Implementation of a hands-free car phone with echo cancellation and noise-dependent loss control

An implementation of a complete hands-free telephone system on a low-cost DSP with 16-bit fixed-point arithmetic is presented. The prototype, consisting of an adaptive echo canceller, was developed for an industrial customer. The main emphasis is laid on the control unit of the system being necessary for a reliable performance in all environments and the attenuation introduced by the loss control unit. Keeping the loss as small as possible, which is most important for a natural communication including full double-talk capabilities, requires exact knowledge of the current system performance and the background noise level. In case of background noise the applied total loss is adjusted to the power of the noise. The measures we used and their application to our system control are discussed.