Citizens Broadband Radio Service

Summary

The Citizens Broadband Radio Service (CBRS) band is 150 MHz of spectrum made available for commercial broadband use on a shared basis with the federal government. NIST is creating models, tools, and datasets to assist in the development and enhancement of commercial systems that protect mission-critical federal systems from harmful radio frequency interference.  

Description

 

USS George H.W. Bush equipped with air traffic control radar system operating in the 3.5 GHz band.  Credit: U.S. Navy photo by Mass Communication Specialist 3rd Class Nicholas Hall [Public domain], via Wikimedia Commons

The FCC Part 96 rules establish a three-tier architecture for sharing the radiofrequency (RF) spectrum from 3550 MHz to 3700 MHz. Commercial users of the 3.5 GHz Citizens Broadband Radio Service (CBRS) band will share this spectrum with existing incumbents, including the federal government which currently operates mission-critical radiolocation services in this spectrum. 

NIST aims to enhance and innovate the wireless communication technologies, models, and algorithms currently used in the 3.5 GHz CBRS band. In addition to the research areas described below, ongoing research emphasizes on investigating machine learning and deep learning techniques for classification of radar and CBRS signals, path loss prediction, and channel estimation and cognitive receiver design.

ESC Sensor Detection and Placement

NIST has designed deep learning detectors to accurately detect the presence of radar signals for commercial 3.5 GHz sensors. Known as Environmental Sensing Capability (ESC) systems, these sensors are responsible for detecting federal incumbent signals and triggering interference protection mechanisms. NIST is also creating software tools and digital waveforms that can be used by the industry and the regulator to test and certify commercial 3.5 GHz sensors. The digital waveforms are either simulated or derived from radar measurements conducted by NASCTN in the 3.5 GHz band. In addition, NIST has developed algorithms to strategically place the sensors along the coasts effectively and efficiently.

NIST radar waveform generator software tool has been adopted by the IEEE 1900.8 Working Group as part of a reference workflow for generating Radio Frequency Machine Learning (RFML) datasets for training radar detection models that enable dynamic spectrum sharing systems. The Working Group aims to standardize storage formats for structured RFML datasets and the interfaces between the functions of a generic RFML model training pipeline.

Simulated radar waveform generator GUI

SAS Incumbent Protection

NIST has developed test procedures and reference implementations that the regulator uses to certify commercial systems mediating access to this RF band.  Among the most important functions of these commercial “Spectrum Access Systems” is interference avoidance. NIST test methods and reference software validate whether these systems meet established requirements to protect incumbents such as the U.S. Navy from harmful RF interference. Furthermore, NIST has utilized upper and lower bounds on the aggregate interference distribution to obtain deterministic results and to greatly simplify incumbent protection procedure, especially in a multi-SAS environment.

NIST test methods and reference tools are part of CBRS standards being developed by the Wireless Innovation Forum, an international group of equipment vendors, broadband service providers, government agencies, and regulators. The Forum’s Spectrum Sharing Committee serves as the CBRS standards body and is comprised of 50 organizations including AT&T, CommScope, CTIA, Ericsson, Federated Wireless, Google, Nokia, Sony, Qualcomm, and Verizon. Government stakeholders include DoD, FCC, and NTIA.

A graphic illustration of systems deployed within the neighborhood of an offshore dynamic protection area (DPA)

GAA Coexistence and Dynamic Spectrum Access

NIST has been engaged in the study of coexistence of the General Authorized Access (GAA) users in the CBRS band. GAA users are the lowest priority users in the CBRS band. They must make sure that they do not cause harmful interference to the higher tier users while cooperating with each other to minimize potential interference among themselves. Towards this goal, the Wireless Innovation Forum (WInnForum) has recommended three schemes to facilitate GAA-GAA coexistence. NIST has published simulation based performance studies of two of these schemes that use real terrain and land cover data of continental USA.

NIST has studied dynamic spectrum access (DSA) for secondary users to exploit white spaces in LTE system. DSA algorithms based on Survival Analysis, that maximize white space utilization while limiting the interference to the primary user below a set threshold, have been designed for LTE systems. Real world LTE spectrum occupancy data were used to validate performance of the algorithms. Analytical model of white space utilization of a DSA system has also been carried out by applying theories from survival analysis and stochastic processes. Preliminary study based on machine learning using real-world LTE data for DSA also has been performed.

PUBLICATIONS

ESC Sensor Detection and Placement

• Reference Data Sets for Training and Evaluating RF Signal Detection and Classification Models (GLOBECOM 2019)

• RF Dataset of Incumbent Radar Signals in the 3.5 GHz CBRS Band (NIST JRES 2019)

• Detection of Incumbent Radar in the 3.5 GHz CBRS Band Using Support Vector Machines (SSPD 2019)

• Detection of Incumbent Radar in the 3.5 GHz CBRS Band (GlobalSIP 2018)

• 3.5 GHz ESC Sensor Test Apparatus Using Field-Measured Waveforms (WInnComm 2018)

• Wideband Spectrum Reconstruction with Multicoset Sub-Nyquist Sampling and Collision Classification (GLOBECOM 2016)

• A Practical Approach to Placing Coastal Sensors for Spectrum Sharing in the 3.5 GHz Band (WCNC 2019)

• Sensor Placement and Detection Coverage for Spectrum Sharing in the 3.5 GHz Band (PIMRC 2018)

• 3.5 GHz Environmental Sensing Capability Detection Thresholds and Deployment (TCCN 2017)

• 3.5 GHz Environmental Sensing Capability Sensitivity Requirements and Deployment (DySPAN 2017)

SAS Incumbent Protection

• Independent Calculation of "Move Lists" for Incumbent Protection in a Multi-SAS Shared Spectrum Environment (WCL 2021)
• Deterministic Move Lists for Federal Incumbent Protection in the CBRS Band (TCCN 2020)
• Effect of Federal Incumbent Activity on CBRS Commercial Service (DySPAN 2019)
• 3.5 GHz Federal Incumbent Protection Algorithms (DySPAN 2018)

GAA Coexistence and Dynamic Spectrum Access

• Performance Impact of Coexistence Groups in a GAA-GAA Coexistence Scheme in the CBRS Band (TCCN 2020)
• GAA-GAA Coexistence in the CBRS Band: Performance Evaluation of Approach 3 (IEEE LCN 2020)
• Performance Study of a GAA-GAA Coexistence Scheme in the CBRS Band (DySPAN 2019)
• A Machine Learning Based Scheme for Dynamic Spectrum Access (WCNC 2021)
• Optimal Dynamic Spectrum Access Scheme for Utilizing White Space in LTE Systems (WCNC 2019)
• Analytical Modeling of White Space Utilization for a Dynamic Spectrum Access System (WCNC 2019)
• Exploiting LTE White Space using Dynamic Spectrum Access Algorithms based on Survival Analysis (ICC 2017)
• Dynamic Spectrum Access Algorithms Based on Survival Analysis (TCCN 2017)

ASSOCIATED PRODUCTS

Publications

• CBRS Operational and Functional Requirements
• Test and Certification for CBRS; SAS as Unit Under Test

Software

• Federal Incumbent Protection Procedure Reference Implementation
• Baseline Deep Learning Detectors for Radar Detection in the 3.5 GHz CBRS Band

Dataset

• Simulated Radar Waveform and RF Dataset Generator for Incumbent Signals in the 3.5 GHz CBRS Band

 

Major Accomplishments

• The team received a NIST Bronze Medal in 2019 recognizing the work in the standardization of CBRS in support of more efficient spectrum sharing between commercial and federal users.
• Led development of the federal incumbent interference protection test procedures, as well as test procedures for multiconstraint interference protection and select communication protocols, being used in certification of commercial systems.
• Created the reference implementation of the standardized federal incumbent protection procedure employed by commercial Spectrum Access Systems.
• Contributed to the CBRS requirements and protocol specifications for commercial systems published by the Wireless Innovation Forum’s Spectrum Sharing Committee, the standards body for CBRS.
• Developed detection algorithms, generation tools, and digital waveforms of emissions in the 3.5 GHz band suitable for development and testing of ESC sensors which are widely used by the industry and academia.
• Granted a patent “Apparatus and Method for Dynamically Controlling Spectrum Access” - US Patent Number 10,390,364.

Wireless (RF)