To Push or Not to Push : Energy Efficient Communications with Delay Constraints

Proactively pushing content to users is a promising way of coping with the explosively growing traffic demand of next-generation mobile networks. However, it is unclear whether content pushing can improve the energy efficiency of delay-constrained communication systems over additive white Gaussian noise (AWGN) and fading channels. With pushing, the energy consumption can be reduced due to the extended transmission time duration. But if the user never needs the pushed content, pushing may lead to energy waste. Based on the random content request delay, this paper derives the user request probability thresholds that determine whether a content file should be pushed under three different Quality-of-Service (QoS) requirements, namely hard delay, average delay, and delay-outage constraints. Moreover, optimal strategies to allocate transmission power in content pushing and on-demand delivery stages are also proposed. It is shown that the energy efficiency of systems with pushing can be significantly improved as the content request probability increases. Numerical results validate the effectiveness of the proposed power allocation strategies for different delay constraints, compared with the corresponding ondemand schemes.