Adaptive compensation techniques for communications systems with Tomlinson-Harashima precoding

To improve compensation to channel or interference changes, we propose adapting an auxiliary feedback filter (FBF) in the receiver of systems which use Tomlinson-Harashima (1971, 1972) precoding. We show how the auxiliary FBF can be adapted in conjunction with the receiver feedforward filter (FFF). Simulations demonstrate the performance advantage of our auxiliary FBF technique relative to FFF updating alone, and how the FFF combines interference suppression with despreading in wideband applications. Error propagation can be effectively avoided by using the auxiliary FBF values to decide when to update the precoder, while transient increases in mean-squared error are avoided by using the FBF values in the update equation.