Frequency-domain turbo equalization, including multi-mode adaptive linear equalization, adaptive decision-directed channel estimation, adaptive noise variance estimation, and dynamic iteration control

A system, comprising:

• a receiver front end to provide frequency domain samples of a single-carrier signal received over a channel;
• a decision system, including,
• an adaptive linear equalizer to equalize the frequency domain samples, 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, an outputs of the adaptive linear equalizer, and an output of the adaptive decision-directed channel estimator,
• a hard decision system to generate hard decisions based on the estimated decisions;
• and
• a digital signal processor to process the hard decisions and output corresponding information to a user interface system.