Suppression of narrow frequency bands in multicarrier transmission systems

A method to enhance capacity in Discrete Multitone Transmission (DMT) systems is presented. This paper addresses the problem, how to reduce the transmit power spectral density (PSD) of the DMT signal in specific narrow frequency bands below a certain level. One example is VDSL signalling [1, 2] in the presence of amateur radio. Only a small amount of egress is allowed inside these very narrow frequency bands. If a DMT system operates in such a situation, in the conventional system all tones inside these frequency bands and a lot of adjacent tones must be loaded with zeros to meet the requirements on the egress. In our proposal we devote some unused tones to reduce the PSD inside these frequency bands. With this method the number of idle tones can be reduced substantially. To demonstrate the increase of the number of usable tones, we will show a realistic example in the context of VDSL.