Vol.3 No.3 September 15, 2007  
Advances in Mobile Multimedia Networks and Multimedia Applications  

Editorial (197-197)
        E. Pardede

 Research articles:

Using a Spatial Context Authentication Proxy for Establishing Secure Wireless Connections (198-217)  
        R. Mayrhofer and R. Gostner   
Spontaneous interaction in wireless ad-hoc networks is often desirable not only between users or devices in direct contact, but also with devices that are accessible only via a wireless network. Secure communication with such devices is difficult because of the required authentication, which is often either password- or certificate-based. An intuitive alternative is context-based authentication, where device authenticity is verified by shared context, and often by direct physical evidence. Devices that are physically separated cannot experience the same context and thus cannot benefit directly from context authentication. We introduce a {\rm context authentication proxy} that is pre-authenticated with one of the devices and can authenticate with the other by shared context. This concept is applicable to a wide range of application scenarios, context sensing technologies, and trust models. We show its practicality in an implementation for setting up IPSec connections based on spatial reference. Our specific scenario is ad-hoc access of mobile devices to secure 802.11 WLANs using a mobile device as authentication proxy. A user study shows that our method and implementation are intuitive to use and compare favourably to a standard, password-based approach.

Multimedia Flow Mobility in Heterogeneous Networks Using Multihomed Mobile IP (218-234)  
        R. Brännström, C. Åhlund, K. Andersson, and D. Granlun   
Communication in next generation networks will use multiple access technologies, creating a heterogeneous network environment. To enable end-user terminals to move between access networks with minimal disruption, the terminals should be able to maintain multiple active network connections. Such a multihomed mobile host will experience differences in capabilities and coverage area depending on the access technologies. This paper proposes and evaluates an extension to Mobile IP enabling multihoming, regardless of the access technology. Mobility of multimedia communication in this environment should adapt to changing conditions and be based on dynamic measurements and user preferences. The proposed architecture gives opportunities for mobile multimedia applications to use multiple access networks simultaneously and the possibility to move individual flows between access networks and between user devices. Media flows are identified by destination IP address, protocol and port number. Evaluation results are presented both from a simulation study and from a real world prototype implementation using three different wireless access technologies: 802.11, UMTS and 802.16-2004.

Multi-Feature Integration with Relevance Feedback on 3D Model Similarity Retrieval (235-254)  
        S. Akbar, J. Kung, and R. Wagner   
In this paper, we combine the use of Reduced Feature Vector Integration (RFI) and Distance Integration (DI) with Relevance Feedback (RF) on 3D model similarity retrieval. The RFI outperforms the individual FVs and gives high probability of providing relevant objects, other than the query itself, on the limited-size of display window. Therefore, user may select as many relevant objects as possible just after the initial query for the next RF iteration. In order to deal with the user’s feedback, we proposed an RF algorithm, which enhances the precision by employing multipoint queries and estimating feature relevance derived from both the variance of the distance of relevant objects and the maximum rank of them. In addition, an Extended Exclusion Set (EES) incorporating with Exclusion Set (ES) is introduced. Using EES and ES, the RF algorithm pushes prospectively irrelevant objects away from the queries. By utilizing both approaches, the small number of RF iterations significantly improves the retrieval precision.

Bathymetry Forecasting Using Multilayer Spatial Images (255-264)  
        P. Paryono   
Earth-observing satellite, such Landsat, provide many multitemporal images of earth surface, either water body or land. By using spectral water body characteristics and field measurement, the bathymetry (water depth) of the study area can be derived from images recorded/acquired at different times. In this study, four multitemporal spatial images were used for generating bathymetry images which were arranged as multilayer images in cubic raster database format. Bathymetric forecasting is needed for a dynamic (rapidly change) area, such as an estuary of a river transporting a lot of sediments. Bathymetric forecasting in this study area utilized linear and quadratic regressions techniques. The spatial image layers representing standard errors values, constants of linear and quadratic equations were generated from the cubic raster database containing multitemporal images. These layers were also arranged in a cubic raster database format. By visual observation on image of standard error, a user may analyse which part of the study area that close to the field reality and which part that does not. The values of each layers were then classified into several classes and were displayed using distinctive colors to ease the user in visual observation. The bathymetric forecasting (either forward or backward) can be calculated from the spatial linear and quadratic equations. In order to provide more impressive visualization, the time series of bathymetric images generated were compiled into one file in animated gif format.

Low Cost Rendering Method for Virtual Factory Considering Interpolation of Occluded Objects (265-282)  
        H. Takahashi, N. Tamura, T. Furue, and O. Yoshie   
Recent technology of computer graphics and image processing enables us to realize the construction of real world on a computer with virtual reality (VR). However, easiness constructing the VR space is not enough for most of users. This is because the methods to construct the VR space require very high working cost or special instruments and skills. We are aiming to use virtual factory (VF) which is constructed on a computer and enables us to walk through it with the viewpoint of workers, as the user interface of ubiquitous maintenance environment. But the construction process of VF costs very much in traditional ways, as well as other VR spaces. To solve the problem, this paper adopts the image-based rendering (IBR), which uses some photographs and generates the image at another viewpoint by interpolation. An efficient IBR algorithm for the straight path is proposed, which is adequate for the use in the VF.

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