4,113 research outputs found
Cost-Efficient Throughput Maximization in Multi-Carrier Cognitive Radio Systems
Cognitive radio (CR) systems allow opportunistic, secondary users (SUs) to
access portions of the spectrum that are unused by the network's licensed
primary users (PUs), provided that the induced interference does not compromise
the primary users' performance guarantees. To account for interference
constraints of this type, we consider a flexible spectrum access pricing scheme
that charges secondary users based on the interference that they cause to the
system's primary users (individually, globally, or both), and we examine how
secondary users can maximize their achievable transmission rate in this
setting. We show that the resulting non-cooperative game admits a unique Nash
equilibrium under very mild assumptions on the pricing mechanism employed by
the network operator, and under both static and ergodic (fast-fading) channel
conditions. In addition, we derive a dynamic power allocation policy that
converges to equilibrium within a few iterations (even for large numbers of
users), and which relies only on local signal-to-interference-and-noise
measurements; importantly, the proposed algorithm retains its convergence
properties even in the ergodic channel regime, despite the inherent
stochasticity thereof. Our theoretical analysis is complemented by extensive
numerical simulations which illustrate the performance and scalability
properties of the proposed pricing scheme under realistic network conditions.Comment: 24 pages, 9 figure
On Green Energy Powered Cognitive Radio Networks
Green energy powered cognitive radio (CR) network is capable of liberating
the wireless access networks from spectral and energy constraints. The
limitation of the spectrum is alleviated by exploiting cognitive networking in
which wireless nodes sense and utilize the spare spectrum for data
communications, while dependence on the traditional unsustainable energy is
assuaged by adopting energy harvesting (EH) through which green energy can be
harnessed to power wireless networks. Green energy powered CR increases the
network availability and thus extends emerging network applications. Designing
green CR networks is challenging. It requires not only the optimization of
dynamic spectrum access but also the optimal utilization of green energy. This
paper surveys the energy efficient cognitive radio techniques and the
optimization of green energy powered wireless networks. Existing works on
energy aware spectrum sensing, management, and sharing are investigated in
detail. The state of the art of the energy efficient CR based wireless access
network is discussed in various aspects such as relay and cooperative radio and
small cells. Envisioning green energy as an important energy resource in the
future, network performance highly depends on the dynamics of the available
spectrum and green energy. As compared with the traditional energy source, the
arrival rate of green energy, which highly depends on the environment of the
energy harvesters, is rather random and intermittent. To optimize and adapt the
usage of green energy according to the opportunistic spectrum availability, we
discuss research challenges in designing cognitive radio networks which are
powered by energy harvesters
Energy-Efficient Resource Allocation Optimization for Multimedia Heterogeneous Cloud Radio Access Networks
The heterogeneous cloud radio access network (H-CRAN) is a promising paradigm
which incorporates the cloud computing into heterogeneous networks (HetNets),
thereby taking full advantage of cloud radio access networks (C-RANs) and
HetNets. Characterizing the cooperative beamforming with fronthaul capacity and
queue stability constraints is critical for multimedia applications to
improving energy efficiency (EE) in H-CRANs. An energy-efficient optimization
objective function with individual fronthaul capacity and inter-tier
interference constraints is presented in this paper for queue-aware multimedia
H-CRANs. To solve this non-convex objective function, a stochastic optimization
problem is reformulated by introducing the general Lyapunov optimization
framework. Under the Lyapunov framework, this optimization problem is
equivalent to an optimal network-wide cooperative beamformer design algorithm
with instantaneous power, average power and inter-tier interference
constraints, which can be regarded as the weighted sum EE maximization problem
and solved by a generalized weighted minimum mean square error approach. The
mathematical analysis and simulation results demonstrate that a tradeoff
between EE and queuing delay can be achieved, and this tradeoff strictly
depends on the fronthaul constraint
Recent Advances in Cloud Radio Access Networks: System Architectures, Key Techniques, and Open Issues
As a promising paradigm to reduce both capital and operating expenditures,
the cloud radio access network (C-RAN) has been shown to provide high spectral
efficiency and energy efficiency. Motivated by its significant theoretical
performance gains and potential advantages, C-RANs have been advocated by both
the industry and research community. This paper comprehensively surveys the
recent advances of C-RANs, including system architectures, key techniques, and
open issues. The system architectures with different functional splits and the
corresponding characteristics are comprehensively summarized and discussed. The
state-of-the-art key techniques in C-RANs are classified as: the fronthaul
compression, large-scale collaborative processing, and channel estimation in
the physical layer; and the radio resource allocation and optimization in the
upper layer. Additionally, given the extensiveness of the research area, open
issues and challenges are presented to spur future investigations, in which the
involvement of edge cache, big data mining, social-aware device-to-device,
cognitive radio, software defined network, and physical layer security for
C-RANs are discussed, and the progress of testbed development and trial test
are introduced as well.Comment: 27 pages, 11 figure
A Game Theoretic Perspective on Self-organizing Optimization for Cognitive Small Cells
In this article, we investigate self-organizing optimization for cognitive
small cells (CSCs), which have the ability to sense the environment, learn from
historical information, make intelligent decisions, and adjust their
operational parameters. By exploring the inherent features, some fundamental
challenges for self-organizing optimization in CSCs are presented and
discussed. Specifically, the dense and random deployment of CSCs brings about
some new challenges in terms of scalability and adaptation; furthermore, the
uncertain, dynamic and incomplete information constraints also impose some new
challenges in terms of convergence and robustness. For providing better service
to the users and improving the resource utilization, four requirements for
self-organizing optimization in CSCs are presented and discussed. Following the
attractive fact that the decisions in game-theoretic models are exactly
coincident with those in self-organizing optimization, i.e., distributed and
autonomous, we establish a framework of game-theoretic solutions for
self-organizing optimization in CSCs, and propose some featured game models.
Specifically, their basic models are presented, some examples are discussed and
future research directions are given.Comment: 8 Pages, 8 Figures, to appear in IEEE Communications Magazin
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
Adaptive Mode Selection in Multiuser MISO Cognitive Networks with Limited Cooperation and Feedback
In this paper, we consider a multiuser MISO downlink cognitive network
coexisting with a primary network. With the purpose of exploiting the spatial
degree of freedom to counteract the inter-network interference and
intra-network (inter-user) interference simultaneously, we propose to perform
zero-forcing beamforming (ZFBF) at the multi-antenna cognitive base station
(BS) based on the instantaneous channel state information (CSI). The challenge
of designing ZFBF in cognitive networks lies in how to obtain the interference
CSI. To solve it, we introduce a limited inter-network cooperation protocol,
namely the quantized CSI conveyance from the primary receiver to the cognitive
BS via purchase. Clearly, the more the feedback amount, the better the
performance, but the higher the feedback cost. In order to achieve a balance
between the performance and feedback cost, we take the maximization of feedback
utility function, defined as the difference of average sum rate and feedback
cost while satisfying the interference constraint, as the optimization
objective, and derive the transmission mode and feedback amount joint
optimization scheme. Moreover, we quantitatively investigate the impact of CSI
feedback delay and obtain the corresponding optimization scheme. Furthermore,
through asymptotic analysis, we present some simple schemes. Finally, numerical
results confirm the effectiveness of our theoretical claims.Comment: 11 pages,6 figures, 4 tables IEEE Transactions on Vehicular
Technology, 201
SAS-Assisted Coexistence-Aware Dynamic Channel Assignment in CBRS Band
The paradigm of shared spectrum allows secondary devices to opportunistically
access spectrum bands underutilized by primary owners. Recently, the FCC has
targeted the sharing of the 3.5 GHz (3550-3700 MHz) federal spectrum with
commercial systems such as small cells. The rules require a Spectrum Access
System (SAS) to accommodate three service tiers: 1) Incumbent Access, 2)
Priority Access (PA), and 3) Generalized Authorized Access (GAA). In this work,
we study the SAS-assisted dynamic channel assignment (CA) for PA and GAA
tiers.We introduce the node-channel-pair conflict graph to capture pairwise
interference, channel and geographic contiguity constraints, spatially varying
channel availability, and coexistence awareness. The proposed conflict graph
allows us to formulate PA CA and GAA CA with binary conflicts as
max-cardinality and max-reward CA, respectively. Approximate solutions can be
found by a heuristic-based algorithm that search for the maximum weighted
independent set. We further formulate GAA CA with non-binary conflicts as
max-utility CA. We show that the utility function is submodular, and the
problem is an instance of matroid-constrained submodular maximization. A
polynomial-time algorithm based on local search is proposed that provides a
provable performance guarantee. Extensive simulations using a real-world Wi-Fi
hotspot location dataset are conducted to evaluate the proposed algorithms. Our
results have demonstrated the advantages of the proposed graph representation
and improved performance of the proposed algorithms over the baseline
algorithms.Comment: Accepted to IEEE TW
Exploiting Social Tie Structure for Cooperative Wireless Networking: A Social Group Utility Maximization Framework
In this paper, we develop a social group utility maximization (SGUM)
framework for cooperative wireless networking that takes into account both
social relationships and physical coupling among users. We show that this
framework provides rich modeling flexibility and spans the continuum between
non-cooperative game and network utility maximization (NUM) -- two
traditionally disjoint paradigms for network optimization. Based on this
framework, we study three important applications of SGUM, in database assisted
spectrum access, power control, and random access control, respectively. For
the case of database assisted spectrum access, we show that the SGUM game is a
potential game and always admits a socially-aware Nash equilibrium (SNE). We
develop a randomized distributed spectrum access algorithm that can
asymptotically converge to the optimal SNE, derive upper bounds on the
convergence time, and also quantify the trade-off between the performance and
convergence time of the algorithm. We further show that the performance gap of
SNE by the algorithm from the NUM solution decreases as the strength of social
ties among users increases and the performance gap is zero when the strengths
of social ties among users reach the maximum values. For the cases of power
control and random access control, we show that there exists a unique SNE.
Furthermore, as the strength of social ties increases from the minimum to the
maximum, a player's SNE strategy migrates from the Nash equilibrium strategy in
a standard non-cooperative game to the socially-optimal strategy in network
utility maximization. Furthermore, we show that the SGUM framework can be
generalized to take into account both positive and negative social ties among
users and can be a useful tool for studying network security problems.Comment: The paper has been accepted by IEEE/ACM Transactions on Networkin
Dynamic spectrum sharing game by lease
We propose and analyze a dynamic implementation of the property-rights model
of cognitive radio. A primary link has the possibility to lease the owned
spectrum to a MAC network of secondary nodes, in exchange for cooperation in
the form of distributed space-time coding (DSTC). The cooperation and
competition between the primary and secondary network are cast in the framework
of sequential game. On one hand, the primary link attempts to maximize its
quality of service in terms of signal-to-interference-plus-noise ratio (SINR);
on the other hand, nodes in the secondary network compete for transmission
within the leased time-slot following a power control mechanism. We consider
both a baseline model with complete information and a more practical version
with incomplete information, using the backward induction approach for the
former and providing approximate algorithm for the latter. Analysis and
numerical results show that our models and algorithms provide a promising
framework for fair and effective spectrum sharing, both between primary and
secondary networks and among secondary nodes.Comment: 15 pages, 4 figures, 1 table. Revisio
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