Wireless communication systems have developed into a high speed and high quality of radio packet communication systems in order to provide data service and multimedia service out of the initial voice-oriented service. In order to provide a high speed and high quality of data service in the wireless communication system, multiple-input multiple-output (MIMO) schemes have been proposed in various ways.
The MIMO schemes can be classified into spatial diversity scheme for increasing transmission reliability by employing multiple paths and spatial multiplexing scheme for improving the data rate by transmitting multiple data streams at the same time. Further, active research has recently been done on a method of obtaining the advantages of the two schemes by properly combining them.
The MIMO schemes can also be classified into open-loop transmission scheme in which channel information is used to schedule user data and closed-loop transmission scheme in which channel information is not used to schedule user data. In the open-loop transmission scheme, a transmitter and a receiver can be constructed relatively simply without uplink radio resources for transmitting channel information since the transmitter does not need channel information. However, the open-loop transmission scheme is disadvantageous in that its performance is degraded when channel correlation is increased or multiples channels are subject to deep fading at the same time because this scheme cannot cope with a channel change adaptively. On the other hand, in the closed-loop transmission scheme, a receiver estimates a channel and then re-transmits an estimated channel to a transmitter, and the transmitter acquires channel information. The transmitter performs pre-processing adapted to a channel in consideration of a channel state every moment, so the capacity of a system can be maximized.
In the closed-loop transmission scheme, system performance can be maximized when all channel information is known. But as channel information increases, radio resources for transmitting the channel information increase. Moreover, channel information for MIMO schemes increases as the number of antenna increases. If radio resource for channel information is allocated too much, radio resources for data may be insufficient. It may result in low data rate.
Thus, there is a need for method of maximizing the data rate while minimizing the amount of feedback information.