截幅效应对DMT调制的影响及一种减小截幅噪声的方法

Chipping Effect in DMT and a Method to Reduce the Clipping Noise

ＤＭＴ（ＤｉｓｃｒｅｔｅＭｕｌｔｉｔｏｎｅ）调制是一种在ＡＤＳＬ（ＡｓｙｍｍｅｔｒｉｃａｌＤｉｇｉｔａｌＳｕｂｓｃｒｉｂｅＬｉｎｅ）中被广泛采用调制技术。本文分析了在ＤＭＴ中对信号进行截幅所产生的影响，计算了Ｄ／Ａ变换产生的量化噪声和截幅噪声，并与未截幅时相比较，在不降低ＳＮＲ的情况下，降低了Ｄ／Ａ变换器的精度的要求，并求出最佳截幅因子。本文分析了一种减小截幅噪声的方法，并说明在非最佳截幅时，通过这种方法可获得与最佳截幅同样的结果。

Discrete Multitone Modulation(DMT) has been widely chosen for Asymmetric Digital Subscriber Lines(ADSL).This Paper analyzes the effect of chipping in DMT based transceivers and compute the chipping noise and the quantization noise produced by the D/A convertor. Compared with the no chipping,the number of bits for D/A converter is reduced without the loss of SNR. This paper analyses a method to reduce the chipping noise and show that by this method we can get the same result under the not optimum chipping as that under the optimum chipping.