Non-orthogonal Multiple Access Cellular Networks Research Articles

Energy-Efficient Power Allocation for Full-Duplex Device-to-Device Underlaying Cellular Networks with NOMA

Full-duplex (FD), Device-to-Device (D2D) and non-orthogonal multiple access (NOMA) are promising wireless communication techniques to improve the utilization of spectrum resources. Meanwhile, introducing FD, D2D and NOMA in cellular networks is very challenging due to the complex interference problem. To deal with the complex interference of FD D2D underlaying NOMA cellular networks, power allocation (PA) is extensively studied as an efficient interference management technique. However, most of the previous research works on PA to optimize energy efficiency only consider the system framework of partially joint combining techniques of FD, D2D and NOMA, and the constraints of optimization problem are very different. In this paper, in order to further improve the energy efficiency of a system, a dual-layer iteration power allocation algorithm is proposed to eliminate the complex interference. The outer-layer iteration is to solve the non-linear fractional objective function based on Dinkelbach, and the inner-layer iteration is to solve the non-convex optimization problem based on D.C. programming. Then, the non-convex and non-linear fractional objective function is transformed into a convex function to solve the optimal power allocation. In this approach, FD D2D users reuse the spectrum with downlink NOMA cellular users. Imperfect self-interference (SI) cancellation at the FD D2D users and the successive interference cancellation (SIC) at the strong NOMA user are considered in the system framework. The optimization problem is constructed to maximize the system’s energy efficiency with the constraints of successful SIC, QoS requirements, the maximum transmit power of BS and FD D2D users. Numerical results demonstrate that the proposed algorithm outperforms the traditional orthogonal multiple access (OMA) in terms of energy efficiency with a higher system sum rate.

Energy Minimization for NOMA Cellular Networks With Two-Dimensional Resource Allocation

In this paper, we investigate the energy minimization for the cellular networks with non-orthogonal multiple access (NOMA). Different from most of existing studies in NOMA networks that considered the resource allocation in only frequency domain or time domain, we discuss the two-dimensional time-frequency communication resource allocation. We formulate the considered problem as a mixed integer non-linear programming (MINLP), and decompose it into three nested subproblems: transmit power optimization, communication resource allocation, and NOMA group partition. Then, we solve them iteratively. For the transmit power optimization subproblem, we first propose a transmit power iteration (TPI) algorithm, after the simplification of the rate requirement constraint, to obtain the transmit powers of cellular users (CUs) in the special case such that a group of CUs only occupies the communication resource in one sub-channel, and prove its optimality and convergence theoretically. Then, a rate requirement allocation based TPI (RRA-TPI) algorithm is further proposed to obtain the transmit powers of CUs in the general cases. For the communication resource allocation and NOMA group partition subproblems, a two-dimensional resource allocation (TDRA) algorithm and a coalition game (CG) algorithm are proposed to solve them, respectively. Simulation results show that via two-dimensional time-frequency resource allocation, we can achieve a significant system energy reduction.

A matching-theoretic approach to resource allocation in D2D-enabled downlink NOMA cellular networks

This paper investigates the resource allocation problem in non-orthogonal multiple-access (NOMA) cellular networks underlaid with OMA-based device-to-device (D2D) communication. This network architecture enjoys the intrinsic features of NOMA and D2D communications; namely, spectral efficiency, massive connectivity, and low-latency. Despite these indispensable features, the combination of NOMA and D2D communications exacerbates the resource allocation problem in cellular networks due to the tight coupling among their constraints and conflict over access to shared resources. The aim of our work is to maximize the downlink network sum-rate, while meeting the minimum rate requirements of the cellular tier and underlay D2D communication, and incorporating interference management as well as other practical constraints. To this end, many-to-many matching and difference-of-convex programming are employed to develop a holistic sub-channels and power allocation algorithmic solution. In addition to analyzing the properties of the proposed solution, its performance is benchmarked against an existing solution and the traditional OMA-based algorithm. The proposed solution demonstrates superiority in terms of network sum-rate, users’ connectivity, minimum rate satisfaction, fairness, and interference management, while maintaining acceptable computational complexity.

Outage Probabilities of Cache and SIC Enabled Downlink MIMO NOMA Cellular Networks With Randomly Distributed Users

For non-orthogonal multiple access (NOMA) based cellular communication networks, cache enabled interference cancelation not only reduces the complexity of successive interference cancelation (SIC), but also improves the received signal-to-interference-and-noise ratios. In this paper, a cache and SIC enabled downlink multiple-input-multiple-output NOMA cellular network with randomly distributed users is studied. To theoretically derive its outage performance, the Wishart matrices are introduced to express the achievable rates of users. From the joint probability density function of the unordered eigenvalues of Wishart matrices, we obtain the moment generating function of the achievable rates. The exact outage probabilities are obtained by employing the inverse Laplace transform. Numerical results demonstrate that our theoretically derived outage probabilities match the simulation results.

Full-duplex NOMA cellular networks: Beamforming design and user scheduling

We consider a full-duplex (FD) cellular network, where two pairs of downlink and uplink users simultaneously communicate with a multi-antenna FD base station (BS) via non-orthogonal multiple access (NOMA). The downlink sum-rate of the system is maximized by optimizing the receive and transmit beamformers at the BS, while specific rates for the uplink users are guaranteed. The resulting non-convex problem is solved using an alternating optimization approach based on semi-definite relaxation and one-dimensional line-search approach. To achieve a low-complexity implementation, we incorporate zero-forcing self-interference suppression constraint at the BS, and derive closed-form expression for the receive beamformer. In order to manage the interference between the downlink and uplink users, two user scheduling algorithms, namely Nearest Near and Furthest Far user (NNFF) Scheduling and Random Near and Random Far (RNRF) User Scheduling are proposed based on the cell partitioning method. Numerical results show that FD-NOMA system with optimum and suboptimum beamforming designs significantly improve the system’s ergodic sum-rate compared to the half-duplex counterpart. Moreover, in the FD-NOMA system, NNFF user scheduling can achieve up to 25% average sum-rate gain as compared with the RNRF user scheduling algorithm.

Outage probability and ergodic capacity analysis of uplink NOMA cellular network with and without interference from D2D pair

We consider the framework of uplink transmission and interference constraint for new system model to provide multiple access scheme for fifth generation (5G) wireless communications. In particular, such considered system contains normal cellular users deploying a non-orthogonal multiple access (NOMA) scheme and underlay device-to-device (D2D) users deploying traditional orthogonal multiple access (OMA). Such potentials motivate us consider uplink in cellular network in which the base station (BS) is required to fulfill two NOMA users’ diverse quality of service (QoS) requests under location arrangement with nearby D2D user pair. With regard to enhanced successive interference cancellation (SIC) scheme, the BS still performs the signal detection of NOMA users based on the decoding order and even though existence of an extra interference from D2D user pair. In term of quality evaluation, the ergodic capacity and outage probability are two underlying metrics need be investigated systematically. As important results, detailed derivations are provided in a scenario that considering coexistence of D2D users and NOMA users. As extended scenario, multiple antenna NOMA users exhibit improved performance and the related comparisons are provided. Finally, simulations in various scenarios are conducted to corroborate the precision of the mathematically derivations and to confirm potential of deployment in NOMA with SIC operation.

Weighted Sum Energy Efficiency Maximization of Device-to-Device groups underlaying NOMA cellular network

The problem of Weighted Sum Energy Efficiency (WSEE) Maximization of Device-to-Device (D2D) groups with underlaid Non-Orthogonal Multiple Access (NOMA) cellular network is investigated in this paper. In the novel network model, transmitters in each of the D2D groups will be able to communicate with multiple D2D receivers in the same spectral sub-band via NOMA protocol. Similarly, Base Station (BS) also communicates with multiple Cellular Users (CUs) via NOMA strategy. Power allocation for this hybrid network is presented in this paper. Optimization problem is formulated as WSEE Maximization of the D2D groups. This framework is suitable for energy-crunch devices, where the nodes can have different energy efficiency requirements. Further, to meet Quality of Service (QoS), rate constraints are imposed on all the receivers in the network. The optimization problem is challenging because of its non-convex sum-of-ratios form. So, it is first converted into an equivalent convex form. Subsequently, a successive convex approximation based algorithm is used to obtain optimal power distribution. The proposed power allocation algorithm is shown to be convergent and the simulation results closely match with the optimal values at all Signal-to-Noise Ratio (SNR) values.

Joint Mode Selection and Resource Allocation for D2D-Enabled NOMA Cellular Networks

The 5G cellular network employs non-orthogonal multiple access (NOMA) to enhance network connectivity and capacity, and device-to-device (D2D) communications to improve spectrum efficiency. However, the underlay D2D communications may destroy the execution condition for the successive interference cancellation (SIC) decoding of NOMA cellular networks by introducing the extra interference, which degrades the cellular transmission reliability. Thus, we develop the interlay mode as a special D2D mode for NOMA system, which enables the power domain multiplexing of the D2D pair and cellular users to eliminate the strong interference between them by the SIC decoding. When D2D pair conducts the selection between the interlay mode and underlay mode, the SIC decoding constraint should be satisfied at both D2D receiver and NOMA base station. In order to maximize the system sum rate while meeting the SIC decoding constraint, we propose a joint D2D mode selection and resource allocation scheme with interlay mode, which can be formulated as a combinatorial optimization problem. To tackle the combinatorial nature of mode selection and spectrum assignment, we first prove that the original problem can be reformulated as a maximum weight clique problem, and then propose a graph-based algorithm by applying branch-and-bound method to obtain its optimal solution. Finally, simulation results are provided to demonstrate that the interlay mode along with the proposed algorithms can coordinate D2D communications and NOMA cellular network to significantly improve the system sum rate and the D2D access rate.

Energy efficiency maximization by joint transmission scheduling and resource allocation in downlink NOMA cellular networks

In this paper, we study joint transmission scheduling, rate selection, sub-channel allocation and power assignment problem to maximize energy efficiency in downlink power-domain non-orthogonal multiple access (NOMA) cellular networks. For the study, a fractional optimization problem is formulated to determine the energy efficient optimal configurations of the parameters for transmission scheduling and transmit power, data rate and sub-channel allocation under a constraint of maximum to minimum throughput ratio of the users. To make the fractional optimization problem tractable, the optimization problem is reformulated as a linear programming (LP) problem. The LP problem is solved numerically for many instances of wireless cellular networks by using the optimization tool CPLEX. The numerical results show that the jointly optimal transmission scheduling and resource allocation in NOMA system provides significantly better performance than the existing resource allocation schemes in NOMA and orthogonal multiple access (OMA) systems. We find that the maximum number of users for energy efficient NOMA downlink transmission is limited by 2 and the majority of the downlink transmissions use OMA technique instead of NOMA technique. Again, we apply the duality theory in the LP problem, develop a sub-gradient algorithm and propose an iterative algorithm for solving the problem optimally. The key feature of the iterative algorithm is that it can be implemented in real time operation of a NOMA system. Via extensive simulation, it is demonstrated that the solution provided by the iterative algorithm is very close to the optimal solution.

Dynamic Fractional Frequency Reuse Diversity Design for Intercell Interference Mitigation in Nonorthogonal Multiple Access Multicellular Networks

Nonorthogonal multiple access (NOMA) is one of the few promising techniques that can ensure the achievement of benefits foreseen in next‐generation 5G wireless networks and beyond. By using superposition coding, NOMA allows multiple users to share the same time and frequency resources, thereby enhancing user connectivity, spectral efficiency, and a considerable increase in user throughput. Interference mitigation is an important consideration in NOMA and is considerably more influencing in multicellular environments. First, a brief description of the impairments that can arise in a NOMA cellular network along with responsible factors is provided. Second, different approaches adopted to minimize these impairments are discussed. Finally, a possible solution is proposed that consists of a coordinated approach between the individual cells in the NOMA domain to minimize interferences and improve user throughput. Adaptive fractional frequency reuse (FFR) is used to allocate distinct frequency resources to edge users of different cells to minimize intercell interference in NOMA. Simulation results prove that the proposed NOMA scheme plays an important role in minimizing impairment effects and enhancing the SINR and the throughput performance of edge users while ensuring fairness in its design.