Power scaling of LDPC decoder stage in long haul networks

Enhancing Forward Error Correction (FEC) is necessary to recover from physical impairments faced by high order modulation transmission in long haul networks. However, the heavy complexity of Soft Decision (SD) FEC increases the power consumed at the receiver side. We present a technique that adjusts the FEC consumption according to each connection path length and highlight the potential energy saving through a long haul network application. Keywords: Green networking, Coherent transmission, WDM networks, Soft Decision FEC, DVFS Introduction The introduction of coherent transceivers has strongly increased the transmission data rate up to 100Gbps per Wavelength Division Multiplex (WDM) channel for systems commercially available today. It has been achieved by means of a QPSK modulation format at 28Gbaud onto each of the two fibre polarisations [1]. For a Bit Error Rate -12 (BER) target of 10 at the receiver side in a single mode fibre based network and span length of 75-100 km, the optical reach is about 1200 km [2] with the protection offered by a Hard Decision (HD) FEC derived from the 7% overhead Reed Solomon (RS) of ITU G709 standard. However, for long haul networking at continent scale network, this reach is not always sufficient for ensuring, without intermediate electronic regeneration, connection between two cities. Low Density Parity Check (LDPC) code [3] is a SD FEC candidate to improve robustness to impairments in optical transmission thanks to its coding performances that approach the Shannon limit.