A new technical assessment conducted by Plum Consulting for a consortium of RFID associations raised concerns about the conclusions of NextNav’s study submitted to the Federal Communications Commission’s (FCC) on the the proposed 5G deployment in the 902–928 MHz band.
The Plum Report, submitted to the federal agency by RAIN Alliance, LoRa Alliance, Wi-Fi Alliance, Wi-SUN Alliance, and Z-Wave Alliance, questions several key assumptions and methodologies in NextNav’s analysis as the previous study did provide sufficient evidence to support the FCC informed decision-making regarding spectrum reallocation.
For now, the Plum Report casts doubt on the viability of NextNav’s proposal, urging the FCC to proceed with caution as it considers the future of this increasingly crowded spectrum band as “a much more rigorous and comprehensive analysis would be needed to fully assess the potential coexistence impact before any consideration is given to authorizing new 5G services in this strategically important band.”
Background on the Proposal
NextNav is a positioning, navigation, timing (PNT) and 3D geolocation technology company. Its April 2024 FCC petition aimed to expand the power level, bandwidth and priority of its licenses. Additionally, NextNav proposes to use 5G connectivity over the relatively low bandwidth.
The petition now in from of the FCC seeks to realign the 902-928 MHz band used by UHF RFID as well as other wireless devices. The company is pushing to reallocate a portion band to support a terrestrial 5G mobile broadband network, transitioning from its current Multilateration Location and Monitoring Service (M-LMS) operations to advanced 5G systems. The proposed allocation splits 15 MHz into a 5 MHz uplink band (902–907 MHz) and a 10 MHz downlink band (918–928 MHz). The downlink would integrate positioning, navigation, and timing (PNT) services as well.
To alleviate concerns about potential interference with existing services in this frequency range, particularly unlicensed “Part 15” technologies, NextNav commissioned a technical coexistence study. According to the company’s findings, their 5G deployment would “operate within the existing noise environment” and only marginally affect incumbent devices.
“This plan offers enormous benefits to the public by creating a complement and backup to GPS, while also unleashing much-needed spectrum for 5G broadband,” NextNav spokesperson Howard Waterman said previously.
Key Findings in the Plum Report
The Plum Report challenges these claims, stating that NextNav’s analysis overlooks critical factors and relies on flawed assumptions. The review identified seven primary shortcomings in NextNav’s study: geographic density of 5G base stations; base station loading factors; uplink traffic analysis; simplistic indoor/outdoor assumptions; overlooked adjacent channel interference; assumptions about Part 15 devices’ behavior; and limited scenario flexibility
On the geographic density issue, the Plum Report highlighted that NextNav has assumed number of 5G base stations is “significantly too low,” resulting in unrealistic interference projections. Real-world networks, as exemplified by existing long term evolution (LTE) deployments, often exhibit base station densities up to ten times greater than what NextNav forecasts.
Additionally, it is alleged that the NextNav report inaccurately models Part 15 devices as constantly active in a peer-to-peer communication topology. Plum’s authors emphasized most Part 15 systems operate in a centralized “star” topology, with minimal simultaneous transmissions due to mechanisms like listen-before-talk (LBT) protocols.
Part 15 Ecosystem Vulnerabilities
As for the indoor/outdoor issue, the NextNav study models a 70 percent indoor and 30 percent outdoor distribution for Part 15 devices without independently analyzing outdoor-only scenarios. Plum argues that outdoor devices, essential for applications like streetlights, smart meters, and agricultural sensors, face a much higher risk of interference.
To that end, the review underscored that many Part 15 devices are geographically widespread and used in outdoor scenarios that could make them particularly vulnerable to 5G interference. Examples include:
- Smart city infrastructure: Streetlights, traffic management systems, and environmental sensors.
- Utility monitoring: Smart meters and grid monitoring tools.
- Agriculture: Soil and weather sensors, as well as equipment for livestock tracking.
Plum officials further highlighted interference risks in the opposite direction—from Part 15 devices to 5G receivers. High-density deployments of unlicensed devices may elevate the noise floor at sensitive 5G base station receivers, particularly those serving urban or suburban environments. This reciprocal interference issue was entirely absent from NextNav’s study.
The Plum Report concluded NextNav’s coexistence report “falls well short of providing a sufficient technical basis” for FCC decision-making. Given the complexity of coexistence challenges in the strategically vital Lower 900 MHz band, the firm calls for a deeper analysis before advancing any proposals for spectrum reallocation.