Adaptive thresholds for AMR codec mode selection

The speech codecs from the adaptive multi-rate (AMR) codec family enable provisioning of excellent speech quality, at the same time providing a way forward towards state-of-the-art, spectrally efficient, high capacity cellular networks. One straightforward way to characterize the benefit of AMR speech codecs is that the robustness to interference and noise in radio networks is increased and that this advantage over other, nonadaptive, speech codecs can be capitalized on in several different ways, e.g., by enhancing speech quality or improving system capacity. In this paper, improved mode adaptation, where codec mode switching thresholds are adaptive to radio conditions, is discussed. Example simulations show that an adaptive thresholds algorithm applied to GSM can significantly improve objective speech quality. Corresponding improvements were also found in informal listening tests.