SUMMARY
Device-to-device (D2D) communication is an essential part of the future fifth generation (5G) system that can be seen as a “network of networks,” consisting of multiple seamlessly-integrated radio access technologies (RATs). Public safety communications, autonomous driving, socially-aware networking, and infotainment services are example use cases of D2D technology. High data rate communications and use of several active air interfaces in the described network create energy consumption challenges for both base stations and the end user devices. In this paper, we review the status of 3rd Generation Partnership Project (3GPP) standardization, which is the most important standardization body for 5G systems. We define a set of application scenarios for D2D communications in 5G networks. We use the recent models of 3GPP long term evolution (LTE) and WiFi interfaces in analyzing the power consumption from both the infrastructure and user device perspectives. The results indicate that with the latest radio interfaces, the best option for energy saving is the minimization of active interfaces and sending the data with the best possible data rate. Multiple recommendations on how to exploit the results in future networks are given.