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Optimum and sub-optimum linear MMSE multi-user detection for multi-carrier CDMA transmission systems

This paper investigates optimum and sub-optimum linear minimum mean square error (MMSE) multi-user detection (MUD) techniques for multi-carrier code division multiple access transmission systems. In a first step, we present two formulations of MMSE MUD techniques that are optimum for any number of users and any power distribution and achieve exactly the same performance with a different computational complexity. In a second step, we present a simplification of optimum MMSE MUD techniques that achieves sub-optimum performance but at a reduced complexity that is similar to single-user detection techniques. Simulation results on indoor channels show that optimum and sub-optimum MMSE MUD techniques outperform the MMSE single-user detection technique, especially for low and medium system loads as well as in the case of the near-far effect.