A centralized process position trace method of mobile station using radio LAN is provided, in which a position of a mobile station is traced in a building in order to transmit and receive data between mobile station and access point. A two-way communication method is provided in accordance with the invention, in which a position of a mobile station is traced in a building in order to transmit and receive data between mobile station and access point and a patient's emergent situation is informed from the mobile station to home position access point and vice versa by realizing the Medical Application Radio System (called MARS below) protocol suggested by IEEE802.11 in Medical Application Radio System.