8 research outputs found
Towards the Internet of X-things: New Possibilities for Underwater, Underground, and Outer Space Exploration
The rapid growth of the world's population demands more natural resources,
food, and space. World-renowned physicist Stephan Hawking has argued that soon
we will require another world to live on because we are running out of space
and natural resources. This ever-increasing demand for resources and space
needs novel technologies to explore natural resources, produce more crops, and
explore outer space. Internet of X-things (X-IoT) is an enabling technology to
overcome all of the above issues. In this article, we have presented an
overview of a unified framework of X-IoT. The framework of X-IoT consists of
three major categories. The first one is the Internet of underwater things
(IoUT) for smart oceans. The second category is the Internet of underground
things (IoUGT) for smart agriculture, seismic monitoring, and Oil/Gas fields.
The third category is the Internet of space things (IoST) for outer space
exploration, to provide global coverage, and to enable inter-satellite
communications. Through this framework, we get to know what has been done since
recently and how the technical challenges across the broad spectrum of emerging
use cases under the water, underground and over the space are converging toward
future solutions.Comment: Accepted in IEEE ComSoc News (CTN
On Distributed Routing in Underwater Optical Wireless Sensor Networks
Underwater optical wireless communication (UOWC) is becoming an attractive
technology for underwater wireless sensor networks (UWSNs) since it offers
high-speed communication links. Although UOWC overcomes the drawbacks of
acoustic and radio frequency communication channels such as high latency and
low data rate, yet, it has its own limitations. One of the major limitations of
UOWC is its limited transmission range which demands to develop a multi-hop
network with efficient routing protocols. Currently, the routing protocols for
UOWSNs are centralized having high complexity and large end-to-end delay. In
this article, first, we present the existing routing protocols for UOWSNs.
Based on the existing protocols, we then propose distributed routing protocols
to address the problems of high complexity and large end-to-end delay.
Numerical results have been provided to show that the proposed routing protocol
is superior to the existing protocols in terms of complexity and end-to-end
delay. Finally, we have presented open research directions in UOWSNs.Comment: Submitted to IEEE Communications Magazin
End-to-End Performance Analysis of Underwater Optical Wireless Relaying and Routing Techniques Under Location Uncertainty
On the contrary of low speed and high delay acoustic systems, underwater
optical wireless communication (UOWC) can deliver a high speed and low latency
service at the expense of short communication ranges. Therefore, multihop
communication is of utmost importance to improve degree of connectivity and
overall performance of underwater optical wireless networks (UOWNs). In this
regard, this paper investigates relaying and routing techniques and provides
their end-to-end (E2E) performance analysis under the location uncertainty. To
achieve robust and reliable links, we first consider adaptive beamwidths and
derive the divergence angles under the absence and presence of a
pointing-acquisitioning-and-tracking (PAT) mechanism. Thereafter, important E2E
performance metrics (e.g., data rate, bit error rate, transmission power,
amplifier gain, etc.) are obtained for two potential relaying techniques;
decode & forward (DF) and optical amplify & forward (AF). We develop
centralized routing schemes for both relaying techniques to optimize E2E rate,
bit error rate, and power consumption. Alternatively, a distributed routing
protocol, namely Light Path Routing (LiPaR), is proposed by leveraging the
range-beamwidth tradeoff of UOWCs. LiPaR is especially shown to be favorable
when there is no PAT mechanism and available network information. In order to
show the benefits of multihop communications, extensive simulations are
conducted to compare different routing and relaying schemes under different
network parameters and underwater environments
Outlier Detection and Optimal Anchor Placement for 3D Underwater Optical Wireless Sensor Networks Localization
Location is one of the basic information required for underwater optical
wireless sensor networks (UOWSNs) for different purposes such as relating the
sensing measurements with precise sensor positions, enabling efficient
geographic routing techniques, and sustaining link connectivity between the
nodes. Even though various two-dimensional UOWSNs localization methods have
been proposed in the past, the directive nature of optical wireless
communications and three-dimensional (3D) deployment of sensors require to
develop 3D underwater localization methods. Additionally, the localization
accuracy of the network strongly depends on the placement of the anchors.
Therefore, we propose a robust 3D localization method for partially connected
UOWSNs which can accommodate the outliers and optimize the placement of the
anchors to improve the localization accuracy. The proposed method formulates
the problem of missing pairwise distances and outliers as an optimization
problem which is solved through half quadratic minimization. Furthermore,
analysis is provided to optimally place the anchors in the network which
improves the localization accuracy. The problem of optimal anchor placement is
formulated as a combination of Fisher information matrices for the sensor nodes
where the condition of D-optimality is satisfied. The numerical results
indicate that the proposed method outperforms the literature substantially in
the presence of outliers.Comment: 14 pages, 11 figures, Accepted for Publication in IEEE Transactions
on Communication
Opportunistic Routing for Opto-Acoustic Internet of Underwater Things
Internet of underwater things (IoUT) is a technological revolution that could
mark a new era for scientific, industrial, and military underwater
applications. To mitigate the hostile underwater channel characteristics, this
paper hybridizes underwater acoustic and optical wireless communications to
achieve a ubiquitous control and high-speed low-latency networking performance,
respectively. Since underwater optical wireless communications (UOWC) suffers
from limited range, it requires effective multi-hop routing solutions. In this
regard, we propose a Sector-based Opportunistic Routing (SectOR) protocol.
Unlike the traditional routing (TR) techniques which unicast packets to a
unique relay, opportunistic routing (OR) targets a set of candidate relays by
leveraging the broadcast nature of the UOWC channel. OR improves the packet
delivery ratio as the likelihood of having at least one successful packet
reception is much higher than that in conventional unicast routing. Contingent
upon the performance characterization of a single-hop link, we obtain a variety
of local and global metrics to evaluate the fitness of a candidate set (CS) and
prioritize the members of a CS. Since rate-error and range-beamwidth tradeoffs
yield different candidate set diversities, we develop a candidate filtering and
searching algorithm to find the optimal sector-shaped coverage region by
scanning the feasible search space. Moreover, a hybrid acoustic/optic
coordination mechanism is considered to avoid duplicate transmission of the
relays. Numerical results show that SectOR protocol can perform even better
than an optimal unicast routing protocol in well-connected UOWNs
Performance Analysis of Connectivity and Localization in Multi-Hop Underwater Optical Wireless Sensor Networks
Underwater optical wireless links have limited range and intermittent
connectivity due to the hostile aquatic channel impairments and misalignment
between the optical transceivers. Therefore, multi-hop communication can expand
the communication range, enhance network connectivity, and provide a more
precise network localization scheme. In this regard, this paper investigates
the connectivity of underwater optical wireless sensor networks (UOWSNs) and
its impacts on the network localization performance. Firstly, we model UOWSNs
as randomly scaled sector graphs where the connection between sensors is
established by point-to-point directed links. Thereafter, the probability of
network connectivity is analytically derived as a function of network density,
communication range, and optical transmitters' divergence angle. Secondly, the
network localization problem is formulated as an unconstrained optimization
problem and solved using the conjugate gradient technique. Numerical results
show that different network parameters such as the number of nodes, divergence
angle, and transmission range significantly influence the probability of a
connected network. Furthermore, the performance of the proposed localization
technique is compared to well-known network localization schemes and the
results show that the localization accuracy of the proposed technique
outperforms the literature in terms of network connectivity, ranging error, and
number of anchors.Comment: Paper accepted for publication in IEEE Transactions on Mobile
Computin
Performance Analysis of Dual-Hop Underwater Wireless Optical Communication Systems over Mixture Exponential-Generalized Gamma Turbulence Channels
In this work, we present a unified framework for the performance analysis of
dual-hop underwater wireless optical communication (UWOC) systems with
amplify-and-forward fixed gain relays in the presence of air bubbles and
temperature gradients. Operating under either heterodyne detection or intensity
modulation with direct detection, the UWOC is modeled by the unified mixture
Exponential-Generalized Gamma distribution that we have proposed based on an
experiment conducted in an indoor laboratory setup and has been shown to
provide an excellent fit with the measured data under the considered lab
channel scenarios. More specifically, we derive the cumulative distribution
function (CDF) and the probability density function of the end-to-end
signal-to-noise ratio (SNR) in exact closed-form in terms of the bivariate
Fox's H function. Based on this CDF expression, we present novel results for
the fundamental performance metrics such as the outage probability, the average
bit-error rate (BER) for various modulation schemes, and the ergodic capacity.
Additionally, very tight asymptotic results for the outage probability and the
average BER at high SNR are obtained in terms of simple functions. Furthermore,
we demonstrate that the dual-hop UWOC system can effectively mitigate the short
range and both temperature gradients and air bubbles induced turbulences, as
compared to the single UWOC link. All the results are verified via
computer-based Monte-Carlo simulations.Comment: Accepted for publication in IEEE Transactions on Communications.
arXiv admin note: text overlap with arXiv:1810.0631
Global Optimization of Relay Placement for Seafloor Optical Wireless Networks
Optical wireless communication is a promising technology for underwater
broadband access networks, which are particularly important for high-resolution
environmental monitoring applications. This paper focuses on a deep sea
monitoring system, where an underwater optical wireless network is deployed on
the seafloor. We model such an optical wireless network as a general queueing
network and formulate an optimal relay placement problem, whose objective is to
maximize the stability region of the whole system, i.e., the supremum of the
traffic volume that the network is capable of accommodating. The formulated
optimization problem is further shown to be non-convex, so that its global
optimization is non-trivial. In this paper, we develop a global optimization
method for this problem and we provide an efficient algorithm to compute an
optimal solution. Through numerical evaluations, we show that a significant
performance gain can be obtained by using the derived optimal solution