1. A receiving apparatus in a wireless communication system, comprising: a detector for estimating a desired signal and an interference signal by multiple-input, multiple-output (MIMO) -detecting received signals; a first decoder for iteratively decoding the interference signal output from the detector; a second decoder for iteratively decoding the desired signal output from the decoder; and a log likelihood ratio (LLR) updater for updating an internal LLR value of the second decoder using an internal LLR value of the first decoder.