Wireless Networks
F. Rahdari; M. Sheikh-Hosseini; M. Jamshidi
Abstract
Background and Objectives: This research addresses the performance drop of edge users in downlink non-orthogonal multiple access (NOMA) systems. The challenging issue is pairing the users, which becomes more critical in the case of edge users due to poor signal quality as well as the similarity of users' ...
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Background and Objectives: This research addresses the performance drop of edge users in downlink non-orthogonal multiple access (NOMA) systems. The challenging issue is pairing the users, which becomes more critical in the case of edge users due to poor signal quality as well as the similarity of users' channel gains.Methods: To study this issue, the capabilities of intelligent reflecting surface (IRS) technology are investigated to enhance system performance by modifying the propagation environment through intelligent adjusting of the IRS components. In doing so, an optimization problem is formulated to determine the optimal user powers and phase shifts of IRS elements. The objective is to maximize the system sum rate by considering the channel gain difference constraint. Additionally, the study addresses the effect of the IRS location in the cell on system performance.Results: The proposed approach is evaluated for various scenarios and compared with benchmarks in terms of average bit error rate (BER) and sum rate. The numerical results show that IRS-assisted NOMA improves the performance of edge users and distributes resources more fairly compared to conventional NOMA.Conclusion: Simulation results demonstrate that using IRS-assisted NOMA can effectively address the issue of edge users. By modifying the channel between the BS and the edge users using IRS, the channel gain difference of the users is increased, thereby enhancing the overall system performance. Particularly, the proposed IRS-NOMA system offers a gain of about 4 dB at a BER of 0.01 and 3 dB at the sum rate of 0.1 bps/Hz compared to conventional NOMA. In addition, it was observed that the location of the IRS in the cell affects the system's performance.
Wireless Communications
M.B. Noori Shirazi; M.R. Zahabi
Abstract
Background and Objectives: Non-orthogonal multiple access (NOMA) is a promising solution to meet a high data rate demand in the new generation of cellular networks. Moreover, simultaneous wireless information and power transfer (SWIPT) was introduced to enhance the performance in terms of energy efficiency. ...
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Background and Objectives: Non-orthogonal multiple access (NOMA) is a promising solution to meet a high data rate demand in the new generation of cellular networks. Moreover, simultaneous wireless information and power transfer (SWIPT) was introduced to enhance the performance in terms of energy efficiency. In this paper, a single-cell cooperative NOMA system with energy harvesting full-duplex (FD) relaying is proposed to improve the sum rate and energy efficiency. Methods: A downlink model consisting of a base station (BS), two cell-center users (nearly located users), and two cell-edge users (far located users) are considered. In each signalling interval, the BS transmits a superposition signal of cell-center and cell-edge users based on the power domain (PD) NOMA strategy. Employing a relay selection criterion, a cell-center user is paired with a cell-edge user and acts as an FD decode and forward (DF) relay to improve the cell-edge user performance. An energy harvesting (EH) model is considered where a power splitting (PS) protocol is adopted at the relay node. The other cell-center user saves the harvested energy from the BS to exploit in the subsequent signalling intervals. Two problems of power allocation for sum rate and energy efficiency maximization in constraints of the minimum required data rate for each user and maximum transmit power at the BS are formulated for the proposed scheme. Due to the non-convexity, the optimization problems are transformed and approximated to the convex optimization problems and solved by iterative algorithms. Difference of convex (DC) programming is employed for solving the sum rate maximization problem where an effective combination of DC programming, bisection method, and Dinkelbach algorithm is utilized for dealing with the energy efficiency maximization problem. Results: The sum rate and energy efficiency over maximum available power at the BS are presented. Also, the effects of the power splitting factor and the cell radius on the sum rate and energy efficiency are investigated. Moreover, a comparison with the OMA and NOMA schemes is studied for the different minimum required data rates. Conclusion: Simulation results validate that the proposed scheme outperforms the OMA and NOMA schemes in terms of sum rate in all SNR regimes. Moreover, the energy efficiency of the proposed scheme achieves considerably better performance than OMA for all SNR values and obtains remarkable better performance than NOMA in most SNR values.
