Adaptive digital notch filtering
Kaluri V. Rangarao · Defense Technical Information Center (DTIC) · 1991
The problem of narrow band interference while transmitting broad-band signals like Direct Sequence Spread Spectrum is a common source of problems in Electronic Warfare. This can occur either due to intentional jamming or due to unavoidable signal sources present in the vicinity of the receiver. Lack of improper information on these narrow band interferers makes it difficult to cancel them. In this thesis the above problem is addressed by using an adaptive notch filtering technique. Before adopting such a technique other methods like the Least Square Estimator and the Maximum Likelihood Estimator were explored. However the Kwan and Martin adaptive notch filter structure was found both relevant and suitable for the problem of interest. The Kwan and Martin method has the difficulty of increasing hardware complexity with number of notches. This makes it difficult to implement in real time. A new algorithm was developed for the purpose of implementing the structure in real-time. This new algorithm offers the same performance at reduced hardware complexity. This algorithm was simulated and the results were presented. A hardware feasibility is discussed by proposing a simple structure based upon existing commercial signal processing chips.