36 research outputs found
Bidirectional User Throughput Maximization Based on Feedback Reduction in LiFi Networks
Channel adaptive signalling, which is based on feedback, can result in almost
any performance metric enhancement. Unlike the radio frequency (RF) channel,
the optical wireless communications (OWCs) channel is fairly static. This
feature enables a potential improvement of the bidirectional user throughput by
reducing the amount of feedback. Light-Fidelity (LiFi) is a subset of OWCs, and
it is a bidirectional, high-speed and fully networked wireless communication
technology where visible light and infrared are used in downlink and uplink
respectively. In this paper, two techniques for reducing the amount of feedback
in LiFi cellular networks are proposed, i) Limited-content feedback (LCF)
scheme based on reducing the content of feedback information and ii)
Limited-frequency feedback (LFF) based on the update interval scheme that lets
the receiver to transmit feedback information after some data frames
transmission. Furthermore, based on the random waypoint (RWP) mobility model,
the optimum update interval which provides maximum bidirectional user equipment
(UE) throughput, has been derived. Results show that the proposed schemes can
achieve better average overall throughput compared to the benchmark one-bit
feedback and full-feedback mechanisms.Comment: 30 pages, 9 figures, submitted to IEEE Transactions on Communication
Analysis of random orientation and user mobility in LiFi networks
Mobile data traffic is anticipated to surpass 49 exabyte per month by 2021. Smartphones, as
the main factor of generating this huge data traffic (86%), are expected to require average speed
connection of 20 Mbps by 2021. Light-fidelity (LiFi) is a novel bidirectional, high-speed and
fully networked optical wireless communication and it is a promising solution to undertake
this huge data traffic. However, to support seamless connectivity in LiFi networks, real-time
knowledge of channel state information (CSI) from each user is required at the LiFi access point
(AP). The CSI availability enables us to achieve optimal resource allocation and throughput
maximization but it requires feedback transmitted through the uplink channel. Furthermore,
the important aspects of the indoor LiFi channel such as the random orientation of user device,
user mobility and link blockage need to be carefully analysed and effective solutions should be
developed.
In contrast to radio frequency (RF) channels, the LiFi channel is relatively less random. This feature
of LiFi channel enables a potential reduction in the amount of feedback required to achieve
high throughputs in a dynamic LiFi network. Based on this feature, two techniques for reducing
the amount of feedback in LiFi cellular networks are proposed: 1) limited-content feedback
scheme based on reducing the content of feedback information and 2) limited-frequency feedback
scheme based on the update interval. It is shown that these limited-feedback schemes can
provide almost the same downlink performance as full feedback scheme. Furthermore, an optimum
update interval which provides maximum bidirectional user equipment (UE) throughput,
has been derived.
Device orientation and its statistics is an important determinant factor that can affect the users
throughput remarkably in LiFi networks. However, device orientation has been ignored in many
previous performance studies of LiFi networks due to the lack of a proper statistical model. In
this thesis, a novel model for the orientation of user device are proposed based on experimental
measurements. The statistics of the device orientation for both sitting and walking activities are
presented. Moreover, the statistics of the line-of-sight (LOS) channel gain are calculated. The
influence of random device orientation on the received signal-to-noise-ratio (SNR) and bit-error
ratio (BER) performance of LiFi systems has been also evaluated.
To support the seamless connectivity of future LiFi-enabled devices in the presence of random
device orientation, mobility and blockage, efficient handover between APs are required. In this
thesis, an orientation-based random waypoint (ORWP) mobility model is proposed to analyze
the performance of mobile users considering the effect of random device orientation. Based on
this model, an analysis of handover due to random orientation and user mobility is presented.
Finally, in order to improve seamless connectivity, a multi-directional receiver (MDR) configuration
is proposed. The MDR configuration shows a robust performance in the presence of user
mobility, random device orientation and blockage
Impact of Device Orientation on Error Performance of LiFi Systems
Most studies on optical wireless communications (OWCs) have neglected the
effect of random orientation in their performance analysis due to the lack of a
proper model for the random orientation. Our recent empirical-based research
illustrates that the random orientation follows a Laplace distribution for a
static user equipment (UE). In this paper, we analyze the device orientation
and assess its importance on system performance. The reliability of an OWC
channel highly depends on the availability and alignment of line-of-sight (LOS)
links. In this study, the effect of receiver orientation including both polar
and azimuth angles on the LOS channel gain are analyzed. The probability of
establishing a LOS link is investigated and the probability density function
(PDF) of signal-to-noise ratio (SNR) for a randomly-oriented device is derived.
By means of the PDF of SNR, the bit-error ratio (BER) of DC-biased optical
orthogonal frequency division multiplexing (DCO-OFDM) in additive white
Gaussian noise (AWGN) channels is evaluated. A closed-form approximation for
the BER of UE with random orientation is presented which shows a good match
with Monte-Carlo simulation results. Furthermore, the impact of the UE's random
motion on the BER performance has been assessed. Finally, the effect of random
orientation on the average signal-to-interference-plus-noise ratio (SINR) in a
multiple access points (APs) scenario is investigated.Comment: 10 pages, 11 figures, journa
Multi-Hop Wireless Optical Backhauling for LiFi Attocell Networks: Bandwidth Scheduling and Power Control
The backhaul of hundreds of light fidelity (LiFi) base stations (BSs)
constitutes a major challenge. Indoor wireless optical backhauling is a novel
approach whereby the interconnections between adjacent LiFi BSs are provided by
way of directed line-of-sight (LOS) wireless infrared (IR) links. Building on
the aforesaid approach, this paper presents the top-down design of a multi-hop
wireless backhaul configuration for multi-tier optical attocell networks by
proposing the novel idea of super cells. Such cells incorporate multiple
clusters of attocells that are connected to the core network via a single
gateway based on multi-hop decode-and-forward (DF) relaying. Consequently, new
challenges arise for managing the bandwidth and power resources of the
bottleneck backhaul. By putting forward user-based bandwidth scheduling (UBS)
and cell-based bandwidth scheduling (CBS) policies, the system-level modeling
and analysis of the end-to-end multi-user sum rate is elaborated. In addition,
optimal bandwidth scheduling under both UBS and CBS policies are formulated as
constrained convex optimization problems, which are solved by using the
projected subgradient method. Furthermore, the transmission power of the
backhaul system is opportunistically reduced by way of an innovative fixed
power control (FPC) strategy. The notion of backhaul bottleneck occurrence
(BBO) is introduced. An accurate approximate expression of the probability of
BBO is derived, and then verified using Monte Carlo simulations. Several
insights are provided into the offered gains of the proposed schemes through
extensive computer simulations, by studying different aspects of the
performance of super cells including the average sum rate, the BBO probability
and the backhaul power efficiency (PE).Comment: 36 pages, 21 figures, 1 tabl
Li-Fi technology-based long-range FSO data transmit system evaluation
Visible light is used by a technology known as Light Fidelity to establish wireless internet connections very quickly. This article offers line-of-sight communication between the transmitter and receiver using LED technology. Li-Fi technology is a method that transmits data using LED light, which is faster and more efficient than Wi-Fi. Since it is practically ubiquitous, light can be used for communication as well. A cutting-edge technology called optical communication includes a subset called Li-Fi. By sending out visible light, the Li-Fi device enables wireless intranet communication. An in-depth study and analysis of Li-Fi, a novel technology that transmits data at high speeds over a wide spectrum by using light as a medium of transmission
Physical Layer Security for Visible Light Communication Systems:A Survey
Due to the dramatic increase in high data rate services and in order to meet
the demands of the fifth-generation (5G) networks, researchers from both
academia and industry are exploring advanced transmission techniques, new
network architectures and new frequency spectrum such as the visible light
spectra. Visible light communication (VLC) particularly is an emerging
technology that has been introduced as a promising solution for 5G and beyond.
Although VLC systems are more immune against interference and less susceptible
to security vulnerabilities since light does not penetrate through walls,
security issues arise naturally in VLC channels due to their open and
broadcasting nature, compared to fiber-optic systems. In addition, since VLC is
considered to be an enabling technology for 5G, and security is one of the 5G
fundamental requirements, security issues should be carefully addressed and
resolved in the VLC context. On the other hand, due to the success of physical
layer security (PLS) in improving the security of radio-frequency (RF) wireless
networks, extending such PLS techniques to VLC systems has been of great
interest. Only two survey papers on security in VLC have been published in the
literature. However, a comparative and unified survey on PLS for VLC from
information theoretic and signal processing point of views is still missing.
This paper covers almost all aspects of PLS for VLC, including different
channel models, input distributions, network configurations,
precoding/signaling strategies, and secrecy capacity and information rates.
Furthermore, we propose a number of timely and open research directions for
PLS-VLC systems, including the application of measurement-based indoor and
outdoor channel models, incorporating user mobility and device orientation into
the channel model, and combining VLC and RF systems to realize the potential of
such technologies