DMT 기반의 xDSL 모뎀의 비동기식 샘플링 방식 ( Non-synchronized Sampling Techniques for DMT-based xDSL Modems )

In this paper, we analyze timing errors (sampling phase-offset and sampling frequency-offset) occurring in DMT-based xDSL systems and then propose non-synchronized sampling (full digital PLL) techniques to compensate the sampling errors at the digital receiver. In the previous paper, the non-synchronized sampling technique with the frequency-domain rotor was proposed to compensate the sampling phase-offset in the DMT-based xDSL systems using delay-rotor property. However, the delay-rotor property dose not hold any longer if the signal passed through an analog low-pass filter is sampled with phase errors. In this paper, a non-synchronization sampling technique, which can compensate the sampling phase-offset perfectly by making data portion cyclic-convolutionized even in the case of sampling phase-offset present, is proposed. Also, an improved hybrid time-domain/frequency-domain correction technique is proposed for the case where both sampling phase-offset and sampling frequency-offset exist. A time-domain correction technique which does not require any additional overhead for the case with both offsets is proposed. Finally, the performances of the proposed non-synchronized sampling techniques are investigated by applying them to a DMT-based ADSL system and compared with the ones of the previous techniques through computer simulations.