Vol.4 No.3&4 October 1, 2008     
Engineering Context-Sensitive Mobile Applications

Editorial (163-164)
        M. Aleksy and M. Schader

Research Articles in the Theme Issue:

Towards High-Quality Mobile Applications (165-184)  
        P. Kamthan 
The development and evolution of mobile applications is viewed from an engineering perspective. A methodology for deploying patterns as means for improving the pragmatic quality of mobile applications is proposed. To that regard, relevant quality attributes and corresponding stakeholder types for mobile applications are identified. The role of the development process and the challenges in making optimal use of patterns are presented. The underling feasibility issues involved at each step are analyzed. The activities of selection and application of patterns are explored. The use of patterns during macro- and micro-architecture design of mobile applications is illustrated. The implications of the use of patterns in a Mobile Social Web context are briefly highlighted.

On Foundation of Engineering Context-sensitive Applications (185-199)  
        L. Yan 
The communication environment surrounding our daily experience is more and more characterized by mobile devices that can exchange multimedia information and provide access to various services of complex nature. The trend is now clear that future consumer computing experience will be based on multiple pervasive communication devices and services, where navigability, context-sensitivity, adaptability and ubiquity are key characteristics. Several issues have been studied, models and methodologies proposed, and tools and systems implemented. However, when we look at the foundation and what we are missing in research, some of the most relevant issues probably are a formal model of context-sensitive and a notion of synthesizing reliable complex systems from vast numbers of unreliable components. In this paper, we discuss a formal foundation and software engineering techniques for mobile context-aware and context-dependent service derivation and application development, emphasizing the relationships between context and system.

Techniques for the Efficient Resource Management of Context-Sensitive Mobile Applications and Their Utilization in Industrial Field Service  (200-209)  
        M. Aleksy, R. Gitzel, G. Vollmar, N.e Fantana, C. Stich.and M. Takizawa  
Context-sensitive mobile applications require a certain amount of flexibility due to the fact that they have to provide services for many different situations. The limited resources available make resource management a major challenge in such applications. In this paper, we present different techniques for the efficient use of resources of mobile devices. These techniques support the development of adaptable and flexible context-sensitive applications. Afterwards, we present some application scenarios from industrial field service in which some of these techniques can be utilized to improve service processes by providing tailored information and knowledge support.

SALSA – a Framework for Context-Sensitive Service Discovery in Mobile Commerce Applications (210-226)  
        C. Atkinson, P. Bostan and T. Butter 
In an effort to increase the average revenue per user, over the past few years mobile network operators have introduced many new services for mobile devices connected to the internet. However, none of them has proven to be the desired killer application, and many have failed completely. Most of the attention to date has focused on location-aware applications, but the increasingly powerful miniaturized sensorsthat will probably be embedded in future mobile devices offers many more types of context information than just location. When these additional types of context information are used as well, applications and services can be made much more context-sensitive, and service providers can offer more value to end users. This, in turn, will lead to higher acceptance and adoption of Mobile Commerce services. However, creating context-sensitive applications and services for mobile devices is not a trivial task and developer’s experience with these new kinds of technologies is low. Thus, the development of such services and applications, or the migration of conventional services to context-sensitive services, would be significantly boosted by framework support for client and service development. In this paper we introduce a framework for context-sensitive service discovery that offers systematic development support and also reduces the effort involved in migrating from pure information services to context-sensitive services.

Proxy Agents for Adaptive Delivery of Multimedia (227-240)  
        R. Aversa, B. Di Martino, N. Mazzocca, and S. Venticinque 
Adaptive delivery of multimedia means the capability of adapting content exploitation according to available resources, session parameters and user profile, in order to improve quality of service. It can be exploited to support people with disabilities in accessing available services, or to change the way of exploiting a resource according to working conditions. For example a text document can be delivered as audiostream when an user is driving, or when it cannot exploit a content as it is, because he is blind. Different kinds of multimedia fruition allow also to conceive new value added services and new models of interaction with contents. Here we present architecture design, and prototypal implementation, of a framework that can be integrated, transparently, in web applications, to add mobile agents based adaptive delivery. Mobile agents technology has been exploited to augment flexibility of classical solutions and to develop advanced facilities. We set up a case study on semantic and location based information retrieval to demonstrate effectiveness of our approach.

A Context-Aware Fuzzy-Based Handover System for Wireless Cellular Network and its Performance Evaluation (241-258)  
        L. Barolli, J. Anno, F. Xhafa, A. Durresi, and A. Koyama 

Presently, the wireless mobile networks and devices are becoming increasingly popular to provide users the access anytime and anywhere.The mobile systems are based on cellular approach and the area is covered by cells that overlap each other. In mobile cellular systems the handover is a very important process to maintain the desired Quality of Service (QoS). Many handover algorithms are proposed in the literature. However, to make a better handover and keep the QoS in wireless networks is very difficult. During handover decision in cellular networks, there is a risk of making incorrect decision based on incomplete or outdated information. For this reason, we use Fuzzy Logic (FL) which can operate with imprecision data. The context-triggered actions are carried out based on simple IF-THEN rules. In different from other works, we use Random Walk (RW) model and FL to design a new handover system, which is able to avoid ping-pong effect and has a good handover decision. The performance evaluation via simulations shows that proposed system can avoid ping-pong effect and has a good handover decision.

Other Research Articles:

Joint Error Concealment and Error Recovery for Consecutive Frame Losses under the unbalanced Multiple Description Coding Architecture (259-274)  
        F. Huang, L.-F. Sun, B. Li and Y.-Z. Zhong 
Real-time video transmission over error-prone wireless networks often experiences consecutive frame losses due to either temporary link outages or traffic congestion. Although error concealment (EC) techniques have been extensively studied, they usually cannot handle the problem. Thus, we envision using EC under the unbalanced multiple description coding (UMDC) architecture. UMDC has almost no coding delay and can produce two descriptions at any bit-rates adaptive to different path bandwidths. In this paper, we propose an iterative EC algorithm able to adaptively exploit both the high-resolution (HR) and low-resolution (LR) information via multi-hypothesis weights. It is applied to both lost HR frames and following undecoded ones. Considering error propagation, we design an interframe error recovery (ER) algorithm for the undecoded HR frames. It iteratively uses multi-frame recovery principle to frame-by-frame reduce error drift in the HR stream with respect to the intermediate information from EC. The joint design of EC and ER can be applied to most UMD approaches. Extensive experiments have been carried out under different conditions. The proposed EC technique exhibits high PSNR gains versus the usual ones under the UMDC architecture and the classical ones without the support of UMDC. The proposed ER technique is efficient in reducing error drift, especially in high motion scenes. In conclusion, joint EC and ER can provide satisfactory performance on both PSNR and visual quality.

An Efficient Error-Robust Wireless Video Transmission (275-292)  
        G. A. AL-Suhail 
Video transmission often suffers from various errors over wireless networks. Due to errors, the discarded link layer packets impose a serious limitation on the maximum achievable throughput over wireless channel. To face this challenge and to improve the overall TCP-Friendly video throughput, this paper proposes a new robust error-model for MPEG-4 video stream over a point-to-point wireless network. A noisy wireless channel is modeled for random bit errors causing packet loss with some restrictions on the design parameters including packet length, modulation format, and channel SNR. By this model, efficient bandwidth access from wireless network is achieved via a hybrid scheme of channel coding which acts as a Forward Error Correction (FEC), and Automatic Repeat Request (ARQ) protocol at a radio link layer. The new results show that a good video quality of service (QoS) can be estimated in terms of play-out frame rate (in frames/sec) when a maximum channel coding throughput is achieved. Further, this proposed model can improve drastically the end-to-end video quality at high wireless channel errors and low-delay of ARQ scheme.

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