Mobile databases will play an important role in mobile computing environment, to provide data storing and data retrieval functionalities which are needed by most applications. In mobile computing environment, the wireless communication poses some problems, which require us to minimize its use. Replication is a database technique that is commonly used to fulfill the requirement in minimizing network usage. In this paper, we propose two replica allocation strategies, called primary-copy tracking replica allocation (PTRA) and user majority replica allocation (UMRA), which are better suited to the mobile computing environment. Their proposals are intended to cope with cost performance issues in data replication due to user mobility in mobile computing environment. To investigate their effectiveness, we provide access cost analysis and comparison on these strategies and the static replica allocation (SRA) strategy. We show that our proposed strategies outperform the SRA strategy when user mobility (inter-cell movement) is relatively low as compared with data access rate.

In the urban area, buildings are the main scatterer which dominate the mobile propagation characteristics. However, reflection, diffraction, and scattering on the building surfaces in the radio environment induce undesirable multipath propagation. Multipath prediction with respect to a building surface has been conventionally based on an assumption that reflection from the surface has a substantial specular direction. However non-specular scattering from the building surface can affect the channel characteristics as well as specular scattering. This paper presents multipath characteristics of non-specular wave scattering from building surface roughness based on the experimental results. Superresolution method was applied as an approach to handle the signal parameters (DoA, ToA) of the individual incoming waves reflected from building surface roughness. The results show that the multipaths can be detected at many scatterers, such as ground, window's glass, window's frames and bricks surface, as well as directly from the transmitter. Most of the scattered waves are arriving closely from specular directions. The measured reflection coefficients were well bounded by reflection coefficients of the theoretically smooth and random rough surface. The Fresnel reflection coefficient formula, considering the finite thickness of the building surface and Gaussian scattering correction, give better prediction for glass and bricks reflection coefficient measurement.

The usage of light-weight mobile devices is increasing rapidly, leading to demand for more telecommunication services. Consequently, mobile ad hoc networks and their applications have become feasible with the proliferation of light-weight mobile devices. Many protocols have been developed to handle service discovery and routing in ad hoc networks. However, the majority of them did not consider one critical aspect of this type of network, which is the limited of available energy in each node. Cluster Based Routing Protocol (CBRP) is a robust/scalable routing protocol for Mobile Ad hoc Networks (MANETs) and superior to existing protocols such as Ad hoc On-demand Distance Vector (AODV) in terms of throughput and overhead. Therefore, based on this strength, methods to increase the efficiency of energy usage are incorporated into CBRP in this work. In order to increase the stability (in term of life-time) of the network and to decrease the energy consumption of inter-cluster gateway nodes, an Enhanced Gateway Cluster Based Routing Protocol (EGCBRP) is proposed. Three methods have been introduced by EGCBRP as enhancements to the CBRP: improving the election of cluster Heads (CHs) in CBRP which is based on the maximum available energy level, implementing load balancing for inter-cluster traffic using multiple gateways, and implementing sleep state for gateway nodes to further save the energy. Furthermore, we propose an Energy Efficient Cluster Based Routing Protocol (EECBRP) which extends the EGCBRP sleep state concept into all idle member nodes, excluding the active nodes in all clusters. The experiment results show that the EGCBRP decreases the overall energy consumption of the gateway nodes up to 10% and the EECBRP reduces the energy consumption of the member nodes up to 60%, both of which in turn contribute to stabilizing the network.

Recently, mobile computing has received much attention from database community. Sharing information among mobile users is one of the most challenging issues in mobile computing due to user mobility. Replication is a promising technique to this issue. However, adopting replication into mobile computing is a non-trivial task, since we are still facing other problems such as the lack in disk capacity and wireless network bandwidth used by mobile users. We have proposed a dynamic replica allocation strategy called User Majority Replica Allocation (UMRA) that is well suited to the modern architecture of mobile computing environment while avoiding such problems mentioned above. In this paper, we propose two relocation decision policies for UMRA and we provide a cost analysis for them. We also provide a cost analysis for another replica allocation strategy called Static Replica Allocation (SRA) for a comparison purpose.

This paper presents a system for reading comics on cellular phones. It is necessary for comic images to be divided into frames and the contents such as speech text to be displayed at a comfortable reading size, since it is difficult to display high-resolution images in a low resolution cellular phone environment. We have developed a scheme how to decompose comic images into constituent elements frames, speech text and drawings. We implemented a system on the internet for a cellular phone company in our country, that provides downloadable comic data and a program for reading.

As Object-Oriented Database Systems (OODBS) play an increasingly important role in advanced database systems, OODBS performance becomes a significant issue. It is well known that there is a strong relationship between performance and the concurrency control algorithms employed by the Database Management System (DBMS). Class Granularity Locking (CGL) and Class Hierarchy Granularity Locking (CHGL) are proposed as the concurrency control algorithms for OODBS to minimize the locking overhead. However, their basic characteristics, including the licking overhead and concurrency, have not been extensively investigated and it is not known which one is most appropriate for the general case. In this paper, we construct a simulation model for OODBS and carry out several performance evaluation studies on these two Class-Hierarchy Locking protocols and the Non Class-Hierarchy Locking (NCL) protocol. The NCL protocal is a variation of the conventional two phase locking protocol being applied to OODBS data structures.