分接泄漏算法:一种用于数字实现的稳定运行的算法,分数间隔自适应均衡器

R. Gitlin, H. C. Meadors, S. Weinstein
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引用次数: 139

摘要

分数间隔均衡器是一种非递归自适应滤波器,其分接权重间隔为符号间隔的分数。与抽头间隔为一个符号间隔的传统同步均衡器相比,这种均衡器可以在存在严重线性失真的情况下显著提高调制解调器的性能。然而,当使用传统分接调整算法时,数字实现的分数间隔均衡器通常会表现出长期的不稳定性。这是因为,与同步均衡器相比,分数间隔均衡器通常会有许多组抽头值,这导致几乎相等的均方误差(mse)值。其中一些抽头设置——由于数字抽头更新电路中的偏差而不可避免地会达到——大到足以导致寄存器溢出,从而导致性能下降。在本文中,我们报告了如何对分接调整算法进行简单的修改来解决上述问题。改进的抽头调整算法通过系统地“泄漏”或降低所有均衡器抽头权重的大小来防止大系数值的积累。对于工作在9.6 kb/s的实验调制解调器,已经证明了抽头泄漏调节算法可以防止大均衡器抽头值的积累,同时允许实现分数间隔均衡器的全部性能增益。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
The tap-leakage algorithm: An algorithm for the stable operation of a digitally implemented, fractionally spaced adaptive equalizer
A fractionally spaced equalizer is a nonrecursive adaptive filter whose tap weights are spaced a fraction of a symbol interval apart. Such an equalizer can significantly enhance modem performance in the presence of severe linear distortion, when compared with a conventional synchronous equalizer whose taps are spaced a symbol interval apart. However, a digitally implemented, fractionally spaced equalizer generally will exhibit long-term instability when the conventional tap-adjustment algorithm is used. This occurs because, in contrast to the synchronous equalizer, a fractionally spaced equalizer generally will have many sets of tap values, which result in nearly equal values of mean-squared error (mse). Some of these tap settings — which invariably will be attained because of biases in the digital tap-updating circuitry — are large enough to cause register overflows and consequent performance deterioration. In this paper we report how a simple modification in the tap-adjustment algorithm provides a solution to the above problem. The modified tap-adjustment algorithm prevents the buildup of large coefficient values by systematically “leaking” or decreasing the magnitudes of all the equalizer tap weights. For an experimental modem operating at 9.6 kb/s, it has been demonstrated that the tap-leakage adjustment algorithm prevents the accumulation of large equalizer tap values, while permitting the full performance gain of a fractionally spaced equalizer to be realized.
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