709 research outputs found
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
Secure Beamforming Design in Relay-Assisted Internet of Things
A secure downlink transmission system which is exposed to multiple
eavesdroppers and is appropriate for Internet of Things (IoT) applications is
considered. A worst case scenario is assumed, in the sense that, in order to
enhance their interception ability all eavesdroppers are located close to each
other, near the controller and collude to form joint receive beamforming. For
such a system, a novel cooperative non-orthogonal multiple access (NOMA) secure
transmission scheme for which an IoT device with a stronger channel condition
acts as an energy harvesting relay in order to assist a second IoT device
operating under weaker channel conditions, is proposed and its performance is
analyzed and evaluated. A secrecy sum rate (SSR) maximization problem is
formulated and solved under three constraints: i) Transmit power; ii)
Successive interference cancellation; iii) Quality of Service. By considering
both passive and active eavesdroppers scenarios, two optimization schemes are
proposed to improve the overall system SSR. On the one hand, for the passive
eavesdropper scenario, an artificial noise-aided secure beamforming scheme is
proposed. Since this optimization problem is nonconvex, instead of using
traditional but highly complex, bruteforce two-dimensional search, it is
conveniently transformed into a convex one by using an epigraph reformulation.
On the other hand, for the active multi-antennas eavesdroppers' scenario, the
orthogonal-projection-based beamforming scheme is considered, and by employing
the successive convex approximation method, a suboptimal solution is proposed.
Furthermore, since for single antenna transmission the
orthogonal-projection-based scheme may not be applicable a simple power control
scheme is proposed.Comment: IEEE Internet of Things Journal, Accepte
Resource Allocation for Downlink NOMA Systems: Key Techniques and Open Issues
This article presents advances in resource allocation (RA) for downlink
non-orthogonal multiple access (NOMA) systems, focusing on user pairing (UP)
and power allocation (PA) algorithms. The former pairs the users to obtain the
high capacity gain by exploiting the channel gain difference between the users,
while the later allocates power to users in each cluster to balance system
throughput and user fairness. Additionally, the article introduces the concept
of cluster fairness and proposes the divideand- next largest difference-based
UP algorithm to distribute the capacity gain among the NOMA clusters in a
controlled manner. Furthermore, performance comparison between multiple-input
multiple-output NOMA (MIMO-NOMA) and MIMO-OMA is conducted when users have
pre-defined quality of service. Simulation results are presented, which
validate the advantages of NOMA over OMA. Finally, the article provides avenues
for further research on RA for downlink NOMA.Comment: 5G, NOMA, Resource allocation, User pairing, Power allocatio
Optimal User Scheduling and Power Allocation for Millimeter Wave NOMA Systems
This paper investigates the application of non-orthogonal multiple access
(NOMA) in millimeter wave (mmWave) communications by exploiting beamforming,
user scheduling and power allocation. Random beamforming is invoked for
reducing the feedback overhead of considered systems. A nonconvex optimization
problem for maximizing the sum rate is formulated, which is proved to be
NP-hard. The branch and bound (BB) approach is invoked to obtain the optimal
power allocation policy, which is proved to converge to a global optimal
solution. To elaborate further, low complexity suboptimal approach is developed
for striking a good computational complexity-optimality tradeoff, where
matching theory and successive convex approximation (SCA) techniques are
invoked for tackling the user scheduling and power allocation problems,
respectively. Simulation results reveal that: i) the proposed low complexity
solution achieves a near-optimal performance; and ii) the proposed mmWave NOMA
systems is capable of outperforming conventional mmWave orthogonal multiple
access (OMA) systems in terms of sum rate and the number of served users.Comment: Submitted for possible publicatio
Rate-Splitting for Multi-Antenna Non-Orthogonal Unicast and Multicast Transmission: Spectral and Energy Efficiency Analysis
In a Non-Orthogonal Unicast and Multicast (NOUM) transmission system, a
multicast stream intended to all the receivers is superimposed in the power
domain on the unicast streams. One layer of Successive Interference
Cancellation (SIC) is required at each receiver to remove the multicast stream
before decoding its intended unicast stream. In this paper, we first show that
a linearly-precoded 1-layer Rate-Splitting (RS) strategy at the transmitter can
efficiently exploit this existing SIC receiver architecture. We further propose
multi-layer transmission strategies based on the generalized RS and
power-domain Non-Orthogonal Multiple Access (NOMA). Two different objectives
are studied for the design of the precoders, namely, maximizing the Weighted
Sum Rate (WSR) of the unicast messages and maximizing the system Energy
Efficiency (EE), both subject to Quality of Service (QoS) rate requirements of
all the messages and a sum power constraint. A Weighted Minimum Mean Square
Error (WMMSE)-based algorithm and a Successive Convex Approximation (SCA)-based
algorithm are proposed to solve the WSR and EE problems, respectively.
Numerical results show that the proposed RS-assisted NOUM transmission
strategies are more spectrally and energy efficient than the conventional
Multi-User Linear-Precoding (MU-LP), Orthogonal Multiple Access (OMA) and
power-domain NOMA in a wide range of user deployments (with a diversity of
channel directions, channel strengths and qualities of channel state
information at the transmitter) and network loads (underloaded and overloaded
regimes). It is superior for the downlink multi-antenna NOUM transmission.Comment: Accepted by IEEE Transaction on Communication
Beamforming Design and Power Allocation for Secure Transmission with NOMA
In this work, we propose a novel beamforming design to enhance physical layer
security of a non-orthogonal multiple access (NOMA) system with the aid of
artificial noise (AN). The proposed design uses two scalars to balance the
useful signal strength and interference at the strong and weak users, which is
a generalized version of the existing beamforming designs in the context of
physical layer security for NOMA. We determine the optimal power allocation
among useful signals and AN together with the two optimal beamforming scalars
in order to maximize the secrecy sum rate (SSR). Our asymptotic analysis in the
high signal-to-noise ratio regime provides an efficient and near-optimal
solution to optimizing the beamforming scalars and power allocation
coefficients. Our analysis indicates that it is not optimal to form a beam
towards either the strong user or the weak user in NOMA systems for security
enhancement. In addition, the asymptotically optimal power allocation informs
that, as the transmit power increases, more power should be allocated to the
weak user or AN signals, while the power allocated to the strong user keeps
constant. Our examination shows that the proposed novel beamforming design can
significantly outperform two benchmark schemes
Precoder Design for Signal Superposition in MIMO-NOMA Multicell Networks
The throughput of users with poor channel conditions, such as those at a cell
edge, is a bottleneck in wireless systems. A major part of the power budget
must be allocated to serve these users in guaranteeing their quality-of-service
(QoS) requirement, hampering QoS for other users and thus compromising the
system reliability. In nonorthogonal multiple access (NOMA), the message
intended for a user with a poor channel condition is decoded by itself and by
another user with a better channel condition. The message intended for the
latter is then successively decoded by itself after canceling the interference
of the former. The overall information throughput is thus improved by this
particular successive decoding and interference cancellation. This paper aims
to design linear precoders/beamformers for signal superposition at the base
stations of NOMA multi-input multi-output multi-cellular systems to maximize
the overall sum throughput subject to the users' QoS requirements, which are
imposed independently on the users' channel condition. This design problem is
formulated as the maximization of a highly nonlinear and nonsmooth function
subject to nonconvex constraints, which is very computationally challenging.
Path-following algorithms for its solution, which invoke only a simple convex
problem of moderate dimension at each iteration are developed. Generating a
sequence of improved points, these algorithms converge at least to a local
optimum. Extensive numerical simulations are then provided to demonstrate their
merit.Comment: to appear in IEEE Journal on Selected Areas in Communications (JSAC),
201
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
Precoded Chebyshev-NLMS based pre-distorter for nonlinear LED compensation in NOMA-VLC
Visible light communication (VLC) is one of the main technologies driving the
future 5G communication systems due to its ability to support high data rates
with low power consumption, thereby facilitating high speed green
communications. To further increase the capacity of VLC systems, a technique
called non-orthogonal multiple access (NOMA) has been suggested to cater to
increasing demand for bandwidth, whereby users' signals are superimposed prior
to transmission and detected at each user equipment using successive
interference cancellation (SIC). Some recent results on NOMA exist which
greatly enhance the achievable capacity as compared to orthogonal multiple
access techniques. However, one of the performance-limiting factors affecting
VLC systems is the nonlinear characteristics of a light emitting diode (LED).
This paper considers the nonlinear LED characteristics in the design of
pre-distorter for cognitive radio inspired NOMA in VLC, and proposes singular
value decomposition based Chebyshev precoding to improve performance of
nonlinear multiple-input multiple output NOMA-VLC. A novel and generalized
power allocation strategy is also derived in this work, which is valid even in
scenarios when users experience similar channels. Additionally, in this work,
analytical upper bounds for the bit error rate of the proposed detector are
derived for square -quadrature amplitude modulation.Comment: R. Mitra and V. Bhatia are with Indian Institute of Technology
Indore, Indore-453552, India, Email:[email protected],
[email protected]. This work was submitted to IEEE Transactions on
Communications on October 26, 2016, decisioned on March 3, 2017, and revised
on April 25, 2017, and is currently under review in IEEE Transactions on
Communication
Power-Efficient Resource Allocation for MC-NOMA with Statistical Channel State Information
In this paper, we study the power-efficient resource allocation for
multicarrier non-orthogonal multiple access (MC-NOMA) systems. The resource
allocation algorithm design is formulated as a non-convex optimization problem
which takes into account the statistical channel state information at
transmitter and quality of service (QoS) constraints. To strike a balance
between system performance and computational complexity, we propose a
suboptimal power allocation and user scheduling with low computational
complexity to minimize the total power consumption. The proposed design
exploits the heterogeneity of QoS requirement to determine the successive
interference cancellation decoding order. Simulation results demonstrate that
the proposed scheme achieves a close-to-optimal performance and significantly
outperforms a conventional orthogonal multiple access (OMA) scheme.Comment: 7 Pages, 5 figures, accepted to IEEE GLOBECOM 201
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