Energy Saving Transmission Time and Power Management for D2D Connection with A Relay Node Using the Same Band with A Cellular Connection

The incorporation of Device-to-Device (D2D) communication, utilizing the same spectral resources as cellular networks, is regarded as a pivotal development for the next generation of wireless communication infrastructures. This is especially relevant when relay nodes are introduced to broaden the transmission distance of D2D links. However, the performance bottleneck persists due to the bidirectional interference stemming from both D2D and conventional cellular links, compelling an escalation in transmission power for these connections. Given the paramount importance of energy conservation for both mobile network operators and users, this study tackles the issue of optimizing transmission time selection and power management (TTSPM) in a scenario where a D2D connection with the rely node and a cellular connection coexist on the same sub-channel, aiming to minimize the overall energy expenditure during transmission. First, we formulate the optimization problem as a NP-hard mixed integer nonlinear programming (MINLP) problem. To solve it, we follow the idea of dividing and conquering and separately investigate four possible resource sharing forms of the two considered links. For the first three resource sharing forms, we prove the TTSPM problem can be transformed into convex optimization problems and then present algorithms to obtain the regional optimal solution corresponding to each form. For the forth resource sharing form, we develop a simulative game-theory based approach to tackle the TTSPM problem since it is still a non-convex optimization problem. As virtual non-cooperative players, cellular connections and D2D connection with the rely nodes are viewed as non-cooperative, we establish the presence of Nash equilibrium within the formulated game and develop algorithms to determine the optimal response of each participant, considering the strategy adopted by their counterpart. Numerical analyses reveal that the TTSPM method, by selecting the optimal regional solution from four potential forms of resource allocation, significantly reduces the overall energy required for transmission across the two analyzed links, outperforming the results documented in prior studies.