What is more, the electromagnetic environment of a squirrel cage motor is
simulated using the finite element method to investigate the interference and the
possibility of providing power to the IR communication devices using power
scavenging.
In the conclusion, the key findings of the thesis are summarised. A solution is
proposed for sensor data transfer using an optical channel for rotor monitoring
applications, which involves the design of the IR transceiver, the implementation of
the developed protocol and the power consumption estimation