Uplink Non-Orthogonal Multiple Access for 5G Wireless Networks (1705.04108v1)

Abstract: Orthogonal Frequency Division Multiple Access (OFDMA) as well as other orthogonal multiple access techniques fail to achieve the system capacity limit in the uplink due to the exclusivity in resource allocation. This issue is more prominent when fairness among the users is considered in the system. Current Non-Orthogonal Multiple Access (NOMA) techniques introduce redundancy by coding/spreading to facilitate the users' signals separation at the receiver, which degrade the system spectral efficiency. Hence, in order to achieve higher capacity, more efficient NOMA schemes need to be developed. In this paper, we propose a NOMA scheme for uplink that removes the resource allocation exclusivity and allows more than one user to share the same subcarrier without any coding/spreading redundancy. Joint processing is implemented at the receiver to detect the users' signals. However, to control the receiver complexity, an upper limit on the number of users per subcarrier needs to be imposed. In addition, a novel subcarrier and power allocation algorithm is proposed for the new NOMA scheme that maximizes the users' sum-rate. The link-level performance evaluation has shown that the proposed scheme achieves bit error rate close to the single-user case. Numerical results show that the proposed NOMA scheme can significantly improve the system performance in terms of spectral efficiency and fairness comparing to OFDMA.

• The paper demonstrates a novel uplink NOMA scheme that enhances spectral efficiency by enabling multiple users to share the same subcarrier.
• It introduces a joint processing technique at the receiver to balance sum-rate maximization with low detection complexity.
• Numerical results reveal up to 95% of the theoretical capacity and improved fairness compared to traditional OFDMA methods.

Uplink Non-Orthogonal Multiple Access for 5G Wireless Networks

The paper "Uplink Non-Orthogonal Multiple Access for 5G Wireless Networks" by Mohammed Al-Imari et al. proposes a novel Non-Orthogonal Multiple Access (NOMA) scheme for uplink transmission in 5G networks. The authors address the inherent limitations of Orthogonal Multiple Access (OMA) techniques, specifically the suboptimal spectral efficiency due to exclusive resource allocation. In existing OMA techniques like OFDMA, resources are exclusively allocated, thus failing to achieve maximum system capacity, particularly when user fairness is considered. The proposed NOMA approach offers a significant advancement towards improving spectral efficiency and fairness while managing receiver complexity.

Overview of Proposed NOMA Scheme

The core of the proposed NOMA scheme is its ability to allow multiple users to share the same subcarrier without requiring spreading or coding redundancy, which usually diminishes spectral efficiency. The paper introduces a joint processing technique at the receiver for signal detection, which alleviates the complexity through an imposed limit on the number of users per subcarrier. This scheme promotes a balance between maximizing sum-rate and controlling complexity, ensuring that optimum Multi-User Detection (MUD) techniques can operate effectively within practical constraints.

Subcarrier and Power Allocation

The authors propose a subcarrier and power allocation algorithm designed to enhance the sum-rate. The algorithm is suboptimal yet demonstrates low complexity. It considers both user-specific rate maximization and global system objective enhancement to allocate subcarriers. The implementation of such allocation strategies acknowledges the flexibility of NOMA by sharing more than one user per resource block, unlike the rigid exclusivity observed in traditional OFDMA systems.

Numerical Results

The paper provides compelling numerical results that highlight the advantages of the proposed NOMA scheme over OFDMA. The bit error rate (BER) comparison shows negligible performance degradation for NOMA when uncoded, and this gap vanishes with coding applied. Simulation results indicate that the proposed NOMA significantly improves spectral efficiency, achieving about 95% of the theoretical upper system bound under certain configurations, while OFDMA only reaches 81%. Further, the proposed NOMA scheme outperforms OFDMA in terms of fairness as quantified by Jain’s fairness index. This enhanced fairness is attributed to NOMA’s capability to share subcarriers among users, enabling better resource allocation and user support.

Implications and Future Directions

The findings in the paper have substantial implications for 5G and beyond, where spectral efficiency and fairness are crucial. By leveraging non-orthogonality, the proposed scheme promises efficient spectral utilization and equitable user access, critical in dense network environments. The approach’s practical implementation potential, devoid of conventional redundancy, suggests that it can be integrated effectively into real-world systems. The research invites future exploration into optimizing decoder performance and integrating other advanced MUD techniques. Additionally, extending this work could involve comparing the proposed scheme with emerging NOMA variants and evaluating its overload capabilities in heterogeneous network scenarios.

In summary, this paper presents a well-argued case for adopting Non-Orthogonal Multiple Access techniques in uplink communication for 5G networks. The proposed mechanism strikes a strategic balance between performance gains and operational complexity, indicating a promising pathway for the evolution of next-generation wireless communication systems.