Suppression of CW Interference and Colored Noise in QPSK System Using Decision-Feedback Filters

Toshiaki OGAWA
Shinsaku MORI

IEICE TRANSACTIONS (1976-1990)   Vol.E72    No.7    pp.804-810
Publication Date: 1989/07/25
Online ISSN: 
Print ISSN: 0000-0000
Type of Manuscript: PAPER
Category: Digital Signal Processing

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In this paper, we consider the performance of QPSK systems using complex transversal filters with additional decision-feedback (DF) taps, in the presence of colored noise and single continuous wave (CW) interference. Both one-sided and two-sided transversal filters with DF are considered. The general analytic expressions for the optimum tap weights and minimum mean square errors are obtained. We calculate the output signal-to-noise ratio of the filters and compare the theoretical results with the computer simulated results. The relations between the spectrum of the colored noise as well as CW interference and the corresponding frequency response of the DF filters are considered. We also consider the transient behavior of the adaptive DF filters. It is shown that the DF filters can suppress not only CW interference but also colored noise and that the two-sided transversal filter with DF has best performance in the presence of the colored noise and CW interference, while the one-sided transversal filter with DF is preferred when the white Gaussian noise and CW interference are included in the system. It is also shown that the frequency response of the DF filters is changed according to the spectrum distribution of the colored noise and CW interference in order to suppress them more effectively. The simulated results are in good agreement with the theoretical results.