1. An apparatus, comprising: an adaptive linear equalizer to equalize frequency domain samples of a single-carrier signal received over a channel, including to compute a first gradient based on the frequency domain samples of the received signal and prior decisions, compute a first variable step size based on the first gradient, and adapt filter coefficients of the adaptive linear equalizer based on the first variable step size; an adaptive decision-directed channel estimator to estimate a characteristic of the channel in the frequency domain, including to compute a second gradient based on the frequency domain samples of the received signal and the prior decisions, compute a second variable step size based on the second gradient, and adapt a prior estimate of the characteristic of the channel based on the second gradient; a turbo equalizer to generate estimated decisions based on prior estimated decisions, the output of the adaptive linear equalizer, and an output of the adaptive decision-directed channel estimator; and a hard decision system to generate hard decisions based on the estimated decisions.