4,851 research outputs found
Natural Regulation of Energy Flow in a Green Quantum Photocell
Manipulating the flow of energy in nanoscale and molecular photonic devices
is of both fundamental interest and central importance for applications in
light harvesting optoelectronics. Under erratic solar irradiance conditions,
unregulated power fluctuations in a light harvesting photocell lead to
inefficient energy storage in conventional solar cells and potentially fatal
oxidative damage in photosynthesis. Here, we show that regulation against these
fluctuations arises naturally within a two-channel quantum heat engine
photocell, thus enabling the efficient conversion of varying incident solar
spectrum at Earth's surface. Remarkably, absorption in the green portion of the
spectrum is avoided, as it provides no inherent regulatory benefit. Our
findings illuminate a quantum structural origin of regulation, provide a novel
optoelectronic design strategy, and may elucidate the link between
photoprotection in photosynthesis and the predominance of green plants on
Earth.Comment: 17 pages, 4 figure
On the Spectral Efficiency and Fairness in Full-Duplex Cellular Networks
To increase the spectral efficiency of wireless networks without requiring
full-duplex capability of user devices, a potential solution is the recently
proposed three-node full-duplex mode. To realize this potential, networks
employing three-node full-duplex transmissions must deal with self-interference
and user-to-user interference, which can be managed by frequency channel and
power allocation techniques. Whereas previous works investigated either
spectral efficient or fair mechanisms, a scheme that balances these two metrics
among users is investigated in this paper. This balancing scheme is based on a
new solution method of the multi-objective optimization problem to maximize the
weighted sum of the per-user spectral efficiency and the minimum spectral
efficiency among users. The mixed integer non-linear nature of this problem is
dealt by Lagrangian duality. Based on the proposed solution approach, a
low-complexity centralized algorithm is developed, which relies on large scale
fading measurements that can be advantageously implemented at the base station.
Numerical results indicate that the proposed algorithm increases the spectral
efficiency and fairness among users without the need of weighting the spectral
efficiency. An important conclusion is that managing user-to-user interference
by resource assignment and power control is crucial for ensuring spectral
efficient and fair operation of full-duplex networks.Comment: 6 pages, 4 figures, accepted in IEEE ICC 2017. arXiv admin note: text
overlap with arXiv:1603.0067
Performance Analysis of Network-Assisted Two-Hop D2D Communications
Network-assisted single-hop device-to-device (D2D) communication can increase
the spectral and energy efficiency of cellular networks by taking advantage of
the proximity, reuse, and hop gains when radio resources are properly managed
between the cellular and D2D layers. In this paper we argue that D2D technology
can be used to further increase the spectral and energy efficiency if the key
D2D radio resource management algorithms are suitably extended to support
network assisted multi-hop D2D communications. Specifically, we propose a
novel, distributed utility maximizing D2D power control (PC) scheme that is
able to balance spectral and energy efficiency while taking into account mode
selection and resource allocation constraints that are important in the
integrated cellular-D2D environment. Our analysis and numerical results
indicate that multi-hop D2D communications combined with the proposed PC scheme
can be useful not only for harvesting the potential gains previously identified
in the literature, but also for extending the coverage of cellular networks.Comment: 6 pages and 7 figure
Distributed Spectral Efficiency Maximization in Full-Duplex Cellular Networks
Three-node full-duplex is a promising new transmission mode between a
full-duplex capable wireless node and two other wireless nodes that use
half-duplex transmission and reception respectively. Although three-node
full-duplex transmissions can increase the spectral efficiency without
requiring full-duplex capability of user devices, inter-node interference - in
addition to the inherent self-interference - can severely degrade the
performance. Therefore, as methods that provide effective self-interference
mitigation evolve, the management of inter-node interference is becoming
increasingly important. This paper considers a cellular system in which a
full-duplex capable base station serves a set of half-duplex capable users. As
the spectral efficiencies achieved by the uplink and downlink transmissions are
inherently intertwined, the objective is to device channel assignment and power
control algorithms that maximize the weighted sum of the uplink-downlink
transmissions. To this end a distributed auction based channel assignment
algorithm is proposed, in which the scheduled uplink users and the base station
jointly determine the set of downlink users for full-duplex transmission.
Realistic system simulations indicate that the spectral efficiency can be up to
89% better than using the traditional half-duplex mode. Furthermore, when the
self-interference cancelling level is high, the impact of the user-to-user
interference is severe unless properly managed.Comment: 7 pages, 3 figures, accepted in IEEE ICC 2016 - Workshop on Novel
Medium Access and Resource Allocation for 5G Network
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