说明：  In recent years, the number of portable mobile terminal users is increasing with improvement of the wireless communication environment. In addition, mobile multimedia services also bring the increase of wireless traffic and lack of spectrum resources. As a technique for efficient spectrum use, spectrum sharing receives much attention. It dynamically assigns a spectrum channel from a larger area network such as WiMAX to smaller area networks such as WiFi-based wireless LANs and achieves to increase the total wireless communication capacity of this area. In a case where all providers are cooperative, the spectrum sharing can be realized easily and improve user throughput in average. In another case where providers are not cooperative, some spectrum trading methods based on auction theory had been proposed.