Real-Time speech with AX.25 -an evaluation of the possibilities and restrictions

摘要

A study about the possibilities of real-time speech transmission using amateur packet radio is presented. In this study it is shown, that a common 9600 Bit/s- channel has the theoretical possibility of transmitting speech data with only short delays. The restrictions of the AX.25 protocol for real-time transmission are discussed, showing that an appropriate setting of the transmission parameters still allows real-time transmission. A hybrid emulation system tising traces from a real wireless channel as well as coded speech gives an estimation of the expected speech quality and an implementation of a real-time transmission tool allows first experiments. Preliminary results of these experiments show the possibility to use AX.25 for real-time speech transmission even if the resulting speech quality is not yet satisfying. However the tolerance of listeners towards distortions has been much higher than expected and there are possibilities to improve the system with respect to the user perceived speech quality.