As a communication system by which a high-speed communication between a communication terminal and a base station is realized, LTE (Long Term Evolution), MC-CDMA (Multi Carrie Code Division Multiple Access), Wimax (Worldwide Interoperability for Microwave Access)(registered trademark) and the like are known.
In the past, in order to improve communication service in such communication systems, technologies such as MIMO (Multiple Input Multiple Output) system and adaptive modulation (link adaptation) system have been suggested.
MIMO system is a technology in which multiple transmitting antennas and receiving antennas are respectively combined to realize a pseudo broadband in data reception and transmission. The communication apparatus on the transmission side uses the same channel and transmits multiple signals from the multiple transmitting antennas, each signal having data different from each other. Then, the communication apparatus on the reception side receives multiple signals by the multiple receiving antennas and separates these spatially multiplexed signals to extract data. Since different data can be transmitted from the same channel, a faster communication is realized.
The adaptive modulation system is a technology in which a modulation class used for communication is changed depending on the situation of the communication between the communication terminal (mobile station), which is a communication apparatus, and a bases station (see, for example, Patent Document 1). The communication terminal calculates the reception quality information such as CINR (Carrier to Interference and Noise Ratio) based on the signal received from the base station, and sends the information to the base station. The base station specifies the modulation class corresponding to the reception quality information from the predefined MCS (Modulation and Coding System) table. In the MCS table, the higher the reception quality, the higher the speed of data transmission of the modulation class associated to the reception quality. Thus, if the reception quality is good, a higher modulation class by which data is communicated at a high speed is chosen, and if the reception quality is not good, a lower modulation class by which data is communicated at a low speed but data corruption is unlikely to occur is chosen.