# Energy Efficient Underlaid D2D Communication for 5G Applications
## 1 Introduction  
In conventional cellular communication, the cellular user uses communication to uplink and downlink via the base station. Whereas in underlay D2D communication, the cellular users and D2D users share frequency sub-channels; this increases frequency reuse. However, it also causes interference to one another. The cellular users cause interference to D2D users and the D2D users cause interference to cellular users. This decreases the signal-to-interference noise ratio. which consequently decreases the transmission rate of the users. Device-to-device communication draws extensive attention in industry, academia, and standardization bodies with the sudden increase in the demand for higher data rates. Device-to-device communication without the base station (BS) facilitates direct wireless communication between two transceivers. It is used to increase energy efficiency (EE) and to consume less power while transmitting information without loss and it is a key technique for 5G networks. It connects the devices directly and it also improves the quality of the network, as well as itsthroughput, and reduces the latency. It can achieve improved spectral efficiency and energy efficiency. It also uses the same frequencies as cellular networks which pull down the network quality as extra interference will occur [1; 2; 3; 4; 5; 6; 7]. To have better performance, D2D underlaying cellular networks are considered and focused on energy efficiency maximization. The existing technologies work only on a single-cell scenario. More attention was paid to a single-cell scenario, rather than the multiple bands because in multiple bands it takes a lot of power; so research is focused on how to increase energy efficiency with less power consumption. An uplink or a downlinkis taken into consideration to transmit and receive the information [8]. Whenever there is a need for maximum energy efficiency, the usage of energy efficiency optimization is required. The solution to the energy efficiency optimization problem for getting maximum EE (energy efficiency) is given in [9; 10]. The branch and bound (BB) algorithm is a conventional algorithm used for energy optimization in wireless networks [11]. After achieving maximum energy efficiency, interference will occur due to which the information may be lost and not be in a position to send the packets through the transmitter. So, to overcome this, transmission probability and average sum rates are used to find the average sum of values to obtain the maximum value [12; 13; 14]. By considering data rate, energy usage, and battery lifespan, the RICA (A Radial Basis Function (RBF) Iterative Construction Algorithm) algorithm with fixed power provides superior performance [15]. A dynamic reward approach with deep reinforcement learning, a novel iterative power allocation algorithm, and robust power allocation (PA) solution achieve a much higher EE [16; 17; 18; 19; 20]. Due to higher spectral efficiency, underlaid is considered superior to overlaid. The different topologies of underlaid communication by using the same frequency channels as cellular and D2D users is explained in [21; 22; 23]. The improved data rate, efficient bandwidth use, power control, and energy-efficient methods are used [24; 25; 26; 27; 28; 29; 30]. The main purpose of implementing D2D in cellular networks is to reduce the data traffic in the network. Underlaid D2D communication is considered to achieve spectral efficiency by reusing the cellular resources as well as to achieve better link quality [31]. D2D underlaid communication improves spectral efficiency and provides more incentives for local coverage compared to pure cellular networks. Here, centralized management schemes are proposed [32]. The dynamic power control mechanism is studied to control D2D cellular interference by controlling D2D power [33]. Power control methods are discussed in this paper [34]. D2D enables the communication between two approximation distant devices without the help of a base station. It reduces the delay and increases spectral efficiency.