State of the Art, Taxonomy, and Open Issues on Cognitive Radio Networks with NOMA (1801.01997v1)

Abstract: The explosive growth of mobile devices and the rapid increase of wideband wireless services call for advanced communication techniques that can achieve high spectral efficiency and meet the massive connectivity requirement. Cognitive radio (CR) and non-orthogonal multiple access (NOMA) are envisioned to be important solutions for the fifth generation wireless networks. Integrating NOMA techniques into CR networks (CRNs) has the tremendous potential to improve spectral efficiency and increase the system capacity. However, there are many technical challenges due to the severe interference caused by using NOMA. Many efforts have been made to facilitate the application of NOMA into CRNs and to investigate the performance of CRNs with NOMA. This article aims to survey the latest research results along this direction. A taxonomy is devised to categorize the literature based on operation paradigms, enabling techniques, design objectives and optimization characteristics. Moreover, the key challenges are outlined to provide guidelines for the domain researchers and designers to realize CRNs with NOMA. Finally, the open issues are discussed.

• The paper provides a comprehensive survey of state-of-the-art research on CRNs with NOMA, presenting a structured taxonomy and identifying key open issues.
• The paper presents a detailed taxonomy classifying CRN-NOMA integration by operation paradigms, enabling techniques, design objectives, and optimization characteristics.
• The authors identify crucial technical challenges and open issues for CRN-NOMA, including spectrum sensing complexities, security threats, and reliable mmWave communications.

An Overview of Cognitive Radio Networks with NOMA: State of the Art, Taxonomy, and Challenges

The integration of Cognitive Radio Networks (CRNs) with Non-Orthogonal Multiple Access (NOMA) represents a significant advancement in the effective use of electromagnetic spectrum resources while managing the growing demands for high spectral efficiency and connectivity density. In the paper titled "State of the Art, Taxonomy, and Open Issues on Cognitive Radio Networks with NOMA," Zhou et al. methodically inspect the emerging convergence of CR and NOMA, presenting a synthesized taxonomy, a review of recent research efforts, and the elucidation of attendant challenges and open issues within this domain.

Abstract Synopsis

The paper underscores a critical issue: the exponential rise in mobile device usage coupled with demands for broadband connectivity has exacerbated spectrum scarcity. CRs and NOMA are proposed as essential for next-generation wireless networks, notably 5G, due to their potential to enhance spectral efficiency and allow massive user connectivity. NOMA exploits non-orthogonal resource allocation to allow simultaneous access for multiple users, contrary to traditional orthogonal techniques.

Key Contributions and Framework

The authors present a thorough analysis structured around three major contributions:

1. State-of-the-Art Survey: The paper collates and categorizes the latest research on CRNs adopting NOMA. It articulates improvements these technologies bring, particularly in terms of spectral efficiency (SE) and energy efficiency (EE).
2. Taxonomy: A detailed taxonomy emerges, classifying the integration of NOMA within CRNs across several facets:
   • Operation Paradigms: Identifying interweave, overlay, and underlay modes.
   • Enabling Techniques: Touching upon spectrum sensing, MIMO, SWIPT, and secure communications.
   • Design Objectives: SE maximization, EE maximization, interference management, and fairness.
   • Optimization Characteristics: Differentiating between single and multi-objective optimizations and robust versus non-robust approaches.
3. Unveiling Challenges and Open Issues: The authors highlight technical challenges in realizing CRNs with NOMA:
   • Spectrum sensing intricacies due to signal correlation in non-orthogonal environments,
   • Performance degradation due to pilot contamination in massive MIMO,
   • Secure communication under the dual threats of malicious SU and CSI inaccuracies,
   • Achieving high EHE with practical EH models,
   • Ensuring reliable mmWave communications with suitable beamforming and access mechanisms.

These challenges serve as a road map for future exploration and innovation in this space.

Research Landscape and Implications

The analysis establishes a foundational understanding that CRNs with NOMA remain largely exploratory, with predominant research focused on underlay and overlay modes. The paper emphasizes the necessity of accelerated research to elucidate and mitigate challenges, such as interference management and resource optimization, pivotal for real-world implementation.

Prospects and Theoretical Implications

Looking ahead, integrating NOMA techniques within CRNs could lead to transformative improvements in wireless networks, such as improved resource allocation strategies that address multi-objective optimizations and overcome CSI imperfections. The adoption of physical-layer security and cooperative transmission strategies could further augment both SE and EE.

The paper reflects the authors' stance that, despite initial insights, a comprehensive understanding and solution to these challenges will be critical to the widespread adoption and implementation of CRNs integrated with NOMA. The paper is, therefore, an instrumental guide for future research, providing an analytical framework necessary for addressing the complex, intertwined challenges of CRNs with NOMA. This detailed examination and classification serve as a springboard for profound technological developments in wireless communication.