In a UMTS (Universal Mobile Telecommunications System) network, for the purposes of improving spectral efficiency and improving the data rates, system features based on W-CDMA (Wideband Code Division Multiple Access) are maximized by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access). For this UMTS network, for the purposes of further increasing high-speed data rates, providing low delay and so on, long-term evolution (LTE) has been under study.
In a third-generation system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in the LTE system, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. Furthermore, in the UMTS network, for the purpose of achieving further broadbandization and higher speed, successor systems to LTE have been under study (for example, LTE Advanced (LTE-A)). For example, in LTE-A, there is a plan to extend the maximum system band of 20 MHz specified in LTE up to about 100 MHz. And, there is another plan to increase the maximum number of transmission antennas specified in LTE up to “8”.
In the LTE system, there has been proposed a MIMO (Multi Input Multi Output) system as a radio communication technique for improving data rates (spectrum efficiency) by transmitting and receiving data with use of a plurality of antennas (for example, see Non Patent Literature 1). In the MIMO system, a plurality of transmission/reception antennas are provided in a transmitter and a receiver and transmission information sequences are transmitted from different transmission antennas simultaneously. In the meantime, at the receiver side, simultaneously-transmitted information sequences are detected in a separate manner in consideration of different fading fluctuations caused in the respective transmission/reception antennas, thereby enabling increase in data rates (spectrum efficiency).
In the LTE system, there are specified SU-MIMO (Single User MIMO) transmission and MU-MIMO (Multiple User MIMO) transmission. In SU-MIMO transmission, the transmission information sequences that are simultaneously transmitted from different transmission antennas all belong to one user and in MU-MIMO transmission, the transmission information sequences belong to different users. In these SU-MIMO transmission and MU-MIMO transmission, a codebook is prepared for setting a phase/amplitude control amount (precoding matrix (precoding weight)) for an antenna of a transmitter at the receiver side and PMI (Precoding Matrix Indicators) to be assigned to the precoding matrix according to rank, an optimum PMI is selected from the codebook and fed back to the transmitter, and a RI (Rank Indicator) indicating the optimum rank is selected and fed back to the transmitter. At the transmitter side, the PMI and RI fed back from the receiver are used as a basis to specify a precoding weight for each transmission antenna from the codebook, performing precoding and transmitting transmission information sequences.