73,116 research outputs found
Joint Secure Beamforming for Cognitive Radio Networks with Untrusted Secondary Users
In this paper, we consider simultaneous wireless information and power
transfer (SWIPT) in orthogonal frequency division multiple access (OFDMA)
systems with the coexistence of information receivers (IRs) and energy
receivers (ERs). The IRs are served with best-effort secrecy data and the ERs
harvest energy with minimum required harvested power. To enhance physical-layer
security and yet satisfy energy harvesting requirements, we introduce a new
frequency-domain artificial noise based approach. We study the optimal resource
allocation for the weighted sum secrecy rate maximization via transmit power
and subcarrier allocation. The considered problem is non-convex, while we
propose an efficient algorithm for solving it based on Lagrange duality method.
Simulation results illustrate the effectiveness of the proposed algorithm as
compared against other heuristic schemes.Comment: To appear in Globecom 201
Effects of dark energy on the efficiency of charged AdS black holes as heat engine
In this paper, we study the heat engine where charged AdS black holes
surrounded by dark energy is the working substance and the mechanical work is
done via term in the first law of black hole thermodynamics in the
extended phase space. We first investigate the effects of a kind of dark energy
(quintessence field in this paper) on the efficiency of the RN-AdS black holes
as heat engine defined as a rectangle closed path in the plane. We get
the exact efficiency formula and find that quintessence field can improve the
heat engine efficiency which will increase as the field density grows.
At some fixed parameters, we find that bigger volume difference between the
smaller black holes() and the bigger black holes( ) will lead to a
lower efficiency, while the bigger pressure difference will make the
efficiency higher but it is always smaller than 1 and will never be beyond
Carnot efficiency which is the maximum value of the efficiency constrained by
thermodynamics laws, this is consistent to the heat engine in traditional
thermodynamics. After making some special choices for thermodynamical
quantities, we find that the increase of electric charge and normalization
factor can also promote heat engine efficiency which would infinitely
approach the Carnot limit when or goes to infinity.Comment: 28 pages, 16 figures, refernces added, discussion and computation
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One More Weight is Enough: Toward the Optimal Traffic Engineering with OSPF
Traffic Engineering (TE) leverages information of network traffic to generate
a routing scheme optimizing the traffic distribution so as to advance network
performance. However, optimize the link weights for OSPF to the offered traffic
is an known NP-hard problem. In this paper, motivated by the fairness concept
of congestion control, we firstly propose a new generic objective function,
where various interests of providers can be extracted with different parameter
settings. And then, we model the optimal TE as the utility maximization of
multi-commodity flows with the generic objective function and theoretically
show that any given set of optimal routes corresponding to a particular
objective function can be converted to shortest paths with respect to a set of
positive link weights. This can be directly configured on OSPF-based protocols.
On these bases, we employ the Network Entropy Maximization(NEM) framework and
develop a new OSPF-based routing protocol, SPEF, to realize a flexible way to
split traffic over shortest paths in a distributed fashion. Actually, comparing
to OSPF, SPEF only needs one more weight for each link and provably achieves
optimal TE. Numerical experiments have been done to compare SPEF with the
current version of OSPF, showing the effectiveness of SPEF in terms of link
utilization and network load distribution
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