235 research outputs found
Design of a Cognitive VLC Network with Illumination and Handover Requirements
In this paper, we consider a cognitive indoor visible light communications
(VLC) system, comprised of multiple access points serving primary and secondary
users through the orthogonal frequency division multiple access method. A
cognitive lighting cell is divided into two non-overlapping regions that
distinguish the primary and secondary users based on the region they are
located in. Under the assumption of equal-power allocation among subcarriers,
each region is defined in terms of its physical area and the number of
allocated subcarriers within that region. In this paper, we provide the
lighting cell design with cognitive constraints that guarantee fulfilling
certain illumination, user mobility, and handover requirements in each cell. We
further argue that, under some conditions, a careful assignment of the
subcarriers in each region can mitigate the co-channel interference in the
overlapping areas of adjacent cells. Numerical results depict the influence of
different system parameters, such as user density, on defining both regions.
Finally, a realistic example is implemented to assess the performance of the
proposed scheme via Monte Carlo simulations
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
Handover Management through Reconfigurable Intelligent Surfaces for VLC under Blockage Conditions
In this paper, we consider an indoor visible light communication (VLC) system
with multiple "white" light emitting diodes serving to form overlapping
wireless communication cells. In order to maintain seamless connectivity to
mobile users, a handover procedure should be implemented. In particular,
practical conditions such as blockages due to obstacles inside the room
environment and the mobility of users can affect direct VLC connectivity. The
use of reconfigurable intelligent surfaces (RISs) in optical wireless systems
allows to exploit non-direct connectivity links, thus providing efficient
communication links. In this paper, we present a proactive handover mechanism
that exploits the presence of a RIS, in order to redirect the communication
links in case of blockages. The proposed approach has been implemented both in
hard and soft modes and assessed in terms of achievable data rate and handover
latency for a user walking in a given reference room at different user speeds
and blockage conditions. Our presented results and comparisons with
conventional handover methods (i.e., without RIS) are helpful in showing the
superiority of the presented algorithm.Comment: This paper has been accepted to be presented as an invited paper at
the 2024 IEEE International Symposium on Circuits and Systems (ISCAS 2024)
conference. ISCAS 2024 will be held in Singapore from 19-22 May 202
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
Flight: A Flexible Light Communications network architecture for indoor environments
Recent experimental works have demonstrated the feasibility of the visible light based vehicular communications (VVLC) in intelligent transportation systems (ITS). However, in many respects, this technology is in its infancy and requires further research efforts in several areas. This work presents a flexible network architecture named flexible light (Flight), which is designed for VLC to tackle existing mobility challenges in the network environment. Flight proposes a low-latency handover system that decreases the handover delays to a few tens and hundreds of milliseconds. By means of experiments, we emulate and evaluate indoor mobile network scenarios using only VLC technology
Multi-user visible light communications: State-of-the-art and future directions
Visible light communications (VLC) builds upon the dual use of existing lighting infrastructure for wireless data transmission. VLC has recently gained interest as cost-effective, secure, and energy-efficient wireless access technology particularly for indoor user-dense environments. While initial studies in this area are mainly limited to single-user point-to-point links, more recent efforts have focused on multi-user VLC systems in an effort to transform VLC into a scalable and fully networked wireless technology. In this paper, we provide a comprehensive overview of multi-user VLC systems discussing the recent advances on multi-user precoding, multiple access, resource allocation, and mobility management. We further provide possible directions for future research in this emerging topic.King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia ; TÜBİTAKPublisher versio
3G migration in Pakistan
The telecommunication industry in Pakistan has come a long way since the country\u27s independence in 1947. The initial era could be fairly termed as the PTCL (Pakistan Telecommunication Company Limited) monopoly, for it was the sole provider of all telecommunication services across the country. It was not until four decades later that the region embarked into the new world of wireless communication, hence ending the decades old PTCL monopoly. By the end of the late 1990\u27s, government support and international investment in the region opened new doors to innovation and better quality, low cost, healthy competition. Wireless licenses for the private sector in the telecommunication industry triggered a promising chain of events that resulted in a drastic change in the telecommunication infrastructure and service profile. The newly introduced wireless (GSM) technology received enormous support from all stakeholders (consumers, regulatory body, and market) and caused a vital boost in Pakistan\u27s economy. Numerous tangential elements had triggered this vital move in the history of telecommunications in Pakistan. Entrepreneurs intended to test the idea of global joint ventures in the East and hence the idea of international business became a reality. The technology had proven to be a great success in the West, while Pakistan\u27s telecom consumer had lived under the shadow of PTCL dominance for decades and needed more flexibility. At last the world was moving from wired to wireless! Analysts termed this move as the beginning of a new era. The investors, telecommunication businesses, and Pakistani treasury prospered. It was a win-win situation for all involved. The learning curve was steep for both operators and consumers but certainly improved over time. In essence, the principle of deploying the right technology in the right market at the right time led to this remarkable success. The industry today stands on the brink of a similar crossroads via transition from second generation to something beyond. With the partial success of 3G in Europe and the USA, the government has announced the release of three 3G licenses by mid 2009. This decision is not yet fully supported by all but still initiated parallel efforts by the operators and the vendors to integrate this next move into their existing infrastructure
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