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Adaptive transmission in MIMO AF relay networks with orthogonal space-time block codes over Nakagami-m fading
No full textIn this article, we apply different adaptive transmission techniques to
dual-hop multiple-input multiple-output amplify-and-forward relay networks
using orthogonal space-time block coding over independent Nakagami-m fading
channels. The adaptive techniques investigated are optimal simultaneous power
and rate (OSPR), optimal rate with constant power (ORCP), and truncated channel
inversion with fixed rate (TCIFR). The expressions for the channel capacity of
OSPR, ORCP, and TCIFR, and the outage probability of OSPR, and TCIFR are
derived based on the characteristic function of the reciprocal of the
instantaneous signal-to-noise ratio (SNR) at the destination. For sufficiently
high SNR, the channel capacity of ORCP asymptotically converges to OSPR while
OSPR and ORCP achieve higher channel capacity compared to TCIFR. Although TCIFR
suffers from an increase in the outage probability relative to OSPR, it
provides the lowest implementation complexity among the considered schemes.
Along with analytical results, we further adopt Monte Carlo simulations to
validate the theoretical analysis
MRT/MRC for Cognitive AF Relay Networks under Feedback Delay and Channel Estimation Error
No full textIn this paper, we examine the performance of
multiple-input multiple-output cognitive amplify-and-forward (AF) relay systems
with maximum ratio transmission (MRT). In particular, closed-form expressions
in terms of a tight upper bound for outage probability (OP) and symbol error
rate (SER) of the system are derived when considering channel estimation error
(CEE) and feedback delay (FD) in our analysis. Through our works, one can see
the impact of FD and CEE on the system as well as the benefits of deploying
multiple antennas at the transceivers utilizing the spatial diversity of an MRT
system
Network Impact on Quality of Experience of Mobile Video
No full textTo an end user, Quality of Experience (QoE) matters more than Quality of
Service (QoS) because she is the owner of her experience, which is the result
of her perception. In recent times, QoE got increasingly much attention from
service providers, operators, manufacturers and researchers. Amongst others,
they are interested to know how the users perceive the quality of multimedia
streaming and how to predict the QoE by measuring network performance
parameters. Below the network layer, different access networks can be used, but
the internet and transport layers remain the same for everyone on best-effort
internet. We highlight a set of possible factors that are contributing towards
the QoE, from network via transport to application layer, including
applications, codecs, middleware and devices.
To investigate the relationship of QoS and QoE, emulation-based experiments
were designed. For the purpose of emulation, different shapers are in use by
the research community. We selected three popular shapers, NetEm, NISTnet and
KauNet, and investigated their emulation capabilities with focus on delay,
delay variation and bit rate in order to be able to select the best-suited
shaper for future use. Then, we studied the effect of QoS parameters on mobile
video QoE. To evaluate the video QoE, user tests were conducted. We observe a
much larger sensitivity of users to freezes and their placement within the
video than what is predicted by an objective video quality assessment tool that
is recommended by the standardisation organization ITU. Furthermore, we
investigated the role of codec and device on QoE in view of network-induced
problems
On Routing in Cognitive Radio Networks (extended version)
No full textCognitive Radio Networks are expected to resolve important technological and
operational challenges of future
networks, such as Dynamic Spectrum Access, routing in heterogeneous networks
and provisioning of Quality of
Experience for different applications. Accordingly, a number of new terminal
and network functionalities are required
to solve the technical problems and to provide efficient management. The paper
advances a new solution for
routing in Cognitive Radio Networks, providing communication between Secondary
Users occupying different socalled
Spectrum Opportunities, i.e., portions of spectrum not occupied by Primary
Users. This entails solving a complex
process composed by two fundamental elements. These are the multi-constraint
routing and the multi-dimensional
adaptation for multiple cognitive radio dimensions like space, frequency, power
and time. The goal of the paper is
to develop optimization algorithms necessary to provide end-to-end routing
paths for communication between
Secondary Users with associated Quality of Experience demands
Adapting the Streaming Video on the Estimated Motion Position
No full textIn real time video streaming, the frames must meet their timing constraints,
typically specified as their deadlines. Wireless networks may suffer from
bandwidth limitations. To reduce the data transmission over the wireless
networks, we propose an adaption technique in the server side by extracting a
part of the video frames that considered as a Region Of Interest (ROI), and
drop the part outside the ROI from the frames that are between reference
frames. The estimated position of the selection of the ROI is computed by using
the Sum of Squared Differences (SSD) between consecutive frames. The
reconstruction mechanism to the region outside the ROI is implemented in the
mobile side by using linear interpolation between reference frames. We evaluate
the proposed approach by using Mean Opinion Score (MOS) measurements. MOS are
used to evaluate two scenarios with equivalent encoding size, where the users
observe the first scenario with low bit rate for the original videos, while for
the second scenario the users observe our proposed approach with high bit rate.
The results show that our technique significantly reduces the amounts of data
are streamed over wireless networks, while the reconstruction mechanism will
provides acceptable video quality
E-mail Classification using Social Network Information
No full textA majority of E-mail is suspected to be spam. Traditional spam detection fails
to differentiate between user needs and evolving social relationships. Online
Social Networks (OSNs) contain more and more social information, contributed by
users. OSN information may be used to improve spam detection. This paper
presents a method that can use several social networks for detecting spam and a
set of metrics for representing OSN data. The paper investigates the impact of
using social network data extracted from an E-mail corpus to improve spam
detection. The social data model is compared to traditional spam data models by
generating and evaluating classifiers from both model types. The results show
that accurate spam detectors can be generated from the low-dimensional social
data model alone, however, spam detectors generated from combinations of the
traditional and social models were more accurate than the detectors generated
from either model in isolation
Dynamisk fjärrvärmesimulator i praktiken
No full textDHEMOS is a simulation system developed for district heating systems, in which
models for consumption, distribution and production are interconnected. The
focus of
this report has been to continue developing the models related to production
analysis, and the specific goal of the study has been to develop the system
towards production
analysis and to evaluate methods relating to its operational use. The system
has been adapted to handle financial and environmental parameters related to
operational production planning. Functionality to handle load forecasts have
been evaluated and included into the system.
The study has been performed in collaboration with Swedavia who owns and runs
Landvetter Airport. The district heating system at Landvetter Airport has been
the base for all simulation experiments within this study. The process to
calibrate and adjust DHEMOS is described and a number of scenarios are
evaluated in order to find optimal operational situations with the help of
active load control.
The results show that DHEMOS is a competent tool for operational production
planning. By combining the ability to perform load forecasts with practical
usability the system can be used as a support tool when finding optimal
operational strategies in relation to financial, technical and environmental
variables
Using Data Mining for Static Code Analysis of C
No full textStatic analysis of source code is one way to find bugs and problems in large
software projects. Many approaches to static analysis have been proposed. We
proposed a novel way of performing static analysis. Instead of methods based on
semantic/logic analysis we apply machine learning directly to the problem. This
has many benefits. Learning by example means trivial programmer adaptability (a
problem with many other approaches), learning systems also has the advantage to
be able to generalise and find problematic source code constructs that are not
exactly as the programmer initially thought, to name a few. Due to the general
interest in code quality and the availability of large open source code bases
as test and development data, we believe this problem should be of interest to
the larger data mining community. In this work we extend our previous approach
and investigate a new way of doing feature selection and test the suitability
of many different learning algorithms. This on a selection of problems we
adapted from large publicly available open source projects. Many algorithms
were much more successful than our previous proof-of-concept, and deliver
practical levels of performance. This is clearly an interesting and minable
problem
Quality Requirements in Industrial Practice – An Extended Interview Study at Eleven Companies
No full textIn order to create a successful software product and assure its quality, it is
not enough to fulfill the functional requirements, it is also crucial to find
the right balance among competing quality requirements (QR). An extended,
previosluy piloted, interview study was performed to identify specific
challenges associated with the selection, trade-off, and management of QR in
industrial practice. Data was collected through semi-structured interviews with
eleven product managers and eleven project leaders from eleven software
companies. The contribution of this study is fourfold: First, it compares how
QR are handled in two cases, companies working in business-to-business markets,
and companies that are working in business-to-consumer markets. These two are
also compared in terms of impact on the handling of QRs. Second, it compares
the perceptions and priorities of QR by product and project management
respectively. Third, it includes an examination of the interdependencies among
quality requirements perceived as most important by the practitioners. Fourth,
it characterizes the selection and management of QR in down-stream development
activities
Coping with System Sustainability: A Sociocybernetics Framework for Social-Economic System Architecture
No full textThis paper proposes an epistemological model based on cybernetic principles and
activity theory to interpret two levels of problems that are intertwined in our
social-economic system, namely the liveability and sustainability problems. In
the first part of the paper, important principles and concepts from related
fields of cybernetics and activity theory are introduced for later construction
of a model. In the second part, a model is constructed based on the introduced
concepts. To validate the proposed model, the current economic crisis is
studied in the third part. An important contribution of the proposed model is a
theoretical understanding of the two levels problems, and how to construct
macro social-economical policies to avoid similar crisis in the future