Method of operating a radio communication system during a stand-by time interval in a stand-by state. The method comprises: applying clock division processing to a reference clock signal and producing a divided clock signal; applying PLL processing to the divided clock signal producing a PLL clock signal; receiving at least one input signal; when the input signal has a first logic value, interrupting applying PLL processing to the divided clock signal and enabling counting clock signal edges of the divided clock signal; when said counting clock signal edges reaches a first target count value, restarting applying PLL processing; continuing counting clock signal edges until reaching a second target count value; when said counting reaches the second target count value, issuing and sampling an end-count signal based on the PLL clock signal, producing a timing clock signal as a result and providing the timing clock signal to a user circuit.