A wireless spectrum is shared between a primary communication system and secondary communication system operating in an overlapping geographical region. A primary transmitter broadcasts a primary signal, and a secondary transmitter transmits a secondary signal, both using a primary wireless spectrum assigned to the primary communication system. The secondary transmitter transmits the secondary signal to a secondary receiver with power (1−α)P and transmits the primary signal with power αP. The parameter α is computed to ensure a predetermined quality of reception of the primary signal by a hypothetical primary receiver located near the secondary transmitter. The secondary transmitter may compute a feasibility of using cognitive transmission and, when the computed feasibility exceeds or does not exceed a feasibility threshold, it selects to enable or disable, respectively, the use of the primary wireless spectrum to transmit from the secondary transmitter.