Spectrum Sharing Sandbox
PI: Monisha Ghosh; Co-PIs: Nick Laneman, Jane Livingston — University of Notre Dame
About the Project
The Spectrum Sharing Sandbox (S3) is a first-of-its-kind experimental platform designed to gather real-world data on spectrum coexistence within the newly introduced shared spectrum bands: the 3.55–3.7 GHz Citizens Broadband Radio Service (CBRS) and the 5.925–7.125 GHz unlicensed 6 GHz band.
The rapid deployment of private 4G/5G networks in the CBRS band and Wi-Fi 6E in the 6 GHz band has far outpaced the availability of experimental research data. Prior to the authorization of services in these bands, federal incumbents (e.g., Navy radars in CBRS) and the lack of Software Defined Radios operating at 6 GHz severely limited experimental work. Consequently, many critical coexistence and performance issues remain unaddressed.
S3 provides the CISE community with a flexible platform to devise coexistence experiments and collect measurement data. This data can be used to train AI/ML models, inform FCC policymaking, and develop next-generation shared spectrum systems.
Research Challenges
CBRS (3.55–3.7 GHz)
The CBRS band is a low-power allocation sandwiched between two high-power allocations—including the 3.7–3.98 GHz C-band—without any guard bands. Deployed systems employ Time-Division-Duplex (TDD) operations with customizable uplink/downlink splits, creating severe adjacent channel coexistence issues when different operators occupy neighboring bands.
6 GHz (5.925–7.125 GHz)
The 6 GHz band operates under a complex multi-tiered power regime—Low-Power Indoor (LPI) devices, Standard-Power (SP) devices managed by an Automatic Frequency Control (AFC) database, and future Very Low-Power (VLP) rules. The introduction of contention-based protocols (Listen-Before-Talk) and 5G NR-U create unprecedented heterogeneous coexistence problems.
Infrastructure Overview
S3 relies on a hybrid design leveraging commercial equipment, programmable devices, and already-deployed networks to replicate realistic environments rather than purely isolated lab conditions. The platform is deployed across the Notre Dame campus:
University of Notre Dame
- Four outdoor rooftop CBRS nodes (Legends, Fitzpatrick, Rockne, Library)
- Thirteen indoor CBRS nodes installed at the Fitzpatrick-Cushing Hall of Engineering, with 6 operating as a neutral host to select MNOs.
- Enterprise Wi-Fi 6E access points deployed alongside legacy 5 GHz APs at the Notre Dame stadium and select buildings
- NI X410 SDRs running Open-Air-Interface (OAI) 5G NR-U stack
Measurement Approach
Unlike testbeds that rely strictly on low-level I/Q data or basic spectrum measurements, S3 focuses on highly granular system-level parameters:
- System-Level Metrics
- SSID/BSSID for Wi-Fi networks; PCI/RSRP for CBRS/cellular networks
- Smartphone Instrumentation
- QualiPoc for Layer 1/2 data (MIMO streams, channel rank, RRC messaging); SigCap for spatial granularity
- Channel State Information
- Intel 6 GHz Wi-Fi cards extracting detailed CSI and MIMO channel impulse responses
- Targeted I/Q Captures
- SDRs used judiciously for specific interference investigations (e.g., different CBRS uplink/downlink splits)