The voice channel in mobile communication systems have high priority and are

almost always available. By using the voice channel also for data transmissions it

is possible to get the same availability as for voice calls. But due to speech codecs

in the voice channel, regular modems can not be used and special techniques are

needed to transmit data.

This thesis presents methods to transmit data over the voice channel in a GSM,

UMTS or TETRA network. The focus has been on robust data transmission rather

than high data bit rates. Approaches are introduced which improve the reliability

for transmissions even for systems with low rate speech codecs and channels with

some distortion.

The results of the thesis are suggestions of symbol patterns and ways to create

and adapt symbols for specific application and channel conditions to achieve the

desired goal for the application