Understanding 5G: CBRS

The impending deployment of 5G services contains one interesting element called Citizens Broadband Radio Service (CBRS). CBRS is open for shared use, not restricted to a carrier. CBRS reminds me of the citizens band radio a few decades ago that was primarily used by truckers and Hollywood movies. CBRS looks like a form of Wi-Fi rather than usual citizens band radio.

The difference with CBRS is no one owns the frequencies. Compare this to cellular service where each carrier operates on specific licensed frequencies around the country. One of the disadvantages of the carriers owning frequencies is that there are many areas in rural U.S. that do not have coverage. The licensed frequencies cannot be reused by another carrier in these rural areas, while CBRS is open for anyone to use.

I attended the recent DC5G Summit, "Revolutionizing Mobility," held in Washington DC earlier this month. One of the presenters was Dr. Preston Marshall, Engineering Director, Alphabet Access, the parent company of Google. His presentation was titled "How Standards and Sound Spectrum Policy Will Shape the Future of 5G-Connected Worldwide Economy." Part of his presentation covered CBRS, and I include some of Marshall's insight in this article.

Citizens Broadband Radio Service

The Federal Communications Commission (FCC) established the Citizen Broadband Radio Service (CBRS) in 2015. It allows shared commercial use of the 3.5 GHz band with military radars and fixed satellite stations. The FCC defines CBRS as a private, two-way, short-distance voice communications service for personal or business activities available to the general public. It may be used for voice paging. CBRS has 40 channels between 26.965 MHz and 27.405 MHz.

The existing General Mobile Radio Service (GMRS) is a licensed radio service assigned to 462 MHz and 467 MHz. GMRS channels are commonly used for short-distance, two-way voice communications supporting hand-held radios, mobile radios, and repeater systems. The FCC expanded GMRS in 2017 to also allow short data messaging applications including text messaging and GPS location information.

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Source: Dr. Marshall's DC5G presentation

CBRS Spectrum

CBRS shares a spectrum of 3550 to 3700 MHz. The sharing with naval radar systems will exist but the 10 MHz usage is relatively rare. Access to the spectrum is controlled by a Spectrum Access System (SAS). It offers three tiers that are open to all users.

The protected tier has absolute protection from interference. A Priority Access License (PAL) provides protection from lower-level tiers and other PALs. It can be purchased at auction with limited renewal rights. However, a PAL delivers interference protection, and there is no right to exclude other users.

The General Authorized Access (GAA) is any spectrum that would not cause interference to the higher levels tiers. At least 50% of the spectrum is guaranteed for GAA to assure devices are not orphaned. GAA is open to any user, carrier, non-carrier, enterprise, residences, or private citizens. See the graphic below.

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Source: CBRS Alliance

The Three Tier Value

A major value to CBRS is that the technology and equipment can be used by carriers and unlicensed users: The single large band is accessible to carriers and non-carriers with protection rights. This should produce a wide range of products at competitive prices. It also eliminates the partitioning of spectrum among the service models and technologies. If someone buys equipment for CBRS, it is not orphaned even if the buyer of the equipment loses an auction. It becomes relegated to the use of GAA.

The Neutral Host

The introduction of a neutral host combines two concepts, hosting and neutrality. Hosting refers to an entity that provides the resources made available to the clients/users. Neutrality means that the neutral host acts as a shared platform for multiple clients.

Neutrality does not imply strict equality among hosted clients. The allocated resources are subject to commercial agreement between the neutral host and the hosted client. Policy-based management may be applied. The resources of a neutral host should be available without user intervention operating seamlessly and identical to those provided by their hosted clients' dedicated resources.

The neutral host:

  • Obtains use of the resources in a specific geographic area (building or public space)
  • Manages the resources, subject to agreements with resource owners and clients
  • Provides interconnection, allowing hosted clients to make use of the platform(s) that provide continuous services

It is anticipated that the cost of deployment will be much less for CBRS. CBRS can also be integrated with an IT infrastructure buildout. The additional cost to a Wi-Fi access point may be $50 to $100 per access point.

Implications

The spectrum will be accessible to all Mobile Network Operator (MNO) and Mobile Virtual Network Operator (MVNO) that wish to share the neutral host network. The spectrum is not exclusive to one MNO. The current carrier spectrum provisioning is fundamentally different for CBRS. The spectrum will be accessible to non-MNOs, which enables the maximum infrastructure investment and deployment. The spectrum rights are flexible to assure maximum spectrum usage. Most users are supported within the CBRS spectrum compared to licensed spectrum. CBRS delivers a low transaction cost with predictable minimal delay.

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