Timing Synchronization for Upstream Cable OFDMA Signals

Abstract

The most recent broadband data-over-cable standard, known as DOCSIS 3.1, introduced orthogonal frequency-division multiplexing (OFDM) as a major upgrade to improve transmission efficiency. Because OFDM signals are sensitive to synchronization errors, accurate timing recovery is an integral part of a DOCSIS 3.1 system. Many conventional OFDM/OFDMA timing synchronization methods cannot be directly applied, as they require the use of specific training signals which are incompatible with DOCSIS 3.1. In this paper, the performance of a modified Schmidl and Cox (S&C) timing algorithm is first investigated for DOCSIS 3.1 systems and shown to be unsatisfactory under severe channel conditions. Two novel timing algorithms are proposed which take advantage of the mirrored symmetry of the training signal defined in DOCSIS 3.1. It is demonstrated that both algorithms provide accurate timing estimates even under severe channel conditions and heavy traffic flow. The second algorithm is introduced to eliminate the use of multipliers in the first algorithm, hence reducing the hardware complexity. Data skipping and data truncation are also presented as methods of further reducing the hardware complexity and the corresponding cost-performance tradeoff is investigated.