672 research outputs found
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
NOMA-based Energy-Efficient Wireless Powered Communications
In this paper, we study the performance of non-orthogonal multiple access
(NOMA) schemes in wireless powered communication networks (WPCN) focusing on
the system energy efficiency (EE). We consider multiple energy harvesting user
equipments (UEs) that operate based on harvest-then-transmit protocol. The
uplink information transfer is carried out by using power-domain multiplexing,
and the receiver decodes each UE's data in such a way that the UE with the best
channel gain is decoded without interference. In order to determine optimal
resource allocation strategies, we formulate optimization problems considering
two models, namely half-duplex and asynchronous transmission, based on how
downlink and uplink operations are coordinated. In both cases, we have
concave-linear fractional problems, and hence Dinkelbach's method can be
applied to obtain the globally optimal solutions. Thus, we first derive
analytical expressions for the harvesting interval, and then we provide an
algorithm to describe the complete procedure. Furthermore, we incorporate
delay-limited sources and investigate the impact of statistical queuing
constraints on the energy-efficient allocation of operating intervals. We
formulate an optimization problem that maximizes the system effective-EE while
UEs are applying NOMA scheme for uplink information transfer. Since the problem
satisfies pseudo-concavity, we provide an iterative algorithm using bisection
method to determine the unique solution. In the numerical results, we observe
that broadcasting at higher power level is more energy efficient for WPCN with
uplink NOMA. Additionally, exponential decay QoS parameter has considerable
impact on the optimal solution, and in the presence of strict constraints, more
time is allocated for downlink interval under half-duplex operation with uplink
TDMA mode.Comment: 31 pages, 12 figures, to appear on IEEE Transactions on Green
Communications and Networkin
Optimal Resource Allocation in Full-Duplex Ambient Backscatter Communication Networks for Wireless-Powered IoT
This paper considers an ambient backscatter communication (AmBC) network in
which a full-duplex access point (FAP) simultaneously transmits downlink
orthogonal frequency division multiplexing (OFDM) signals to its legacy user
(LU) and receives uplink signals backscattered from multiple BDs in a
time-division-multiple-access manner. To maximize the system throughput and
ensure fairness, we aim to maximize the minimum throughput among all BDs by
jointly optimizing the backscatter time and reflection coefficients of the BDs,
and the FAP's subcarrier power allocation, subject to the LU's throughput
constraint, the BDs' harvested-energy constraints, and other practical
constraints. For the case with a single BD, we obtain closed-form solutions and
propose an efficient algorithm by using the Lagrange duality method. For the
general case with multiple BDs, we propose an iterative algorithm by leveraging
the block coordinated decent and successive convex optimization techniques. We
further show the convergence performances of the proposed algorithms and
analyze their complexities. In addition, we study the throughput region which
characterizes the Pareto-optimal throughput trade-offs among all BDs. Finally,
extensive simulation results show that the proposed joint design achieves
significant throughput gain as compared to the benchmark schemes.Comment: 13 pages. This is the third work focusing on ambient backscatter
communication (AmBC) systems for cognitive (energy- and spectrum- efficient)
IoT. The other two published works are "Modulation in the air: Backscatter
communication over ambient OFDM carrier" (IEEE Trans. Commun., 2018) and
"Cooperative ambient backscatter communications for green
Internet-of-Things"(IEEE IoT Journal, 2018
Full-Duplex Wireless-Powered Communication Network with Energy Causality
In this paper, we consider a wireless communication network with a
full-duplex hybrid access point (HAP) and a set of wireless users with energy
harvesting capabilities. The HAP implements the full-duplex through two
antennas: one for broadcasting wireless energy to users in the downlink and one
for receiving independent information from users via
time-division-multiple-access (TDMA) in the uplink at the same time. All users
can continuously harvest wireless power from the HAP until its transmission
slot, i.e., the energy causality constraint is modeled by assuming that energy
harvested in the future cannot be used for tranmission. Hence, latter users'
energy harvesting time is coupled with the transmission time of previous users.
Under this setup, we investigate the sum-throughput maximization (STM) problem
and the total-time minimization (TTM) problem for the proposed multi-user
full-duplex wireless-powered network. The STM problem is proved to be a convex
optimization problem. The optimal solution strategy is then obtained in
closed-form expression, which can be computed with linear complexity. It is
also shown that the sum throughput is non-decreasing with increasing of the
number of users. For the TTM problem, by exploiting the properties of the
coupling constraints, we propose a two-step algorithm to obtain an optimal
solution. Then, for each problem, two suboptimal solutions are proposed and
investigated. Finally, the effect of user scheduling on STM and TTM are
investigated through simulations. It is also shown that different user
scheduling strategies should be used for STM and TTM.Comment: Energy Harvesting, Wireless Power Transfer, Full-Duplex, Optimal
Resource Allocation, Optimizatio
Is Self-Interference in Full-Duplex Communications a Foe or a Friend?
This paper studies the potential of harvesting energy from the
self-interference of a full-duplex base station. The base station is equipped
with a self-interference cancellation switch, which is turned-off for a
fraction of the transmission period for harvesting the energy from the
self-interference that arises due to the downlink transmission. For the
remaining transmission period, the switch is on such that the uplink
transmission takes place simultaneously with the downlink transmission. A novel
energy-efficiency maximization problem is formulated for the joint design of
downlink beamformers, uplink power allocations and transmission time-splitting
factor. The optimization problem is nonconvex, and hence, a rapidly converging
iterative algorithm is proposed by employing the successive convex
approximation approach. Numerical simulation results show significant
improvement in the energy-efficiency by allowing self-energy recycling.Comment: Accepted for publication in IEEE Signal Processing Letter
Optimal Transmission Using a Self-sustained Relay in a Full-Duplex MIMO System
This paper investigates wireless information and power transfer in a
full-duplex MIMO relay channel where the self-sustained relay harvests energy
from both source transmit signal and self-interference signal to decode and
forward source information to a destination. We present a novel technique to
jointly optimize power splitting at the relay and precoding design (power
allocation) for both the source and relay transmissions. We formulate a new
convex optimization problem, establish the dual problem via closed-form optimal
primal solutions, and design an efficient primal-dual algorithm to maximize the
achievable throughput. Numerical results demonstrate the benefits of using
multiple transmit and receive antennas in both information decoding and energy
harvesting. We also extend our analysis to the case when channel state
information is only available at receiving nodes and show how our algorithm can
optimize the power splitting at the relay for it to remain self-sustained.
Through analysis and simulation, we show how an optimal combination of
non-uniform power splitting, variable power allocation, and self-interference
power harvesting effectively exploits a full-duplex MIMO system to achieve
significant performance gains over existing uniform power splitting and
half-duplex transmission techniques
Fundamental Green Tradeoffs: Progresses, Challenges, and Impacts on 5G Networks
With years of tremendous traffic and energy consumption growth, green radio
has been valued not only for theoretical research interests but also for the
operational expenditure reduction and the sustainable development of wireless
communications. Fundamental green tradeoffs, served as an important framework
for analysis, include four basic relationships: spectrum efficiency (SE) versus
energy efficiency (EE), deployment efficiency (DE) versus energy efficiency
(EE), delay (DL) versus power (PW), and bandwidth (BW) versus power (PW). In
this paper, we first provide a comprehensive overview on the extensive on-going
research efforts and categorize them based on the fundamental green tradeoffs.
We will then focus on research progresses of 4G and 5G communications, such as
orthogonal frequency division multiplexing (OFDM) and non-orthogonal
aggregation (NOA), multiple input multiple output (MIMO), and heterogeneous
networks (HetNets). We will also discuss potential challenges and impacts of
fundamental green tradeoffs, to shed some light on the energy efficient
research and design for future wireless networks.Comment: revised from IEEE Communications Surveys & Tutorial
Cognitive Wireless Powered Network: Spectrum Sharing Models and Throughput Maximization
The recent advance in radio-frequency (RF) wireless energy transfer (WET) has
motivated the study of wireless powered communication network (WPCN), in which
distributed wireless devices are powered via dedicated WET by the hybrid
access-point (H-AP) in the downlink (DL) for uplink (UL) wireless information
transmission (WIT). In this paper, by exploiting the cognitive radio (CR)
technique, we study a new type of CR enabled secondary WPCN, called cognitive
WPCN, under spectrum sharing with the primary wireless communication system. In
particular, we consider a cognitive WPCN, consisting of one single H-AP with
constant power supply and distributed users, shares the same spectrum for its
DL WET and UL WIT with an existing primary communication link, where the WPCN's
WET/WIT and the primary link's WIT may interfere with each other. Under this
new setup, we propose two coexisting models for spectrum sharing of the two
systems, namely underlay and overlay based cognitive WPCNs, depending on
different types of knowledge on the primary user transmission available at the
cognitive WPCN. For each model, we maximize the sum-throughput of the cognitive
WPCN by optimizing its transmission under different constraints applied to
protect the primary user transmission. Analysis and simulation results are
provided to compare the sum-throughput of the cognitive WPCN versus the
achievable rate of the primary user in two coexisting models. It is shown that
the overlay based cognitive WPCN outperforms the underlay based counterpart,
thanks to its fully cooperative WET/WIT design with the primary WIT, while it
also requires higher complexity for implementation.Comment: This is the longer version of a paper to appear in IEEE Transactions
on Cognitive Communications and Networkin
Energy-efficient Resource Allocation for Wirelessly Powered Backscatter Communications
In this letter, we consider a wireless-powered backscatter communication
(WP-BackCom) network, where the transmitter first harvests energy from a
dedicated energy RF source in the sleep state, and then backscatters
information and harvests energy simultaneously through a reflection
coefficient. Our goal is to maximize the achievable energy efficiency of the
WP-BackCom network via jointly optimizing time allocation, reflection
coefficient and transmit power of the dedicated energy RF source. The
optimization problem is non-convex and challenging to solve. We develop an
efficient Dinkelbach-based iterative algorithm to obtain the optimal resource
allocation scheme. The study shows that for each iteration, the
energy-efficient WP-BackCom network is equivalent to either the network in
which the transmitter always operates in the active state, or the network in
which the dedicated energy RF source adopts the maximum allowed power.Comment: It has been accepted by IEEE Communications Letter
Wireless Powered Communications with Non-Orthogonal Multiple Access
We study a wireless-powered uplink communication system with non-orthogonal
multiple access (NOMA), consisting of one base station and multiple energy
harvesting users. More specifically, we focus on the individual data rate
optimization and fairness improvement and we show that the formulated problems
can be optimally and efficiently solved by either linear programming or convex
optimization. In the provided analysis, two types of decoding order strategies
are considered, namely fixed decoding order and time- sharing. Furthermore, we
propose an efficient greedy algorithm, which is suitable for the practical
implementation of the time-sharing strategy. Simulation results illustrate that
the proposed scheme outperforms the baseline orthogonal multiple access scheme.
More specifically, it is shown that NOMA offers a considerable improvement in
throughput, fairness, and energy efficiency. Also, the dependence among system
throughput, minimum individual data rate, and harvested energy is revealed, as
well as an interesting trade-off between rates and energy efficiency. Finally,
the convergence speed of the proposed greedy algorithm is evaluated, and it is
shown that the required number of iterations is linear with respect to the
number of users.Comment: Submitted to IEEE Transactions on Wireless Communication
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