Asynchronous adaptive equalization in voiceband data modems

A new method of implementing an asynchronous adaptive fractionally spaced equalizer is presented for use in voiceband data modems. The method uses finite impulse response (FIR) approximations to interpolation filters to modify equalizer coefficients and a digital phase-locked loop for timing recovery. The method allows for echo cancellation and equalization to be conducted synchronously, simplifying hardware and eliminating the need to recover and resample a continuous-time far-end signal. The penalty imposed is a slightly higher amount of computation for interpolation. It is shown that the interpolation can be done with fixed three-tap FIR filters