1,039 research outputs found
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
All Technologies Work Together for Good: A Glance to Future Mobile Networks
The astounding capacity requirements of 5G have motivated researchers to
investigate the feasibility of many potential technologies, such as massive
multiple-input multiple-output, millimeter wave, full-duplex, non-orthogonal
multiple access, carrier aggregation, cognitive radio, and network
ultra-densification. The benefits and challenges of these technologies have
been thoroughly studied either individually or in a combination of two or
three. It is not clear, however, whether all potential technologies operating
together lead to fulfilling the requirements posed by 5G. This paper explores
the potential benefits and challenges when all technologies coexist in an
ultra-dense cellular environment. The sum rate of the network is investigated
with respect to the increase in the number of small-cells and results show the
capacity gains achieved by the coexistence.Comment: Accepted for publication in IEEE Wireless Communication, Special
Issue-5G mmWave Small Cell Networks: Architecture, Self-Organization and
Managemen
Non-Orthogonal Multiple Access: Common Myths and Critical Questions
Non-orthogonal multiple access (NOMA) has received tremendous attention for
the design of radio access techniques for fifth generation (5G) wireless
networks and beyond. The basic concept behind NOMA is to serve more than one
user in the same resource block, e.g., a time slot, subcarrier, spreading code,
or space. With this, NOMA promotes massive connectivity, lowers latency,
improves user fairness and spectral efficiency, and increases reliability
compared to orthogonal multiple access (OMA) techniques. While NOMA has gained
significant attention from the communications community, it has also been
subject to several widespread misunderstandings, such as The above statements are actually false, and this paper aims at
identifying such common myths about NOMA and clarifying why they are not true.
We also pose critical questions that are important for the effective adoption
of NOMA in 5G and beyond and identify promising research directions for NOMA,
which will require intense investigation in the future.Comment: To appear in the IEEE Wireless Communication
Large-Scale NOMA: Promises for Massive Machine-Type Communication
We investigate on large-scale deployment of non-orthogonal multiple access
(NOMA) for improved spectral and power efficiency in cellular networks to
provide massive wireless connectivity (e.g. for machine-type communication
[mMTC]). First, we describe the basics of single-antenna NOMA technology and
its extension to co-located multiple-antenna NOMA as well as coordinated
multipoint transmission (CoMP)-enabled NOMA technologies. Then we discuss some
of the practical challenges of large-scale deployment of NOMA such as the
inter-NOMA-interference (INI), inter-cell interference, and hardware
implementation complexity. To this end, we present one key enabling technique
to overcome the challenges of large-scale deployment of NOMA. Generally
speaking, for a feasible large-scale NOMA implementation, sophisticated
diversity enhancing techniques can be used to compensate for the degradation in
coding gain and to decrease the complexity resulting from excessive INI and
increased level of required successive interference cancellation (SIC).
Furthermore, to massively extend NOMA over the network coverage area, NOMA
transmitters have to cooperate in a generalized manner to serve all nearby
users simultaneously
NOMA in 5G Systems: Exciting Possibilities for Enhancing Spectral Efficiency
This article provides an overview of power-domain non-orthogonal multiple
access for 5G systems. The basic concepts and benefits are briefly presented,
along with current solutions and standardization activities. In addition,
limitations and research challenges are discussed.Comment: 6 pages, 1 figure, IEEE 5G Tech Focu
Full-Duplex Communications: Performance in Ultra-Dense Small-Cell Wireless Networks
Theoretically, full-duplex (FD) communications can double the
spectral-efficiency (SE) of a wireless link if the problem of self-interference
(SI) is completely eliminated. Recent developments towards SI cancellation
techniques have allowed to realize the FD communications on low-power
transceivers, such as small-cell (SC) base stations. Consequently, the FD
technology is being considered as a key enabler of 5G and beyond networks. In
the context of 5G, FD communications have been initially investigated in a
single SC and then into multiple SC environments. Due to FD operations, a
single SC faces residual SI and intra-cell co-channel interference (CCI),
whereas multiple SCs face additional inter-cell CCI, which grows with the
number of neighboring cells. The surge of interference in the multi-cell
environment poses the question of the feasibility of FD communications. In this
article, we first review the FD communications in single and multiple SC
environments and then provide the state-of-the-art for the CCI mitigation
techniques, as well as FD feasibility studies in a multi-cell environment.
Further, through numerical simulations, the SE performance gain of the FD
communications in ultra-dense massive multiple input multiple-output enabled
millimeter wave SCs is presented. Finally, potential open research challenges
of multi-cell FD communications are highlighted.Comment: Accepted for publication in IEEE Vehicular Technology Magazine,
Special Issue on 5G Technologies and Application
On the Performance of Network NOMA in Uplink CoMP Systems: A Stochastic Geometry Approach
To improve the system throughput, this paper proposes a network
non-orthogonal multiple access (N-NOMA) technique for the uplink coordinated
multi-point transmission (CoMP). In the considered scenario, multiple base
stations collaborate with each other to serve a single user, referred to as the
CoMP user, which is the same as for conventional CoMP. However, unlike
conventional CoMP, each base station in N-NOMA opportunistically serves an
extra user, referred to as the NOMA user, while serving the CoMP user at the
same bandwidth. The CoMP user is typically located at the cell-edge, whereas
users close to the base stations are scheduled as NOMA users. Hence, the
channel conditions of the two kind of users are very distinctive, which
facilitates the implementation of NOMA. Compared to the conventional orthogonal
multiple access based CoMP scheme, where multiple base stations serve a single
CoMP user only, the proposed N-NOMA scheme can support larger connectivity by
serving the extra NOMA users, and improve the spectral efficiency by avoiding
the CoMP user solely occupying the spectrum. A stochastic geometry approach is
applied to model the considered N-NOMA scenario as a Poisson cluster process,
based on which closed-form analytical expressions for outage probabilities and
ergodic rates are obtained. Numerical results are presented to show the
accuracy of the analytical results and also demonstrate the superior
performance of the proposed N-NOMA scheme
Spectrum and Energy Efficient Beamspace MIMO-NOMA for Millimeter-Wave Communications Using Lens Antenna Array
The recent concept of beamspace multiple input multiple output (MIMO) can
significantly reduce the number of required radio-frequency (RF) chains in
millimeter-wave (mmWave) massive MIMO systems without obvious performance loss.
However, the fundamental limit of existing beamspace MIMO is that, the number
of supported users cannot be larger than the number of RF chains at the same
time-frequency resources. To break this fundamental limit, in this paper we
propose a new spectrum and energy efficient mmWave transmission scheme that
integrates the concept of non-orthogonal multiple access (NOMA) with beamspace
MIMO, i.e., beamspace MIMO-NOMA. By using NOMA in beamspace MIMO systems, the
number of supported users can be larger than the number of RF chains at the
same time-frequency resources. Particularly, the achievable sum rate of the
proposed beamspace MIMO-NOMA in a typical mmWave channel model is analyzed,
which shows an obvious performance gain compared with the existing beamspace
MIMO. Then, a precoding scheme based on the principle of zero-forcing (ZF) is
designed to reduce the inter-beam interferences in the beamspace MIMO-NOMA
system. Furthermore, to maximize the achievable sum rate, a dynamic power
allocation is proposed by solving the joint power optimization problem, which
not only includes the intra-beam power optimization, but also considers the
inter-beam power optimization. Finally, an iterative optimization algorithm
with low complexity is developed to realize the dynamic power allocation.
Simulation results show that the proposed beamspace MIMO-NOMA can achieve
higher spectrum and energy efficiency compared with existing beamspace MIMO.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
Full-Duplex Non-Orthogonal Multiple Access for Modern Wireless Networks
Non-orthogonal multiple access (NOMA) is an interesting concept to provide
higher capacity for future wireless communications. In this article, we
consider the feasibility and benefits of combining full-duplex operation with
NOMA for modern communication systems. Specifically, we provide a comprehensive
overview on application of full-duplex NOMA in cellular networks, cooperative
and cognitive radio networks, and characterize gains possible due to
full-duplex operation. Accordingly, we discuss challenges, particularly the
self-interference and inter-user interference and provide potential solutions
to interference mitigation and quality-of-service provision based on
beamforming, power control, and link scheduling. We further discuss future
research challenges and interesting directions to pursue to bring full-duplex
NOMA into maturity and use in practice.Comment: Revised, IEEE Wireless Communication Magazin
Power Control for Multi-Cell Networks with Non-Orthogonal Multiple Access
In this paper, we investigate the problems of sum power minimization and sum
rate maximization for multi-cell networks with non-orthogonal multiple access.
Considering the sum power minimization, we obtain closed-form solutions to the
optimal power allocation strategy and then successfully transform the original
problem to a linear one with a much smaller size, which can be optimally solved
by using the standard interference function. To solve the nonconvex sum rate
maximization problem, we first prove that the power allocation problem for a
single cell is a convex problem. By analyzing the Karush-Kuhn-Tucker
conditions, the optimal power allocation for users in a single cell is derived
in closed form. Based on the optimal solution in each cell, a distributed
algorithm is accordingly proposed to acquire efficient solutions. Numerical
results verify our theoretical findings showing the superiority of our
solutions compared to the orthogonal frequency division multiple access and
broadcast channel.Comment: Accepted in IEEE TWC. Key words: NOMA, multicell, distributed
algorithm, power allocation, rate constraint
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