I. Introduction
Various kinds of radio access networks (RANs), such as Wi-Fi, WiMAX, cellular phone systems, and so on, have been developed and deployed. As one of the approaches to use those RANs optimally, link aggregation techniques have been applied to increase the throughput by simultaneously using multiple RANs [1]. Such techniques efficiently maximize radio resource utilization over multiple RANs. In a standard of the cognitive radio technologies, IEEE 1900.4 [2], multi-homing scenarios aggregating such heterogeneous wireless networks are included in the usecases.