Methods and apparatuses for modular MIMO system and CSI feedback in a wireless communication system. The methods and apparatuses include: identifying configuration information of an antenna system including antenna modules for a MIMO operation; identifying, based on the configuration information, a number of collocated antenna groups that each includes one or more of the antenna modules; identifying, based on the configuration information, a number of the antenna modules for each type of the antenna modules in each of the collocated antenna groups, wherein each of the collocated antenna groups includes one or more types of the antenna modules; generating a CSI report for one or more of the collocated antenna groups in the antenna system; and transmitting, to a BS, the CSI report.