As the energy consumption in information and communication (ICT) systems becomes a more and more important problem, the ICT systems have been being equipped with energy harvesting devices and redesigned from the perspective of energy efficiency. In this paper, a point-to-point communication system with energy harvesting transmitter will be considered in the Rayleigh block-fading channel. In contrast to previous works, the minimum target rate of the considered system must be guaranteed, and both the average energy efficiency (EE) and spectral efficiency (SE) within a finite number of timeslots will be maximized at the same time. Although the induced optimization problem is an integer programming containing future timeslots, a stochastic dynamic programming approach will still be proposed to derive the optimal transmission policy and the closed-form formulas for the average EE and SE. The obtained results are capable of characterizing the tradeoff among the EE, SE, and the delay. The simulation results will verify the theoretical derivations, and illustrate the optimality of the proposed policy.
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