Shoji Shinoda

A new coloring problem of networks related to a channel assignment problem in cellular mobile systems

Recently, a new channel assignment scheme has been proposed (K. Nakano, 1989). This scheme takes the degree of interference into consideration. In the scheme, a channel is simultaneously assigned if the carrier-to-interference ratio is more than the desired value. The authors formulate this new model using a network and a new coloring problem of networks. They show that the new coloring problem is a generalization of the usual coloring problem of graphs and describe some results concerned with this coloring problem. One of the merits of this formulation is that the degree of cochannel interference between cells can be represented.<<ETX>>

Effect of mobility on teletraffic characteristics in a cellular system using terminal-to-terminal communication

This paper considers a new cellular mobile communication system, where a terminal can directly communicate with another terminal. Though there is a theoretical technique to analyze teletraffic characteristics of the system, this technique assumes that nodes never move. So, to analyze the teletraffic characteristics of this system considering mobility, computer simulation is usually used. This paper proposes a technique to theoretically analyze the call arrival rate, the mean holding time and the offered traffic in the new cellular system considering mobility. This paper assumes that the system consists of a single cell, terminals move along a single route and some channels are reserved for terminal-to-terminal communications.

Cut cover problem in directed graphs

Let D=(V, A) be the digraph with a vertex set V and an arc set A. A cut cover in D is a family of (directed) cuts such that each are of A belongs to some cut of this family. A minimum cut cover in U is one of minimum size. We say the problem of finding a minimum cut cover of a given digraph to be the minimum cut cover problem for digraphs. In this paper we consider the problem for digraphs, and show that this problem is NP-complete.

Cover problem corresponding to the p-collection problem

The lower-bounded p-collection problem is the problem where to locate p sinks in a flow network with lower bounds such that the value of a maximum flow is maximum. This paper discusses the cover problems corresponding to the lower bounded p-collection problem. We consider the complexity of the cover problem, and we show polynomial time algorithms for its subproblems in a network with tree structure.

Relations on the bounds of the number of channels on multi-hop wireless networks

For multi-hop wireless networks, we assign channels to communication between terminals. For this assignment problem, modeling using the edge coloring of the graph theory has been proposed. In the modeling, all edges of the graph are assigned colors. In this paper, we assign colors to edges in a subset of the edge set as the other modeling, and we consider the number of assigned colors in the graph. We show some theoretical results and examine this modeling with computer simulation.

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.

The structure of networks realized from terminal capacity matrices

We consider the structure of a flow network realized from a given terminal capacity matrix. As a result, we show a necessary and sufficient condition that a terminal capacity matrix is possible of realizing any graph. And in the case that the correspondence relation of vertices in a graph G and columns of an elementary terminal capacity matrix T/sub E/ are given, we show a sufficient condition and a necessary condition for the structure of the fundamental graph, for which is possible to realize T/sub E/.

Dynamic channel assignment with reuse partitioning in cellular radio systems

Popular reuse partitioning systems with fixed channel assignment in cellular systems are effective to improve the channel utilization in space. This paper explores an application of the reuse partitioning scheme, in which the dynamic channel assignment technique is introduced. In the proposed strategy, a channel can be simultaneously assigned to both the inner cells and the outer cells by reducing the transmitted power in the inner cells. Also, the rearrangement method is applied to this strategy. The simulation results show that the strategy results in higher channel occupancy. The traffic carried can be increased by 1.5 times as compared with the original fixed channel assignment system.