IDMA Vs. CDMA: Detectors, Performance and Complexity

This paper presents comprehensive comparisons of interleave division multiple access (IDMA) and direct sequence code division multiple access (DS-CDMA) in terms of performance and complexity using iterative multiuser detection technique, where we restrict ourself to three suboptimum linear detectors: minimum mean square error (MMSE), rake (or matched filter), and soft-rake detectors from practical concerns. We first analytically compare these detectors, which are found to be equivalent for IDMA with asynchronous users on flat channels, whereas this does not hold for DS-CDMA, which is sensitive to user asynchronism. This implies that, on flat channels, simple detector suffices to get the MMSE output for IDMA while DS-CDMA requires more complexity such as computing matrix inversions. We also discuss several aspects of complexities for IDMA and DSCDMA when the MMSE detector is used. Computer simulations are performed in various scenarios and the performance is analyzed by bit error rate as well as by extrinsic information transfer chart. The analysis reveals some advantages of IDMA over DS-CDMA, particularly in highly user loaded scenarios.