# Analysis of Power Allocation for NOMA-Based D2D Communications Using GADIA
## 1 Introduction  
Recently, a rising consensus in the fifth generation (5G) of wireless network technology has been developed to sustain the massive number of users. It will support a broad range of vertical industries demands by linking everyone and everything, particularly smart devices, machines, and sensors. The 5G network will drive innovation and has the prospect to change the way we live, work and play. According to the International Telecommunication Union (ITU), 5G wireless systems are classified to support three generic services as enhanced Mobile Broadband (eMBB), massive Machine-Type Communications (mMTC), and Ultra-Reliable and Low-Latency Communications (URLLC) [1, 2]. These use cases empower various services provided by the 5G network: (a) the eMBB provides a stable connections service of mobile broadband with significantly high peak data rates that assist in providing consistent user experience; (b) the mMTC furnishes a massive number of Internet of Things (IoT) devices, which are transmitting small data payloads periodically; (c) the URLLC services will open up additional diverse capabilities of the network by expanding its limits for high reliability and low-latency from a restricted set of terminals. The miscellaneous deployment of the 5G network is due to the increase in various new characteristics, i.e., scalable numerology, along with compatibility, elasticspectrum, and ultra-lean design. The current technologies of 5G structures form the basis for numerous new technologies beyond 5G/6G network, as Figure 1 illustrates. There are two approaches to sustain the coexistence of various services, i.e., orthogonal slicing and non-orthogonal slicing. In the orthogonal slicing approach, different resources are assigned to each user to satisfy their requirements. The allocated resources are orthogonal in frequency-time, i.e., no interference [3]. The significant drawback here is an inefficient use of the available resources. In the non-orthogonal slicing approach, the same resources are divided for all services simultaneously. Reusing similar resources enables improvement in spectral efficiency regardless of possible interference between these services [4; 5]. The main purpose of eMBB service is to increase the data rate while maintaining reasonable reliability. Furthermore, an mMTC device is active periodically and utilizes a fixed low transmission rate in the uplink. Furthermore, mMTC has been developed as part of 3 GPP Release 13/14 low power wide area (LPWA) technologies which includes Narrowband Internet of Things (NB-IoT). The enormous number of conceivable active mMTC devices results in difficulties to assign primary resources to particular mMTC devices. Instead, it is essential to provide resources that can be communicated via random access. For example, grant-free random access with an excessive number of non-orthogonal pilot sequences is introduced as a promising technique for supporting mMTC where all active devices (with unique identity) synchronously transmit their pilot sequences and the goal of an access point is to detect the activities of devices [6]. The size of mMTC devices' active division is a random variable whose average value estimates the mMTC traffic arrival rate. The primary purpose of designing the mMTC is to magnify the arrival rate that can be sustained in a shared radio resource. The targeted packet error probability (PER) of an individual mMTC transmission is typically low, e.g., in the order of \(10^{-1}\). Although the URLLC transmissions are periodic, the set of potential URLLC transmitters is much smaller than those of mMTC. For sustaining the URLLC communications, it requires a combination of scheduling algorithms to utilize the available resources for reliable data transmission efficiency. Moreover, to prevent too many resources from being idle due to the periodic traffic, identifying the transmission of URLLC on time because the low latency will require comprehensive coverage, which is highly unlikely in early 5G deployments.