Yoshiharu Tajima

All-channel concentric allocation in cellular systems

A dynamic channel assignment algorithm for cellular systems, i.e., all-channel concentric allocation (ACCA), is proposed, and its performance is evaluated by computer simulation. Computer simulations show that system capacity (offered traffic at a blocking rate of 3%) is improved by a factor of 2.5 compared to conventional fixed channel assignment (FCA). A transmitter power control (TPC) is designated to cooperate with ACCA and enhance system capacity. Simulations confirm that ACCA with TPC accomplishes a system capacity 3.4 times greater than FCA.<<ETX>>

A Novel RAT Virtualization System with Network-Initiated RAT Selection between LTE and WLAN

Various radio access technology (RAT) selection methods between LTE and wireless LAN (WLAN) have been proposed, which aim to improve the capacity of the cellular network and to improve user satisfaction through mobile network operators. However, studies from the viewpoint of mobile virtual network operators (MVNOs) have not yet been investigated sufficiently. We propose a novel RAT virtualization system suitable for MVNO composed of a new network-initiated RAT selection method and RAT selection algorithms. The system conceals a change of IPs associated with a change of RATs and offers a context-aware virtualized RAT for the application server and user application. We demonstrate a new RAT selection method by developing a prototype of the proposed RAT selection system. We also evaluate a system-level performance by using a network simulator (NS-3) and show that our proposed algorithm outperforms conventional algorithms in terms of the WLAN usage ratio and user satisfaction.

Context Aware Cell Selection in Heterogenious Radio Access Environment

The size of data chunk diverges from 101 to 1010 bits. Generally, if a network carries in a way both of big size data and small size data, the performance is extremely degraded by the big size data. Then, we propose to select a wireless cell among of multiple cells by referring context information such as data size and users situation such as moving velocity. Especially, we show the improvement on connection level performance by dynamically selecting a cell based on the above context information. Further, we compare the packet level performance for single cell and multiple cells, and summarize the advantage of multiple cells environment with context aware cell selection.