Soft-Decision Multistage Multiuser Interference Cancellation (Revised)

Successive interference cancellation (SIC) is a family of low complexity multiuser detection methods for DS/CDMA systems. The performance of the multistage SIC depends on the decision function used in the interference cancellation iterations, whether hard decision, soft decision or linear decision. Due to error propagation, multistage SIC with hard data bit decisions may perform more poorly than multistage SIC with linear or soft decision functions. We propose and analyze a family of generalized unit-clipper bit decision functions that better combine linear and hard decisions. Performance within 0.4 dB of the single-user bound can be obtained. We then robustify the above soft-decision SIC to time delay errors as large as half a PN chip.