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Multi-Year Spectral Structure of 6G Candidate Bands at 2.7 GHz and 4.4 GHz

Amir Hossein Fahim Raouf, Ismail Guvenc

Abstract

Mid-band spectrum between 2 and 8 GHz is a critical resource for sixth-generation (6G) systems as it uniquely balances favorable propagation characteristics with scalable bandwidth. Recent U.S. policy highlights candidate bands near 2.7, 4.4, and 7.1 GHz, all of which host substantial federal and non-federal incumbency, including high-power radiolocation and aeronautical telemetry systems. Although these segments are being considered for potential relocation of federal incumbents to enable commercial use, their long-term viability depends on the structural integrity of the spectrum. In such environments, the practical value of spectrum depends on the reliability and contiguity of available spectrum opportunities. This paper presents a measurement-driven feasibility analysis of two representative segments, 2.69-2.9 GHz and 4.4-4.94 GHz, using Software-Defined Radio (SDR) measurements collected during Packapalooza campaigns from 2022 to 2025. Deployment-oriented metrics are introduced to quantify scan-window reliability (SWR), altitude-dependent usable spectrum availability ratio (USAR), largest contiguous clean bandwidth (LCCB), spectral fragmentation, and extreme interference excursions. The results reveal significant year-to-year structural variability. In the 2.69-2.9 GHz band, USAR remains near unity in 2022 and 2023, but drops to approximately 0.65 in 2024 and 0.8 in 2025, accompanied by fragmentation and limited contiguous bandwidth across altitudes. The 4.4-4.94 GHz band exhibits a similar temporal pattern, but with smaller reliability degradation and larger contiguous support, often exceeding several hundred megahertz even during incumbent-dominant periods. The results highlight that wideband feasibility in these candidate bands depends strongly on spectral contiguity and structural stability rather than nominal bandwidth alone.

Multi-Year Spectral Structure of 6G Candidate Bands at 2.7 GHz and 4.4 GHz

Abstract

Mid-band spectrum between 2 and 8 GHz is a critical resource for sixth-generation (6G) systems as it uniquely balances favorable propagation characteristics with scalable bandwidth. Recent U.S. policy highlights candidate bands near 2.7, 4.4, and 7.1 GHz, all of which host substantial federal and non-federal incumbency, including high-power radiolocation and aeronautical telemetry systems. Although these segments are being considered for potential relocation of federal incumbents to enable commercial use, their long-term viability depends on the structural integrity of the spectrum. In such environments, the practical value of spectrum depends on the reliability and contiguity of available spectrum opportunities. This paper presents a measurement-driven feasibility analysis of two representative segments, 2.69-2.9 GHz and 4.4-4.94 GHz, using Software-Defined Radio (SDR) measurements collected during Packapalooza campaigns from 2022 to 2025. Deployment-oriented metrics are introduced to quantify scan-window reliability (SWR), altitude-dependent usable spectrum availability ratio (USAR), largest contiguous clean bandwidth (LCCB), spectral fragmentation, and extreme interference excursions. The results reveal significant year-to-year structural variability. In the 2.69-2.9 GHz band, USAR remains near unity in 2022 and 2023, but drops to approximately 0.65 in 2024 and 0.8 in 2025, accompanied by fragmentation and limited contiguous bandwidth across altitudes. The 4.4-4.94 GHz band exhibits a similar temporal pattern, but with smaller reliability degradation and larger contiguous support, often exceeding several hundred megahertz even during incumbent-dominant periods. The results highlight that wideband feasibility in these candidate bands depends strongly on spectral contiguity and structural stability rather than nominal bandwidth alone.
Paper Structure (15 sections, 10 equations, 8 figures, 1 table)

This paper contains 15 sections, 10 equations, 8 figures, 1 table.

Table of Contents

  1. Introduction
  2. Related Work
  3. Structural Characterization Metrics
  4. Measurement Campaign and Dataset
  5. Measurement Time Resolution and Scan-Window
  6. Noise Reference and Usability Threshold
  7. Scan-Window Usability and Reliability
  8. USAR
  9. Contiguity
  10. Fragmentation
  11. Maximum Measured Power
  12. Measurement Results
  13. 2.69--2.9 GHz
  14. 4.4--4.94 GHz
  15. Conclusion and Forward-Looking Discussion

Figures (8)

  • Figure 1: Altitude--frequency map of $p_{\mathrm{usable}}(f,h)$ for 2.69--2.9 GHz band at Packapalooza (urban), 2025.
  • Figure 2: Altitude-dependent structural metrics for the 2.69--2.9 GHz band across multiple urban datasets (2022--2025): (a) USAR, (b) LCCB, and (c) SFI.
  • Figure 3: Maximum measured aggregated power $P_{\max}(f,h)$ for 2.69--2.9 GHz band at Packapalooza (urban), 2025.
  • Figure 4: CDF and median of received power across 2650--2950 MHz derived from helikite measurements. The black curve shows the median power across snapshots, while colored markers indicate empirical CDF values for each frequency bin. (a) Wheeler 2022, (b) Wheeler 2024, (c) Packapalooza 2022, (d) Packapalooza 2023, (e) Packapalooza 2024, (f) Packapalooza 2025.
  • Figure 5: Altitude--frequency map of $p_{\mathrm{usable}}(f,h)$ for 4.4--4.94 GHz band at Packapalooza (urban), 2025.
  • ...and 3 more figures