Mobility and a wideband has become a development trend of modern communication technologies, and the 3rd Generation Partnership Project (3GPP) has been devoted to a long Term Evolution (LTE) system evolving from a 3G system with the aim of developing the 3GPP radio access technologies toward a high data ratio, a short delay, and optimized packet data applications. The Multi-input Multi-Output (MIMO) technology at the physical layer has become one of crucial technologies in the current mobile communication system due to a number of advantages thereof, for example, the capacity of the system is extended through space division multiplexing of multiple antennas, the throughput of the system is improved using a multiplexing gain of multiple antennas, etc.
As the capacity is extended, interference also becomes higher accordingly due to the correlation between channels in a channel matrix, and if a base station can obtain somehow some Channel State Information (CSI) (which can be an instantaneous value, or can be short-term or middle- to long-term statistic information, then it may optimize power, rates, and even transmit directions applied to respective data streams in some preprocessing scheme, and possibly a part or all of interference between the data streams may be eliminated in advance at a terminal through preprocessing, thus achieving higher performance.
Accordingly it is highly desirable in the industry to improve the extent of matching between the CSI fed back by the terminal, and a channel state.