A non-synchronized sampling scheme

Abstract

When a fixed free-running crystal is used for sampling time generation at a DMT receiver, Inter-Symbol Interference (ISI) and Inter-Carrier Interference (ICI) are caused by sampling time error. The ICI becomes more serious as the DMT symbol length increases. In this paper, the effects of sampling clock offset are investigated in the time domain using a new notion of Inter-sample Interference (IsI) instead of ISI and ICI. Also a new frequency domain timing error correction scheme is proposed. In the proposed scheme, each DMT symbol is partitioned into several short sub-symbols in the time domain, then timing error correction is carried out for each sub-symbol in the frequency domain. Although a one block delay is introduced, the proposed scheme is computationally efficient in that neither over-sampling nor time domain interpolation is required. Furthermore, because long time domain symbols are divided into short sub-symbols, the proposed scheme can also be used for DMT systems using long symbols.