2,263 research outputs found
Harvest the potential of massive MIMO with multi-layer techniques
Massive MIMO is envisioned as a promising technology for 5G wireless networks
due to its high potential to improve both spectral and energy efficiency.
Although the massive MIMO system is based on innovations in the physical layer,
the upper layer techniques also play important roles in harvesting the
performance gains of massive MIMO. In this article, we begin with an analysis
of the benefits and challenges of massive MIMO systems. We then investigate the
multi-layer techniques for incorporating massive MIMO in several important
network deployment scenarios. We conclude this article with a discussion of
open and potential problems for future research.Comment: IEEE Networ
A Survey of Millimeter Wave (mmWave) Communications for 5G: Opportunities and Challenges
With the explosive growth of mobile data demand, the fifth generation (5G)
mobile network would exploit the enormous amount of spectrum in the millimeter
wave (mmWave) bands to greatly increase communication capacity. There are
fundamental differences between mmWave communications and existing other
communication systems, in terms of high propagation loss, directivity, and
sensitivity to blockage. These characteristics of mmWave communications pose
several challenges to fully exploit the potential of mmWave communications,
including integrated circuits and system design, interference management,
spatial reuse, anti-blockage, and dynamics control. To address these
challenges, we carry out a survey of existing solutions and standards, and
propose design guidelines in architectures and protocols for mmWave
communications. We also discuss the potential applications of mmWave
communications in the 5G network, including the small cell access, the cellular
access, and the wireless backhaul. Finally, we discuss relevant open research
issues including the new physical layer technology, software-defined network
architecture, measurements of network state information, efficient control
mechanisms, and heterogeneous networking, which should be further investigated
to facilitate the deployment of mmWave communication systems in the future 5G
networks.Comment: 17 pages, 8 figures, 7 tables, Journal pape
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
Effective Capacity in Wireless Networks: A Comprehensive Survey
Low latency applications, such as multimedia communications, autonomous
vehicles, and Tactile Internet are the emerging applications for
next-generation wireless networks, such as 5th generation (5G) mobile networks.
Existing physical-layer channel models, however, do not explicitly consider
quality-of-service (QoS) aware related parameters under specific delay
constraints. To investigate the performance of low-latency applications in
future networks, a new mathematical framework is needed. Effective capacity
(EC), which is a link-layer channel model with QoS-awareness, can be used to
investigate the performance of wireless networks under certain statistical
delay constraints. In this paper, we provide a comprehensive survey on existing
works, that use the EC model in various wireless networks. We summarize the
work related to EC for different networks such as cognitive radio networks
(CRNs), cellular networks, relay networks, adhoc networks, and mesh networks.
We explore five case studies encompassing EC operation with different design
and architectural requirements. We survey various delay-sensitive applications
such as voice and video with their EC analysis under certain delay constraints.
We finally present the future research directions with open issues covering EC
maximization
Relay-Assisted and QoS Aware Scheduling to Overcome Blockage in mmWave Backhaul Networks
In the scenario where small cells are densely deployed, the millimeter wave
(mmWave) wireless backhaul network has been widely used. However, mmWave is
easily blocked by obstacles, and how to forward the data of the blocked flows
is still a significant challenge. To ensure backhauling capacity, the quality
of service (QoS) requirements of flows should be satisfied. In this paper, we
investigate the problem of optimal scheduling to maximize the number of flows
satisfying their QoS requirements with relays exploited to overcome blockage.
To achieve a practical solution, we propose a relay-assisted and QoS aware
scheduling scheme for the backhaul networks, called RAQS. It consists of a
relay selection algorithm and a transmission scheduling algorithm. The relay
selection algorithm selects non-repeating relays with high link rates for the
blocked flows, which helps to achieve the QoS requirements of flows as soon as
possible. Then, according to the results of relay selection, the transmission
scheduling algorithm exploits concurrent transmissions to satisfy the QoS
requirements of flows as much as possible. Extensive simulations show RAQS can
effectively overcome the blockage problem, and increase the number of completed
flows and network throughput compared with other schemes. In particular, the
impact of relay selection parameter is also investigated to further guide the
relay selection.Comment: 11 pages, 10 figure
Optimal Power Allocation for Secure Directional Modulation Networks with a Full-duplex UAV User
This paper make an investigation of a secure unmanned aerial vehicle
(UAV)-aided communication network based on directional modulation(DM), in which
one ground base station (Alice), one legitimate full-duplex (FD) user (Bob) and
one illegal receiver (Eve) are involved. In this network, Alice acts as a
control center to transmit confidential message and artificial noise (AN). The
UAV user, moving along a linear flight trajectory, is intended to receive the
useful information from Alice. At the same time, it also sends AN signals to
further interference Eve's channel. Aiming at maximizing secrecy rate during
the UAV flight process, a joint optimization problem is formulated
corresponding to power allocation (PA) factors, beamforming vector, AN
projection matrices. For simplicity, maximum ratio transmission, null-space
projection and the leakage-based method are applied to form the transmit
beamforming vector, AN projection matrix at Alice, and AN projection vector at
Bob, respectively. Following this, the optimization problem reduces into a
bivariate optimization programme with two PA factors. We put forward an
alternating iterative algorithm to optimize the two PA factors. Simulation
results demonstrate that the proposed strategy for FD mode achieves a higher SR
than the half-duplex (HD) mode, and outperforms the FD mode with fixed PA
strategy
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
A Survey of Rate-optimal Power Domain NOMA with Enabling Technologies of Future Wireless Networks
The ambitious high data-rate applications in the envisioned future B5G
networks require new solutions, including the advent of more advanced
architectures than the ones already used in 5G networks, and the coalition of
different communications schemes and technologies to enable these applications
requirements. Among the candidate schemes for future wireless networks are NOMA
schemes that allow serving more than one user in the same resource block by
multiplexing users in other domains than frequency or time. In this way, NOMA
schemes tend to offer several advantages over OMA schemes such as improved user
fairness and spectral efficiency, higher cell-edge throughput, massive
connectivity support, and low transmission latency. With these merits,
NOMA-enabled transmission schemes are being increasingly looked at as promising
multiple access schemes for future wireless networks. When the power domain is
used to multiplex the users, it is referred to as PD-NOMA. In this paper, we
survey the integration of PD-NOMA with the enabling communications schemes and
technologies that are expected to meet the various requirements of B5G
networks. In particular, this paper surveys the different rate optimization
scenarios studied in the literature when PD-NOMA is combined with one or more
of the candidate schemes and technologies for B5G networks including MISO,
MIMO, mMIMO, advanced antenna architectures, mmWave and THz, CoMP, cooperative
communications, cognitive radio, VLC, UAV and others. The considered system
models, the optimization methods utilized to maximize the achievable rates, and
the main lessons learnt on the optimization and the performance of these
NOMA-enabled schemes and technologies are discussed in detail along with the
future research directions for these combined schemes. Moreover, the role of
machine learning in optimizing these NOMA-enabled technologies is addressed.Comment: Accepted for publication in IEEE Surveys and Tutorials, July 202
Modeling and Analysis of Two-Way Relay Non-Orthogonal Multiple Access Systems
A two-way relay non-orthogonal multiple access (TWR-NOMA) system is
investigated, where two groups of NOMA users exchange messages with the aid of
one half-duplex (HD) decode-and-forward (DF) relay. Since the
signal-plus-interference-to-noise ratios (SINRs) of NOMA signals mainly depend
on effective successive interference cancellation (SIC) schemes, imperfect SIC
(ipSIC) and perfect SIC (pSIC) are taken into account. In order to characterize
the performance of TWR-NOMA systems, we first derive closed-form expressions
for both exact and asymptotic outage probabilities of NOMA users' signals with
ipSIC/pSIC. Based on the derived results, the diversity order and throughput of
the system are examined. Then we study the ergodic rates of users' signals by
providing the asymptotic analysis in high SNR regimes. Lastly, numerical
simulations are provided to verify the analytical results and show that: 1)
TWR-NOMA is superior to TWR-OMA in terms of outage probability in low SNR
regimes; 2) Due to the impact of interference signal (IS) at the relay, error
floors and throughput ceilings exist in outage probabilities and ergodic rates
for TWR-NOMA, respectively; and 3) In delay-limited transmission mode, TWR-NOMA
with ipSIC and pSIC have almost the same energy efficiency. However, in
delay-tolerant transmission mode, TWR-NOMA with pSIC is capable of achieving
larger energy efficiency compared to TWR-NOMA with ipSIC.Comment: 12 pages, 8 figures. arXiv admin note: substantial text overlap with
arXiv:1801.0817
User-Centric Joint Access-Backhaul Design for Full-Duplex Self-Backhauled Wireless Networks
Full-duplex self-backhauling is promising to provide cost-effective and
flexible backhaul connectivity for ultra-dense wireless networks, but also
poses a great challenge to resource management between the access and backhaul
links. In this paper, we propose a user-centric joint access-backhaul
transmission framework for full-duplex self-backhauled wireless networks. In
the access link, user-centric clustering is adopted so that each user is
cooperatively served by multiple small base stations (SBSs). In the backhaul
link, user-centric multicast transmission is proposed so that each user's
message is treated as a common message and multicast to its serving SBS
cluster. We first formulate an optimization problem to maximize the network
weighted sum rate through joint access-backhaul beamforming and SBS clustering
when global channel state information (CSI) is available. This problem is
efficiently solved via the successive lower-bound maximization approach with a
novel approximate objective function and the iterative link removal technique.
We then extend the study to the stochastic joint access-backhaul beamforming
optimization with partial CSI. Simulation results demonstrate the effectiveness
of the proposed algorithms for both full CSI and partial CSI scenarios. They
also show that the transmission design with partial CSI can greatly reduce the
CSI overhead with little performance degradation.Comment: to appear in IEEE Trans. on Communication
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