919 research outputs found
Power vs. Spectrum 2-D Sensing in Energy Harvesting Cognitive Radio Networks
Energy harvester based cognitive radio is a promising solution to address the
shortage of both spectrum and energy. Since the spectrum access and power
consumption patterns are interdependent, and the power value harvested from
certain environmental sources are spatially correlated, the new power dimension
could provide additional information to enhance the spectrum sensing accuracy.
In this paper, the Markovian behavior of the primary users is considered, based
on which we adopt a hidden input Markov model to specify the primary vs.
secondary dynamics in the system. Accordingly, we propose a 2-D spectrum and
power (harvested) sensing scheme to improve the primary user detection
performance, which is also capable of estimating the primary transmit power
level. Theoretical and simulated results demonstrate the effectiveness of the
proposed scheme, in term of the performance gain achieved by considering the
new power dimension. To the best of our knowledge, this is the first work to
jointly consider the spectrum and power dimensions for the cognitive primary
user detection problem
Thirty Years of Machine Learning: The Road to Pareto-Optimal Wireless Networks
Future wireless networks have a substantial potential in terms of supporting
a broad range of complex compelling applications both in military and civilian
fields, where the users are able to enjoy high-rate, low-latency, low-cost and
reliable information services. Achieving this ambitious goal requires new radio
techniques for adaptive learning and intelligent decision making because of the
complex heterogeneous nature of the network structures and wireless services.
Machine learning (ML) algorithms have great success in supporting big data
analytics, efficient parameter estimation and interactive decision making.
Hence, in this article, we review the thirty-year history of ML by elaborating
on supervised learning, unsupervised learning, reinforcement learning and deep
learning. Furthermore, we investigate their employment in the compelling
applications of wireless networks, including heterogeneous networks (HetNets),
cognitive radios (CR), Internet of things (IoT), machine to machine networks
(M2M), and so on. This article aims for assisting the readers in clarifying the
motivation and methodology of the various ML algorithms, so as to invoke them
for hitherto unexplored services as well as scenarios of future wireless
networks.Comment: 46 pages, 22 fig
From Sensing to Predictions and Database Technique: A Review of TV White Space Information Acquisition in Cognitive Radio Networks
Strategies to acquire white space information is the single most significant
functionality in cognitive radio networks (CRNs) and as such, it has gone some evolution
to enhance information accuracy. The evolution trends are spectrum sensing, prediction
algorithm and recently, geo-location database technique. Previously, spectrum sensing was
the main technique for detecting the presence/absence of a primary user (PU) signal in a
given radio frequency (RF) spectrum. However, this expectation could not materialized as
a result of numerous technical challenges ranging from hardware imperfections to RF
signal impairments. To convey the evolutionary trends in the development of white space
information, we present a survey of the contemporary advancements in PU detection with
emphasis on the practical deployment of CRNs i.e. Television white space (TVWS) networks.
It is found that geo-location database is the most reliable technique to acquire
TVWS information although, it is financially driven. Finally, using financially driven
database model, this study compared the data-rate and spectral efficiency of FCC and
Ofcom TV channelization. It was discovered that Ofcom TV channelization outperforms
FCC TV channelization as a result of having higher spectrum bandwidth. We proposed the
adoption of an all-inclusive TVWS information acquisition model as the future research
direction for TVWS information acquisition techniques
Spectrum prediction in dynamic spectrum access systems
Despite the remarkable foreseen advancements in maximizing network capacities, the in-expansible nature of radio spectrum exposed outdated spectrum management techniques as a core limitation. Fixed spectrum allocation inefficiency has generated a proliferation of dynamic spectrum access solutions to accommodate the growing demand for wireless, and mobile applications. This research primarily focuses on spectrum occupancy prediction which equip dynamic users with the cognitive ability to identify and exploit instantaneous availability of spectrum opportunities. The first part of this research is devoted to identifying candidate occupancy prediction techniques suitable for SOP scenarios are extensively analysed, and a theoretical based model selection framework is consolidated. The performance of single user Bayesian/Markov based techniques both analytically and numerically. Understanding performance bounds of Bayesian/Markov prediction allows the development of efficient occupancy prediction models. The third and fourth parts of this research investigates cooperative decision and data-based occupancy prediction. The expected cooperative prediction accuracy gain is addressed based on the single user prediction model. Specifically, the third contributions provide analytical approximations of single user, as well as cooperative hard fusion based spectrum prediction. Finally, the forth contribution shows soft fusion is superior and more robust compared to hard fusion cooperative prediction in terms of prediction accuracy. Throughout this research, case study analysis is provided to evaluate the performance of the proposed approaches. Analytical approaches and Monte-Carlo simulation are compared for the performance metric of interest. Remarkably, the case study analysis confirmed that the statistical approximation can predict the performance of local and hard fusion cooperative prediction accurately, capturing all the essential aspects of signal detection performance, temporal dependency of spectrum occupancy as well as the finite nature of the network
Intelligent Design in Wireless System
We are living in an era full of data services, and the advancement in statistical learning
encourages the development of intelligent system design algorithms based on practical
data. In our work, we plan to study two potential applications with intelligent design in
wireless systems based on statistical and machine learning techniques.
The first application we study is the spectrum sensing problem in energy harvesting
based cognitive radio networks, which is a promising solution to address the shortage of
both spectrum and energy. Since the spectrum access and power consumption pattern
are interdependent, and the power value harvested from certain environmental sources are
spatially correlated, the new power dimension could provide additional information to enhance
the spectrum sensing accuracy. In our work, the Markovian behavior of the primary
users is considered, based on which we adopt a hidden input Markov model to specify the
primary vs. secondary dynamics in the system. Accordingly, we propose a 2-D spectrum
vs. power (harvested) sensing scheme to improve the primary user detection performance,
which is also capable of estimating the primary transmit power level. Theoretical and
simulated results demonstrate the effectiveness of the proposed scheme, in terms of the
performance gain achieved by considering the new power dimension. To the best of our
knowledge, this is the first work to jointly consider the spectrum and power dimensions
for the cognitive primary user detection problem.
The second work is about spatio-temporal base station traffic prediction with machine
learning. Accurate prediction of user traffic in cellular networks is crucial to improve
the system performance in terms of energy efficiency and resource utilization. However,
existing work mainly considers the temporal traffic correlations within each cell while
neglecting the spatial correlation across neighboring cells. In this work, machine learning models that jointly explore the spatio-temporal correlations are proposed, where a multitask
learning approach is adopted to explore the commonalities and differences across cells
in improving the prediction performance. Base on real data, we demonstrate the benefits
of joint learning over spatial and temporal dimensions
Cross-layer design for multimedia applications in cognitive radio networks.
Ph. D. University of KwaZulu-Natal, Durban 2015.The exponential growth in wireless services and the current trend of development in wireless
communication technologies have resulted into an overcrowded radio spectrum band in such
a way that it can no longer meet the ever increasing requirements of wireless applications.
In contrary however, literature surveys indicate that a large amount of the licensed radio
spectrum bands are underutilized. This has necessitated the need for efficient ways to be
implemented for spectrum sharing among different systems, applications and services in
dynamic wireless environment. Cognitive radio (CR) technology emerges as a way to improve
the overall efficiency of radio spectrum utilization by allowing unlicensed users (also known
as secondary user) to utilize a licensed band when it is vacant.
Multimedia applications are being targeted for CR networks. However, the performance
and success of CR technology will be determined by the quality of service (QoS) perceived
by secondary users. In order to transmit multimedia contents which have stringent QoS
requirements over the CR networks, many technical challenges have to be addressed that are
constrained by the layered protocol architecture. Cross-layer design has shown a promise as
an approach to optimize network performance among different layers. This work is aimed
at addressing the question on how to provide QoS guarantee for multimedia transmission
over CR networks in terms of throughput maximization while ensuring that the interference
to primary users is avoided or minimized. Spectrum sensing is a fundamental problem in
cognitive radio networks for the protection of primary users and therefore the first part of
this work provides a review of some low complex spectrum sensing schemes. A cooperative
spectrum sensing scheme where multi-users are independently performing spectrum sensing
is also developed. In order to address a hidden node problem, a cooperate relay based on
amplify-and-forward technique (AF) is formulated. Usually the performance of a spectrum
sensor is evaluated using receiver operating characteristic (ROC) curve which provides a
trade-off between the probability of miss detection and the probability of false alarm. Due
to hardware limitations, the spectrum sensor can not sense the whole range of radio spec-
trum which results into partial information of the channel state. In order to model a media
access control(MAC) protocol which is able to make channel access decision under partial
information about the state of the system we apply a partially observable Markov decision
process (POMDP) technique as a suitable tool in making decision under uncertainty. A
throughput optimization MAC scheme in presence of spectrum sensing errors is then devel-
oped using the concept of cross-layer design which integrates the design of spectrum sensing
at physical layer (PHY) and sensing and access strategies at MAC layer in order to maximize
the overall network throughput. A problem is formulated as a POMDP and the throughput
performance of the scheme is evaluated using computer simulations under greedy sensing
algorithm. Simulation results demonstrate an improved overall throughput performance.
Further more, multiple channels with multiple secondary users having random message ar-
rivals are considered during simulation and the throughput performance is evaluated under
greedy sensing scheme which forms a benchmark for cross-layer MAC scheme in presence
of spectrum sensing errors. By realizing that speech communication is still the most dom-
inant and common service in wireless application, we develop a cross-layer MAC scheme
for speech transmission in CR networks. The design is aimed at maximizing throughput of
secondary users by integrating the design of spectrum sensing at PHY, quantization param-
eter of speech traffic at application layer (APP), together with strategy for spectrum access
at MAC layer with the main goal to improve the QoS perceived by secondary users in CR
networks. Simulation results demonstrate throughput performance improvement and hence
QoS is improved.
One of the main features of the modern communication systems is the parameterized
operation at different layers of the protocol stack. The feature aims at providing them with
the capability of adapting to the rapidly changing traffic, channel and system conditions.
Another interesting research problem in this thesis is the combination of individual adap-
tation mechanisms into a cross-layer that can maximize their effectiveness. We propose a
joint cross-layer design MAC scheme that integrates the design of spectrum sensing at PHY
layer, access at MAC layer and APP information in order to improve the QoS for video
transmission in CR networks. The end-to-end video distortion which is considered as an
APP parameter resides in the video encoder. This is integrated in the state space and the
problem is formulated as a constrained POMDP. H.264 coding algorithm which is one of the
high efficient video coding standards is considered. The objective is to minimize this end-to-
end video distortion while maximizes the overall network throughput for video transmission
in CR networks. The end-to-end video distortion has signifficant effects to the QoS the per-
ceived by the user and is viewed as the cost in the overall system design. Given the target
system throughput, the packet loss ration when the system is in the state i and a composite
action is taken in time slot t, the system immediate cost is evaluated. The expected total
cost for overall end-to-end video distortion over the total time slots is then computed. A
joint optimal policy which minimizes the expected total end-to-end distortion in total time
slots is computed iteratively. The minimum expected cost (which also known as the value
function) is also evaluated iteratively for the total time slots. The throughput performance
of the proposed scheme is evaluated through computer simulation. In order to study the
throughput performance of the proposed scheme, we considered four simulation scenarios
namely simulation scenario A, simulation scenario B, simulation scenario C, and simulation
scenario D. These simulation scenarios enabled us to study the throughput performance of
the proposed scheme by by computer simulations. In the simulation scenario A, the av-
erage throughput performance as a function of time horizon is studied. The throughput
performance under channel access decision based on belief vector and that of channel access
decision based on the end-to-end distortion are compared. Simulation results show that the
channel access decision based on end-to-end distortion outperforms that of channel access
decision based on a belief vector. In the simulation scenario B we aimed at studying the
spectral efficiency as a function of prescribed collision probability. The simulation results
show that, at large values of collision probability the overall spectral efficiency performs
poorly. However, there is an optimal value of collision probability of which the spectral
efficiency approaches that of the perfect channel access decision. In the simulation scenario
C, we aimed at studying the average throughput performance and the spectral efficiency
both as a function of prescribed collision probability. The simulation results show that both
average throughput and the spectral efficiency are highly affected by the increase in collision
probability. However, there is an optimal prescribed collision probability which achieves the
maximum average throughput and maximum spectral efficiency
A survey of machine learning techniques applied to self organizing cellular networks
In this paper, a survey of the literature of the past fifteen years involving Machine Learning (ML) algorithms applied to self organizing cellular networks is performed. In order for future networks to overcome the current limitations and address the issues of current cellular systems, it is clear that more intelligence needs to be deployed, so that a fully autonomous and flexible network can be enabled. This paper focuses on the learning perspective of Self Organizing Networks (SON) solutions and provides, not only an overview of the most common ML techniques encountered in cellular networks, but also manages to classify each paper in terms of its learning solution, while also giving some examples. The authors also classify each paper in terms of its self-organizing use-case and discuss how each proposed solution performed. In addition, a comparison between the most commonly found ML algorithms in terms of certain SON metrics is performed and general guidelines on when to choose each ML algorithm for each SON function are proposed. Lastly, this work also provides future research directions and new paradigms that the use of more robust and intelligent algorithms, together with data gathered by operators, can bring to the cellular networks domain and fully enable the concept of SON in the near future
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