Infinite length results and design implications for time-domain equalizers

We show that maximum shortening signal-to-noise ratio (SNR) time-domain equalizers (TEQs) are often nearly symmetric. Constraining the TEQ to be symmetric causes only a 3% loss in bit rate (averaged over eight standard ADSL channels). Symmetric TEQs have greatly reduced design and implementation complexity. We also show that for infinite length TEQs, minimum mean squared error (MMSE) target impulse responses have all zeros on the unit circle, which can lead to poor bit rate performance.