Wireless operators are under constant pressure to expand network capacity and enhance network speed and performance to meet user expectations. Among a number of options available to carriers to help overcome these challenges is adding spectrum. But licensed spectrum is a finite resource, and subscribers are using more and more wireless services and bandwidth.
To address the spectrum shortage in the U.S., the FCC created the new Citizens Broadband Radio Service (CBRS) in 2015 in the 3500-3700 MHz band. This spectrum adds critical new capacity opportunities for carriers, but requires the implementation of a spectrum sharing system, officially called a Spectrum Access System (SAS). The SAS has emerged as one of the preferred dynamic spectrum access solutions in the U.S.
For an example about how a SAS will help operate in CBRS, check out this short video.
With a SAS, spectrum is managed and assigned on a dynamic, as-needed basis across three tiers of access:
- Tier 1 is incumbent users such as the federal government and fixed satellite users,
- Tier 2 is Priority Access License users—licensed wireless carriers who acquire spectrum through an auction,
- Tier 3 is General Authorized Access users who will deploy “lightly-licensed” devices.
If spectrum is not needed by one tier it can be accessed by another via the SAS, securely and without interference. In CBRS, the Tier 1 incumbents include Navy radar and commercial satellite communications systems. To protect them from interference, CBRS comes with two key requirements:
- The use of a SAS to manage spectrum use among stakeholders and enable operators to share the spectrum without interfering with incumbent operations.
- The deployment and use of an environmental sensing capability (ESC) to detect federal frequency use in the 3550-3650 MHz band in exclusion zones where U.S. Navy radar systems can operate, primarily along the Pacific, Atlantic and Gulf coasts. The ESC informs the SAS of radar operation and the SAS reacts to ensure there is no interference between CBRS and radar operations.
SAS is expected to be used first for wide-scale shared wireless broadband use in CBRS, but it could play a significant role in managing spectrum for future 5G networks.
CommScope is developing its own SAS and ESC solutions. To learn more about CommScope’s role in CBRS, check out this recent interview I did.
About the Author
With close to 30 years of spectrum management experience, Mark Gibson is responsible for developing domestic and international business opportunities for Comsearch, a CommScope company. In addition to leading Comsearch’s business development efforts for AWS, 700 MHz and TV white space products and services, he has led efforts to address spectrum sharing between the federal government and commercial users. Mark has authored several papers on spectrum sharing and relocation and has advised numerous wireless participants in their system design. He has spoken worldwide on spectrum management and related issues. Mark earned a bachelor of science in electrical engineering from the University of Maryland.