This paper addresses the problem of energy-efficient resource allocation inthe downlink of a cellular OFDMA system. Three definitions of the energyefficiency are considered for system design, accounting for both the radiatedand the circuit power. User scheduling and power allocation are optimizedacross a cluster of coordinated base stations with a constraint on the maximumtransmit power (either per subcarrier or per base station). The asymptoticnoise-limited regime is discussed as a special case. %The performance of bothan isolated and a non-isolated cluster of coordinated base stations is examinedin the numerical experiments. Results show that the maximization of the energyefficiency is approximately equivalent to the maximization of the spectralefficiency for small values of the maximum transmit power, while there is awide range of values of the maximum transmit power for which a moderatereduction of the data rate provides a large saving in terms of dissipatedenergy. Also, the performance gap among the considered resource allocationstrategies reduces as the out-of-cluster interference increases.
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