629 research outputs found
Millimeter-Wave Communication with Non-Orthogonal Multiple Access for 5G
To further improve the system capacity for 5G, we explore the integration of
non-orthogonal multiple access (NOMA) in mmWave communications (mmWave-NOMA)
for future 5G systems. Compared with the conventional NOMA, the distinguishing
feature of mmWave-NOMA is that, it is usually characterized by transmit/receive
beamforming with large antenna arrays. In this paper, we focus on the design
challenges of mmWave-NOMA due to beamforming. Firstly, we study how beamforming
affects the sum-rate performance of mmWave-NOMA, and find that with
conventional single-beam forming, the performance may be offset by the relative
angle between NOMA users. Then, we consider multi-beam forming for mmWave-NOMA,
which is shown to be able to achieve promising performance enhancement as well
as robustness. We further investigate the challenging joint design of the
intertwined power allocation and user pairing for mmWave-NOMA. We also discuss
the challenges and propose some potential solutions in detail. Finally, we
consider hybrid spatial division multiple access (SDMA) and NOMA in mmWave
communications, where some possible system configurations and the corresponding
solutions are discussed to address the multi-user issues including multi-user
precoding and multi-user interference (MUI) mitigation.Comment: This paper explores mmWave communications with NOMA for 5G, and
focuses on the beamforming issues with phased array
Multi-Beam NOMA for Hybrid mmWave Systems
In this paper, we propose a multi-beam non-orthogonal multiple access (NOMA)
scheme for hybrid millimeter wave (mmWave) systems and study its resource
allocation. A beam splitting technique is designed to generate multiple analog
beams to serve multiple users for NOMA transmission. Compared to conventional
mmWave orthogonal multiple access (mmWave-OMA) schemes, the proposed scheme can
serve more than one user on each radio frequency (RF) chain. Besides, in
contrast to the recently proposed single-beam mmWave-NOMA scheme which can only
serve multiple NOMA users within the same beam, the proposed scheme can perform
NOMA transmission for the users with an arbitrary angle-of-departure (AOD)
distribution. This provides a higher flexibility for applying NOMA in mmWave
communications and thus can efficiently exploit the potential multi-user
diversity. Then, we design a suboptimal two-stage resource allocation for
maximizing the system sum-rate. In the first stage, assuming that only analog
beamforming is available, a user grouping and antenna allocation algorithm is
proposed to maximize the conditional system sum-rate based on the coalition
formation game theory. In the second stage, with the zero-forcing (ZF) digital
precoder, a suboptimal solution is devised to solve a non-convex power
allocation optimization problem for the maximization of the system sum-rate
which takes into account the quality of service (QoS) constraint. Simulation
results show that our designed resource allocation can achieve a
close-to-optimal performance in each stage. In addition, we demonstrate that
the proposed multi-beam mmWave-NOMA scheme offers a higher spectral efficiency
than that of the single-beam mmWave-NOMA and the mmWave-OMA schemes.Comment: Submitted for possible journal publicatio
A Multi-Beam NOMA Framework for Hybrid mmWave Systems
In this paper, we propose a multi-beam non-orthogonal multiple access (NOMA)
framework for hybrid millimeter wave (mmWave) systems. The proposed framework
enables the use of a limited number of radio frequency (RF) chains in hybrid
mmWave systems to accommodate multiple users with various angles of departures
(AODs). A beam splitting technique is introduced to generate multiple analog
beams to facilitate NOMA transmission. We analyze the performance of a system
when there are sufficient numbers of antennas driven by a single RF chain at
each transceiver. Furthermore, we derive the sufficient and necessary
conditions of antenna allocation, which guarantees that the proposed multi-beam
NOMA scheme outperforms the conventional time division multiple access (TDMA)
scheme in terms of system sum-rate. The numerical results confirm the accuracy
of the developed analysis and unveil the performance gain achieved by the
proposed multi-beam NOMA scheme over the single-beam NOMA scheme.Comment: 7 pages, 5 figures, accepted for ICC 201
Hybrid Precoding-Based Millimeter-Wave Massive MIMO-NOMA with Simultaneous Wireless Information and Power Transfer
Non-orthogonal multiple access (NOMA) has been recently considered in
millimeter-wave (mmWave) massive MIMO systems to further enhance the spectrum
efficiency. In addition, simultaneous wireless information and power transfer
(SWIPT) is a promising solution to maximize the energy efficiency. In this
paper, for the first time, we investigate the integration of SWIPT in mmWave
massive MIMO-NOMA systems. As mmWave massive MIMO will likely use hybrid
precoding (HP) to significantly reduce the number of required radio-frequency
(RF) chains without an obvious performance loss, where the fully digital
precoder is decomposed into a high-dimensional analog precoder and a
low-dimensional digital precoder, we propose to apply SWIPT in HP-based
MIMO-NOMA systems, where each user can extract both information and energy from
the received RF signals by using a power splitting receiver. Specifically, the
cluster-head selection (CHS) algorithm is proposed to select one user for each
beam at first, and then the analog precoding is designed according to the
selected cluster heads for all beams. After that, user grouping is performed
based on the correlation of users' equivalent channels. Then, the digital
precoding is designed by selecting users with the strongest equivalent channel
gain in each beam. Finally, the achievable sum rate is maximized by jointly
optimizing power allocation for mmWave massive MIMO-NOMA and power splitting
factors for SWIPT, and an iterative optimization algorithm is developed to
solve the non-convex problem. Simulation results show that the proposed
HP-based MIMO-NOMA with SWIPT can achieve higher spectrum and energy efficiency
compared with HP-based MIMO-OMA with SWIPT.Comment: To appear in IEEE Journal on Selected Areas in Communications.
Simulation codes are provided to reproduce the results presented in this
paper:
http://oa.ee.tsinghua.edu.cn/dailinglong/publications/publications.htm
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
A Two-Stage Beam Alignment Framework for Hybrid MmWave Distributed Antenna Systems
In this paper, we investigate the beam alignment problem in millimeter-wave
(mmWave) distributed antenna systems where a home base station communicates
with multiple users through a number of distributed remote radio units (RRUs).
Specifically, a two-stage schedule-and-align (TSSA) scheme is proposed to
facilitate efficient communications. In the first stage, a coarse beam scanning
over the entire angular space is performed while beam indices and the
corresponding peak-to-background ratios of the received power-angle-spectrum
are obtained from users' feedback. Then, by exploiting the user feedback, an
efficient user scheduling algorithm is developed to improve the system spectral
efficiency and to reduce the system misalignment probability. Next, the second
stage of beam search is performed by each RRU with reconfigured search angles,
search steps, and power levels to obtain a refined beam alignment. Simulation
results show that the proposed TSSA scheme can significantly outperform the
conventional one-stage method in both centralized and distributed mmWave
systems in terms of beam alignment accuracy and spectral efficiency.Comment: 5 pages, 5 figures, accepted by IEEE SPAWC 201
A Survey on Non-Orthogonal Multiple Access for 5G Networks: Research Challenges and Future Trends
Non-orthogonal multiple access (NOMA) is an essential enabling technology for
the fifth generation (5G) wireless networks to meet the heterogeneous demands
on low latency, high reliability, massive connectivity, improved fairness, and
high throughput. The key idea behind NOMA is to serve multiple users in the
same resource block, such as a time slot, subcarrier, or spreading code. The
NOMA principle is a general framework, and several recently proposed 5G
multiple access schemes can be viewed as special cases. This survey provides an
overview of the latest NOMA research and innovations as well as their
applications. Thereby, the papers published in this special issue are put into
the content of the existing literature. Future research challenges regarding
NOMA in 5G and beyond are also discussed.Comment: to appear in IEEE JSAC, 201
Joint Tx-Rx Beamforming and Power Allocation for 5G Millimeter-Wave Non-Orthogonal Multiple Access (MmWave-NOMA) Networks
In this paper, we investigate the combination of non-orthogonal multiple
access and millimeter-Wave communications (mmWave-NOMA). A downlink cellular
system is considered, where an analog phased array is equipped at both the base
station and users. A joint Tx-Rx beamforming and power allocation problem is
formulated to maximize the achievable sum rate (ASR) subject to a minimum rate
constraint for each user. As the problem is non-convex, we propose a
sub-optimal solution with three stages. In the first stage, the optimal power
allocation with a closed form is obtained for an arbitrary fixed Tx-Rx
beamforming. In the second stage, the optimal Rx beamforming with a closed form
is designed for an arbitrary fixed Tx beamforming. In the third stage, the
original problem is reduced to a Tx beamforming problem by using the previous
results, and a boundary-compressed particle swarm optimization (BC-PSO)
algorithm is proposed to obtain a sub-optimal solution. Extensive performance
evaluations are conducted to verify the rational of the proposed solution, and
the results show that the proposed sub-optimal solution can achieve a
near-upper-bound performance in terms of ASR, which is significantly improved
compared with those of the state-of-the-art schemes and the conventional mmWave
orthogonal multiple access (mmWave-OMA) system.Comment: 11Pages, 10 figure
Signal Processing for MIMO-NOMA: Present and Future Challenges
Non-orthogonal multiple access (NOMA), as the newest member of the multiple
access family, is envisioned to be an essential component of 5G mobile
networks. The combination of NOMA and multi-antenna multi-input multi-output
(MIMO) technologies exhibits a significant potential in improving spectral
efficiency and providing better wireless services to more users. In this
article, we introduce the basic concepts of MIMO-NOMA and summarize the key
technical problems in MIMO-NOMA systems. Then, we explore the problem
formulation, beamforming, user clustering, and power allocation of
single/multi-cluster MIMO-NOMA in the literature along with their limitations.
Furthermore, we point out an important issue of the stability of successive
interference cancellation (SIC) that arises using achievable rates as
performance metrics in practical NOMA/MIMO-NOMA systems. Finally, we discuss
incorporating NOMA with massive/millimeter wave MIMO, and identify the main
challenges and possible future research directions in this area.Comment: 14 pages (single column), 4 figures. This work has been accepted by
the IEEE Wireless Communications, the special issue of non-orthogonal
multiple access for 5
Deep Learning for Physical-Layer 5G Wireless Techniques: Opportunities, Challenges and Solutions
The new demands for high-reliability and ultra-high capacity wireless
communication have led to extensive research into 5G communications. However,
the current communication systems, which were designed on the basis of
conventional communication theories, signficantly restrict further performance
improvements and lead to severe limitations. Recently, the emerging deep
learning techniques have been recognized as a promising tool for handling the
complicated communication systems, and their potential for optimizing wireless
communications has been demonstrated. In this article, we first review the
development of deep learning solutions for 5G communication, and then propose
efficient schemes for deep learning-based 5G scenarios. Specifically, the key
ideas for several important deep learningbased communication methods are
presented along with the research opportunities and challenges. In particular,
novel communication frameworks of non-orthogonal multiple access (NOMA),
massive multiple-input multiple-output (MIMO), and millimeter wave (mmWave) are
investigated, and their superior performances are demonstrated. We vision that
the appealing deep learning-based wireless physical layer frameworks will bring
a new direction in communication theories and that this work will move us
forward along this road.Comment: Submitted a possible publication to IEEE Wireless Communications
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