Songqiao Han

A new methodology of qos evaluation and service selection for ubiquitous computing

Ubiquitous Computing (UbiComp) has become a new computing model in computer systems. However, the characteristics of UbiComp, such as context-awareness, mobility and resource-limitedness, pose challenges for service infrastructure to provide effective service provision. In this paper, we present a suit of user-oriented models and methods that support dynamic Quality of Service (QoS) evaluation and adaptive service selection for UbiComp: 1) We propose a user-oriented QoS model with hierarchical structure to achieve scalability and flexibility; 2) An extended context model with time dimension is employed in QoS evaluation; 3) To capture the weights of quality criteria, we design a user preference model based on linguistic variable; 4) We also model QoS evaluation and service selection as the combination of first order logic inference and hierarchical fuzzy logic evaluation. A case study is presented to demonstrate the effectiveness of our approach.

A resource aware software partitioning algorithm based on mobility constraints in pervasive grid environments

Pervasive computing suffers from resource limitations of mobile devices, while grid computing can utilize almost unlimited resources distributed in the whole Internet. The conjunction of such two paradigms generates a new promising one, called pervasive grid computing, where mobile users can use handheld devices to access abundant resources and services in the grid. In this paper, a novel software partitioning algorithm is presented, which is suitable for pervasive grid to optimally allocate software components between a mobile device and one or more servers, with the goal of saving the resources of mobile devices. The algorithm takes into account component mobility constraints to not only prevent violating execution requirements of the application, but also to fully exploit component mobility, replication and rebinding to conserve more resources as compared to previous works. Another distinguishing feature of the algorithm is its generality, which can be applied to minimize network bandwidth usage, response time and energy consumption, respectively or simultaneously. Extensive simulation results have demonstrated the validity and effectiveness of the proposed algorithm in various environments.

An adaptable software architecture based on mobile components in pervasive computing

Distributed applications operating in pervasive computing environment should have abilities to cope with the high heterogeneity and variability of this environment. In a high abstract level, the dynamic software architecture can be used to provide the flexibility and adaptation for the applications by modifying the structure of software, such as adding, removing, replacing components, in the execution time. Besides, mobile codes technologies have provided ability to move around for components. However, software architecture supporting component migration has not been deeply studied. In this paper, an adaptable software architecture for pervasive computing is introduced. We revisit software architecture, and describe its elements related to mobility, especially components and connectors, in formal forms. Due to the components’ correlation, the migration relationships between two components are proposed and discussed in detail. As an example, multiple notable design paradigms are expressed in a unified way by using our mobile component approach, which shows the effectiveness and generality of our model.

Energy saving of mobile devices based on component migration and replication in pervasive computing

Energy is a vital resource in pervasive computing. Remote execution, a static approach to energy saving of mobile devices, is not applicable to the constantly varying environment in pervasive computing. This paper presents a dynamic software configuration approach to minimizing energy consumption by moving or/and replicating the appropriate components of an application among the machines. After analyzing three types of energy costs of the distributed applications, we set up a math optimization model of energy consumption. Based on the graph theory, the optimization problem of energy cost can be transformed into the Min-cut problem of a cost graph. Then, we propose two novel optimal software allocation algorithms for saving power. The first makes use of component migration to reasonably allocate the components among the machines at runtime, and the second is to replicate some components among machines to further save more energy than component migration. The simulations reveal that the two proposed algorithms can effectively save energy of mobile devices, and obtain better performance than the previous approaches in most of cases.

Context-Based Qos Model and its Application in Ubiquitous Computing

In the mobile and resource-constrained ubiquitous computing environments, we need an effective quality of service (QoS) model to support dynamic service selection in tune with the variation of context. To serve this purpose, we explore the concept of QoS and propose a context-based QoS model with hierarchical structure. Based on the context model, the QoS model can identify different types of context and evaluate the impact of context upon service selection through first-order logic inference and fuzzy logic evaluation. Quantitative methods are employed to quantify quality factors. The application of the model is demonstrated in the process of service selection. Two experiments have been conducted to evaluate the model. The result of the experiments has proved that with the application of the QoS model, service selection is of better scalability and performance

A pervasive service framework for pervasive computing applications

Currently, the growth of pervasive computing has introduced an increasing number of services in daily life. There is an urgent need for service provision framework of pervasive computing applications. In this paper, we propose a pervasive service framework that includes a component-based service model and a user-oriented Quality of Service (QoS) model. The fuzzy expression of user preference is covered in our design. Moreover, we reduce the kernel of the service selection problem to Multiple Attribute Decision Making (MADM) problem with incomplete preference, which can be solved by classic methods. The result of experiments on current implementation justifies our design.

User-Centric Service Provision Model for Adaptive Ubiquitous Computing Applications

The rapid popularity of wireless networks and portable devices spurs mobile users to access various information services. Service provision in ubiquitous computing has become a challenging issue. In this paper, we present a user-centric service provision model (TJCSPM). UCSPM is designed to support user-oriented quality of service (QoS) evaluation and dynamic service delivery, according to various contexts such as device capability, network status and user preference, etc. Unlike most service provision middleware, UCSPM can provide appropriate services to mobile users, which are not only suitable for being delivered to resource-limited environments, but also with a high degree of satisfaction of users. We have developed a prototype of context-aware expo assistant application to demonstrate the effectiveness of UCSPM.

An On-Demand QoS Service Composition Protocol for MANETs

This paper presents an active quality of service (QoS) aware service composition protocol for mobile ad hoc networks (MANETs), with the goal of conserving resources subject to QoS requirements. A problem of QoS based service composition in MANETs is transformed into a problem of the service path discovery. We extend Dynamic Source Routing protocol to discover and compose elementary services across the network. Some message processing measures are taken to effectively reduce control overhead. Simulation results demonstrate the effectiveness of the proposed protocol.

A Proactive Service Mechanism Based on Linguistic Variable and Multiple Attribute Decision Making

To develop practical ubiquitous computing (UbiComp) applications, we design, formalize and implement a proactive service mechanism (PSM). However, in UbiComp environments, imprecise and incomplete context information, as well as limited resource, introduces novel challenging issues for PSM from service model and quality of service (QoS) model to service selection algorithm. In our design, we propose a user-oriented QoS model and a component-based service model to support adaptive service selection. In particular, we design fuzzy linguistic terms to help the user express his/her preference to quality criteria with natural language. Furthermore, the users preference can be mapped into the weights of quality criteria by employing fuzzy set theory. The kernel of the service selection problem is identified as multiple attribute decision making (MADM) problem with incomplete preference, which can be solved by classic methods. Finally, we conduct several experiments to testify the performance and scalability of our design

Self-Adaptive Pervasive Computing Application Based on Code Mobility

A traditional application with only one design paradigm can not well adapt to the constant variations of contexts and user preferences in pervasive computing. In this paper, we argue that a pervasive computing application should support multiple design paradigms and present an approach to dynamically selecting the most appropriate paradigm at runtime according to environmental changes. Based on analyzing the characteristics of adaptive software architecture, this paper presents the general paradigm selection rules which can be combined with the specific context to automatically or semi-automatically create the applicable software (re)configuration strategies. For mobile components paradigm, a novel heuristic software partitioning algorithm is proposed to reasonably allocate a pervasive computing application among machines for resource conservation. Finally, we discuss a case study that demonstrates the flexibility and effectiveness of our approach