A Simple User Grouping and Pairing Scheme for Non-Orthogonal Multiple Access in VLC System

In this paper, a simple user grouping and pairing scheme is proposed for non-orthogonal multiple access (NOMA) and is applied for the downlink visible light communication (VLC) system. The proposed scheme is a mix of both NOMA and the conventional orthogonal multiple access (OMA) schemes. In the proposed scheme, every two users are paired using NOMA and all pairs are allocated with conventional OMA. The performance of the proposed scheme is compared to the performance of the conventional OMA in terms of the maximum sum rate. Simulation results show that the proposed scheme provides higher sum rate compared with the OMA scheme

Advanced NOMA Assisted Semi-Grant-Free Transmission Schemes for Randomly Distributed Users

Non-orthogonal multiple access (NOMA) assisted semi-grant-free (SGF) transmission has recently received significant research attention due to its outstanding ability of serving grant-free (GF) users with grant-based (GB) users' spectrum, {\color{blue}which can greatly improve the spectrum efficiency and effectively relieve the massive access problem of 5G and beyond networks. In this paper, we investigate the performance of SGF schemes under more practical settings.} Firstly, we study the outage performance of the best user scheduling SGF scheme (BU-SGF) by considering the impacts of Rayleigh fading, path loss, and random user locations. Then, a fair SGF scheme is proposed by applying cumulative distribution function (CDF)-based scheduling (CS-SGF), which can also make full use of multi-user diversity. Moreover, by employing the theories of order statistics and stochastic geometry, we analyze the outage performances of both BU-SGF and CS-SGF schemes. Results show that full diversity orders can be achieved only when the served users' data rate is capped, which severely limit the rate performance of SGF schemes. To further address this issue, we propose a distributed power control strategy to relax such data rate constraint, and derive closed-form expressions of the two schemes' outage performances under this strategy. Finally, simulation results validate the fairness performance of the proposed CS-SGF scheme, the effectiveness of the power control strategy, and the accuracy of the theoretical analyses.Comment: 41 pages, 8 figure

Energy Efficient Uplink Transmission in Cooperative mmWave NOMA Networks with Wireless Power Transfer

In 5G wireless networks, cooperative non-orthogonal multiple access (NOMA) and wireless power transfer (WPT) are efficient ways to improve the spectral efficiency (SE) and energy efficiency (EE). In this paper, a new cooperative NOMA scheme with WPT is proposed, where EE optimization with a constrained maximum transmit power and minimum required SE is considered for the user grouping and transmit power allocation of users. We obtain a sub-optimal solution by decoupling the original problem in two sub-problems: an iterative algorithm is considered for the user grouping, while, in addition, we utilize the Bat Algorithm (BA) for solving the power allocation problem, where BA was proved to be able to achieve a higher accuracy and efficiency with respect to other meta-heuristic algorithms. Furthermore, to validate the performance of the proposed system, analytical expressions for the energy outage probability and outage probability of users are derived, confirming the effectiveness of the simulation results. It is demonstrated that the proposed cooperative NOMA with WPT offers a considerable improvement in terms of SE and EE of the network compared to other methods. Finally, the effectiveness of BA in solving the EE optimization problem is demonstrated through a high convergence speed by comparing it with other methods