Energy- and Spectral-Efficiency Trade-Off in OFDMA Downlink Channels

In this paper, a trade-off metric of unified energy efficiency (EE) and spectral efficiency (SE) is investigated in orthogonal frequency division multiple access downlink networks. The weighted product of the EE and SE of users is adopted to balance EE and SE. A maximization problem of the minimum weighted utility is formulated, and the original problem is divided into two sub-problems; one is a subcarrier allocation (SA) problem, and the other is power allocation (PA). For the SA problem, a sub-optimal algorithm employing a search method is utilized. To solve the PA problem, quasi-concavity of the utility function with respect to total transmit power in the PA sub-problem is shown. Based on the quasi-concavity, an iterative search algorithm of the optimal PA is developed. Through simulations, the efficiency of the algorithm is examined.