8.Multi-Stage Interference Canceler

An interference canceler facilitates increased system capacity in wideband CDMA by reducing the cross-correlation between spread codes that occurs when multiple users with different spread codes communicate on the same carrier wave frequency. Three methods are used to achieve interference cancellation: orthogonalizing filters, decorrelators, and multi-stage interference cancelers.

The orthogonalizing filter, which is used in single-user reception systems, orthogonalizes the tap coefficient of the matched filter against the spread codes of interference signals. While the configuration is simple, it is difficult to apply to a multi-path environment using scrambling codes.

The decorrelator, which is employed in multi-user reception systems, is a method to reduce cross-correlation by calculating the inverse of the cross-correlation matrix between spread codes. While channel predictions are not necessary, the processing involved is complex.

The multi-stage interference canceler is also used in multi-user reception systems. It is a method to improve the signal-to-interference ratio by generating interference replicas of other users and subtracting these values from the received signals. As stages are repeated, the precision of channel predictions can be improved.

Realizing Interference Canceling

Created 1999/03