Rejection of Multiple CW Interference in QPSK Systems Using Decision-Feedback Filters

Iwao SASASE  Shinsaku MORI  

IEICE TRANSACTIONS (1976-1990)   Vol.E71   No.12   pp.1282-1290
Publication Date: 1988/12/25
Online ISSN: 
Print ISSN: 0000-0000
Type of Manuscript: PAPER
Category: Radio Communication

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We analyze the performance of QPSK systems using complex transversal filters with decision-feedback (DF) taps in the presence of multiple continuous wave (CW) interference and Gaussian noise. The general analytic expressions for the optimum tap weights and minimum mean square errors in the presence of multiple CW interference for both one-sided and two-sided transversal filters with and without DF taps are derived. We find that the output signal-to-noise ratio (SNR) of the one-sided DF filter is most improved among the four types of the filter structures and that multiple CW interference can be almost completely rejected. We also consider the transient behavior of the DF filters in the presence of multiple CW interference. It is found that the magnitudes of the tap weights are proportional to the relative multiple interference power ratios, while they converge to their corresponding steady-state values with the equal rate. It is also found that one-sided DF filter has shorter setting time compared to two-sided DF filter.