19,376 research outputs found
Resource Allocation and Interference Mitigation Techniques for Cooperative Multi-Antenna and Spread Spectrum Wireless Networks
This chapter presents joint interference suppression and power allocation
algorithms for DS-CDMA and MIMO networks with multiple hops and
amplify-and-forward and decode-and-forward (DF) protocols. A scheme for joint
allocation of power levels across the relays and linear interference
suppression is proposed. We also consider another strategy for joint
interference suppression and relay selection that maximizes the diversity
available in the system. Simulations show that the proposed cross-layer
optimization algorithms obtain significant gains in capacity and performance
over existing schemes.Comment: 10 figures. arXiv admin note: substantial text overlap with
arXiv:1301.009
Joint Power Adjustment and Interference Mitigation Techniques for Cooperative Spread Spectrum Systems
This paper presents joint power allocation and interference mitigation
techniques for the downlink of spread spectrum systems which employ multiple
relays and the amplify and forward cooperation strategy. We propose a joint
constrained optimization framework that considers the allocation of power
levels across the relays subject to an individual power constraint and the
design of linear receivers for interference suppression. We derive constrained
minimum mean-squared error (MMSE) expressions for the parameter vectors that
determine the optimal power levels across the relays and the linear receivers.
In order to solve the proposed optimization problem efficiently, we develop
joint adaptive power allocation and interference suppression algorithms that
can be implemented in a distributed fashion. The proposed stochastic gradient
(SG) and recursive least squares (RLS) algorithms mitigate the interference by
adjusting the power levels across the relays and estimating the parameters of
the linear receiver. SG and RLS channel estimation algorithms are also derived
to determine the coefficients of the channels across the base station, the
relays and the destination terminal. The results of simulations show that the
proposed techniques obtain significant gains in performance and capacity over
non-cooperative systems and cooperative schemes with equal power allocation.Comment: 6 figures. arXiv admin note: text overlap with arXiv:1301.009
Multi-Antenna Relay Aided Wireless Physical Layer Security
With growing popularity of mobile Internet, providing secure wireless
services has become a critical issue. Physical layer security (PHY-security)
has been recognized as an effective means to enhance wireless security by
exploiting wireless medium characteristics, e.g., fading, noise, and
interference. A particularly interesting PHY-security technology is cooperative
relay due to the fact that it helps to provide distributed diversity and
shorten access distance. This article offers a tutorial on various
multi-antenna relaying technologies to improve security at physical layer. The
state of the art research results on multi-antenna relay aided PHY-security as
well as some secrecy performance optimization schemes are presented. In
particular, we focus on large-scale MIMO (LS-MIMO) relaying technology, which
is effective to tackle various challenging issues for implementing wireless
PHY-security, such as short-distance interception without eavesdropper channel
state information (CSI) and with imperfect legitimate CSI. Moreover, the future
directions are identified for further enhancement of secrecy performance.Comment: 17 pages, 4 figures, IEEE Communications Magazine, 201
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
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 Iterative Power Allocation and Linear Interference Suppression Algorithms in Cooperative DS-CDMA Networks
This work presents joint iterative power allocation and interference
suppression algorithms for spread spectrum networks which employ multiple hops
and the amplify-and-forward cooperation strategy for both the uplink and the
downlink. We propose a joint constrained optimization framework that considers
the allocation of power levels across the relays subject to individual and
global power constraints and the design of linear receivers for interference
suppression. We derive constrained linear minimum mean-squared error (MMSE)
expressions for the parameter vectors that determine the optimal power levels
across the relays and the linear receivers. In order to solve the proposed
optimization problems, we develop cost-effective algorithms for adaptive joint
power allocation, and estimation of the parameters of the receiver and the
channels. An analysis of the optimization problem is carried out and shows that
the problem can have its convexity enforced by an appropriate choice of the
power constraint parameter, which allows the algorithms to avoid problems with
local minima. A study of the complexity and the requirements for feedback
channels of the proposed algorithms is also included for completeness.
Simulation results show that the proposed algorithms obtain significant gains
in performance and capacity over existing non-cooperative and cooperative
schemes.Comment: 9 figures; IET Communications, 201
Aerial-Terrestrial Communications: Terrestrial Cooperation and Energy-Efficient Transmissions to Aerial-Base Stations
Hybrid aerial-terrestrial communication networks based on Low Altitude
Platforms (LAPs) are expected to optimally meet the urgent communication needs
of emergency relief and recovery operations for tackling large scale natural
disasters. The energy-efficient operation of such networks is important given
the fact that the entire network infrastructure, including the battery operated
ground terminals, exhibits requirements to operate under power-constrained
situations. In this paper, we discuss the design and evaluation of an adaptive
cooperative scheme intended to extend the survivability of the battery operated
aerial-terrestrial communication links. We propose and evaluate a real-time
adaptive cooperative transmission strategy for dynamic selection between direct
and cooperative links based on the channel conditions for improved energy
efficiency. We show that the cooperation between mobile terrestrial terminals
on the ground could improve the energy efficiency in the uplink depending on
the temporal behavior of the terrestrial and the aerial uplink channels. The
corresponding delay in having cooperative (relay-based) communications with
relay selection is also addressed. The simulation analysis corroborates that
the adaptive transmission technique improves the overall energy efficiency of
the network whilst maintaining low latency enabling real time applications.Comment: To Appear In IEEE Transactions On Aerospace And Electronic Systems,
201
Opportunistic Spectrum Sharing in Dynamic Access Networks: Deployment Challenges, Optimizations, Solutions, and Open Issues
In this paper, we investigate the issue of spectrum assignment in CRNs and
examine various opportunistic spectrum access approaches proposed in the
literature. We provide insight into the efficiency of such approaches and their
ability to attain their design objectives. We discuss the factors that impact
the selection of the appropriate operating channel(s), including the important
interaction between the cognitive linkquality conditions and the time-varying
nature of PRNs. Protocols that consider such interaction are described. We
argue that using best quality channels does not achieve the maximum possible
throughput in CRNs (does not provide the best spectrum utilization). The impact
of guard bands on the design of opportunistic spectrum access protocols is also
investigated. Various complementary techniques and optimization methods are
underlined and discussed, including the utilization of variablewidth spectrum
assignment, resource virtualization, full-duplex capability, cross-layer
design, beamforming and MIMO technology, cooperative communication, network
coding, discontinuousOFDM technology, and software defined radios. Finally, we
highlight several directions for future research in this field
Adaptive Power Allocation Strategies using DSTC in Cooperative MIMO Networks
Adaptive Power Allocation (PA) algorithms with different criteria for a
cooperative Multiple-Input Multiple-Output (MIMO) network equipped with
Distributed Space-Time Coding (DSTC) are proposed and evaluated. Joint
constrained optimization algorithms to determine the power allocation
parameters, the channel parameters and the receive filter are proposed for each
transmitted stream in each link. Linear receive filter and maximum-likelihood
(ML) detection are considered with Amplify-and-Forward (AF) and
Decode-and-Forward (DF) cooperation strategies. In the proposed algorithms, the
elements in the PA matrices are optimized at the destination node and then
transmitted back to the relay nodes via a feedback channel. The effects of the
feedback errors are considered. Linear MMSE expressions and the PA matrices
depend on each other and are updated iteratively. Stochastic gradient (SG)
algorithms are developed with reduced computational complexity. Simulation
results show that the proposed algorithms obtain significant performance gains
as compared to existing power allocation schemes.Comment: 5 figures, 9 pages. IET Communications, 201
Link Adaptation with Untrusted Relay Assignment: Design and Performance Analysis
In this paper, a link adaptation and untrusted relay assignment (LAURA)
framework for efficient and reliable wireless cooperative communications with
physical layer security is proposed. Using sharp channel codes in different
transmission modes, reliability for the destination and security in the
presence of untrusted relays (low probability of interception) are provided
through rate and power allocation. Within this framework, several schemes are
designed for highly spectrally efficient link adaptation and relay selection,
which involve different levels of complexity and channel state information
requirement. Analytical and simulation performance evaluation of the proposed
LAURA schemes are provided, which demonstrates the effectiveness of the
presented designs. The results indicate that power adaptation at the source
plays a critical role in spectral efficiency performance. Also, it is shown
that relay selection based on the signal to noise ratio of the source to relays
channels provides an interesting balance of performance and complexity within
the proposed LAURA framework
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