In order to meet the increasing demand for wireless data traffic since the commercialization of 4G communication systems, the development focus is on the 5th Generation (5G) or pre-5G communication system. For this reason, the 5G or pre-5G communication system is called a beyond 4G network communication system or post Long Term Evolution (LTE) system.
Consideration is being given to implementing the 5G communication system in millimeter wave (mmWave) frequency bands (e.g., 60 GHz bands) to accomplish higher data rates. In order to increase the propagation distance by mitigating propagation loss in the 5G communication system, discussions are underway about various techniques such as beamforming, massive MIMO, Full Dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large scale antenna.
Also, in order to enhance network performance of the 5G communication system, developments are underway of various techniques such as evolved small cell, advanced small cell, cloud Radio Access Network (RAN), ultra-dense network, Device to Device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), and interference cancellation.
Furthermore, the ongoing research is incorporating Advanced Coding Modulation (ACM) schemes such as a Hybrid FSK and QAM modulation and a Sliding Window Superposition Coding (SWSC) and advanced access technologies such as Filter Bank Multi Carrier (FBMC), Non-Orthogonal Multiple Access (NOMA), and Sparse Code Multiple Access (SCMA).
Recently, a direct inter-device communication technology has come into the spotlight. This technology, which is referred to as Device to Device (D2D) communication, is promising in licensed band communication systems such as a cellular communication system and unlicensed band communication systems such as a WLAN system. D2D communication is attractive in the mobile communication systems in terms of increasing traffic accommodation capability and reducing overload at a base station. That is, D2D communication is made in such a way that terminals (User Equipment (UE)) located in the same cell or neighboring cells are communicating through a D2D link established therebetween without the involvement of a base station (e.g., evolved Node B (eNB)), resulting in a reduction of the number of communication links from 2 to 1. Meanwhile, LTE systems use a Carrier Aggregation (CA) scheme to combine separate frequency resources for high speed communication, and the CA scheme may make it possible to use the legacy cellular communication and D2D communication simultaneously.