An Efficient Approach to Minimum Phase Prefiltering of Short Length Filters

Motivations for performing prefiltering based on root finding are presented, for an interference canceling receiver employing a reduced-state equalizer such as DFSE or RSSE. Since the interference canceling filter (ICF) has a MMSE-DFE structure, that shortens the channel impulse response (CIR), a low complexity minimum phase prefilter can be applied before equalization. Root-finding based prefiltering for second order filters are of particular interest, since closed form solutions can be obtained with less computations. For such second order filters, CIR can be classified as minimum, mixed or maximum phase, based on few inequalities which directly use the complex-valued channel coefficients. Proposed inequalities help in retaining maximum accuracy with low complexity, by avoiding some approximation algorithms involved in root identification on DSP. While samples corresponding to minimum and maximum phase channels are processed directly, root-finding is employed only to transform the mixed phase channels to their minimum phase equivalents.