1. A receiving apparatus in a wireless communication system, comprising: a multiple-input, multiple-output (MIMO) detector configured to estimate a desired signal and an interference signal based on received signals in accordance with a MIMO detection scheme; a first decoder configured to iteratively decode the interference signal output from the detector; a second decoder configured to iteratively decode the desired signal output from the detector; and a log likelihood ratio (LLR) updater configured to update an internal LLR value of the second decoder using an internal LLR value of the first decoder, wherein the first decoder is further configured to detect a sign-inverted log likelihood ratio and to provide the sign-inverted log likelihood ratio to the LLR updater.