Integrated noise reduction and echo cancellation for IS-136 systems

In this paper, we present a combined speech quality enhancement solution for IS-136 systems. Since echo and background noise are the two major factors that adversely affect the speech quality in most transmission systems, our solution consists of echo cancellation and noise reduction elements. These are used in conjunction with the IS-641 (enhanced fullrate standard for IS-136 systems) coder to form an integrated speech-processing unit. The echo canceller uses the normalized least mean square (NLMS) method. Because of the existence of high levels of background noise, variable step-size techniques are employed. The noise reduction consists of a single microphone method and it uses a spectral amplitude enhancement gain function with minimal spectral distortion. The noise reduction is utilized in the pre-compression configuration, and it comes after the echo canceller on the send path reducing the residual echo as well as noise