Theoretical analysis of distortion due to notch filtering in DS-CDMA systems

Wideband DS-CDMA can be used as an overlay to narrowband communication system to provide increased capacity. In order to achieve better performance in the transmission of the DS-CDMA signal, it has been shown that a narrowband interference rejection technique should be used at the receiver. A transform domain notch filter-based narrowband interference rejection technique, which is one of the most useful techniques in a sense of practicality, distorts the DS-CDMA signal while it can drastically improve the bit error rate (BER) performance of the DS-CDMA system. We discuss the performance of a band-limited DS-CDMA system with notch filtering. Here we theoretically analyze the signal-to-noise plus interference power ratio (S/(N+I)) of the DS-CDMA signal and derive a closed-form expression of the SI(N+I) when we assume an ideal notch filter, which can perfectly reject the narrowband interference. Then, we compare the theoretical results with computer simulation results using a DSP-based notch filter