| Summary: | For the Energy harvesting (EH) transmitter equipped with a Reliable Energy Backup (REB), the following problem is challenging and important: how to minimize the amount of energy supplied by the REB, such that the harvested energy is efficiently utilized for transmitting a given amount of data within a fixed delay constraint. In this paper, we first develop a stochastic model for this problem. We then discuss the optimization issue of delay-constrained data transmission over a fading wireless channel. We transform the delay constraint into the penalty function, and then the energy constrained control problem is modeled as a Markov decision process (MDP) without constraint, by which we obtain the optimal energy supplementary policy and the minimum of the expected energy consumption from REB. In the special case that the energy of the transmitter is supplied by REB alone, we find that the optimal energy supplementary policy is non-decreasing in the elapsed transmission time and for the remaining task of data transmission. This substantially reduces the computational complexity required to implement the optimal energy supplementary policy for a general EH wireless device. Numerical studies validate the theoretical findings, and observations are outlined to demonstrate the characteristics of the optimal energy supplementary policy and the minimum expected energy expenditure from the REB.
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