Pipelining Tomlinson-Harashima precoders

Like decision feedback equalizers (DFEs), Tomlinson-Harashima precoders (TH precoders) contain nonlinear feedback loops, which limit their use for high speed applications. Unlike in DFEs where the output levels of the nonlinear devices are finite, in TH precoders the output levels of the modulo devices are infinite, or finite but very large. Thus, it is difficult to apply look-ahead and pre-computation techniques to pipeline TH precoders, which were successfully applied to pipeline IIR filters and DFEs in the past. However, a TH precoder can be viewed as an IIR filter with an input equal to the sum of the original input to the TH precoder and a finite-level compensation signal. Based on this point of view, this paper presents a novel approach to pipeline the TH precoder.