Optimized Flexible Power Selection for Opportunistic Underlay Cognitive Radio Networks

A flexible transmit power selection concept for underlay cognitive users is proposed in this paper. We have employed an opportunistic, sensing based spectrum sharing method. Besides the power constraint to avoid interference at PU, the transmit power constraints of secondary user is also considered. Received Signal Strength Indicator based carrier selection method has been adopted. To resolve hidden terminal problem, twin scan concept is used at both ends (secondary transmitter and receiver) with same carrier frequency. Secondary transmitter selects suitable carrier frequency to initiate communication with the minimum power level as defined by the proposed algorithm. If received signal strength at the corresponding secondary receiver is below the predefined required receiver threshold, then power level is stepped up automatically. To maximize secondary user channel capacity, we have considered flexible power selection strategy as per channel state information. If the cognitive receiver is unable to recover the received information, even with the peak transmit power, it will again perform the frequency scanning operation. This is repeated till the best result is achieved. A power control circuit is designed to check the power selection concept.