Naoyuki Karasawa

A Web server selection algorithm using QoS measurement

We compared several server algorithms and found that performance of server selection can be improved using QoS statistics (average of past weeks QoS values) and real time QoS probing. Specifically, a set of candidate servers are selected based on QoS statistics for a given time section of the day and day of the week. A target server is, then, selected among the pre-selected candidate servers based on real time QoS measurement using echoping.

Traffic characteristics of dynamic channel assignment under non uniform traffic distribution

This paper describes communication traffic characteristics in cellular systems where dynamic channel assignment is used and the traffic intensity in each cell is not equal. Clique packing is used as a model of dynamic channel assignment, and communication traffic characteristics of clique packing under the unequal load are discussed. Communication traffic characteristics of practical dynamic channel assignment methods, such as first-available method, are also discussed by using the clique packing model. The results of this paper contribute to estimation of the blocking performance of dynamic channel assignment under the unequal traffic load.

PHS based ad hoc networks

This paper considers PHS based wireless ad hoc networks. In ad hoc networks, a terminal uses a communication channel based on PHS, and communicates with another terminal by using the direct communication mode of PHS. It is assumed that if a terminal fails to send the information, the terminal retries to send the information after an appropriate time interval. The paper considers some schemes for link scheduling and setting the time interval for retrial. To evaluate the schemes, we actually develop ad hoc networks. From the evaluation, characteristics of the schemes are discussed.

An architecture, topology and performance of the multihop Bluetooth network (MBNET)

We propose a novel Bluetooth network architecture, called multihop Bluetooth network (MBNET). In the MBNET, one of the nodes is the base station. Each node is assumed to have two Bluetooth devices. The fundamental difference of MBNET from a conventional Bluetooth network architecture, called scatternet, is that no Bluetooth device belongs to multiple piconets. Thus, there is no piconet-switch overhead. The basic design principle of the MBNET topology is that each node should have at least two disjointed paths to the base station. We argue the topology optimization of the MBNET, from perspectives such as performance and reliability, and present several topology design guidelines using simple examples. In MBNET, the base station is in charge of designing MBNET topology and needs to obtain the entire node information. We briefly describe a node information management method, which is composed of hierarchical neighbor discovery protocol, neighbor information reporting protocol, and in-service neighbor discovery protocol. We present an algorithm to construct the topology of MBNET and evaluate its performance. It is shown that the proposed algorithm has a satisfactory performance in providing every node two disjointed paths to the base station.

A circuit-connection-based multihop wireless infrastructure for local communities

The concept of an open community network is presented as a vision for general-purpose ad hoc networks. An open community network is a novel information infrastructure for local communities based on wireless multihopping technologies. A method for calculating number of PHS (Personal Handy Phone System) devices per CP to meet traffic demands is presented and numerical examples are given. An experimental system for an open community network using PHS is described and some research issues for developing an open community network are identified.