# Device-To-Device Communication in 5G Environment: Issues, Solutions, and Challenges
## 5 Power Control  
Power control can be defined as the process of adjusting the BS's power levels during DownLink (DL) transmissions and the user equipment (UE) during UpLink (UL) transmissions. The need to increase the transmission power of a device exists because it can also increase the link capacity. However, this will lead to incremental interference among the devices that share the same resources. One of the benefits of power control techniques is its help protecting energy resources. These techniques allocate radio resources that have been used in resource allocation to different users or devices. Examples of the radio resources are time slots in Time Division Multiple Access (TDMA) or frequency bands in Frequency Division Multiple Access (FDMA). The role of resource allocation is important in fulfilling the immediate increase in resource demand. To improve the overall system throughput and system capacity, resource utilization and joint optimization are considered crucial. This section presents resource management techniques and various power control schemes that highlight the importance of combining power control and mode selection together with link adaption techniques to achieve an optimal system performance. Power control algorithms can be split into two broad categories, which are centralized and distributed. For centralized algorithms, the BS is responsible for making the decisions for resource allocation and power control, while for distributed algorithms, user equipment is responsible. One of the examples for the centralized algorithm is LTE power control. Important parameters that need to be considered to produce a structured power control algorithm are maximum transmit power, target-received power per resource block, number of resource blocks, and path loss. Table 5 offers a summary of the power control issues and proposed solutions in D2D communications. Recent Advances in Power Control Schemes  
The benefits of the D2D technique are obscured with the interference problem over D2D links and cellular links. That is why there are plenty of proposed methods and schemes to minimize the interference, such as using resource allocation, power control, signal processing, mode selection, etc. [PERSON] et al. in [PERSON] et al. (2018) used the interior point scheme to assess the optimal power of D2D communications. By approximating the interior point method, the authors are aiming to reduce the computation complexity. To achieve the goals, the inversion of the Hessain matrix will be replaced with a diagonal metric. This simplified process causes the updating of the Newton method. The results show that by using lower computational complexity, near-optimal throughput can be achieved. The authors in [PERSON] et al. (2018) highlight the problem of nonconvexity of sum-rates maximization to power constraints. The authors then emphasize this problem using the problem of power allocation model as a potential game. The authors proposed two iterative algorithms using the potential games convergence properties. The proposed solutions are better than the traditional rate maximization scheme because the solutions are confluent with the objective function local maxima. [PERSON] et al., in [PERSON] et al. (2018), proposed a channel