  In this letter, we propose a novel adaptive reduced-rank strategy based on
joint iterative optimization (JIO) of filters according to the minimization of
the bit error rate (BER) cost function. The proposed optimization technique
adjusts the weights of a subspace projection matrix and a reduced-rank filter
jointly. We develop stochastic gradient (SG) algorithms for their adaptive
implementation and introduce a novel automatic rank selection method based on
the BER criterion. Simulation results for direct-sequence
code-division-multiple-access (DS-CDMA) systems show that the proposed adaptive
algorithms significantly outperform the existing schemes.
