Cancellation moderating factor controlling scheme using signal power ratio for multi-antenna CDMA interference canceller

In a CDMA non-linear interference canceller, the generated interference signal replica is multiplied by a positive number smaller than unity, which is called the cancellation moderating factor (CMF), to prevent the interference enhancement due to subtracting the inaccurate replicas. A CMF controlling scheme applicable both to a multistage parallel interference canceller (MPIC) cascaded with an adaptive array antenna and to an MPIC with multi-antenna reception is proposed. The proposed scheme uses the ratio of the interference signal´s power to the desired signal´s power in order to mitigate the replica subtraction error owing to inaccurate channel estimation. The performance of the proposed scheme is evaluated by computer simulations assuming an asynchronous uplink single chip-rate variable spreading factor DS-CDMA system. The simulation results show that the proposed scheme improves the bit error rate performance compared with the scheme using the log likelihood ratio of the transmitted bit for CMF control and fixed CMF setting over an exponentially decaying 5-path Rayleigh distributed channel.