Energy-Efficient Use of Licensed and Unlicensed Bands in D2D-Assisted Cellular Network Systems

To date, the amount of research conducted regarding the subject of energy-efficient transmission in device-to-device (D2D)-assisted cellular network systems simultaneously utilizing both licensed and unlicensed bands is lacking. This topic is of substantial relevance to emerging 5th-generation (5G) cellular network systems, so the present study was conducted in order to address it in a practical manner. Specifically, this study proposes a simple yet effective algorithm aimed at ensuring efficient energy usage when such network systems make transmissions while utilizing both licensed and unlicensed bands. Based on novel system configurations with respect to bandwidth and link mode configurations, the proposed D2D-assisted transmission algorithm was designed with a system-level perspective in mind in order to yield greater efficiency in terms of transmission mode selection and link mode selection. As a result of these features, the proposed algorithm can not only maintain acceptable rates of transmission for all the connected users, but can also enhance system performance by a significant degree in terms of both energy efficiency and connection efficiency. Moreover, the results of simulations conducted to test the algorithm indicate that it is not only feasible, but, given its simple yet effective design, also easy to implement, such that it can serve as a valuable reference for the operators of 5G networks.