1,612 research outputs found
A Survey on QoE-oriented Wireless Resources Scheduling
Future wireless systems are expected to provide a wide range of services to
more and more users. Advanced scheduling strategies thus arise not only to
perform efficient radio resource management, but also to provide fairness among
the users. On the other hand, the users' perceived quality, i.e., Quality of
Experience (QoE), is becoming one of the main drivers within the schedulers
design. In this context, this paper starts by providing a comprehension of what
is QoE and an overview of the evolution of wireless scheduling techniques.
Afterwards, a survey on the most recent QoE-based scheduling strategies for
wireless systems is presented, highlighting the application/service of the
different approaches reported in the literature, as well as the parameters that
were taken into account for QoE optimization. Therefore, this paper aims at
helping readers interested in learning the basic concepts of QoE-oriented
wireless resources scheduling, as well as getting in touch with its current
research frontier.Comment: Revised version: updated according to the most recent related
literature; added references; corrected typo
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
Effective Capacity Analysis of Cognitive Radio Channels for Quality of Service Provisioning
In this paper, cognitive transmission under quality of service (QoS)
constraints is studied. In the cognitive radio channel model, it is assumed
that the secondary transmitter sends the data at two different average power
levels, depending on the activity of the primary users, which is determined by
channel sensing performed by the secondary users. A state-transition model is
constructed for this cognitive transmission channel. Statistical limitations on
the buffer lengths are imposed to take into account the QoS constraints. The
maximum throughput under these statistical QoS constraints is identified by
finding the effective capacity of the cognitive radio channel. This analysis is
conducted for fixed-power/fixed-rate, fixed-power/variable-rate, and
variable-power/variable-rate transmission schemes under different assumptions
on the availability of channel side information (CSI) at the transmitter. The
impact upon the effective capacity of several system parameters, including
channel sensing duration, detection threshold, detection and false alarm
probabilities, QoS parameters, and transmission rates, is investigated. The
performances of fixed-rate and variable-rate transmission methods are compared
in the presence of QoS limitations. It is shown that variable schemes
outperform fixed-rate transmission techniques if the detection probabilities
are high. Performance gains through adapting the power and rate are quantified
and it is shown that these gains diminish as the QoS limitations become more
stringent
Throughput of Cognitive Radio Systems with Finite Blocklength Codes
In this paper, throughput achieved in cognitive radio channels with finite
blocklength codes under buffer limitations is studied. Cognitive users first
determine the activity of the primary users' through channel sensing and then
initiate data transmission at a power level that depends on the channel sensing
decisions. It is assumed that finite blocklength codes are employed in the data
transmission phase. Hence, errors can occur in reception and retransmissions
can be required. Primary users' activities are modeled as a two-state Markov
chain and an eight-state Markov chain is constructed in order to model the
cognitive radio channel. Channel state information (CSI) is assumed to be
perfectly known by either the secondary receiver only or both the secondary
transmitter and receiver. In the absence of CSI at the transmitter, fixed-rate
transmission is performed whereas under perfect CSI knowledge, for a given
target error probability, the transmitter varies the rate according to the
channel conditions. Under these assumptions, throughput in the presence of
buffer constraints is determined by characterizing the maximum constant arrival
rates that can be supported by the cognitive radio channel while satisfying
certain limits on buffer violation probabilities. Tradeoffs between throughput,
buffer constraints, coding blocklength, and sensing duration for both
fixed-rate and variable-rate transmissions are analyzed numerically. The
relations between average error probability, sensing threshold and sensing
duration are studied in the case of variable-rate transmissions.Comment: To appear in the IEEE Journal on Selected Areas in Communications-
Cognitive Radio Serie
QoS Provisioning for Multimedia Transmission in Cognitive Radio Networks
In cognitive radio (CR) networks, the perceived reduction of application
layer quality of service (QoS), such as multimedia distortion, by secondary
users may impede the success of CR technologies. Most previous work in CR
networks ignores application layer QoS. In this paper we take an integrated
design approach to jointly optimize multimedia intra refreshing rate, an
application layer parameter, together with access strategy, and spectrum
sensing for multimedia transmission in a CR system with time varying wireless
channels. Primary network usage and channel gain are modeled as a finite state
Markov process. With channel sensing and channel state information errors, the
system state cannot be directly observed. We formulate the QoS optimization
problem as a partially observable Markov decision process (POMDP). A low
complexity dynamic programming framework is presented to obtain the optimal
policy. Simulation results show the effectiveness of the proposed scheme
Probability Density Function Estimation in OFDM Transmitter and Receiver in Radio Cognitive Networks based on Recurrent Neural Network
The most important problem in telecommunication is bandwidth limitation due
to the uncontrolled growth of wireless technology. Deploying dynamic spectrum
access techniques is one of the procedures provided for efficient use of
bandwidth. In recent years, cognitive radio network introduced as a tool for
efficient use of spectrum. These radios are able to use radio resources by
recognizing surroundings via sensors and signal operations that means use these
resources only when authorized users do not use their spectrum. Secondary users
are unauthorized ones that must avoid from interferences with primary users
transmission. Secondary users must leave channel due to preventing damages to
primary users whenever these users discretion. In this article, spectrum
opportunities prediction based on Recurrent Neural Network for bandwidth
optimization and reducing the amount of energy by predicting spectrum holes
discovery for quality of services optimization proposed in OFDM-based cognitive
radio network based on probability density function. The result of the
simulation represent acceptable value of SNR and bandwidth optimization in
these networks that allows secondary users to taking spectrum and sending data
without collision and overlapping with primary users.Comment: OFDM, Cognitive Radio Networks, Recurrent Neural Network, Probability
Density Functio
On the Throughput and Energy Efficiency of Cognitive MIMO Transmissions
In this paper, throughput and energy efficiency of cognitive multiple-input
multiple-output (MIMO) systems operating under quality-of-service (QoS)
constraints, interference limitations, and imperfect channel sensing, are
studied. It is assumed that transmission power and covariance of the input
signal vectors are varied depending on the sensed activities of primary users
(PUs) in the system. Interference constraints are applied on the transmission
power levels of cognitive radios (CRs) to provide protection for the PUs whose
activities are modeled as a Markov chain. Considering the reliability of the
transmissions and channel sensing results, a state-transition model is
provided. Throughput is determined by formulating the effective capacity. First
derivative of the effective capacity is derived in the low-power regime and the
minimum bit energy requirements in the presence of QoS limitations and
imperfect sensing results are identified. Minimum energy per bit is shown to be
achieved by beamforming in the maximal-eigenvalue eigenspace of certain
matrices related to the channel matrix. In a special case, wideband slope is
determined for more refined analysis of energy efficiency. Numerical results
are provided for the throughput for various levels of buffer constraints and
different number of transmit and receive antennas. The impact of interference
constraints and benefits of multiple-antenna transmissions are determined. It
is shown that increasing the number of antennas when the interference power
constraint is stringent is generally beneficial. On the other hand, it is shown
that under relatively loose interference constraints, increasing the number of
antennas beyond a certain level does not lead to much increase in the
throughput
Cross-layer Design in Cognitive Radio Standards
The growing demand for wireless applications and services on the one hand,
and limited available radio spectrum on the other hand have made cognitive
radio (CR) a promising solution for future mobile networks. It has attracted
considerable attention by academia and industry since its introduction in 1999
and several relevant standards have been developed within the last decade.
Cognitive radio is based on four main functions, spanning across more than one
layer of OSI model. Therefore, solutions based on cognitive radio technology
require cross layer (CL) designs for optimum performance. This article briefly
reviews the basics of cognitive radio technology as an introduction and
highlights the need for cross layer design in systems deploying CR technology.
Then some of the published standards with CL characteristics are outlined in a
later section, and in the final section some research examples of cross layer
design ideas based on the existing CR standards conclude this article
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
QoS group based optimal retransmission medium access protocol for wireless sensor networks
This paper presents, a Group Based Optimal Retransmission Medium Access
(GORMA) Protocol is designed that combines protocol of Collision Avoidance (CA)
and energy management for low-cost, short-range, low-data rate and low-energy
sensor nodes applications in environment monitoring, agriculture, industrial
plants etc. In this paper, the GORMA protocol focuses on efficient MAC protocol
to provide autonomous Quality of Service (QoS) to the sensor nodes in one-hop
QoS retransmission group and two QoS groups in WSNs where the source nodes do
not have receiver circuits. Hence, they can only transmit data to a sink node,
but cannot receive acknowledgement control signals from the sink node. The
proposed protocol GORMA provides QoS to the nodes which work independently on
predefined time by allowing them to transmit each packet an optimal number of
times within a given period. Our simulation results shows that the performance
of GORMA protocol, which maximize the delivery probability of one-hop QoS group
and two QoS groups and minimize the energy consumption.Comment: 9 pages in IEEE format and 6 figure
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