137 research outputs found
On Optimal Policies in Full-Duplex Wireless Powered Communication Networks
The optimal resource allocation scheme in a full-duplex Wireless Powered
Communication Network (WPCN) composed of one Access Point (AP) and two wireless
devices is analyzed and derived. AP operates in a full-duplex mode and is able
to broadcast wireless energy signals in downlink and receive information data
in uplink simultaneously. On the other hand, each wireless device is assumed to
be equipped with Radio-Frequency (RF) energy harvesting circuitry which gathers
the energy sent by AP and stores it in a finite capacity battery. The harvested
energy is then used for performing uplink data transmission tasks. In the
literature, the main focus so far has been on slot-oriented optimization. In
this context, all the harvested RF energy in a given slot is also consumed in
the same slot. However, this approach leads to sub-optimal solutions because it
does not take into account the Channel State Information (CSI) variations over
future slots. Differently from most of the prior works, in this paper we focus
on the long-term weighted throughput maximization problem. This approach
significantly increases the complexity of the optimization problem since it
requires to consider both CSI variations over future slots and the evolution of
the batteries when deciding the optimal resource allocation. We formulate the
problem using the Markov Decision Process (MDP) theory and show how to solve
it. Our numerical results emphasize the superiority of our proposed full-duplex
WPCN compared to the half-duplex WPCN and reveal interesting insights about the
effects of perfect as well as imperfect self-interference cancellation
techniques on the network performance.Comment: Proc. IEEE Symp. Modeling and Optimization in Mobile, Ad Hoc and
Wireless Networks (WiOpt), May 201
Placement Optimization of Energy and Information Access Points in Wireless Powered Communication Networks
The applications of wireless power transfer technology to wireless
communications can help build a wireless powered communication network (WPCN)
with more reliable and sustainable power supply compared to the conventional
battery-powered network. However, due to the fundamental differences in
wireless information and power transmissions, many important aspects of
conventional battery-powered wireless communication networks need to be
redesigned for efficient operations of WPCNs. In this paper, we study the
placement optimization of energy and information access points in WPCNs, where
the wireless devices (WDs) harvest the radio frequency energy transferred by
dedicated energy nodes (ENs) in the downlink, and use the harvested energy to
transmit data to information access points (APs) in the uplink. In particular,
we are interested in minimizing the network deployment cost with minimum number
of ENs and APs by optimizing their locations, while satisfying the energy
harvesting and communication performance requirements of the WDs. Specifically,
we first study the minimum-cost placement problem when the ENs and APs are
separately located, where an alternating optimization method is proposed to
jointly optimize the locations of ENs and APs. Then, we study the placement
optimization when each pair of EN and AP are co-located and integrated as a
hybrid access point, and propose an efficient algorithm to solve this problem.
Simulation results show that the proposed methods can effectively reduce the
network deployment cost and yet guarantee the given performance requirements,
which is a key consideration in the future applications of WPCNs.Comment: This paper is accepted and to appear in IEEE Transactions on Wireless
Communication
Generalized Wireless-Powered Communications: When to Activate Wireless Power Transfer?
Wireless-powered communication network (WPCN) is a key technology to power
energy-limited massive devices, such as on-board wireless sensors in autonomous
vehicles, for Internet-of-Things (IoT) applications. Conventional WPCNs rely
only on dedicated downlink wireless power transfer (WPT), which is practically
inefficient due to the significant energy loss in wireless signal propagation.
Meanwhile, ambient energy harvesting is highly appealing as devices can
scavenge energy from various existing energy sources (e.g., solar energy and
cellular signals). Unfortunately, the randomness of the availability of these
energy sources cannot guarantee stable communication services. Motivated by the
above, we consider a generalized WPCN where the devices can not only harvest
energy from a dedicated multiple-antenna power station (PS), but can also
exploit stored energy stemming from ambient energy harvesting. Since the
dedicated WPT consumes system resources, if the stored energy is sufficient,
WPT may not be needed to maximize the weighted sum rate (WSR). To analytically
characterize this phenomenon, we derive the condition for WPT activation and
reveal how it is affected by the different system parameters. Subsequently, we
further derive the optimal resource allocation policy for the cases that WPT is
activated and deactivated, respectively. In particular, it is found that when
WPT is activated, the optimal energy beamforming at the PS does not depend on
the devices' stored energy, which is shown to lead to a new unfairness issue.
Simulation results verify our theoretical findings and demonstrate the
effectiveness of the proposed optimal resource allocation.Comment: TV
Power-Efficient and Secure WPCNs with Hardware Impairments and Non-Linear EH Circuit
In this paper, we design a robust resource allocation algorithm for a
wireless-powered communication network (WPCN) taking into account residual
hardware impairments (HWIs) at the transceivers, the imperfectness of the
channel state information, and the non-linearity of practical radio frequency
energy harvesting circuits. In order to ensure power-efficient secure
communication, physical layer security techniques are exploited to deliberately
degrade the channel quality of a multiple-antenna eavesdropper. The resource
allocation algorithm design is formulated as a non-convex optimization problem
for minimization of the total consumed power in the network, while guaranteeing
the quality of service of the information receivers in terms of secrecy rate.
The globally optimal solution of the optimization problem is obtained via a
two-dimensional search and semidefinite programming relaxation. To strike a
balance between computational complexity and system performance, a
low-complexity iterative suboptimal resource allocation algorithm is then
proposed.
Numerical results demonstrate that both the proposed optimal and suboptimal
schemes can significantly reduce the total system power consumption required
for guaranteeing secure communication, and unveil the impact of HWIs on the
system performance: (1) residual HWIs create a system performance bottleneck in
the high transmit/receive power regimes; (2) increasing the number of transmit
antennas can effectively reduce the system power consumption and alleviate the
performance degradation due to residual HWIs; (3) imperfect CSI increases the
system power consumption and exacerbates the impact of residual HWIs.Comment: Submitted for possible journal publicatio
Optimizing Throughput Fairness of Cluster-based Cooperation in Underlay Cognitive WPCNs
In this paper, we consider a secondary wireless powered communication network
(WPCN) underlaid to a primary point-to-point communication link. The WPCN
consists of a multi-antenna hybrid access point (HAP) that transfers wireless
energy to a cluster of low-power wireless devices (WDs) and receives sensing
data from them. To tackle the inherent severe user unfairness problem in WPCN,
we consider a cluster-based cooperation where a WD acts as the cluster head
that relays the information of the other WDs. Besides, we apply energy
beamforming technique to balance the dissimilar energy consumptions of the WDs
to further improve the fairness. However, the use of energy beamforming and
cluster-based cooperation may introduce more severe interference to the primary
system than the WDs transmit independently. To guarantee the performance of
primary system, we consider an interference-temperature constraint to the
primary system and derive the throughput performance of each WD under the peak
interference-temperature constraint. To achieve maximum throughput fairness, we
jointly optimize the energy beamforming design, the transmit time allocation
among the HAP and the WDs, and the transmit power allocation of each WD to
maximize the minimum data rate achievable among the WDs (the max-min
throughput). We show that the non-convex joint optimization problem can be
transformed to a convex one and then be efficiently solved using off-the-shelf
convex algorithms. Moreover, we simulate under practical network setups and
show that the proposed method can effectively improve the throughput fairness
of the secondary WPCN, meanwhile guaranteeing the communication quality of the
primary network.Comment: The paper has been submitted for potential journal publication. arXiv
admin note: text overlap with arXiv:1707.0320
Traffic-Aware Backscatter Communications in Wireless-Powered Heterogeneous Networks
With the emerging Internet-of-Things services, massive machine-to-machine
(M2M) communication will be deployed on top of human-to-human (H2H)
communication in the near future. Due to the coexistence of M2M and H2H
communications, the performance of M2M (i.e., secondary) network depends
largely on the H2H (i.e., primary) network. In this paper, we propose ambient
backscatter communication for the M2M network which exploits the energy
(signal) sources of the H2H network, referring to traffic applications and
popularity. In order to maximize the harvesting and transmission opportunities
offered by varying traffic sources of the H2H network, we adopt a Bayesian
nonparametric (BNP) learning algorithm to classify traffic applications
(patterns) for secondary user (SU). We then analyze the performance of SU using
the stochastic geometrical approach, based on a criterion for optimal traffic
pattern selection. Results are presented to validate the performance of the
proposed BNP classification algorithm and the criterion, as well as the impact
of traffic sources and popularity.Comment: 14 pages, 10 figure
A Discrete Time-Switching Protocol for Wireless-Powered Communications with Energy Accumulation
This paper investigates a wireless-powered communication network (WPCN) setup
with one multi-antenna access point (AP) and one single-antenna source. It is
assumed that the AP is connected to an external power supply, while the source
does not have an embedded energy supply. But the source could harvest energy
from radio frequency (RF) signals sent by the AP and store it for future
information transmission. We develop a discrete time-switching (DTS) protocol
for the considered WPCN. In the proposed protocol, either energy harvesting
(EH) or information transmission (IT) operation is performed during each
transmission block. Specifically, based on the channel state information (CSI)
between source and AP, the source can determine the minimum energy required for
an outage-free IT operation. If the residual energy of the source is
sufficient, the source will start the IT phase. Otherwise, EH phase is invoked
and the source accumulates the harvested energy. To characterize the
performance of the proposed protocol, we adopt a discrete Markov chain (MC) to
model the energy accumulation process at the source battery. A closed-form
expression for the average throughput of the DTS protocol is derived. Numerical
results validate our theoretical analysis and show that the proposed DTS
protocol considerably outperforms the existing harvest-then-transmit protocol
when the battery capacity at the source is large.Comment: Presented at Globecom'1
Capacity of a Full-Duplex Wirelessly Powered Communication System with Self-Interference and Processing Cost
In this paper, we investigate the capacity of a point-to-point, full-duplex
(FD), wirelessly powered communication system impaired by self-interference.
This system is comprised of an energy transmitter (ET) and an energy harvesting
user (EHU), both operating in a FD mode. The ET transmits energy towards the
EHU. The EHU harvests this energy and uses it to transmit information back to
the ET. As a result of the FD mode, both nodes are affected by
self-interference. The self-interference has a different effect at the two
nodes: it impairs the decoding of the received signal at the ET, however, it
provides an additional source of energy for the EHU. This paper derives the
capacity of this communication system assuming a processing cost at the EHU and
additive white Gaussian noise channel with block fading. Thereby, we show that
the capacity achieving scheme is relatively simple and therefore applicable to
devices with limited resources. Moreover, our numerical results show
significant improvements in terms of data rate when the capacity achieving
strategy is employed compared to half-duplex transmission. Moreover, we show
the positive and negative effects of the self-interference at the EHU and the
ET, respectively. Furthermore, we show the crippling effect of the processing
cost and demonstrate that failing to take it into consideration gives a false
impression in terms of achievable rate
Group Cooperation with Optimal Resource Allocation in Wireless Powered Communication Networks
This paper considers a wireless powered communication network (WPCN) with
group cooperation, where two communication groups cooperate with each other via
wireless power transfer and time sharing to fulfill their expected information
delivering and achieve "win-win" collaboration. To explore the system
performance limits, we formulate optimization problems to respectively maximize
the weighted sum-rate and minimize the total consumed power. The time
assignment, beamforming vector and power allocation are jointly optimized under
available power and quality of service requirement constraints of both groups.
For the WSR-maximization, both fixed and flexible power scenarios are
investigated. As all problems are non-convex and have no known solution
methods, we solve them by using proper variable substitutions and the
semi-definite relaxation. We theoretically prove that our proposed solution
method guarantees the global optimum for each problem. Numerical results are
presented to show the system performance behaviors, which provide some useful
insights for future WPCN design. It shows that in such a group
cooperation-aware WPCN, optimal time assignment has the greatest effect on the
system performance than other factors.Comment: 13 pages, 14 figures, to appear in IEEE Transactions on Wireless
Communications Information Theory (cs.IT
Towards Optimal Resource Allocation in Wireless Powered Communication Networks with Non-Orthogonal Multiple Access
The optimal allocation of time and energy resources is characterized in a
Wireless Powered Communication Network (WPCN) with non-Orthogonal Multiple
Access (NOMA). We consider two different formulations; in the first one
(max-sum), the sum-throughput of all users is maximized. In the second one
(max-min), and targeting fairness among users, we consider maximizing the
min-throughput of all users. Under the above two formulations, two NOMA
decoding schemes are studied, namely, low complexity decoding (LCD) and
successive interference cancellation decoding (SICD). Due to the non-convexity
of three of the studied optimization problems, we consider an approximation
approach, in which the non-convex optimization problem is approximated by a
convex optimization problem, which satisfies all the constraints of the
original problem. The approximated convex optimization problem can then be
solved iteratively. The results show a trade-off between maximizing the sum
throughout and achieving fairness through maximizing the minimum throughput
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