Energy-efficient cooperative download for smartphone users through contact time estimation

In this paper, aiming to reduce cellular network load, we propose a cooperative download method by which user terminals exchange fragments of a content called chunks through short-range wireless communication like Bluetooth or Wi-Fi with other user terminals who want the same content. In order to reduce the cellular network load, it is necessary to receive as many chunks as possible via short-range wireless communication. Our basic idea is to predict contact time when other user terminals get within a range of short-range wireless communication and to obtain chunks efficiently from other user terminals. To predict the contact time, each terminal periodically registers information of its location and retaining and requiring chunks with a server in the fixed network. The server calculates for each terminal the probability and time to contact other terminals so that the terminal can determine its communication schedule with those meeting terminals to obtain chunks efficiently. Through computer simulations with measured energy consumption parameters, we confirmed that terminals using our method obtained from other terminals 50% more chunks with 20 % less energy consumption than the method of greedily collecting chunks by always turning on the wireless device.