Power allocation grouping scheme considering constraints in two separate stages for OFDM-based cognitive radio system

A power allocation grouping scheme for orthogonal frequency division multiplexing (OFDM)-based Cognitive Radio systems is proposed that can improve capacity while the interference power for primary user receivers stays at constant level. In this scheme, all idle subcarriers are divided into four groups based on the inserted interference power level into the primary user frequency band. Then, the power is allocated to subcarriers in two stages. At the first stage, considering interference constraint, the power is assigned to subcarriers into groups 1, 2 and 3. At the second stage, the remaining power is allocated to other idle subcarriers with water filling algorithm. The numerical results show that the capacity is improved by 20 bps up to 45 bps with the increase in maximum power budget over cognitive radio system. Indeed, the interference power level is unchanged with increasing the transmit power for proposed cognitive radio system.