When a wide area base station (macrocell) installed outdoors and a radio communication terminal (mobile station) perform radio communication each other, fading is often caused by buildings and movement of the radio communication terminal, leading to significant slowdown in a communication speed. In addition, in a radio communication system of OFDMA scheme which has been recently employed by WiMAX (Worldwide Interoperability for Microwave Access), UMB (Ultra Mobile Broadband), LTE (Long Term Evolution) and next-generation PHS, different frequency channels (subchannels) are allocated to different users (radio communication terminals) to perform communication. In such a radio communication system, a reception level and CINR (Carrier to Interference and Noise Ratio) are deteriorated for some frequencies allocated, as affected by multipath.
In order to address such a problem, in WiMAX and LTE adopting OFDMA, a transmitter transmits a frame in which reference signals (pilot subcarriers) are inserted based on a predetermined regulation. Then, a receiver calculates a correction value based on the reference signals included in the frame received and multiplies data signals, except the reference signals, by the correction value. A method to reduce influence by fading, such as data signal (data subcarrier) amplitude and phase distortion, in the above manner has been employed. The reference signal is also used in a multi-antenna system (AAS: Adaptive Array System, MIMO: Multi Input Multi Output) for the receiver side to identify an antenna on the transmitter side which sent the reference signal.
As a conventional communication technology adopting OFDMA scheme, there has been one disclosed, which enables to support as many number of users and/or antennas as possible by dynamically changing the number of pilot symbols and the number of groups of the pilot subcarriers among different users, based on the number of simultaneously supportable users and antennas and a precision requirement in radio channel estimation (for example, see Patent Document 1).
USPTO Backgrounds
USPTO Backgrounds