In a system for transmitting digital signals in a radio subscriber terminal network, for the digital signal transmission from the base station of a radio cell to the radio subscribers located in the radio cell, the total transmitting power of the base station is divided into a plurality of frequency sub-bands andor periods with different transmitting powers. Each of a plurality of group communication devices coverts media, such as video, audio, image andor data into data packets suitable for transmission over a data network, such as the Internet. A first connector is disposed generally in a direction perpendicular to the electrode extensions of both subsets and in electrical contact with the electrode extensions of the second subset. Signal to noise ratios are obtained for each run of an orthogonal array in order to identify important subsets. A respective set of parameters that define a respective failure characteristic of the semiconductor device is determined for each of the stress bias zones such that the failure characteristic is accurately determined for a wide range of operating voltages.