Decorrelator based narrowband interference suppression in spread spectrum communications

Multiuser detectors for a synchronous code division multiple access (CDMA) channel are adopted for detecting a spread spectrum signal in the presence of a digitally modulated narrowband interference (NBI). The bit error probability of a decorrelating detector is independent of the ratio of the power of a digitally modulated NBI signal to that of a spread spectrum signal but not independent of the time offset between two signals. A decorrelating decision feedback detector achieves the bit error probability which is independent of both the power ratio and the time offset between two signals in the regions of practical interest where the power of the NBI is greater than that of the spread spectrum signal. The bit error probability of a decorrelating decision feedback detector is lower than that of a decorrelating detector and coincides with an optimum single user bound in the regions of practical interest.