The invention relates to a transmitting device including a quadrature modulator for carrying out the quadrature modulation of a complex input signal and including a power amplifier connected in outgoing circuit to the quadrature modulator. Therefore, the filter tap coefficients are directly updated without tracking channels in the time-varying channel environment, and accordingly, detection performance very similar to those of the channel tracking and conventional V-BLAST scheme is provided with reduced complexity. The start-up circuit is configured to be turned on during a start-up stage of the bandgap reference circuit, and to be turned off after the start-up stage. A certificate grace period is then determined at the relying party from a function of the maximum permissible grace period, the uncertainty interval and at least one attribute defined in the PKI certificate.