3,128 research outputs found
Directional Relays for Multi-Hop Cooperative Cognitive Radio Networks
In this paper, we investigate power allocation and beamforming in a relay assisted cognitive radio (CR) network. Our objective is to maximize the performance of the CR network while limiting interference in the direction of the primary users (PUs). In order to achieve these goals, we first consider joint power allocation and beamforming for cognitive nodes in direct links. Then, we propose an optimal power allocation strategy for relay nodes in indirect transmissions. Unlike the conventional cooperative relaying networks, the applied relays are equipped with directional antennas to further reduce the interference to PUs and meet the CR network requirements. The proposed approach employs genetic algorithm (GA) to solve the optimization problems. Numerical simulation results illustrate the quality of service (QoS) satisfaction in both primary and secondary networks. These results also show that notable improvements are achieved in the system performance if the conventional omni-directional relays are replaced with directional ones
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
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
Decentralized Fair Scheduling in Two-Hop Relay-Assisted Cognitive OFDMA Systems
In this paper, we consider a two-hop relay-assisted cognitive downlink OFDMA
system (named as secondary system) dynamically accessing a spectrum licensed to
a primary network, thereby improving the efficiency of spectrum usage. A
cluster-based relay-assisted architecture is proposed for the secondary system,
where relay stations are employed for minimizing the interference to the users
in the primary network and achieving fairness for cell-edge users. Based on
this architecture, an asymptotically optimal solution is derived for jointly
controlling data rates, transmission power, and subchannel allocation to
optimize the average weighted sum goodput where the proportional fair
scheduling (PFS) is included as a special case. This solution supports
decentralized implementation, requires small communication overhead, and is
robust against imperfect channel state information at the transmitter (CSIT)
and sensing measurement. The proposed solution achieves significant throughput
gains and better user-fairness compared with the existing designs. Finally, we
derived a simple and asymptotically optimal scheduling solution as well as the
associated closed-form performance under the proportional fair scheduling for a
large number of users. The system throughput is shown to be
, where is the
number of users in one cluster, is the number of subchannels and is
the active probability of primary users.Comment: 29 pages, 9 figures, IEEE JOURNAL OF SELECTED TOPICS IN SIGNAL
PROCESSIN
Joint Cooperative Spectrum Sensing and MAC Protocol Design for Multi-channel Cognitive Radio Networks
In this paper, we propose a semi-distributed cooperative spectrum sen sing
(SDCSS) and channel access framework for multi-channel cognitive radio networks
(CRNs). In particular, we c onsider a SDCSS scheme where secondary users (SUs)
perform sensing and exchange sensing outcomes with ea ch other to locate
spectrum holes. In addition, we devise the p -persistent CSMA-based cognitive
MAC protocol integrating the SDCSS to enable efficient spectrum sharing among
SUs. We then perform throughput analysis and develop an algorithm to determine
the spectrum sensing and access parameters to maximize the throughput for a
given allocation of channel sensing sets. Moreover, we consider the spectrum
sensing set optimization problem for SUs to maxim ize the overall system
throughput. We present both exhaustive search and low-complexity greedy
algorithms to determine the sensing sets for SUs and analyze their complexity.
We also show how our design and analysis can be extended to consider reporting
errors. Finally, extensive numerical results are presented to demonstrate the
sig nificant performance gain of our optimized design framework with respect to
non-optimized designs as well as the imp acts of different protocol parameters
on the throughput performance.Comment: accepted for publication EURASIP Journal on Wireless Communications
and Networking, 201
RF-Powered Cognitive Radio Networks: Technical Challenges and Limitations
The increasing demand for spectral and energy efficient communication
networks has spurred a great interest in energy harvesting (EH) cognitive radio
networks (CRNs). Such a revolutionary technology represents a paradigm shift in
the development of wireless networks, as it can simultaneously enable the
efficient use of the available spectrum and the exploitation of radio frequency
(RF) energy in order to reduce the reliance on traditional energy sources. This
is mainly triggered by the recent advancements in microelectronics that puts
forward RF energy harvesting as a plausible technique in the near future. On
the other hand, it is suggested that the operation of a network relying on
harvested energy needs to be redesigned to allow the network to reliably
function in the long term. To this end, the aim of this survey paper is to
provide a comprehensive overview of the recent development and the challenges
regarding the operation of CRNs powered by RF energy. In addition, the
potential open issues that might be considered for the future research are also
discussed in this paper.Comment: 8 pages, 2 figures, 1 table, Accepted in IEEE Communications Magazin
Techniques for Cooperative Cognitive Radio Networks
The frequency spectrum is an essential resource for wireless communication.
Special sections of the spectrum are used for military purposes, governments
sell some frequency bands to broadcasting and mobile communications companies
for commercial use, others such as ISM (Industrial, Science and Medical) bands
are available for the public free of charge. As the spectrum becomes
overcrowded, there seem to be two possible solutions: pushing the frequency
limits higher to frequencies of 60 GHz and above, or reaggregating the densely
used licensed frequency bands. The new Cognitive Radio (CR) approach comes with
the feasible solution to spectrum scarcity. Secondary utilization of a licensed
spectrum band can enhance the spectrum usage and introduce a reliable solution
to its dearth. In such a cognitive radio network, secondary users can access
the spectrum under the constraint that a minimum quality of service is
guaranteed for the licensed primary users. In this thesis, we focus on spectrum
sharing techniques in cognitive radio network where there is a number of
secondary users sharing unoccupied spectrum holes. More specifically, we
introduce two collaborative cognitive radio networks in which the secondary
user cooperate with the primary user to deliver the data of the primary user.Comment: Master's thesi
Optimizing Throughput Fairness of Cluster-based Cooperation in Underlay Cognitive WPCNs
In this paper, we consider a secondary wireless powered communication network
(WPCN) underlaid to a primary point-to-point communication link. The WPCN
consists of a multi-antenna hybrid access point (HAP) that transfers wireless
energy to a cluster of low-power wireless devices (WDs) and receives sensing
data from them. To tackle the inherent severe user unfairness problem in WPCN,
we consider a cluster-based cooperation where a WD acts as the cluster head
that relays the information of the other WDs. Besides, we apply energy
beamforming technique to balance the dissimilar energy consumptions of the WDs
to further improve the fairness. However, the use of energy beamforming and
cluster-based cooperation may introduce more severe interference to the primary
system than the WDs transmit independently. To guarantee the performance of
primary system, we consider an interference-temperature constraint to the
primary system and derive the throughput performance of each WD under the peak
interference-temperature constraint. To achieve maximum throughput fairness, we
jointly optimize the energy beamforming design, the transmit time allocation
among the HAP and the WDs, and the transmit power allocation of each WD to
maximize the minimum data rate achievable among the WDs (the max-min
throughput). We show that the non-convex joint optimization problem can be
transformed to a convex one and then be efficiently solved using off-the-shelf
convex algorithms. Moreover, we simulate under practical network setups and
show that the proposed method can effectively improve the throughput fairness
of the secondary WPCN, meanwhile guaranteeing the communication quality of the
primary network.Comment: The paper has been submitted for potential journal publication. arXiv
admin note: text overlap with arXiv:1707.0320
Green Cellular Networks: A Survey, Some Research Issues and Challenges
Energy efficiency in cellular networks is a growing concern for cellular
operators to not only maintain profitability, but also to reduce the overall
environment effects. This emerging trend of achieving energy efficiency in
cellular networks is motivating the standardization authorities and network
operators to continuously explore future technologies in order to bring
improvements in the entire network infrastructure. In this article, we present
a brief survey of methods to improve the power efficiency of cellular networks,
explore some research issues and challenges and suggest some techniques to
enable an energy efficient or "green" cellular network. Since base stations
consume a maximum portion of the total energy used in a cellular system, we
will first provide a comprehensive survey on techniques to obtain energy
savings in base stations. Next, we discuss how heterogeneous network deployment
based on micro, pico and femto-cells can be used to achieve this goal. Since
cognitive radio and cooperative relaying are undisputed future technologies in
this regard, we propose a research vision to make these technologies more
energy efficient. Lastly, we explore some broader perspectives in realizing a
"green" cellular network technologyComment: 16 pages, 5 figures, 2 table
Performance of Joint Spectrum Sensing and MAC Algorithms for Multichannel Opportunistic Spectrum Access Ad Hoc Networks
We present an analytical framework to assess the link layer throughput of
multichannel Opportunistic Spectrum Access (OSA) ad hoc networks. Specifically,
we focus on analyzing various combinations of collaborative spectrum sensing
and Medium Access Control (MAC) protocol abstractions. We decompose
collaborative spectrum sensing into layers, parametrize each layer, classify
existing solutions, and propose a new protocol called Truncated Time Division
Multiple Access (TTDMA) that supports efficient distribution of sensing results
in "k out of N" fusion rule. In case of multichannel MAC protocols we evaluate
two main approaches of control channel design with (i) dedicated and (ii)
hopping channel. We propose to augment these protocols with options of handling
secondary user (SU) connections preempted by primary user (PU) by (i)
connection buffering until PU departure and (ii) connection switching to a
vacant PU channel. By comparing and optimizing different design combinations we
show that (i) it is generally better to buffer preempted SU connections than to
switch them to PU vacant channels and (ii) TTDMA is a promising design option
for collaborative spectrum sensing process when k does not change over time.Comment: 43 pages, 14 figures. Includes a concluding discussion on the
validity of the analytical model in P. Pawelczak, S. Pollin, H-S. W. So, A.
Bahai, R.V. Prasad, R. Hekmat, Performance Analysis of Multichannel Medium
Access Control Algorithms for Opportunistic Spectrum Access, IEEE
Transactions on Vehicular Technology, vol. 58, no. 6, pp. 3014-3031, Jul.
200
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