# Device-To-Device Communication in 5G Environment: Issues, Solutions, and Challenges
## 1 Introduction
Standalone D2D is one the drawbacks of D2D because it only uses links that are managed by devices where there is no possibility of channel management and centralized relay, whereas for network-assisted D2D, the BS, together with the help of operator-controlled links, can only partially maintain channel selections and relay. Thus, in-depth research attention is needed to manage the interference in D2D communication ([PERSON] and [PERSON], 2018). There are many challenges that should be tackled in order to successfully execute D2D communication technology. Specifically, D2D communications require complex resource management techniques, efficient device discovery mechanisms, intelligent mode selection algorithms, robust security protocols, and mobility management procedures. There have been many research studies in D2D communications that aimed to improve spectral efficiency and interference management. Nevertheless, extensive reviews of comprehensive studies that examine various aspects of D2D communications, including the requirements and challenges, are largely missing. The authors in ([PERSON] and [PERSON], 2018) provided a thorough survey on under-explored and over-explored domains in D2D communications. In ([PERSON] and [PERSON], 2018), the authors discussed a literature review and recent advances in D2D communications from the interference management perspectives. The authors in ([PERSON] and [PERSON], 2018) present a survey that emphasizes different technologies and studied cases that support D2D communications. The authors also discussed the power control, interference management and resource allocation issues in D2D communications. A good overview of the foundational principles in the D2D communication model and its related issues in view of recent advances will need a comprehensive analysis of the existing literature. The motivation of this paper is to equip readers with a primer addressing to some of the problems, solutions, recent advances and challenges in D2D communications. Contrary to the existing surveys, as shown in Table 1, we classified the previous surveys and challenges in D2D communications into the specific domains of device discovery, interference management, privacy and security, power control, and mode selection. These domains are considered crucial for improving network optimization ([PERSON] and [PERSON], 2018). Regarding these features, we draw conclusions from recent works focusing on their problem areas, proposed methods, and the techniques considered. Contradictory to previous surveys that have collectively discussed device discovery, interference management, privacy and security, power control, and mode selection, this paper focuses on presenting the recent problems, solution techniques and limitations of the proposed solutions, and also analyzes new challenges in D2D communications. Moreover, the majority of the research cited in this paper is up to date, and has not been discussedahead of this survey. We have eliminated some previous outdated papers that have been cited in other existing surveys, and present the latest directions related to the domain in the 5G environment in which D2D communication will play a pivotal role. The main objective of this paper is to equip readers with the latest and state-of-the-art papers of proposed solutions (proposed schemes, outcomes, and limitations) on D2D communications and the challenges that still need to be addressed. To be more specific, the contributions of this paper are as follows:  
1. Presenting an extensive literature review of the recent advances in specific D2D domains, which are security and privacy, discovery process, interference management, power control techniques and mode selection schemes for D2D applications in 5G technologies;
2. Highlighting open research issues or challenges that need further potential research studies in the future. The remaining sections of the paper are organized as follows. Section 2 provides an analysis and review on D2D device discovery techniques.