44 research outputs found
Recommended from our members
A connection-level call admission control using genetic algorithm for MultiClass multimedia services in wireless networks
Call admission control in a wireless cell in a personal communication system (PCS) can be modeled as an M/M/C/C queuing system with m classes of users. Semi-Markov Decision Process (SMDP) can be used to optimize channel utilization with upper bounds on handoff blocking probabilities as Quality of Service constraints. However, this method is too time-consuming and therefore it fails when state space and action space are large. In this paper, we apply a genetic algorithm approach to address the situation when the SMDP approach fails. We code call admission control decisions as binary strings, where a value of â1â in the position i (i=1,âŠm) of a decision string stands for the decision of accepting a call in class-i; a value of â0â in the position i of the decision string stands for the decision of rejecting a call in class-i. The coded binary strings are feed into the genetic algorithm, and the resulting binary strings are founded to be near optimal call admission control decisions. Simulation results from the genetic algorithm are compared with the optimal solutions obtained from linear programming for the SMDP approach. The results reveal that the genetic algorithm approximates the optimal approach very well with less complexity
Link layer protocol performance of indoor infrared wireless communications
The increasing deployment of portable computers and mobile devices leads to an increasing demand for wireless connections. Infrared presentsseveral advantagesover
radio for indoor wireless connectivity but infrared link quality is affected by ambient infrared noise and by low power transmission levels due to eye safety limitations. The Infrared Data Association (IrDA) has developed the widely used IrDA 1.x protocol standard for short range, narrow beam, point to point connections.IrDA addressedthe
requirement for indoor multipoint connectivity with the development of the Advanced Infrared (AIr) protocol stack.
This work analyses infrared link layer design based on IrDA proposals for addressing link layer topics and suggests implementation issues and protocol modifications that improve the operation of short range infrared connections. The performance of optical wireless links is measuredby the utilization, which can be drawn at the data link layer. A new mathematical model is developed that reaches a simple
equation that calculates IrDA 1.x utilization. The model is validated by comparing its outcome with simulation results obtained using the OPNET modeler. The mathematical
model is employed to study the effectiveness on utilization of physical and link layer parameters.The simple equation gives insights for the optimum control of the infrared
link for maximum utilization. By differentiating the utilization equation, simple formulas are derived for optimum values of the window and frame size parameters.
Analytical results indicate that significant utilization increase is observed if the optimum values are implemented, especially for high error rate links. A protocolimprovement that utilizes special Supervisory frames (S-frames) to pass transmission control is proposed to deal with delays introduced by F-timer expiration. Results indicate that employing the special S-frame highly improves utilization when optimum window and frame size values are implemented. The achieved practical utilization increase for optimum parameter implementation is confirmed by meansof simulation. AIr protocol trades speedfor range by employing Repetition Rate (RR) coding to achieve the increased transmission range required for wireless LAN connectivity. AIr employs the RTS/CTS medium reservation scheme to cope with hidden stations and CSMA/CA techniques with linear contention window (CW) adjustment for medium
access. A mathematical model is developed for the AIr collision avoidance (CA) procedures and validated by comparing analysis with simulation results. The model is
employed to examine the effectiveness of the CA parameters on utilization. By differentiating the utilization equation, the optimum CW size that maximises utilization
as a function of the number of the transmitting stations is derived. The proposed linear CW adjustment is very effective in implementing CW values close to optimum and thus minimizing CA delays. AIr implements a Go-Back-N retransmission scheme at high or low level to cope with transmission errors. AIr optionally implements a Stop-and-Wait retransmission scheme to efficiently implement RR coding. Analytical models for the AIr retransmission schemes are developed and employed to compare protocol utilization for different link parametervalues. Finally, the effectiveness of the proposedRR coding on utilization for different retransmission schemes is explored
Performance evaluation of cooperation strategies for m-health services and applications
Health telematics are becoming a major improvement for patientsâ lives, especially for
disabled, elderly, and chronically ill people. Information and communication technologies have
rapidly grown along with the mobile Internet concept of anywhere and anytime connection.
In this context, Mobile Health (m-Health) proposes healthcare services delivering, overcoming
geographical, temporal and even organizational barriers. Pervasive and m-Health services aim
to respond several emerging problems in health services, including the increasing number of
chronic diseases related to lifestyle, high costs in existing national health services, the need
to empower patients and families to self-care and manage their own healthcare, and the need
to provide direct access to health services, regardless the time and place. Mobile Health (m-
Health) systems include the use of mobile devices and applications that interact with patients
and caretakers. However, mobile devices have several constraints (such as, processor, energy,
and storage resource limitations), affecting the quality of service and user experience. Architectures
based on mobile devices and wireless communications presents several challenged issues
and constraints, such as, battery and storage capacity, broadcast constraints, interferences, disconnections,
noises, limited bandwidths, and network delays. In this sense, cooperation-based
approaches are presented as a solution to solve such limitations, focusing on increasing network
connectivity, communication rates, and reliability. Cooperation is an important research topic
that has been growing in recent years. With the advent of wireless networks, several recent
studies present cooperation mechanisms and algorithms as a solution to improve wireless networks
performance. In the absence of a stable network infrastructure, mobile nodes cooperate
with each other performing all networking functionalities. For example, it can support intermediate
nodes forwarding packets between two distant nodes.
This Thesis proposes a novel cooperation strategy for m-Health services and applications.
This reputation-based scheme uses a Web-service to handle all the nodes reputation and networking
permissions. Its main goal is to provide Internet services to mobile devices without
network connectivity through cooperation with neighbor devices. Therefore resolving the above
mentioned network problems and resulting in a major improvement for m-Health network architectures
performances. A performance evaluation of this proposal through a real network
scenario demonstrating and validating this cooperative scheme using a real m-Health application
is presented. A cryptography solution for m-Health applications under cooperative environments,
called DE4MHA, is also proposed and evaluated using the same real network scenario and
the same m-Health application. Finally, this work proposes, a generalized cooperative application
framework, called MobiCoop, that extends the incentive-based cooperative scheme for
m-Health applications for all mobile applications. Its performance evaluation is also presented
through a real network scenario demonstrating and validating MobiCoop using different mobile
applications
Mobile agent based distributed network management : modeling, methodologies and applications
The explosive growth of the Internet and the continued dramatic increase for all wireless services are fueling the demand for increased capacity, data rates, support of multimedia services, and support for different Quality of Services (QoS) requirements for different classes of services. Furthermore future communication networks will be strongly characterized by heterogeneity. In order to meet the objectives of instant adaptability to the users\u27 requirements and of interoperability and seamless operation within the heterogeneous networking environments, flexibility in terms of network and resource management will be a key design issue. The new emerging technology of mobile agent (MA) has arisen in the distributed programming field as a potential flexible way of managing resources of a distributed system, and is a challenging opportunity for delivering more flexible services and dealing with network programmability.
This dissertation mainly focuses on: a) the design of models that provide a generic framework for the evaluation and analysis of the performance and tradeoffs of the mobile agent management paradigm; b) the development of MA based resource and network management applications. First, in order to demonstrate the use and benefits of the mobile agent based management paradigm in the network and resource management process, a commercial application of a multioperator network is introduced, and the use of agents to provide the underlying framework and structure for its implementation and deployment is investigated. Then, a general analytical model and framework for the evaluation of various network management paradigms is introduced and discussed. It is also illustrated how the developed analytical framework can be used to quantitatively evaluate the performances and tradeoffs in the various computing paradigms. Furthermore, the design tradeoffs for choosing the MA based management paradigm to develop a flexible resource management scheme in wireless networks is discussed and evaluated. The integration of an advanced bandwidth reservation mechanism with a bandwidth reconfiguration based call admission control strategy is also proposed. A framework based on the technology of mobile agents, is introduced for the efficient implementation of the proposed integrated resource and QoS management, while the achievable performance of the overall proposed management scheme is evaluated via modeling and simulation. Finally the use of a distributed cooperative scheme among the mobile agents that can be applied in the future wireless networks is proposed and demonstrated, to improve the energy consumption for the routine management processes of mobile terminals, by adopting the peer-to-peer communication concept of wireless ad-hoc networks. The performance evaluation process and the corresponding numerical results demonstrate the significant system energy savings, while several design issues and tradeoffs of the proposed scheme, such as the fairness of the mobile agents involved in the management activity, are discussed and evaluated
Wireless Sensor Networks Formation: Approaches and Techniques
Nowadays, wireless sensor networks (WSNs) emerge as an active research area in which challenging topics involve energy consumption, routing algorithms, selection of sensors location according to a given premise, robustness, efficiency, and so forth. Despite the open problems in WSNs, there are already a high number of applications available. In all cases for the design of any application, one of the main objectives is to keep the WSN alive and functional as long as possible. A key factor in this is the way the network is formed. This survey presents most recent formation techniques and mechanisms for the WSNs. In this paper, the reviewed works are classified into distributed and centralized techniques. The analysis is focused on whether a single or multiple sinks are employed, nodes are static or mobile, the formation is event detection based or not, and network backbone is formed or not. We focus on recent works and present a discussion of their advantages and drawbacks. Finally, the paper overviews a series of open issues which drive further research in the area