1. Field of the Invention
Aspects of the invention relate to wireless data communication, and more particularly to precoding in a multiple input multiple output (MIMO) communication system.
2. Description of the Related Art
Precoding may be a process to assign appropriate users to each spatial beam in a multiple input multiple output (MIMO) communication system. Precoding also may be a process to assign appropriate streams to each spatial beam in single user MIMO communication system.
A vector or a matrix corresponding to each spatial beam exists in a precoding codebook. The greater a distance between spatial beams specified by the vector or the matrix, the more the communication quality of wireless communication can be improved.
Research on the above subject has been ongoing. Papers describing the result of such research have recently been published, such as the paper entitled “Frequency Domain Adaptive Precoding for E-UTRA MIMO,” R1-062189, presented by Motorola at the 3GPP TSG RAN WG1 Meeting #46, in Tallinn, Estonia, Aug. 28-Sep. 1, 2006 (3rd Generation Partnership Project, Technical Specification Group Radio Access Networks, Working Group 1).
Generally, in a MIMO communication system in which a number of receiving antennas is the same as a number of transmitting antennas and the receiving antennas are symmetrical to the transmitting antennas, a regular matrix-based codebook is widely used. Also, in a MIMO communication system in which the number of transmitting antennas is different from the number of receiving antennas and the receiving antennas are asymmetrical to the transmitting antennas, a vector-based codebook is widely used. In a MIMO communication system in which only one stream is transmitted to a UE, a vector codebook may be used.
However, in the case of the matrix-based codebook, it is difficult to calculate distance between matrices in a codebook. Also, in the case of the vector-based codebook, it is difficult to support a multi-rank system in order to improve a communication quality.
Accordingly, there is a need for a method that can more effectively generate a codebook in a precoding procedure for a MIMO communication system.