Multi-user cognitive OFDM with adaptive sub-carrier and power allocation

Multi-user cognitive orthogonal frequency division multiplexing (MU-COFDM) is a promising technique for achieving high transmission capacity in future cellular and wireless local area network (WLAN) systems. Multi-user resource allocation with the target of maximizing the transmit capacity of cognitive users and satisfying the proportional rate constraint between cognitive users is proposed under the condition of primary user´s interference constraint. Since the optimal solution to the problem is extremely computationally complex to obtain, a low-complexity suboptimal algorithm that separates sub-carrier allocation and power allocation is proposed. In the proposed algorithm, sub-carrier allocation is first performed by assuming an equal power distribution, and then each sub-carrier is assigned to the user with the best subcarrier efficiency function. After sub-carrier allocation, we use best to be better algorithm and linear water-filling to inject power. The proposed algorithm is shown to be superior to the traditional power allocation algorithm, while reducing the complexity from exponential to linear in the number of subcarriers.