Pipelined parallel decision feedback decoders (PDFDs) for high speed Ethernet over copper

One of the powerful, yet simple, algorithms to decode trellis codes as well as to combat intersymbol interference (ISI) is the parallel decision feedback decoding algorithm. However, for high-speed applications, such as gigabit Ethernet over copper, the implementation and design of a parallel decision feedback decoder (PDFD) is challenging due to the long critical path in the decoder structure. Straightforward pipelined designs usually introduce significant hardware overhead. To solve these problems, first, based on an optimized scheduling of the computations in the parallel decision feedback decoding algorithm, a low complexity pipelined PDFD is proposed. Next, we present a retiming and reformulation technique for the decision feedback unit (DFU) in the PDFD which can remove the DFU from the critical path of the PDFD with negligible hardware overhead. Compared with similar designs in the literature, the proposed design can reduce hardware overhead by 60% while achieving similar speedup for gigabit Ethernet systems.