Effect of Phase Distortions Caused by Narrowband Filtering Frequency-Hopped Signals

Abstract

We investigate the ability of finite impulse response (FIR), and infinite impulse response (IIR) filters to remove narrowband interference from a frequency-hopped signal. It is possible to construct narrowband IIR filters with very few taps; however, these filters have a non-linear phase response, and Monte-Carlo simulations demonstrate that this increases the probability of bit error. FIR filters have a linear phase response, but require several orders of magnitude more taps to produce the same narrowband filter frequency response. Finally we consider forward and reverse processing with the IIR filter. By filtering the signal with an IIR filter and then time-reversing the signal and filtering it again, it is possible to have linear phase at the expense of an increase in processing complexity. Monte-Carlo simulations demonstrate that forward and reverse processing significantly reduces the probability of bit error when IIR filters are used.