Analysis of direct and indirect adaptive linear equalization for slowly varying channels

The coefficients of an equalizer can be adjusted to track the underlying channel variations either directly, or indirectly where the channel is first estimated, and the equalizer is then computed based on the channel estimate. In this paper, the performance of direct and indirect linear adaptive equalizers for slowly-varying channels with autoregressive (AR) coefficients is investigated. Explicit expressions are derived which characterize the performance of the equalizers. The results indicate that the indirect equalizer outperforms the direct equalizer. Simulations are conducted to verify the analytic results.