129 research outputs found
New expressions on the performance of a novel multi-hop relay-assisted hybrid FSO / RF communication system with receive diversity
In this paper a novel multi-hop relay-assisted hybrid Free Space Optical /
Radio Frequency (FSO / RF) communication system is presented, in which a mobile
user is connected to the Base Station via a multi-hop relay-assisted hybrid FSO
/ RF link with receive diversity. In this structure, received signal at each
relay is demodulated and forwarded. This is the first time that in a multi-hop
hybrid FSO / RF system, receive diversity is used. Bit Error Rate (BER) and
Outage Probability (P_out) are investigated as system performance criteria. New
exact and asymptotic expressions are derived for these criteria, and MATLAB
simulations are provided to verify the obtained results. For the first time
impact of number of receive antennas and number of relays on the performance of
such a structure is investigated. Results indicate that proposed structure has
low dependence on number of receive antennas; therefore, in the proposed
structure use of single receive antenna has the same performance as the
multi-antenna, while low complexity and power consumption. The proposed
structure shows independent performance at moderate and strong atmospheric
turbulence regimes. Hence, it does not require adaptive processing to match
itself according to atmospheric turbulence condition, therefore is cost
effective and particularly suitable for urban areas that encounter frequent
changes in atmospheric turbulence.Comment: arXiv admin note: text overlap with arXiv:1806.02597,
arXiv:1806.0226
Performance analysis of a novel hybrid FSO / RF communication system
In this paper, a novel dual-hop relay-assisted hybrid Free Space Optical /
Radio Frequency (FSO / RF) communication system is presented. In this structure
an access point connects users within the building to the Base Station via a
hybrid parallel FSO / RF link, this link is proposed firstly. Parallel
combination of FSO and RF links and use of an access point, will increase
capacity, reliability and data rate of the system. It is the first time that
the effect of number of users on the performance of a dual-hop relay-assisted
hybrid parallel FSO / RF system is investigated. FSO link is considered in
Gamma-Gamma atmospheric turbulence with the effect of pointing error and RF
link is considered in Rayleigh fading. For the first time, closed-form
expressions are derived for Bit Error Rate (BER) and Outage Probability (P_out)
of the proposed system. Derived expressions are verified through MATLAB
simulations. It is shown that the performance of the proposed system is almost
independent of atmospheric turbulence intensity, thereby when atmospheric
turbulence strengthens, low power consumption is required for maintenance of
the system performance. Hence the proposed structure is particularly suitable
for mobile communication systems in which a small mobile battery supplies
transmitter power. Also the proposed system performance of the system is
preferable even at low signal to noise ratio (SNR). Therefore, proposed
structure significantly reduces power consumption while maintaining performance
of the system.Comment: 8 pages, 5figue
Performance evaluation of a novel relay assisted hybrid FSO / RF communication system with receive diversity
One of the main problems in mobile communication systems is the degradation
of Radio Frequency (RF) connection when mobile user is far from base station.
One way to solve this problem is to increase the transmitter power, but the
mobile transmitter is not able to supply much power. Another way is to use a
relay; among relay schemes, amplify and forward is better for long range
communications. Amplify and forward relay is not affordable in terms of power
consumption and performance, because it consumes a lot of power inefficiently
and enhances the noise. Therefore, in other cases, except in the case of long
range links, other relay protocols, such as decode and forward, as well as
demodulate and forward, are preferable. In this paper, a novel multi-hop hybrid
Free Space Optical (FSO) / RF link is presented; it is made up of two main
parts. The first part establishes the connection between the mobile user and
source base station, and the second part establishes the connection between the
source and the destination base stations. In the first part, a mobile user
wants to connect to the source base station via a long range link; therefore, a
fixed gain amplify and forward relay with multiple receive antennas is used for
communication establishment. In the second part, the source and the destination
base stations are connected via a multi-hop hybrid parallel FSO / RF link with
demodulate and forward relaying. Considering the FSO link in Gamma-Gamma
atmospheric turbulence with the effect of pointing error in moderate to strong
regime and the Negative Exponential atmospheric turbulence in saturate regime,
and the RF link in Rayleigh fading, new closed form exact and asymptotic
expressions are derived for the Outage Probability and Bit Error Rate of the
proposed structure. Derived expressions are verified with MATLAB simulations
Ergodic Sum Rate Analysis of UAV-Based Relay Networks with Mixed RF-FSO Channels
Unmanned aerial vehicle (UAV)-based communications is a promising new
technology that can add a wide range of new capabilities to the current network
infrastructure. Given the flexibility, cost-efficiency, and convenient use of
UAVs, they can be deployed as temporary base stations (BSs) for on-demand
situations like BS overloading or natural disasters. In this work, a UAV-based
communication system with radio frequency (RF) access links to the mobile users
(MUs) and a free-space optical (FSO) backhaul link to the ground station (GS)
is considered. In particular, the RF and FSO channels in this network depend on
the UAV's positioning and (in)stability. The relative position of the UAV with
respect to the MUs impacts the likelihood of a line-of-sight (LOS) connection
in the RF link and the instability of the hovering UAV affects the quality of
the FSO channel. Thus, taking these effects into account, we analyze the
end-to-end system performance of networks employing UAVs as buffer-aided (BA)
and non-buffer-aided (non-BA) relays in terms of the ergodic sum rate.
Simulation results validate the accuracy of the proposed analytical derivations
and reveal the benefits of buffering for compensation of the random
fluctuations caused by the UAV's instability. Our simulations also show that
the ergodic sum rate of both BA and non-BA UAV-based relays can be enhanced
considerably by optimizing the positioning of the UAV. We further study the
impact of the MU density and the weather conditions on the end-to-end system
performance
Resource Allocation for Mixed RF and Hybrid RF/FSO Relaying
In this paper, we consider a mixed RF and hybrid RF/FSO system where several
mobile users transmit their data over an RF link to a relay node (e.g. a small
cell base station) and the relay forwards the information to a destination
(e.g. a macro cell base station) over a hybrid RF/FSO backhaul link. The relay
and the destination employ multiple antennas for transmission and reception
over the RF links while each mobile user has a single antenna. The RF links are
full-duplex with respect to the FSO link and half-duplex with respect to each
other, i.e., either the user-relay RF link or the relay-destination RF link is
active. For this communication setup, we derive the optimal resource allocation
policy for sharing the RF bandwidth resource between the RF links. Our
numerical results show the effectiveness of the proposed communication
architecture and resource allocation policy, and their superiority compared to
existing schemes which employ only one type of backhaul link
Optical Communication in Space: Challenges and Mitigation Techniques
In recent years, free space optical communication has gained significant
importance owing to its unique features: large bandwidth, license-free
spectrum, high data rate, easy and quick deployability, less power and low mass
requirements. FSO communication uses the optical carrier in the near infrared
band to establish either terrestrial links within the Earth's atmosphere or
inter-satellite or deep space links or ground-to-satellite or
satellite-to-ground links. However, despite the great potential of FSO
communication, its performance is limited by the adverse effects viz.,
absorption, scattering, and turbulence of the atmospheric channel. This paper
presents a comprehensive survey on various challenges faced by FSO
communication system for ground-to-satellite or satellite-to-ground and
inter-satellite links. It also provides details of various performance
mitigation techniques in order to have high link availability and reliability.
The first part of the paper will focus on various types of impairments that
pose a serious challenge to the performance of optical communication system for
ground-to-satellite or satellite-to-ground and inter-satellite links. The
latter part of the paper will provide the reader with an exhaustive review of
various techniques both at physical layer as well as at the other layers i.e.,
link, network or transport layer to combat the adverse effects of the
atmosphere. It also uniquely presents a recently developed technique using
orbital angular momentum for utilizing the high capacity advantage of the
optical carrier in case of space-based and near-Earth optical communication
links. This survey provides the reader with comprehensive details on the use of
space-based optical backhaul links in order to provide high-capacity and
low-cost backhaul solutions.Comment: 41 pages, 13 Figures and 8 Tables. arXiv admin note: substantial text
overlap with arXiv:1506.0483
Aeronautical Ad Hoc Networking for the Internet-Above-The-Clouds
The engineering vision of relying on the ``smart sky" for supporting air
traffic and the ``Internet above the clouds" for in-flight entertainment has
become imperative for the future aircraft industry. Aeronautical ad hoc
Networking (AANET) constitutes a compelling concept for providing broadband
communications above clouds by extending the coverage of Air-to-Ground (A2G)
networks to oceanic and remote airspace via autonomous and self-configured
wireless networking amongst commercial passenger airplanes. The AANET concept
may be viewed as a new member of the family of Mobile ad hoc Networks (MANETs)
in action above the clouds. However, AANETs have more dynamic topologies,
larger and more variable geographical network size, stricter security
requirements and more hostile transmission conditions. These specific
characteristics lead to more grave challenges in aircraft mobility modeling,
aeronautical channel modeling and interference mitigation as well as in network
scheduling and routing. This paper provides an overview of AANET solutions by
characterizing the associated scenarios, requirements and challenges.
Explicitly, the research addressing the key techniques of AANETs, such as their
mobility models, network scheduling and routing, security and interference are
reviewed. Furthermore, we also identify the remaining challenges associated
with developing AANETs and present their prospective solutions as well as open
issues. The design framework of AANETs and the key technical issues are
investigated along with some recent research results. Furthermore, a range of
performance metrics optimized in designing AANETs and a number of
representative multi-objective optimization algorithms are outlined
Free Space Optical Communication: Challenges and Mitigation Techniques
In recent years, free space optical (FSO) communication has gained
significant importance owing to its unique features: large bandwidth, license
free spectrum, high data rate, easy and quick deployability, less power and low
mass requirement. FSO communication uses optical carrier in the near infrared
(IR) and visible band to establish either terrestrial links within the Earths
atmosphere or inter-satellite or deep space links or ground to satellite or
satellite to ground links. However, despite of great potential of FSO
communication, its performance is limited by the adverse effects (viz.,
absorption, scattering and turbulence) of the atmospheric channel. Out of these
three effects, the atmospheric turbulence is a major challenge that may lead to
serious degradation in the bit error rate (BER) performance of the system and
make the communication link infeasible. This paper presents a comprehensive
survey on various challenges faced by FSO communication system for both
terrestrial and space links. It will provide details of various performance
mitigation techniques in order to have high link availability and reliability
of FSO system. The first part of the paper will focus on various types of
impairments that poses a serious challenge to the performance of FSO system for
both terrestrial and space links. The latter part of the paper will provide the
reader with an exhaustive review of various techniques used in FSO system both
at physical layer as well as at the upper layers (transport, network or link
layer) to combat the adverse effects of the atmosphere. Further, this survey
uniquely offers the current literature on FSO coding and modulation schemes
using various channel models and detection techniques. It also presents a
recently developed technique in FSO system using orbital angular momentum to
combat the effect of atmospheric turbulence.Comment: 28 pages, 13 figures and 8 table
A Contemporary Survey on Free Space Optical Communication: Potential, Technical Challenges, Recent Advances and Research Direction
Optical wireless communication (OWC) covering an ultra-wide range of
unlicensed spectrum has emerged as an extent efficient solution to mitigate
conventional RF spectrum scarcity ranging from communication distances from nm
to several kilometers. Free space optical (FSO) systems operating near IR (NIR)
band in OWC links has received substantial attention for enormous data
transmission between fixed transceivers covering few kilometers path distance
due to high optical bandwidth and higher bit rate as well. Despite the
potential benefits of FSO technology, its widespread link reliability suffers
especially in the long-range deployment due to atmospheric turbulence, cloud
induced fading, some other environmental factors such as fog, aerosol,
temperature variations, storms, heavy rain, cloud, pointing error, and
scintillation. FSO has the potential to offloading massive traffic demands from
RF networks, consequently the combined application of FSO/RF and radio over FSO
(RoFSO) systems is regarded as an excellent solution to support 5G and beyond
for improving the limitations of an individual system. This survey presents the
overview of several key technologies and implications of state-of-the-art
criteria in terms of spectrum reuse, classification, architecture and
applications are described for understanding FSO. This paper provides
principle, significance, demonstration, and recent technological development of
FSO technology among different appealing optical wireless technologies. The
opportunities in the near future, the potential challenges that need to be
addressed to realize the successful deployment of FSO schemes are outlined.Comment: 59 pages, 14 figure
Performance Analysis of Relay-Assisted OWC Over Foggy Channel with Pointing Error
Signal fading due to atmospheric channel impairments and pointing error is a
major bottleneck for the performance of optical wireless communication (OWC).
In this paper, we consider an amplify-and-forward (AF) optical relaying to
enhance the performance of the OWC system with a negligible line-of-sight (LOS)
link under the combined effect of fog and pointing error. We analyze the
end-to-end performance of the relay-assisted system, which consists of
complicated probability distribution functions. We derive analytical
expressions of the outage probability, average signal-to-noise ratio (SNR), and
ergodic rate in terms of OWC system parameters. We also develop an exact
integral-form expression of these performance metrics using the half-harmonic
mean of individual SNRs to validate the tightness of the derived analytical
expressions. The numerical and simulation analysis shows that the proposed
dual-hop relaying has significant performance improvement when comparing to the
direct transmission over considered channel impairments. Compared to the direct
transmission, the relay-assisted system requires almost times less
transmission power to achieve the same outage probability. The considered
system also provides a significant gain in the average SNR and ergodic rate for
practical scenarios of OWC deployment.Comment: 6 pages, 4 figure
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