235 research outputs found
Partitioning of Distributed MIMO Systems based on Overhead Considerations
Distributed-Multiple Input Multiple Output (DMIMO) networks is a promising
enabler to address the challenges of high traffic demand in future wireless
networks. A limiting factor that is directly related to the performance of
these systems is the overhead signaling required for distributing data and
control information among the network elements. In this paper, the concept of
orthogonal partitioning is extended to D-MIMO networks employing joint
multi-user beamforming, aiming to maximize the effective sum-rate, i.e., the
actual transmitted information data. Furthermore, in order to comply with
practical requirements, the overhead subframe size is considered to be
constrained. In this context, a novel formulation of constrained orthogonal
partitioning is introduced as an elegant Knapsack optimization problem, which
allows the derivation of quick and accurate solutions. Several numerical
results give insight into the capabilities of D-MIMO networks and the actual
sum-rate scaling under overhead constraints.Comment: IEEE Wireless Communications Letter
Outage Probability of Cognitive Relay Networks Over Generalized Fading Channels with Interference Constraints
AbstractIn this paper, we evaluate the outage probability (OP) of a cognitive relay network operating over generalized fading channels, modeled by the generalized-K and generalized-gamma distributions. In particular, secondary users, based on the underlay approach, cooperate employing decode-and-forward protocol, satisfying in any case an interference constraint on the primary destination users. The derived results include exact expressions as well as approximated ones for high values of the maximum allowed transmitted power. Numerical evaluated results show that the OP of cognitive relay networks is highly related with the fading/shadowing channel conditions as well as interfering constraints, with the latter resulting in higher OP compared to the conventional relaying systems
A Survey on UAV-Aided Maritime Communications: Deployment Considerations, Applications, and Future Challenges
Maritime activities represent a major domain of economic growth with several
emerging maritime Internet of Things use cases, such as smart ports, autonomous
navigation, and ocean monitoring systems. The major enabler for this exciting
ecosystem is the provision of broadband, low-delay, and reliable wireless
coverage to the ever-increasing number of vessels, buoys, platforms, sensors,
and actuators. Towards this end, the integration of unmanned aerial vehicles
(UAVs) in maritime communications introduces an aerial dimension to wireless
connectivity going above and beyond current deployments, which are mainly
relying on shore-based base stations with limited coverage and satellite links
with high latency. Considering the potential of UAV-aided wireless
communications, this survey presents the state-of-the-art in UAV-aided maritime
communications, which, in general, are based on both conventional optimization
and machine-learning-aided approaches. More specifically, relevant UAV-based
network architectures are discussed together with the role of their building
blocks. Then, physical-layer, resource management, and cloud/edge computing and
caching UAV-aided solutions in maritime environments are discussed and grouped
based on their performance targets. Moreover, as UAVs are characterized by
flexible deployment with high re-positioning capabilities, studies on UAV
trajectory optimization for maritime applications are thoroughly discussed. In
addition, aiming at shedding light on the current status of real-world
deployments, experimental studies on UAV-aided maritime communications are
presented and implementation details are given. Finally, several important open
issues in the area of UAV-aided maritime communications are given, related to
the integration of sixth generation (6G) advancements
Functional inequalities for modified Bessel functions
In this paper our aim is to show some mean value inequalities for the
modified Bessel functions of the first and second kinds. Our proofs are based
on some bounds for the logarithmic derivatives of these functions, which are in
fact equivalent to the corresponding Tur\'an type inequalities for these
functions. As an application of the results concerning the modified Bessel
function of the second kind we prove that the cumulative distribution function
of the gamma-gamma distribution is log-concave. At the end of this paper
several open problems are posed, which may be of interest for further research.Comment: 14 page
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