Communication during free movement needs to be based on wireless communication. For wireless communication, cell phone network as well as wireless LAN hot spots may be good candidates (Fig.1). At present, cell phones are being mainly used because of their wide communicable area, and LAN is being used at limited hot spots. However, as the purpose of cell phone is to transmit voice, its bandwidth is quite narrow and you need to pay high fees. In the ubiquitous communication in future, proliferation of wireless LAN will play a major role.
In order to expand the wireless LAN area, preparation of a sufficient number of access points is prerequisite. Wireless terminals will communicate with nearby access points. However, since access points are usually connected each other by cables, and they would require huge construction costs for installation of access points. Installation must be made systematically because it is not easy to move or transplant them. Moreover, as wireless LAN has a short range of radio waves, a large number of access points will have to be established.
Thus, under the current situation, a great deal of efforts and time are required for preparing the necessary number of access points. If we could find a good way to realize wireless connection of access points, it would greatly contribute to the expansion of wireless LAN area (Fig.2). In order to solve the problem associated with the preparation for access points, our Laboratory is under study a system called "WAPL" (Wireless Access Point Link). Under the WAPL system, wireless LAN hot spots area will be expanded by just installing access points. The characteristic of the system is that repair work of access points can easily be done, should troubles or congestion of network have taken place.