On the Start-Up Problem in Digital Echo Cancelers

Digital echo cancellation techniques make it possible to realize efficient full-duplex data transmission over a single loop. The purpose of this paper is to elucidate the solution to the start-up problem in these devices and to present a new, fast, and simple tap-adjustment procedure. The theory indicates that a modified stochastic gradient tap-adjustment algorithm, using pseudorandom input data sequences for the initial training period, converges in N steps, where N is the total number of canceler taps, and that this is the fastest possible convergence time.