  In this paper we propose minimum mean squared error (MMSE) iterative
successive parallel arbitrated decision feedback (DF) receivers for direct
sequence code division multiple access (DS-CDMA) systems. We describe the MMSE
design criterion for DF multiuser detectors along with successive, parallel and
iterative interference cancellation structures. A novel efficient DF structure
that employs successive cancellation with parallel arbitrated branches and a
near-optimal low complexity user ordering algorithm are presented. The proposed
DF receiver structure and the ordering algorithm are then combined with
iterative cascaded DF stages for mitigating the deleterious effects of error
propagation for convolutionally encoded systems with both Viterbi and turbo
decoding as well as for uncoded schemes. We mathematically study the relations
between the MMSE achieved by the analyzed DF structures, including the novel
scheme, with imperfect and perfect feedback. Simulation results for an uplink
scenario assess the new iterative DF detectors against linear receivers and
evaluate the effects of error propagation of the new cancellation methods
against existing ones.
