8,611 research outputs found
Throughput Optimization in FDD MU-MISO Wireless Powered Communication Networks
In this paper, we consider a frequency-division duplexing (FDD) multiple-user
multiple-input-single-output (MU-MISO) wireless-powered communication network
(WPCN) consisting of one hybrid data-and-energy access point (HAP) with
multiple antennas which coordinates energy/information transfer to/from several
single-antenna wireless devices (WD). Typically, in such a system, wireless
energy transfer (WET) requires such techniques as energy beamforming (EB) for
efficient transfer of energy to the WDs. Yet, efficient EB can only be
accomplished if channel state information (CSI) is available to the
transmitter, which, in FDD systems is only achieved through uplink (UL)
feedback. Therefore, while in our scheme we use the downlink (DL) channels for
WET only, the UL channel frames are split into two phases: the CSI feedback
phase during which the WDs feed CSI back to the HAP and the WIT phase where the
HAP performs wireless information transmission (WIT) via
space-division-multiple-access (SDMA). To ensure rate fairness among the WDs,
this paper maximizes the minimum WIT data rate among the WDs. Using an
iterative solution, the original optimization problem can be relaxed into two
sub-problems whose convexity conditions are derived. Finally, the behavior of
this system when the number of HAP antennas increases is analyzed. Simulation
results verify the truthfulness of our analysis
On Green Energy Powered Cognitive Radio Networks
Green energy powered cognitive radio (CR) network is capable of liberating
the wireless access networks from spectral and energy constraints. The
limitation of the spectrum is alleviated by exploiting cognitive networking in
which wireless nodes sense and utilize the spare spectrum for data
communications, while dependence on the traditional unsustainable energy is
assuaged by adopting energy harvesting (EH) through which green energy can be
harnessed to power wireless networks. Green energy powered CR increases the
network availability and thus extends emerging network applications. Designing
green CR networks is challenging. It requires not only the optimization of
dynamic spectrum access but also the optimal utilization of green energy. This
paper surveys the energy efficient cognitive radio techniques and the
optimization of green energy powered wireless networks. Existing works on
energy aware spectrum sensing, management, and sharing are investigated in
detail. The state of the art of the energy efficient CR based wireless access
network is discussed in various aspects such as relay and cooperative radio and
small cells. Envisioning green energy as an important energy resource in the
future, network performance highly depends on the dynamics of the available
spectrum and green energy. As compared with the traditional energy source, the
arrival rate of green energy, which highly depends on the environment of the
energy harvesters, is rather random and intermittent. To optimize and adapt the
usage of green energy according to the opportunistic spectrum availability, we
discuss research challenges in designing cognitive radio networks which are
powered by energy harvesters
Resource Allocation and Fairness in Wireless Powered Cooperative Cognitive Radio Networks
We integrate a wireless powered communication network with a cooperative
cognitive radio network, where multiple secondary users (SUs) powered
wirelessly by a hybrid access point (HAP) help a primary user relay the data.
As a reward for the cooperation, the secondary network gains the spectrum
access where SUs transmit to HAP using time division multiple access. To
maximize the sum-throughput of SUs, we present a secondary sum-throughput
optimal resource allocation (STORA) scheme. Under the constraint of meeting
target primary rate, the STORA scheme chooses the optimal set of relaying SUs
and jointly performs the time and energy allocation for SUs. Specifically, by
exploiting the structure of the optimal solution, we find the order in which
SUs are prioritized to relay primary data. Since the STORA scheme focuses on
the sum-throughput, it becomes inconsiderate towards individual SU throughput,
resulting in low fairness. To enhance fairness, we investigate three resource
allocation schemes, which are (i) equal time allocation, (ii) minimum
throughput maximization, and (iii) proportional time allocation. Simulation
results reveal the trade-off between sum-throughput and fairness. The minimum
throughput maximization scheme is the fairest one as each SU gets the same
throughput, but yields the least SU sum-throughput.Comment: Accepted in IEEE Transactions on Communication
GATE: Greening At The Edge
Dramatic data traffic growth, especially wireless data, is driving a
significant surge in energy consumption in the last mile access of the
telecommunications infrastructure. The growing energy consumption not only
escalates the operators' operational expenditures (OPEX) but also leads to a
significant rise of carbon footprints. Therefore, enhancing the energy
efficiency of broadband access networks is becoming a necessity to bolster
social, environmental, and economic sustainability. This article provides an
overview on the design and optimization of energy efficient broadband access
networks, analyzes the energy efficient design of passive optical networks,
discusses the enabling technologies for next generation broadband wireless
access networks, and elicits the emerging technologies for enhancing the energy
efficiency of the last mile access of the network infrastructure.Comment: 7 Pages, 12 Figures, Submitted to IEEE Wireless Communication
Deep Reinforcement Learning for Time Scheduling in RF-Powered Backscatter Cognitive Radio Networks
In an RF-powered backscatter cognitive radio network, multiple secondary
users communicate with a secondary gateway by backscattering or harvesting
energy and actively transmitting their data depending on the primary channel
state. To coordinate the transmission of multiple secondary transmitters, the
secondary gateway needs to schedule the backscattering time, energy harvesting
time, and transmission time among them. However, under the dynamics of the
primary channel and the uncertainty of the energy state of the secondary
transmitters, it is challenging for the gateway to find a time scheduling
mechanism which maximizes the total throughput. In this paper, we propose to
use the deep reinforcement learning algorithm to derive an optimal time
scheduling policy for the gateway. Specifically, to deal with the problem with
large state and action spaces, we adopt a Double Deep-Q Network (DDQN) that
enables the gateway to learn the optimal policy. The simulation results clearly
show that the proposed deep reinforcement learning algorithm outperforms
non-learning schemes in terms of network throughput
Stackelberg Game for Distributed Time Scheduling in RF-Powered Backscatter Cognitive Radio Networks
In this paper, we study the transmission strategy adaptation problem in an
RF-powered cognitive radio network, in which hybrid secondary users are able to
switch between the harvest-then-transmit mode and the ambient backscatter mode
for their communication with the secondary gateway. In the network, a monetary
incentive is introduced for managing the interference caused by the secondary
transmission with imperfect channel sensing. The sensing-pricing-transmitting
process of the secondary gateway and the transmitters is modeled as a
single-leader-multi-follower Stackelberg game. Furthermore, the follower
sub-game among the secondary transmitters is modeled as a generalized Nash
equilibrium problem with shared constraints. Based on our theoretical
discoveries regarding the properties of equilibria in the follower sub-game and
the Stackelberg game, we propose a distributed, iterative strategy searching
scheme that guarantees the convergence to the Stackelberg equilibrium. The
numerical simulations show that the proposed hybrid transmission scheme always
outperforms the schemes with fixed transmission modes. Furthermore, the
simulations reveal that the adopted hybrid scheme is able to achieve a higher
throughput than the sum of the throughput obtained from the schemes with fixed
transmission modes
Throughput Maximization for Two-way Relay Channels with Energy Harvesting Nodes: The Impact of Relaying Strategies
In this paper, we study the two-way relay channel with energy harvesting
nodes. In particular, we find transmission policies that maximize the
sum-throughput for two-way relay channels when the relay does not employ a data
buffer. The relay can perform decode-and-forward, compress-and-forward,
compute-and-forward or amplify-and-forward relaying. Furthermore, we consider
throughput improvement by dynamically choosing relaying strategies, resulting
in hybrid relaying strategies. We show that an iterative generalized
directional water-filling algorithm solves the offline throughput maximization
problem, with the achievable sum-rate from an individual or hybrid relaying
scheme. In addition to the optimum offline policy, we obtain the optimum online
policy via dynamic programming. We provide numerical results for each relaying
scheme to support the analytic findings, pointing out to the advantage of
adapting the instantaneous relaying strategy to the available harvested energy.Comment: accepted for publication in IEEE Transactions on Communications,
April 19, 201
Uplink Time Scheduling with Power Level Modulation in Wireless Powered Communication Networks
In this paper, we propose downlink signal design and optimal uplink
scheduling for the wireless powered communication networks (WPCNs). Prior works
give attention to resource allocation in a static channel because users are
equipped with only energy receiver and users cannot update varying uplink
schedulling. For uplink scheduling, we propose a downlink signal design scheme,
called a power level modulation, which conveys uplink scheduling information to
users. First, we design a downlink energy signal using power level modulation.
Hybrid-access point (H-AP) allocates different power level in each subslot of
the downlink energy signal according to channel condition and users optimize
their uplink time subslots for signal transmission based on the power levels of
their received signals. Further, we formulate the sum throughput maximization
problem for the proposed scheme by determining the uplink and downlink time
allocation using convex optimization problem. Numerical results confirm that
the throughput of the proposed scheme outperforms that of the conventional
schemes
Joint Link Scheduling and Brightness Control for Greening VLC-based Indoor Access Networks
Demands for broadband wireless access services is expected to outstrip the
spectrum capacity in the near-term - "spectrum crunch". Deploying additional
femotocells to address this challenge is cost-inefficient, due to the backhaul
challenge and the exorbitant system maintenance. According to an Alcatel-Lucent
report, most of the mobile Internet access traffic happens indoor. Leveraging
power line communication and the available indoor infrastructure, visible light
communication (VLC) can be utilized with small one-time cost. VLC also
facilitates the great advantage of being able to jointly perform illumination
and communications, and little extra power beyond illumination is required to
empower communications, thus rendering wireless access with small power
consumption. In this study, we investigate the problem of minimizing total
power consumption of a general multi-user VLC indoor network while satisfying
users' traffic demands and maintaining an acceptable level of illumination. We
utilize the column generation method to obtain an -bounded solution.
Several practical implementation issues are integrated with the proposed
algorithm, including different configurations of light source and ways of
resolving the interference among VLC links. Through extensive simulations, we
show that our approach reduces the power consumption of the state-of-art
VLC-based scheduling algorithms by more than 60\% while maintaining the
required illumination
RF-Powered Cognitive Radio Networks: Technical Challenges and Limitations
The increasing demand for spectral and energy efficient communication
networks has spurred a great interest in energy harvesting (EH) cognitive radio
networks (CRNs). Such a revolutionary technology represents a paradigm shift in
the development of wireless networks, as it can simultaneously enable the
efficient use of the available spectrum and the exploitation of radio frequency
(RF) energy in order to reduce the reliance on traditional energy sources. This
is mainly triggered by the recent advancements in microelectronics that puts
forward RF energy harvesting as a plausible technique in the near future. On
the other hand, it is suggested that the operation of a network relying on
harvested energy needs to be redesigned to allow the network to reliably
function in the long term. To this end, the aim of this survey paper is to
provide a comprehensive overview of the recent development and the challenges
regarding the operation of CRNs powered by RF energy. In addition, the
potential open issues that might be considered for the future research are also
discussed in this paper.Comment: 8 pages, 2 figures, 1 table, Accepted in IEEE Communications Magazin
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