Data transmission over mobile voice channel based on M-FSK modulation

Voice channel in mobile communication systems has high priority and is almost always available. Its use as a bearer for data transmission allows to take advantage of this availability. But medium rate speech coders and associated VAD (Voice Activity Detector) and DTX (Discontinuous Transmission) which are well suited to voice signals, can strongly degrade other types of signals such as data modulated signals. In this paper we propose and evaluate a system for data transmission over mobile voice channel based on M-FSK modulation with optimized parameters. The parameters of the M-FSK modulation are tuned using real mobile communications voice channel in order to minimize the degradation introduced by the speech coder and by the discontinuous transmission (DTX) Our experiments show that it is possible to find a set of parameters for the M-FSK modulation which allows to achieve a moderate bit error rate (ie <10⁻²) without error-correcting code.