To reduce the energy consumption of a smartphone, multiple data transfer requests from applications can be bundled together and granted at once in order to reduce the time the radio interface is on. The side effect of bundling is the increased delay experienced by mobile applications. While several bundling algorithms have been proposed in the literature, a general and systematic solution to balance the energy-delay tradeoff is missing. In this paper, we formulate bundling as a cost minimization problem, in which the tradeoff between energy and delay is captured by a cost function. We then propose an online algorithm for minimizing the bundling cost and show that the algorithm is 4-competitive with respect to the optimal offline algorithm that knows the entire sequence of data transfer requests a priori. We evaluate the performance of the proposed algorithm and the accuracy of our results in a range of realistic scenarios using both model-driven simulations and real experiments on a smartphone. Our results show that depending on the delay tolerance level of a user, energy savings ranging from zero (delay intolerant) to about 100% (delay tolerant) can be achieved using our algorithm.
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