3,727 research outputs found
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
Potential Games for Energy-Efficient Resource Allocation in Multipoint-to-Multipoint CDMA Wireless Data Networks
The problem of noncooperative resource allocation in a
multipoint-to-multipoint cellular network is considered in this paper. The
considered scenario is general enough to represent several key instances of
modern wireless networks such as a multicellular network, a peer-to-peer
network (interference channel), and a wireless network equipped with
femtocells. In particular, the problem of joint transmit waveforms adaptation,
linear receiver design, and transmit power control is examined. Several utility
functions to be maximized are considered, and, among them, we cite the received
SINR, and the transmitter energy efficiency, which is measured in bit/Joule,
and represents the number of successfully delivered bits for each energy unit
used for transmission. Resorting to the theory of potential games,
noncooperative games admitting Nash equilibria in multipoint-to-multipoint
cellular networks regardless of the channel coefficient realizations are
designed. Computer simulations confirm that the considered games are
convergent, and show the huge benefits that resource allocation schemes can
bring to the performance of wireless data networks.Comment: Submitted to Physical Communication, ELSEVIE
Non-cooperative games for spreading code optimization, power control and receiver design in wireless data networks
This paper focuses on the issue of energy efficiency in wireless data
networks through a game theoretic approach. The case considered is that in
which each user is allowed to vary its transmit power, spreading code, and
uplink receiver in order to maximize its own utility, which is here defined as
the ratio of data throughput to transmit power. In particular, the case in
which linear multiuser detectors are employed at the receiver is treated first,
and, then, the more challenging case in which non-linear decision feedback
multiuser receivers are adopted is addressed. It is shown that, for both
receivers, the problem at hand of utility maximization can be regarded as a
non-cooperative game, and it is proved that a unique Nash equilibrium point
exists. Simulation results show that significant performance gains can be
obtained through both non-linear processing and spreading code optimization; in
particular, for systems with a number of users not larger than the processing
gain, remarkable gains come from spreading code optimization, while, for
overloaded systems, the largest gainscome from the use of non-linear
processing. In every case, however, the non-cooperative games proposed here are
shown to outperform competing alternatives.Comment: appeared in the Proceedings of the 13th European Wireless Conference,
Paris (France), April 200
A Survey on MIMO Transmission with Discrete Input Signals: Technical Challenges, Advances, and Future Trends
Multiple antennas have been exploited for spatial multiplexing and diversity
transmission in a wide range of communication applications. However, most of
the advances in the design of high speed wireless multiple-input multiple
output (MIMO) systems are based on information-theoretic principles that
demonstrate how to efficiently transmit signals conforming to Gaussian
distribution. Although the Gaussian signal is capacity-achieving, signals
conforming to discrete constellations are transmitted in practical
communication systems. As a result, this paper is motivated to provide a
comprehensive overview on MIMO transmission design with discrete input signals.
We first summarize the existing fundamental results for MIMO systems with
discrete input signals. Then, focusing on the basic point-to-point MIMO
systems, we examine transmission schemes based on three most important criteria
for communication systems: the mutual information driven designs, the mean
square error driven designs, and the diversity driven designs. Particularly, a
unified framework which designs low complexity transmission schemes applicable
to massive MIMO systems in upcoming 5G wireless networks is provided in the
first time. Moreover, adaptive transmission designs which switch among these
criteria based on the channel conditions to formulate the best transmission
strategy are discussed. Then, we provide a survey of the transmission designs
with discrete input signals for multiuser MIMO scenarios, including MIMO uplink
transmission, MIMO downlink transmission, MIMO interference channel, and MIMO
wiretap channel. Additionally, we discuss the transmission designs with
discrete input signals for other systems using MIMO technology. Finally,
technical challenges which remain unresolved at the time of writing are
summarized and the future trends of transmission designs with discrete input
signals are addressed.Comment: 110 pages, 512 references, submit to Proceedings of the IEE
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
Energy Efficient Power and Channel Allocation in Underlay Device to Multi Device Communications
In this paper, we optimize the energy efficiency (bits/s/Hz/J) of
device-to-multi-device (D2MD) wireless communications. While the
device-to-device scenario has been extensively studied to improve the spectral
efficiency in cellular networks, the use of multicast communications opens the
possibility of reusing the spectrum resources also inside the groups. The
optimization problem is formulated as a mixed integer non-linear joint
optimization for the power control and allocation of resource blocks (RBs) to
each group. Our model explicitly considers resource sharing by letting
co-channel transmission over a RB (up to a maximum of r transmitters) and/or
transmission through s different channels in each group. We use an iterative
decomposition approach, using first matching theory to find a stable even if
sub-optimal channel allocation, to then optimize the transmission power vectors
in each group via fractional programming. Additionally, within this framework,
both the network energy efficiency and the max-min individual energy efficiency
are investigated. We characterize numerically the energy-efficient capacity
region, and our results show that the normalized energy efficiency is nearly
optimal (above 90 percent of the network capacity) for a wide range of
minimum-rate constraints. This performance is better than that of other
matching-based techniques previously proposed
Energy-Efficient Joint User-RB Association and Power Allocation for Uplink Hybrid NOMA-OMA
In this paper, energy efficient resource allocation is considered for an
uplink hybrid system, where non-orthogonal multiple access (NOMA) is integrated
into orthogonal multiple access (OMA). To ensure the quality of service for the
users, a minimum rate requirement is pre-defined for each user. We formulate an
energy efficiency (EE) maximization problem by jointly optimizing the user
clustering, channel assignment and power allocation. To address this hard
problem, a many-to-one bipartite graph is first constructed considering the
users and resource blocks (RBs) as the two sets of nodes. Based on swap
matching, a joint user-RB association and power allocation scheme is proposed,
which converges within a limited number of iterations. Moreover, for the power
allocation under a given user-RB association, we first derive the feasibility
condition. If feasible, a low-complexity algorithm is proposed, which obtains
optimal EE under any successive interference cancellation (SIC) order and an
arbitrary number of users. In addition, for the special case of two users per
cluster, analytical solutions are provided for the two SIC orders,
respectively. These solutions shed light on how the power is allocated for each
user to maximize the EE. Numerical results are presented, which show that the
proposed joint user-RB association and power allocation algorithm outperforms
other hybrid multiple access based and OMA-based schemes.Comment: Non-orthogonal multiple access (NOMA), energy efficiency (EE), power
allocation (PA), uplink transmissio
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
Robust Radio Resource Allocation in MISO-SCMA Assisted C-RAN in 5G Networks
In this paper, by considering multiple slices, a downlink transmission of a
sparse code multiple access (SCMA) based cloud-radio access network (C-RAN) is
investigated. In this regard, by supposing multiple input and single output
(MISO) transmission technology, a novel robust radio resource allocation is
proposed where considering uncertain channel state information (CSI), the worst
case approach is applied. The main goal of the proposed radio resource
allocation is to, maximize the system sum rate with maximum available power at
radio remote head (RRH), minimum rate requirement of each slice, maximum
frounthaul capacity of each RRH, user association, and SCMA constraints. To
solve the proposed optimization problem in an efficient manner, an iterative
method is deployed where in each iteration, beamforming and joint codebook
allocation and user association subproblem are solved separately. By
introducing some auxiliary variables, the joint codebook allocation and user
association subproblem is transformed into an integer linear programming, and
to solve the beamforming optimization problem, minorization-maximization
algorithm (MMA) is applied. Via numerical results, the performance of the
proposed system model versus different system parameters and for different
channel models are investigated.Comment: 11 pages, 8 figure
Secure Communications in NOMA System: Subcarrier Assignment and Power Allocation
Secure communication is a promising technology for wireless networks because
it ensures secure transmission of information. In this paper, we investigate
the joint subcarrier (SC) assignment and power allocation problem for
non-orthogonal multiple access (NOMA) amplify-and-forward two-way relay
wireless networks, in the presence of eavesdroppers. By exploiting cooperative
jamming (CJ) to enhance the security of the communication link, we aim to
maximize the achievable secrecy energy efficiency by jointly designing the SC
assignment, user pair scheduling and power allocation. Assuming the perfect
knowledge of the channel state information (CSI) at the relay station, we
propose a low-complexity subcarrier assignment scheme (SCAS-1), which is
equivalent to many-to-many matching games, and then SCAS-2 is formulated as a
secrecy energy efficiency maximization problem. The secure power allocation
problem is modeled as a convex geometric programming problem, and then solved
by interior point methods. Simulation results demonstrate that the
effectiveness of the proposed SSPA algorithms under scenarios of using and not
using CJ, respectively
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