  This paper presents adaptive bidirectional minimum mean-square error
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 and conjugate
gradient 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
multiuser DS-CDMA systems show the advantages of the proposed algorithms.
