7,154 research outputs found
Network-Assisted Resource Allocation with Quality and Conflict Constraints for V2V Communications
The 3rd Generation Partnership Project (3GPP) has recently established in
Rel. 14 a network-assisted resource allocation scheme for vehicular broadcast
communications. Such novel paradigm is known as vehicle--to--vehicle (V2V)
\textit{mode-3} and consists in eNodeBs engaging only in the distribution of
sidelink subchannels among vehicles in coverage. Thereupon, without further
intervention of the former, vehicles will broadcast their respective signals
directly to their counterparts. Because the allotment of subchannels takes
place intermittently to reduce signaling, it must primarily be conflict-free in
order not to jeopardize the reception of signals. We have identified four
pivotal types of allocation requirements that must be guaranteed: one quality
of service (QoS) requirement and three conflict conditions which must be
precluded in order to preserve reception reliability. The underlying problem is
formulated as a maximization of the system sum-capacity with four types of
constraints that must be enforced. In addition, we propose a three-stage
suboptimal approach that is cast as multiple independent knapsack problems
(MIKPs). We compare the two approaches through simulations and show that the
latter formulation can attain acceptable performance at lesser complexity
Poster Abstract: Hierarchical Subchannel Allocation for Mode-3 Vehicle-to-Vehicle Sidelink Communications
In V2V Mode-3, eNodeBs assign subchannels to vehicles in order for them to
periodically broadcast CAM messages \cite{b2}. A crucial aspect is to ensure
that vehicles in the same cluster will broadcast in orthogonal time
subchannels\footnote{A subchannel is a time-frequency resource chunk capable of
sufficiently conveying a CAM message.} to avoid conflicts. In general,
resource/subchannel allocation problems can be represented as weighted
bipartite graphs. However, in this scenario there is an additional time
orthogonality constraint which cannot be straightforwardly handled by
conventional graph matching methods \cite{b3}. Thus, in our approach the
mentioned constraint has been taken into account. We also perform the
allocation task in a sequential manner based on the constrainedness of each
cluster. To illustrate the gist of the problem, in Fig. 1 we show two partially
overlapping clusters where a conflict between vehicles and is
generated as the allotted subchannels are in the same subframe
An analytic model for the transition from decelerated to accelerated cosmic expansion
We consider the scenario where our observable universe is devised as a
dynamical four-dimensional hypersurface embedded in a five-dimensional bulk
spacetime, with a large extra dimension, which is the {\it generalization of
the flat FRW cosmological metric to five dimensions}. This scenario generates a
simple analytical model where different stages of the evolution of the universe
are approximated by distinct parameterizations of the {\it same} spacetime. In
this model the evolution from decelerated to accelerated expansion can be
interpreted as a "first-order" phase transition between two successive stages.
The dominant energy condition allows different parts of the universe to evolve,
from deceleration to acceleration, at different redshifts within a narrow era.
This picture corresponds to the creation of bubbles of new phase, in the middle
of the old one, typical of first-order phase transitions. Taking today, we find that the cross-over from deceleration to acceleration
occurs at , regardless of the equation of state in the very
early universe. In the case of primordial radiation, the model predicts that
the deceleration parameter "jumps" from to at . At the present time and the equation of state of the
universe is , in agreement with observations and some
theoretical predictions.Comment: The abstract and introduction are improved and the discussion section
is expanded. A number of references are adde
Poster: Resource Allocation with Conflict Resolution for Vehicular Sidelink Broadcast Communications
In this paper we present a graph-based resource allocation scheme for
sidelink broadcast V2V communications. Harnessing available information on
geographical position of vehicles and spectrum resources utilization, eNodeBs
are capable of allotting the same set of sidelink resources to different
vehicles distributed among several communications clusters. Within a
communications cluster, it is crucial to prevent time-domain allocation
conflicts since vehicles cannot transmit and receive simultaneously, i.e., they
must transmit in orthogonal time resources. In this research, we present a
solution based on a bipartite graph, where vehicles and spectrum resources are
represented by vertices whereas the edges represent the achievable rate in each
resource based on the SINR that each vehicle perceives. The aforementioned time
orthogonality constraint can be approached by aggregating conflicting vertices
into macro-vertices which, in addition, reduces the search complexity. We show
mathematically and through simulations that the proposed approach yields an
optimal solution. In addition, we provide simulations showing that the proposed
method outperforms other competing approaches, specially in scenarios with high
vehicular density.Comment: arXiv admin note: substantial text overlap with arXiv:1805.0655
Wave-like Solutions for Bianchi type-I cosmologies in 5D
We derive exact solutions to the vacuum Einstein field equations in 5D, under
the assumption that (i) the line element in 5D possesses self-similar symmetry,
in the classical understanding of Sedov, Taub and Zeldovich, and that (ii) the
metric tensor is diagonal and independent of the coordinates for ordinary 3D
space. These assumptions lead to three different types of self-similarity in
5D: homothetic, conformal and "wave-like". In this work we present the most
general wave-like solutions to the 5D field equations. Using the standard
technique based on Campbell's theorem, they generate a large number of
anisotropic cosmological models of Bianchi type-I, which can be applied to our
universe after the big-bang, when anisotropies could have played an important
role. We present a complete review of all possible cases of self-similar
anisotropic cosmologies in 5D. Our analysis extends a number of previous
studies on wave-like solutions in 5D with spatial spherical symmetry
Lorentz violation and the speed of gravitational waves in brane-worlds
Lorentz violation in a brane-world scenario is presented and used to obtain a
relationship between the speed of gravitational waves in the bulk and that on
the brane. Lorentz violating effects would manifest themselves in gravitational
waves travelling with a greater speed in the bulk than on the brane and this
effect is independent of the signature of the extra dimension.Comment: 8 pages, to appear in PL
Confinement and stability of the motion of test particles in thick branes
We consider the motion of test particles in a thick brane version of
Randall-Sundrum type II model. It is known that gravity alone cannot explain
the confinement of test particles in this kind of brane. In this paper we show
that a stable confinement in a domain wall is possible by admitting a direct
interaction between test particles and a scalar field. This interaction is
implemented by a modification of the Lagrangian of the particle which is
inspired by a Yukawa-type interaction between fermions and scalar fields.Comment: 1 figure. Extended analysis to treat general thick branes RSII-type.
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