4,717 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
Reconfigurable Wireless Networks
Driven by the advent of sophisticated and ubiquitous applications, and the
ever-growing need for information, wireless networks are without a doubt
steadily evolving into profoundly more complex and dynamic systems. The user
demands are progressively rampant, while application requirements continue to
expand in both range and diversity. Future wireless networks, therefore, must
be equipped with the ability to handle numerous, albeit challenging
requirements. Network reconfiguration, considered as a prominent network
paradigm, is envisioned to play a key role in leveraging future network
performance and considerably advancing current user experiences. This paper
presents a comprehensive overview of reconfigurable wireless networks and an
in-depth analysis of reconfiguration at all layers of the protocol stack. Such
networks characteristically possess the ability to reconfigure and adapt their
hardware and software components and architectures, thus enabling flexible
delivery of broad services, as well as sustaining robust operation under highly
dynamic conditions. The paper offers a unifying framework for research in
reconfigurable wireless networks. This should provide the reader with a
holistic view of concepts, methods, and strategies in reconfigurable wireless
networks. Focus is given to reconfigurable systems in relatively new and
emerging research areas such as cognitive radio networks, cross-layer
reconfiguration and software-defined networks. In addition, modern networks
have to be intelligent and capable of self-organization. Thus, this paper
discusses the concept of network intelligence as a means to enable
reconfiguration in highly complex and dynamic networks. Finally, the paper is
supported with several examples and case studies showing the tremendous impact
of reconfiguration on wireless networks.Comment: 28 pages, 26 figures; Submitted to the Proceedings of the IEEE (a
special issue on Reconfigurable Systems
Intelligent Wireless Communications Enabled by Cognitive Radio and Machine Learning
The ability to intelligently utilize resources to meet the need of growing
diversity in services and user behavior marks the future of wireless
communication systems. Intelligent wireless communications aims at enabling the
system to perceive and assess the available resources, to autonomously learn to
adapt to the perceived wireless environment, and to reconfigure its operating
mode to maximize the utility of the available resources. The perception
capability and reconfigurability are the essential features of cognitive radio
while modern machine learning techniques project great potential in system
adaptation. In this paper, we discuss the development of the cognitive radio
technology and machine learning techniques and emphasize their roles in
improving spectrum and energy utility of wireless communication systems. We
describe the state-of-the-art of relevant techniques, covering spectrum sensing
and access approaches and powerful machine learning algorithms that enable
spectrum- and energy-efficient communications in dynamic wireless environments.
We also present practical applications of these techniques and identify further
research challenges in cognitive radio and machine learning as applied to the
existing and future wireless communication systems
Joint Link Adaptation and User Scheduling with HARQ in Multi-Cell Environments
Inter-cell interference (ICI) is one of the most critical factors affecting
performance of cellular networks. In this paper, we investigate a joint link
adaptation and user scheduling problem for multi-cell downlink employing HARQ
techniques, where the ICI exists among cells. We first propose an approximation
method on aggregated ICI for analyzing an effective
signal-to-interference-and-noise ratio (SINR) with the HARQ technique at users,
named identical path-loss approximation (IPLA). Based on the proposed IPLA, we
propose a transmission rate selection algorithm maximizing an expected
throughput at each user. We also propose a simple but effective cross-layer
framework jointly combining transmission rate adaptation and user scheduling
techniques, considering both HARQ and ICI. It is shown that statistical
distribution of the effective SINR at users based on the IPLA agrees well with
the empirical distribution, while the conventional Gaussian approximation (GA)
does not work well in the case that dominant ICIs exist. Thus, IPLA enables
base stations to choose more accurate transmission rates. Furthermore, the
proposed IPLA-based cross-layer policy outperforms existing policies in terms
of both system throughput and user fairness.Comment: Accepted for publication to IEEE Transactions on Vehicular Technolog
KPI/KQI-Driven Coordinated Multi-Point in 5G: Measurements, Field Trials, and Technical Solutions
The fifth generation (5G) systems are expected to be able to support massive
number of wireless devices and intense demands for high data rates while
maintaining low latency. Coordinated multipoint (CoMP) is advocated by recent
advances and is envisioned to continue its adoption in 5G to meet these
requirements by alleviating inter-cell interference and improving spectral
efficiency. The higher requirements in 5G have raised the stakes on developing
a new CoMP architecture. To understand the merits and limitations of CoMP in
5G, this article systematically investigates evaluation criteria including key
performance indicators (KPIs) and key quality indicators (KQIs) in 5G, conducts
empirical measurements and field tests, and then proposes a KPI/KQI-driven CoMP
architecture that fulfills KPI requirements and provides KQI guarantee for each
user
Distortion-Aware Concurrent Multipath Transfer for Mobile Video Streaming in Heterogeneous Wireless Networks
The massive proliferation of wireless infrastructures with complementary
characteristics prompts the bandwidth aggregation for Concurrent Multipath
Transfer (CMT) over heterogeneous access networks. Stream Control Transmission
Protocol (SCTP) is the standard transport-layer solution to enable CMT in
multihomed communication environments. However, delivering high-quality
streaming video with the existing CMT solutions still remains problematic due
to the stringent QoS (Quality of Service) requirements and path asymmetry in
heterogeneous wireless networks. In this paper, we advance the state of the art
by introducing video distortion into the decision process of multipath data
transfer. The proposed Distortion-Aware Concurrent Multipath Transfer (CMT-DA)
solution includes three phases: 1) per-path status estimation and congestion
control; 2) quality-optimal video flow rate allocation; 3) delay and loss
controlled data retransmission. The term `flow rate allocation' indicates
dynamically picking appropriate access networks and assigning the transmission
rates. We analytically formulate the data distribution over multiple
communication paths to minimize the end-to-end video distortion and derive the
solution based on the utility maximization theory. The performance of the
proposed CMT-DA is evaluated through extensive semi-physical emulations in
Exata involving H.264 video streaming. Experimental results show that CMT-DA
outperforms the reference schemes in terms of video PSNR (Peak Signal-to-Noise
Ratio), goodput, and inter-packet delay.Comment: This paper has already accepted for publication in IEEE Transactions
on Mobile Computing on Jun, 23rd, 201
User Association and Interference Management in Massive MIMO HetNets
Two key traits of 5G cellular networks are much higher base station (BS)
densities - especially in the case of low-power BSs - and the use of massive
MIMO at these BSs. This paper explores how massive MIMO can be used to jointly
maximize the offloading gains and minimize the interference challenges arising
from adding small cells. We consider two interference management approaches:
joint transmission (JT) with local precoding, where users are served
simultaneously by multiple BSs without requiring channel state information
exchanges among cooperating BSs, and resource blanking, where some macro BS
resources are left blank to reduce the interference in the small cell downlink.
A key advantage offered by massive MIMO is channel hardening, which enables to
predict instantaneous rates a priori. This allows us to develop a unified
framework, where resource allocation is cast as a network utility maximization
(NUM) problem, and to demonstrate large gains in cell-edge rates based on the
NUM solution. We propose an efficient dual subgradient based algorithm, which
converges towards the NUM solution. A scheduling scheme is also proposed to
approach the NUM solution. Simulations illustrate more than 2x rate gain for
10th percentile users vs. an optimal association without interference
management
Game Theoretic Methods for the Smart Grid
The future smart grid is envisioned as a large-scale cyber-physical system
encompassing advanced power, communications, control, and computing
technologies. In order to accommodate these technologies, it will have to build
on solid mathematical tools that can ensure an efficient and robust operation
of such heterogeneous and large-scale cyber-physical systems. In this context,
this paper is an overview on the potential of applying game theory for
addressing relevant and timely open problems in three emerging areas that
pertain to the smart grid: micro-grid systems, demand-side management, and
communications. In each area, the state-of-the-art contributions are gathered
and a systematic treatment, using game theory, of some of the most relevant
problems for future power systems is provided. Future opportunities for
adopting game theoretic methodologies in the transition from legacy systems
toward smart and intelligent grids are also discussed. In a nutshell, this
article provides a comprehensive account of the application of game theory in
smart grid systems tailored to the interdisciplinary characteristics of these
systems that integrate components from power systems, networking,
communications, and control.Comment: IEEE Signal Processing Magazine, Special Issue on Signal Processing
Techniques for the Smart Gri
V2X Meets NOMA: Non-Orthogonal Multiple Access for 5G Enabled Vehicular Networks
Benefited from the widely deployed infrastructure, the LTE network has
recently been considered as a promising candidate to support the
vehicle-to-everything (V2X) services. However, with a massive number of devices
accessing the V2X network in the future, the conventional OFDM-based LTE
network faces the congestion issues due to its low efficiency of orthogonal
access, resulting in significant access delay and posing a great challenge
especially to safety-critical applications. The non-orthogonal multiple access
(NOMA) technique has been well recognized as an effective solution for the
future 5G cellular networks to provide broadband communications and massive
connectivity. In this article, we investigate the applicability of NOMA in
supporting cellular V2X services to achieve low latency and high reliability.
Starting with a basic V2X unicast system, a novel NOMA-based scheme is proposed
to tackle the technical hurdles in designing high spectral efficient scheduling
and resource allocation schemes in the ultra dense topology. We then extend it
to a more general V2X broadcasting system. Other NOMA-based extended V2X
applications and some open issues are also discussed.Comment: Accepted by IEEE Wireless Communications Magazin
Game Theoretical Power Control for Open-Loop Overlaid Network MIMO Systems with Partial Cooperation
Network MIMO is considered to be a key solution for the next generation
wireless systems in breaking the interference bottleneck in cellular systems.
In the MIMO systems, open-loop transmission scheme is used to support mobile
stations (MSs) with high mobilities because the base stations (BSs) do not need
to track the fast varying channel fading. In this paper, we consider an
open-loop network MIMO system with BSs serving K private MSs and
common MS based on a novel partial cooperation overlaying scheme. Exploiting
the heterogeneous path gains between the private MSs and the common MSs, each
of the BSs serves a private MS non-cooperatively and the BSs also serve
the common MSs cooperatively. The proposed scheme does not require closed
loop instantaneous channel state information feedback, which is highly
desirable for high mobility users. Furthermore, we formulate the long-term
distributive power allocation problem between the private MSs and the common
MSs at each of the BSs using a partial cooperative game. We show that the
long-term power allocation game has a unique Nash Equilibrium (NE) but standard
best response update may not always converge to the NE. As a result, we propose
a low-complexity distributive long-term power allocation algorithm which only
relies on the local long-term channel statistics and has provable convergence
property. Through numerical simulations, we show that the proposed open-loop
SDMA scheme with long-term distributive power allocation can achieve
significant performance advantages over the other reference baseline schemes.Comment: 18pages, 7 figures, IEEE Transactions on Wireless Communication,
accepte
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