AMR voice transmission over mobile internet

A very flexible transmission system for voice over mobile internet is proposed. With mobile internet a combination of a lossy packet-switched network and a wireless link of a mobile network is assumed. The new system allows to adaptively change the speech codec rate, and, thus, the payload of a packet, the number of transmitted packets and the number of used carriers on the mobile link depending on the packet error rate of the packet-switched network, and the downlink quality of the wireless link in a very flexible way. The proposed system is based on the Adaptive Multi-Rate (AMR) speech codec and a systematic convolutional code. Packeting of the speech data is done in such a way, that a packet-loss can be assumed as puncturing of the convolutional code. Thus, the only information that must be transmitted to the decoder is a bad frame indication, defining whether a certain packet out of the set of transmitted packets has been received or not. In a coding experiment the performance of the proposed system is analyzed and compared to a reference system using the G.711 codec. The proposed system outperforms the reference system over a wide range of signal to noise ratios of the wireless link and the packet error rates of the packet-switched network.