Summary: TimeVarying versus TimeInvariant FiniteLength MMSEDFE on Stationary
Naofal AlDhahir \Lambda
, Member IEEE
A time--varying and a time--invariant structure for the finite--length MMSE--DFE are presented and their
performances are compared on a stationary channel impaired by ISI and additive Gaussian noise. The time--
varying structure has an innovations error sequence but incurs a throughput loss on ISI channels because
of its block--processing nature. Conditions under which the time--invariant structure exhibits near--optimal
performance are described. Both structures converge to the canonical MMSE--DFE of  as their filters'
lengths become infinite.
The infinite--length minimum--mean--square--error decision feedback equalizer (MMSE--DFE) was shown to
be a canonical (information lossless) receiver structure in . In practice, the MMSE--DFE is implemented
using finite--impulse--response (FIR) filters whose lengths are set by implementational complexity constraints.
These constraints cause the conventional 1 MMSE--DFE structure to lose its canonical property since the
error sequence is no longer stationary and hence can not be whitened by the joint action of the finite--length
time--invariant feedforward and feedback filters, as in the infinite--length case. This non--stationarity was
extensively studied and shown to have a well--defined structure in . To restore the canonical property of the
MMSE--DFE under the finite--length constraint, time variance was introduced in the feedforward and feedback