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Communications over Unlicensed sub-8 GHz Spectrum: Opportunities and Challenges

Karim Saifullin, Hussein Al-Shatri, Mohamed-Slim Alouini

TL;DR

This survey analyzes unlicensed sub-8 GHz spectrum, covering TVWS, ISM, CBRS, and U-NII bands, and examines regulatory frameworks, standards, and practical deployments. It details database- and MAC/PHY-based coexistence strategies that enable shared use across diverse technologies, from LPWANs to high-throughput LTE/NR and Wi‑Fi. The authors highlight ongoing regulatory evolution and the emergence of unified spectrum coordination concepts, as well as real-world applications such as private networks, FWA, and IoT. The work underscores the importance of advanced interference mitigation and cross-technology coexistence to unlock the full potential of license-exempt spectrum for both academic research and industry deployment.

Abstract

The utilization of unlicensed spectrum presents a promising solution to the issue of spectrum scarcity in densely populated areas, while also offering a cost-effective means to connect underserved regions. In response to this potential, both academia and industry are actively exploring innovative applications of unlicensed spectrum. This work offers a thorough overview of unlicensed spectrum bands below 8 GHz, including TV White Spaces, Civil Broadband Radio Services, Industrial Scientific Medical bands, and the Unlicensed National Information Infrastructure. The paper focuses on three key aspects: regulations, existing technologies, and applications. It is essential to recognize that "unlicensed" does not equate to "unregulated"; therefore, a clear understanding of permissible and prohibited activities is crucial. From a technological perspective, we examine the current technologies, their capabilities, and relevant applications. Additionally, the shared nature of this spectrum introduces challenges related to interference among users. These collisions can be managed through two primary strategies, that we described: a database-driven approach and coexistence mechanisms at the MAC and PHY layers. This work may serve as a starting point for those who are interested in the unlicensed spectrum, both in academia and industry.

Communications over Unlicensed sub-8 GHz Spectrum: Opportunities and Challenges

TL;DR

This survey analyzes unlicensed sub-8 GHz spectrum, covering TVWS, ISM, CBRS, and U-NII bands, and examines regulatory frameworks, standards, and practical deployments. It details database- and MAC/PHY-based coexistence strategies that enable shared use across diverse technologies, from LPWANs to high-throughput LTE/NR and Wi‑Fi. The authors highlight ongoing regulatory evolution and the emergence of unified spectrum coordination concepts, as well as real-world applications such as private networks, FWA, and IoT. The work underscores the importance of advanced interference mitigation and cross-technology coexistence to unlock the full potential of license-exempt spectrum for both academic research and industry deployment.

Abstract

The utilization of unlicensed spectrum presents a promising solution to the issue of spectrum scarcity in densely populated areas, while also offering a cost-effective means to connect underserved regions. In response to this potential, both academia and industry are actively exploring innovative applications of unlicensed spectrum. This work offers a thorough overview of unlicensed spectrum bands below 8 GHz, including TV White Spaces, Civil Broadband Radio Services, Industrial Scientific Medical bands, and the Unlicensed National Information Infrastructure. The paper focuses on three key aspects: regulations, existing technologies, and applications. It is essential to recognize that "unlicensed" does not equate to "unregulated"; therefore, a clear understanding of permissible and prohibited activities is crucial. From a technological perspective, we examine the current technologies, their capabilities, and relevant applications. Additionally, the shared nature of this spectrum introduces challenges related to interference among users. These collisions can be managed through two primary strategies, that we described: a database-driven approach and coexistence mechanisms at the MAC and PHY layers. This work may serve as a starting point for those who are interested in the unlicensed spectrum, both in academia and industry.

Paper Structure

This paper contains 32 sections, 5 figures, 13 tables.

Table of Contents

  1. Introduction
  2. Unlicensed spectrum overview
  3. Introduction
  4. TV White Spaces Spectrum
  5. Introduction
  6. Regulations
  7. Database spectrum management
  8. Standards
  9. Product overview and applications
  10. Conclusion
  11. Industrial Scientific Medical bands
  12. The 3.55 to 3.7 GHz spectrum: Civil Broadband Radio Services
  13. The 5150 to 7125 MHz spectrum: Unlicensed National Information Infrastructure
  14. Unified spectrum coordination system
  15. An Overview of Wireless Technologies Employing Unlicensed Spectrum
  16. ...and 17 more sections

Figures (5)

  • Figure 1: Technology use cases by range and required throughput. Green rectangles represent cellular technologies, red and magenta indicate Wi-Fi-based technologies. Blue rectangles correspond to short-range devices, while orange rectangles represent long-range, low-throughput devices.
  • Figure 2: Evolution of Wi-Fi standards. Circle radius corresponds to the peak throughput.
  • Figure 3: Types of LTE utilizing unlicensed spectrum
  • Figure 4: NR-U deployment options
  • Figure 5: CSMA/CA protocol example