Passband echo cancellation techniques for high-speed modem applications

The author describes passband algorithms for the cancellation of data echoes in high-speed modems. The conventional, all-real single-filter canceler is discussed, along with the hybrid passband/baseband Weinstein canceler. In addition, a new passband echo canceler which exceeds the performance of some other fully-passband echo cancelers while limiting resource requirements is introduced. This canceler employs the concept of adding out-of-band noise to the adaptive filter input signal; this increases the number of degrees of freedom available to the echo canceler during convergence, thus increasing the level of echo cancellation achieved. The performance of each type of passband echo canceler is examined, and their relative performance is demonstrated. Some potential advantages and unique applications of the new noise-enhanced echo cancellation technique are identified