Method and apparatus for transmitting ACK/NACK information in an orthogonal frequency division multiple access system based on time division duplexing

ABSTRACT A method is provided for transmitting control information by a Base Station (BS) in a Time Division Duplexing (TDD)-based Orthogonal Frequency Division Multiple Access (OFDMA) system. The method includes determining a TDD ratio value; when a value obtained by dividing a number of consecutive Forward-Link (FL) time slots of a predetermined time interval by a number of consecutive Reverse-Link (RL) time slots is not a positive integer, grouping Mobile Stations (MSs) into multiple groups and generating group index information; and transmitting, to the MSs, control information including the TDD ratio value and the group index information.