While working on the d2d technology some challenging

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While working on the D2D technology, some challenging issues like interference management, radio resource allocation, procedures management, and communication session setup appear in the cellular network and are reported in the recent literature [6-9]. A. Asadi et. al. [3], have been proposed several taxonomies of possible D2D architectures. In particular, D2D communications separate into two main categories, in-band, and out-band. The first category uses radio spectrum that occurs on the cellular spectrum while the other use unlicensed spectrum. When the communication is in the unlicensed spectrum, the coordination between radio interfaces is either controlled autonomously by mobile terminations (MTs) or by BS (i.e., controlled). Interference mitigation between cellular and D2D communications is the main challenging issues on in-band D2D communications and several research proposals focus on the study of this problem [10-11]. Concerning out-band D2D communications, the research focuses on inter-technology architectural design and power consumption [12]. All these proposals point out the potentialities of the different approaches in terms of energy consumption and of bandwidth resources. Fig. 3. Generation of cellular communication Fig. 4. D2D Communication Category One of the most significant challenges in in-band D2D communication is how to allocate spectrum for such type of communication. The classification of D2D communication as resource allocation is depicted in Fig. 4. Up to now, there are three resource allocation modes for reusing licensed spectrum resources[13]: Underlay Mode: D2D pairs and cellular user equipment (UEs) share the same spectrum resources, which has the advantage of achieving the best spectrum efficiency. It is noticed that in underlay mode, one of the key issues is to effectively control the D2D-to-cellular and cellular-to-D2D interference. Overlay Mode: Dedicated frequency resources are allocated for D2D communications, and the remaining part is allocated for cellular communications. In such mode, there is no interference issue between D2D and cellular communications. One research focus is how to optimize the resource allocation ratio. Cellular Mode: Instead of communicating directly with each other, D2D UEs communicate with the eNB acting as an intermediate relay, which is the same as the traditional cellular system. III. APPLICATION SCENARIOS AND ADVANTAGES OF D2D COMMUNICATIONS In this section, first, different D2D communications application scenario is explored then discuss more the advantages of D2D communications while comparing with similar networks. A. Use cases and usage scenarios Various use cases and application scenarios of D2D communications have been proposed. As shown in Fig. 5 and according to the participation of cellular base stations or core networks, D2D communications scenarios categorize into three representative types.
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  • Fall '19
  • Radio resource management, Cellular network, Cell site

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