Recursive interference canceller using slope optimized soft limiters for DS-CDMA downlink channels in frequency selective fading

In this paper, we present a multistage partial PIC using adaptive slope optimized soft limiters and propose a recursive PIC which can significantly reduce the circuit complexity. With the proposed simple modification using soft limiters we can overcome the drawbacks and combine the advantages of conventional PIC, SIC, Partial PIC, and HNN. To enhance the performance and simplify the circuit, a normalization method of Rake receiver output for avoiding deorthogonalization of signature waveforms resulted from fading and, in stead of canceling the interference at the input of the Rake receiver, an accurate interference cancellation method at the output of Rake receiver are suggested. To verify the efficiency of the proposed interference canceller, the simulations were carried for high data rate channels with spreading gain 4 in frequency selective fading environment which is the worst case of operation and the results show that the error floor problem of existing MUDs and PICs for high rate multiuser channels can be completely solved with slope optimized soft limiters without any other circuits for received signal power ranking. It is also pointed out that the optimal performance can be obtained with more stages of PIC and antenna diversity. The existing PICs have been recognized as the state of art and the most realistic one of the existing MUDs. Since the proposed PIC has the same structure of conventional PIC except the only slight change of limiter, the proposed PIC showing significantly improved performance over the existing PICs even for the worst operation situations can be said to be more realistic for IMT-2000 systems than any other MUM and PICs.