Asymptotically optimal subcarrier matching and power allocation for cognitive relays with power and interference constraints

This paper considers the resources allocation problem in decode-and-forward (DF) relayed OFDM based cognitive radio (CR) system. The subcarrier matching and power allocation are optimized jointly under the individual power constraints in source and relay so that the sum rate is maximized while the interference induced to the primary system is kept below a pre-specified interference temperature limit. Therefore, the dual decomposition technique is adopted to obtain an asymptotically optimal solution. Moreover, a suboptimal scheme is presented to get rid of the high computational complexity of the optimal scheme. The suboptimal algorithm solves the problem in two phases. The subcarriers powers are adjusted in the first phase considering the interference that can be induced to the primary system in addition to the available power budgets. The subcarriers are matched in the second phase based on the fixed powers and the channel qualities. The performance of the different schemes is discussed throughout numerical simulation.