328 research outputs found
Hologram selection in realistic indoor optical wireless systems with angle diversity receivers
In this paper, we introduce a new adaptive optical wireless system that employs a finite vocabulary of stored holograms. We propose a fast delay, angle, and power adaptive holograms (FDAPA-Holograms) approach based on a divide and conquer (DandC) methodology and evaluate it with angle diversity receivers in a mobile optical wireless system. The ultimate goal is to increase the signal-to-noise ratio (SNR), reduce the effect of intersymbol interference, and eliminate the need to calculate the hologram at each transmitter and receiver location. A significant improvement is achieved in the presence of demanding background illumination noise, receiver noise, multipath propagation, mobility, and shadowing typical in a realistic indoor environment. The combination of beam delay, angle, and power adaptation offers additional degrees of freedom in the link design, resulting in a system that is able to achieve higher data rates (5 Gb/s). At a higher data rate of 5 Gb/s and under eye safety regulations, the proposed FDAPA-Holograms system offers around 13 dB SNR with full mobility in a realistic environment where shadowing exists. The fast search algorithm introduced that is based on a D&C algorithm reduces the computation time required to identify the optimum hologram. Simulation results show that the proposed system, FDAPA-Holograms, can reduce the time required to identify the optimum hologram position from 64 ms taken by a classic adaptive hologram to about 14 ms
Wavelet transform - artificial neural network receiver with adaptive equalisation for a diffuse indoor optical wireless OOK link
This paper presents an alternative approach for signal detection and equalization using the continuous wavelet transform (CWT) and the artificial neural network (ANN) in diffuse indoor optical wireless links (OWL). The wavelet analysis is used for signal preprocessing (feature extraction) and the ANN for signal detection. Traditional receiver architectures based on matched filter (MF) experience significant performance degradation in the presence of artificial light interference (ALI) and multipath induced intersymbol interference (ISI). The proposed receiver structure reduces the effect of ALI and ISI by selecting a particular scale of CWT that corresponds to the desired signal and classifying the signal into binary 1 and 0 based on an observation vector. By selecting particular scales corresponding to the signal, the effect of ALI is reduced. We show that there is little variation when using 30 and 5 neurons in the first layer, with one layer ANN model showing a consistently worse BER performance than other models, whilst the 15 neuron model show some behaviour anomalies from a BER of approximately 10-3. The simulation results show that the Wavelet-ANN architecture outperforms the traditional MF based receiver even with the filter is matched to the ISI affected pulse shape. The Wavelet-ANN receiver is also capable of providing a bit error rate (BER) performance comparable to the equalized forms of traditional receiver structure
Optical Wireless Data Center Networks
Bandwidth and computation-intensive Big Data applications in disciplines like social media, bio- and nano-informatics, Internet-of-Things (IoT), and real-time analytics, are pushing existing access and core (backbone) networks as well as Data Center Networks (DCNs) to their limits. Next generation DCNs must support continuously increasing network traffic while satisfying minimum performance requirements of latency, reliability, flexibility and scalability. Therefore, a larger number of cables (i.e., copper-cables and fiber optics) may be required in conventional wired DCNs. In addition to limiting the possible topologies, large number of cables may result into design and development problems related to wire ducting and maintenance, heat dissipation, and power consumption.
To address the cabling complexity in wired DCNs, we propose OWCells, a class of optical wireless cellular data center network architectures in which fixed line of sight (LOS) optical wireless communication (OWC) links are used to connect the racks arranged in regular polygonal topologies. We present the OWCell DCN architecture, develop its theoretical underpinnings, and investigate routing protocols and OWC transceiver design. To realize a fully wireless DCN, servers in racks must also be connected using OWC links. There is, however, a difficulty of connecting multiple adjacent network components, such as servers in a rack, using point-to-point LOS links. To overcome this problem, we propose and validate the feasibility of an FSO-Bus to connect multiple adjacent network components using NLOS point-to-point OWC links. Finally, to complete the design of the OWC transceiver, we develop a new class of strictly and rearrangeably non-blocking multicast optical switches in which multicast is performed efficiently at the physical optical (lower) layer rather than upper layers (e.g., application layer).
Advisors: Jitender S. Deogun and Dennis R. Alexande
MIMO MC-CDMA systems over indoor optical wireless communication channels
Optical wireless communication systems offer a number of advantages over their radio frequency counterparts. The advantages include freedom from fading, freedom from spectrum regulations and abundant bandwidth. The main limitations of optical wireless systems include background noise attributed to natural and artificial light sources and multipath propagation. The former degrades the signal to noise ratio while the latter limits the maximum achievable data rate. This thesis investigates the use of transmit power adaptation in the design of optical wireless spot-diffusing systems to increase the power associated with the main impulse response components, resulting in a compact impulse response and a system that is able to achieve higher data rates. The work also investigates the use of imaging diversity receivers that can reject the background noise components received in directions not associated with the signal. The two techniques help improve the optical wireless system performance. The multibeam transmitter and the multi-detector angle diversity receiver or imaging receiver form a multiple input multiple output (MIMO) system. The work also investigates additional methods that can improve the performance such as transmitter beam angle adaptation, and improved modulation and coding in the form of multi-carrier code division multiple access (MC-CDMA). Furthermore, the work investigates the robustness of a link design that adopts the combination of these methods in a realistic environment with full mobility.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Adaptation techniques in optical wireless communications
The need for high-speed local area networks to meet the recent developments
in multimedia and video transmission applications has recently focused interest
on optical wireless communication. Optical wireless systems boast some
advantages over radio frequency (RF) systems, including a large unregulated
spectrum, freedom from fading, confidentiality and immunity against
interference from electrical devices. They can satisfy the dual need for mobility
and broadband networking. However, optical wireless links are not without
flaws. They are affected by background noise (artificial and natural light
sources) and suffer from multipath dispersion. The former can degrade the
signal-to-noise ratio, while the latter restricts the maximum transmission rate
available.
The aim of this thesis is to investigate a number of techniques to overcome
these drawbacks and design a robust high-speed indoor optical wireless system
with full mobility. Beam delay and power adaptation in a multi-spot diffusing
system is proposed in order to increase the received optical signal, reduce the
delay spread and enable the system to operate at higher data rates. The thesis
proposes employing angle diversity receivers and imaging diversity receivers as
in order to reduce background noise components. Moreover, the work
introduces and designs a high-speed fully adaptive optical wireless system that
employs beam delay, angle and power adaptation in a multi-spot diffusing
configuration and investigates the robustness of the link design in a realistic
indoor office. Furthermore, a new adaptive optical wireless system based on a
finite vocabulary of stored holograms is introduced. This method can effectively
optimise the spots’ locations and reduce the design complexity of an adaptive
optical wireless system. A fast adaptation approach based on a divide-andconquer
methodology is proposed and integrated with the system to reduce the
time required to identify the optimum hologram. The trade-off between complexity and performance enhancement of the adaptive finite holograms
methods compared with the original beam power and angle adaptation is
investigated
A review of communication-oriented optical wireless systems
This article presents an overview of optical wireless (OW) communication systems that operate both in the short-
(personal and indoor systems) and the long-range (outdoor and hybrid) regimes. Each of these areas is discussed
in terms of (a) key requirements, (b) their application framework, (c) major impairments and applicable mitigation
techniques, and (d) current and/or future trends. Personal communication systems are discussed within the context
of point-to-point ultra-high speed data transfer. The most relevant application framework and related standards are
presented, including the next generation Giga-IR standard that extends personal communication speeds to over 1
Gb/s. As far as indoor systems are concerned, emphasis is given on modeling the dispersive nature of indoor OW
channels, on the limitations that dispersion imposes on user mobility and dispersion mitigation techniques. Visible
light communication systems, which provide both illumination and communication over visible or hybrid visible/
infrared LEDs, are presented as the most important representative of future indoor OW systems. The discussion on
outdoor systems focuses on the impact of atmospheric effects on the optical channel and associated mitigation
techniques that extend the realizable link lengths and transfer rates. Currently, outdoor OW is commercially
available at 10 Gb/s Ethernet speeds for Metro networks and Local-Area-Network interconnections and speeds are
expected to increase as faster and more reliable optical components become available. This article concludes with
hybrid optical wireless/radio-frequency (OW/RF) systems that employ an additional RF link to improve the overall
system reliability. Emphasis is given on cooperation techniques between the reliable RF subsystem and the
broadband OW system
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