Heterogeneous wireless systems such as a combination of mobile broadband wireless access (MBWA) and wireless local area network (WLAN) are candidates to attain the large capacity in the next generation mobile communication systems. For capacity expansion, small cells of multiple wireless network are deployed densely in these systems. Because a number of the cells overlap, users must discover a lot of cells at once for cell selection. As a result, radio resources are much used for cell discovery in dense small cell environment. We have proposed the efficient network selection scheme using the positioning information and the map information. Using the map information, users can select the cell which has a better channel quality without cell discovery. In this paper, for further enhancement of system performance, new selection scheme considering the traffic load is evaluated. Using this load information, user select a network based on the expected throughput and their location. Consequently, users can avoid the congested network and select one which has a low traffic demand. We discuss the user throughput of the proposed scheme by comparing with the conventional one where users select by measured instantaneous signal strength. The simulation results show that the proposed scheme can improve the average user throughput by 52.8 % in comparison with the conventional one. These performances can be achieved by feasible positioning accuracy.

For large scale disaster relief, we propose a location and short message system using the Quasi-Zenith Satellite System (QZSS). The target capacity of the proposed system is the transmission of 3 million message data (MD) or more within one hour. To control random access of mobile terminal (MT), Frame Slotted ALOHA is used. Frame Slotted ALOHA cannot provide optimum control, since the hub station (HUB) does not know the number of MTs. For realizing large capacity, we propose Frame Slotted ALOHA with Flag Method in which the HUB can estimate the number of MT quickly. The proposed Flag Method is divided into two modes. The send flag mode can estimate the number of MT within a short time. The send message data mode can control random packet access using estimated number of MD in send flag mode. Computer simulation shows that it is possible to accommodate 3 million MD by using the proposed Flag Method within 48 m 19 s.

No abstract

No abstract