Log-likelihood ratio based successive interference cancellation in CDMA systems

We propose a new successive interference cancellation (SIC) scheme that cancels the interference in order of the magnitude of log-likelihood ratio (LLR) in CDMA systems. The motivation is that the reliability of a decision increases with increasing magnitude of LLR. As a result, the error propagation associated with a wrong direction and the resulting error probability for the remaining users can be minimized. We show that the magnitude of LLR depends on the signal strength as well as the instantaneous multi-user interference (MUI), and the proposed LLR-based SIC scheme, taking both the signal strength and the instantaneous interference into account, significantly outperforms the conventional signal strength-based SIC scheme. We also examine the effect of channel estimation error for various SIC schemes.