SUMMARY
With the explosive growth of high-rate multimedia services and promptly boomed energy consumption in wireless networks, energy-efficient design is become more and more important. In this paper, we investigate energy-efficient design for relay-aided multiple-input multiple-output-orthogonal frequency division multiplexing (MIMO-OFDM) cognitive radio networks. We formulate an energy-efficient power allocation problem, which takes a form of nonlinear fractional programming. To solve the problem, we first make a joint concave approximation to the original problem which facilitates the optimal algorithm development. Then, we derive an equivalent parametric optimization problem of the approximated problem. Finally, an iteration energy-efficient power allocation algorithm is presented. Numerical results reveal that the proposed algorithm can improve energy efficiency over traditional capacity maximization method.