An Economical, ISI-Immune Frequency Offset Estimator for DOCSIS Upstream Channels

This paper discusses the design and implementation of frequency offset estimation algorithms for DOCSIS upstream channels. A cost-effective estimator which approaches the Cramer-Rao bound for high SNRs is derived. The effect of ISI generated by upstream micro-reflections in typical cable networks is considered, and a condition upon the transmitted preamble sequence which guarantees unbiased estimation is presented. It is shown that the proposed estimator is unbiased for a wide range of preamble sequences, which is generally not the case for burst frequency estimators. This flexibility may be utilized by selecting a broadband preamble which is suitable for performing channel estimation and frequency offset estimation simultaneously, thereby increasing the efficiency of the upstream channels.