What is Spectrum Sharing?
Spectrum sharing is a way to optimize the use of the airwaves, or wireless communications channels, by enabling multiple categories of users to safely share the same frequency bands.
Spectrum sharing is necessary because growing demand is crowding the airwaves. Smartphones, the Internet of Things, military and public safety radios, wearable devices, smart vehicles and countless other devices all depend on the same wireless bands of the electromagnetic spectrum to share data, voice and images.
As the nation’s measurement authority, the National Institute of Standards and Technology (NIST) develops measurement tools, data and methods to make fair, efficient spectrum sharing possible. This work supports not only the trillion-dollar U.S. telecommunications industry and its hundreds of millions of customers but also the U.S. military, which has spectrum in the 3.5 gigahertz (GHz) frequency band that is a focus of pioneering U.S. spectrum-sharing efforts.
NIST’s work also promises to improve the performance and reliability of future wireless systems used in hospital operating rooms, manufacturing facilities, stadiums, public-safety settings, utilities and elsewhere.
What is NIST Doing to Support Spectrum Sharing?
NIST’s Communications Technology Laboratory (CTL) conducts basic research in spectrum sharing.
CTL’s research focuses on two approaches to spectrum sharing. The first is tiered access, in which “smart” systems preserve a primary user’s right to exclusive use of certain frequencies and guide the capabilities of secondary users. Tiered access is used in the Citizens Broadband Radio Service (CBRS). The second approach is coexistence, where multiple technologies use the same spectrum at the same time. This is the case with, for example, Bluetooth and 2.4-GHz Wi-Fi systems.
In general, CTL conducts research to understand the behavior of wireless systems and develops innovative ways to characterize spectrum activity in both indoor and outdoor environments. The goal is to quantify spectrum use and user behavior so that policymakers and industry leaders can make informed decisions based on NIST’s impartial analysis. CTL has developed test methods and tools that regulators can use to certify users of shared spectrum to protect against interference with primary users such as the military.
One of CTL’s four divisions is the National Advanced Spectrum and Communications Test Network (NASCTN), which has a broad mission to provide trusted, unbiased data for addressing specific questions about spectrum sharing. For instance, one NASCTN project developed a new test method and performed complex measurements to quantitatively assess the impact of wireless communications signals on the performance of GPS receivers operating in a specific frequency band. Such data can be used by both industry and spectrum regulators in spectrum sharing proposal and approval processes.
CTL built the National Broadband Interoperability Test Bed (NBIT) to support coexistence research and NASCTN. Technological advances in computing, signal processing and computational speed are enabling systems to work in cluttered environments, but coexistence requires that devices resist interference and avoid interfering with neighbors. To evaluate whether this is happening, new metrics are needed. Accordingly, CTL is developing ways to measure how well wireless devices coexist while operating in shared frequency bands.
Spectrum sharing may lead to disputes over frequency use in both space and time. Therefore, CTL is also developing forensics tools to monitor wireless spectrum use for the purposes of detecting and reporting breaches. The idea is to “fingerprint” spectrum use in time and space in ways that stand up to scrutiny.
Physical tests of spectrum sharing poses geographic challenges. CTL has already played a major role in the development of standards, test procedures and certification tools for the CBRS.
CTL is also conducting research on additional strategies for ensuring that secondary users don’t interfere with military users. For example, CTL is working to develop distributed sensor networks that could quickly localize and identify signals in coastal zones, which may span thousands of square miles of diverse terrain.
CTL is also studying an additional possible solution involving the use of unmanned aerial vehicles (UAVs), which could be outfitted with wireless sensors to monitor spectrum usage. UAVs also might simulate naval radar from different points at sea, to provide reliable data for secondary users who would be expected to clear the airwaves when they detect the primary user.