Cascade Adaptive IIR Notch Filter for Multiple NBI Suppression in QPSK DS-CDMA System
Bit Error Ratio (BER) performance of Quadri-Phase Shift Keying Direct-Sequence Code-Division Multiple Access (QPSK DSCDMA) communication system in the presence of multiple Narrow-Band Interference (NBI) using a NBI suppression filter is analyzed in this paper. The NBI suppression filter is realized as a cascade structure of first-order complex coefficient adaptive Infinite Impulse Response (IIR) notch filter sections with a simplified gradient-based adaptation algorithm. The QPSK DS-CDMA system operates in an environment characterized by Rayleigh frequency non-selective slow fading channel. Using the Standard Gaussian Approximation (SGA) method and ignoring steady-state leakage NBI, a general closed-form BER expression relating QPSK DS-CDMA signal and NBI suppression filter parameters is derived. Validity of the derived BER expression is confirmed by computer simulations.