# Analysis of Power Allocation for NOMA-Based D2D Communications Using GADIA
## 1 Introduction
Enormous diversity is essential to high-reliable communication [7], and it can be accomplished only by utilizing multiple frequency or spatial resources. The transmission rate of a URLLC is relatively insufficient, and the main requirement is a high-reliability level (with a PER generally lower than \(10^{-5}\)). That is undoubtedly a fundamental purpose that is considered by both academia and industry. Notably, wireless local area networks have enhanced increasingly popular over recent years, demanding massive connections between numerous devices and a base station and between devices termed as device-to-device communication (D2D) [8]. Due to the spectrum scarcity for cellular users, it requires more local facilities. Integrating D2D links within the existing cellular infrastructure can improve the spectrum energy efficiency, increase the network coverage, and enhance communication reliability [9]. Several techniques have been merged into a D2D scheme to provide more reliable communication in ultimate wireless networks, e.g., massive multiple-input multiple-output (MIMO) [10; 11], nonorthogonal multiple access (NOMA) [12], and mmWave communications [13]. In particular, NOMA has recently gained significant attention as a promising multiple access applicent for superposition coding, and successive interference cancellation [14]. It is determined as NOMA in the power domain, and the network can assist multiple users simultaneously and frequency resources as current systems. Furthermore, this technology can manage challenges related to bandwidth limitations by exploiting the frequency resource concurrently while expecting no additional physical facilities. This paper studies the concern of boosting the coexistence of the three heterogeneous services across similar Radio Access Network (RAN) architecture whose specific characteristics and requirements will be elaborated later. The eMBB traffic can be analyzed to be a direct extension of the 4G broadband service. Massive payloads illustrate it, and the device operations stay stable over a prolonged period. That permitsthe network to manage wireless resources to the eMBB devices ensure that no more than two devices using the same resource concurrently. In this paper, we focus on URLLC in 5G wireless networks. Taking the above challenges into account, the key contributions of this work are summarized as follows:  
1. The 5G main techniques (i.e., eMBB, mMTC, URLLC) are introduced, which act as different services in various 5G applications. 2. The requirements of the future application and the fundamental open problems toward the design of NOMA-based RAN are briefly explained. 3. An overview of the new generation of radio access technology is conducted, i.e., NOMA. Further, the basic principles of NOMA, including superposition coding (SC) and successive interference cancellation (SIC) for downlink channels, are presented. 4. Considering NOMA, we propose a novel algorithm where the downlink results are combined with D2D mode and utilize Greedy Asynchronous Distributed Interference Avoidance Algorithm (GADIA) to establish two different application scenarios. Mainly, we analyze the max-min fairness optimization problem for a given fairness index in the network. The proposed optimization framework has been proven theoretically and confirmed numerically by comparing with Monte Carlo simulations for the same system model as the one introduced in [15]. To the best of our knowledge, NOMA-based D2D is a device group on the max-min fairness optimization problem that was not yet studied in the context of the heterogeneous network where both the cellular and D2D devices are active. The remainder of this paper is organized as follows. In Section 2, we overview the related work. In Section 3, we consider the 5G network and explain the challenges and research directions. The main principles of NOMA and performance analysis are provided in Section 4. Sections 5 and 6 formulates and solves the max-min optimization problem subject to the power constraints.