  This paper presents adaptive bidirectional minimum mean-square error (MMSE)
parameter estimation algorithms for fast-fading channels. The time correlation
between successive channel gains is exploited to improve the estimation and
tracking capabilities of adaptive algorithms and provide robustness against
time-varying channels. Bidirectional normalized least mean-square (NLMS) and
conjugate gradient (CG) algorithms are devised along with adaptive mixing
parameters that adjust to the time-varying channel correlation properties. An
analysis of the proposed algorithms is provided along with a discussion of
their performance advantages. Simulations for an application to interference
suppression in DS-CDMA systems show the advantages of the proposed algorithms.
