What is CBRS?
How is the CBRS spectrum shared?
What is a CBSD?
What is the role of SAS?
What is CPAS?
What is the role of ESC?
What are CBSD Categories?
What is a Domain Proxy?
What is a CBRS Cellular Network?
Do UEs have power limitations?
Does the SAS assign channels to GAA CBSDs?
Do GAA CBSDs have exclusive access to their granted channel?
What is the CBSD Registration Procedure?
What is the Spectrum Inquiry Procedure?
What is the Grant Procedure?
What is the Heartbeat Procedure?
Why would a CBSD relinquish a grant?
Why would a CBSD de-register with the SAS?
Can a CBSD register with multiple SAS at the same time?
What is the role of a CPI?
CBRS (Citizens Broadband Radio Service) is a wireless broadband spectrum operating in the 3550 MHz to 3700 MHz frequency range in the United States. The spectrum is shared among federal and non-federal users, including military radar systems, satellite earth stations, and commercial users. The FCC (Federal Communications Commission) created CBRS to increase wireless broadband access while protecting existing users.
In traditional spectrum management, specific bands are allocated for certain uses and licensed to specific entities. In contrast, the FCC's approach to CBRS involves dynamic spectrum-sharing that allows for more flexible and efficient spectrum use.
Private operators can utilize CBRS to deploy wireless networks to larger or remote areas where Wi-Fi does not serve effectively.
Note that CBRS-based networks may alternately be referred to as Private Wireless Networks, Private Cellular Networks (PCNs) or Private LTE (PLTE).
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The FCC uses a three-tiered hierarchy for the CBRS spectrum sharing, with different priority levels assigned to each tier:
- Incumbent Access Tier (IAT): Federal incumbents, such as military radar systems, operating within the 3550-3650 MHz range. Non-federal incumbents include Fixed Satellite Service (FSS) earth stations operating in the 3600-3650 MHz range and Wireless Broadband Service (WBS) licensees operating in the 3650-3700 MHz range. Incumbents have the highest priority in the CBRS spectrum, and their operations take precedence over all other tiers.
- Priority Access Tier (PAT): This tier comprises users who have acquired Priority Access Licenses (PALs) from the FCC operating in the 3550-3650 MHz range. PALs are distributed through an auction process and assigned on a county-by-county basis, with a maximum of seven licenses per county. PAT users have priority access to their designated 10 MHz segments within the licensed county. PAT users must avoid causing harmful interference to IAT users.
- General Authorized Access Tier (GAA): This tier consists of unlicensed users with access to any portion of the 3550-3700 MHz range if not being used by IAT or PAT users. GAA users share the available spectrum with other GAA users and have the lowest priority access to the CBRS band. Their operations must not cause harmful interference to users in the higher tiers.
The Spectrum Access System (SAS) is a key component of the CBRS sharing framework. SAS is responsible for managing and coordinating spectrum access among PAL and GAA users. SAS dynamically assigns and monitors available spectrum resources based on real-time demand and interference mitigation techniques.
By implementing this three-tiered sharing model and utilizing the SAS, CBRS enables a balanced approach to spectrum allocation, ensuring incumbent protection while allowing PAL and GAA users to share and access the spectrum efficiently.
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The FCC defines CBSDs as devices GAA and PAL tiers use to access the CBRS spectrum. CBSDs can also be referred to as Access Points (APs) or Radios. CBSDs may be a microcell or the combination of a Remote Radio Head (RRH) and a Base Band Unit (BBU). CBSDs are required to be certified with the FCC and comply with technical and operational requirements. For CBSDs to utilize the CBRS spectrum, authorization via a grant process must be followed.
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The SAS manages spectrum access by issuing grants to CBRS users. CBSDs must register with the SAS and request access to specific frequencies. The SAS evaluates requests based on factors like interference management and spectrum availability and, if approved, issues a grant. CBSDs must regularly communicate with the SAS through a heartbeat process to maintain their active grant status.
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Coordinated Periodic Activity among Sasses (CPAS) is a nightly process where all SASs share information and coordinate their efforts to enforce spectrum management rules and maintain a harmonized ecosystem for CBRS operators.
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Environmental Sensing Capability (ESC) is a network of sensors deployed along the U.S. coastline that detects the presence of incumbent users, particularly federal radar systems, in the CBRS band. The ESC provides real-time information to the SAS, which adjusts spectrum access for PAL and GAA users to prevent interference.
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CBSD Categories refer to the classification of CBSDs based on their power levels and deployment scenarios. The two main categories are Category A and Category B:
- Category A: These devices are lower-power CBSDs intended for indoor use. They have a maximum EIRP of 30 dBm/10 MHz. Category A devices are often used in smaller coverage areas, such as within buildings. If installed outdoors, Category A CBSDs must not have antennas over 6 meters high; if they do, they'll be classified and regulated as Category B CBSDs.
- Category B: These devices are higher-power CBSDs for outdoor use. They have a maximum EIRP of 47 dBm/10 MHz with antennas installed at a minimum height of 6 meters (19.685 feet) above ground level (AGL). Category B devices are typically deployed in wider coverage areas and are used to provide broader network coverage.
See “FCC 96.41 (General radio requirements) and FCC 96.43 (General radio requirements)”.
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A Domain Proxy (DP) is a middleman in CBRS networks that facilitates communication between CBSDs and the SAS. It is located on the network's core (EPC) and manages key processes, including the aggregation of requests and responses. By acting as a single point of contact between CBSDs and the SAS, the Domain Proxy simplifies communication, reduces overhead, and streamlines the coordination of multiple CBSDs with the SAS.
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A CBRS cellular network is a communication system that enables wireless connectivity for users within a geographical area on the CBRS spectrum. The network is designed to accommodate numerous simultaneous connections. The foundation of the network relies on three main components:
- User Equipment (UE): UE devices, also referred to as mobile devices, send and receive signals to and from the Radio Access Network (RAN). Examples include smartphones, tablets, cellular routers, and IoT devices.
- Radio Access Network (RAN): The cellular infrastructure that establishes and maintains connections between UE devices and the Evolved Packet Core (EPC). The RAN consists of CBSDs, antennas, and the backhaul network providing connectivity to the Evolved Packet Core (EPC).
- Evolved Packet Core (EPC): The EPC, also referred to as the network core, is the central nervous system of a cellular network responsible for coordinating data traffic and ensuring it reaches its intended destination. It separates data into packets and routes them to destinations like other cellular devices, external networks, or the Internet.
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Yes, the maximum EIRP limit for UEs is 23 dBm per 10 MHz bandwidth. This helps prevent interference with other wireless services and ensures efficient spectrum use.
See “FCC 96.41 (General radio requirements)”.
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No, for CBSDs operating under GAA, the SAS does not assign specific channels. Instead, the SAS manages spectrum allocation to ensure the protection of incumbent and PAL users from interference while promoting efficient spectrum use. The SAS does this by providing CBSDs with frequency ranges that they are allowed to operate within based on their locations and the availability of the spectrum. The CBSD is responsible for selecting the specific channel within the authorized frequency ranges.
See "FCC Part 96.41 (Spectrum Access System functions), Part 96.59 (Spectrum use notification from CBSDs), and Part 96.63 (Frequency assignment)".
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No, for CBSDs operating under GAA, the frequencies they are granted are not exclusively reserved for their use. GAA frequencies are shared resources available to all GAA users. The SAS must allow access to any frequencies not currently occupied by higher-tier users (i.e., incumbents or PAL holders) upon request from a GAA user. The SAS will deny GAA access only when these higher-tier users already use the requested frequency to protect them from harmful interference. The SAS can enforce the FCC's rules on transmit power to help mitigate the potential for harmful interference with other GAA users; however, the SAS is not obligated to provide, nor does it guarantee, protection from other GAA interference. GAA users are expected to deconflict among themselves.
For exclusive access to a channel, a PAL would be required.
See “FCC Part 96.35 (General authorized access use)”.
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The registration procedure in the CBRS is an essential step that allows a CBSD to communicate with the SAS and potentially gain access to the CBRS spectrum. Here's a high-level overview of this process:
- Registration Request: The CBSD begins the registration process by sending a Registration Request to the SAS. This request includes information about the CBSD, such as its identification, contact information, and technical characteristics. For example, it may include the CBSD's unique identifier (cbsdId), its geographic location, antenna characteristics, and other details required by the SAS.
- Registration Verification: The SAS receives the Registration Request and verifies the information provided by the CBSD. This could involve checking the CBSD's identity, ensuring that it meets technical requirements, or other checks as determined by the SAS's policies and procedures.
- Registration Response: Once the SAS has completed its verification process, it sends a Registration Response back to the CBSD. This response indicates whether the registration was successful or not. If the registration was successful, the CBSD is now registered with the SAS and may proceed with further interactions, such as sending a Spectrum Inquiry or Grant Request. If the registration was not successful, the response will typically include details about why the request was denied, and the CBSD may need to correct any issues and try again.
See “WINNF-TS-0016, 8.3 CBSD Registration Procedure”.
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The Spectrum Inquiry procedure in the Citizens Broadband Radio Service (CBRS) is a process that allows a Citizens Broadband Service Device (CBSD) to discover available spectrum in its vicinity. Here's a high-level overview of this process:
- Spectrum Inquiry Request: Once the CBSD has been successfully registered with the Spectrum Access System (SAS), it can initiate a Spectrum Inquiry by sending a Spectrum Inquiry Request to the SAS. This request typically includes the CBSD's unique identifier (cbsdId) and may also include other details, such as the frequencies or frequency ranges the CBSD is interested in.
- Spectrum Analysis: Upon receiving the Spectrum Inquiry Request, the SAS analyzes the current spectrum usage near the CBSD. This involves considering factors such as existing incumbents, Priority Access Licenses (PALs), and other General Authorized Access (GAA) users.
- Spectrum Inquiry Response: After completing its analysis, the SAS sends a Spectrum Inquiry Response back to the CBSD. This response provides information about the availability of the spectrum. It may indicate which frequencies or frequency ranges are available for use, and whether they are available on a Priority Access or General Authorized Access basis.
The CBSD can then use the information provided in the Spectrum Inquiry Response to make an informed decision about whether to request a grant for specific frequencies or frequency ranges.
See “WINNF-TS-0016, 8.4 CBSD Spectrum Inquiry Procedure”.
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The Grant procedure in the Citizens Broadband Radio Service (CBRS) is a process that allows a Citizens Broadband Service Device (CBSD) to request and potentially gain access to a specific portion of the CBRS spectrum for transmission. Here's a high-level overview of this process:
- Grant Request: After the CBSD has successfully registered with the Spectrum Access System (SAS) and has determined available spectrum through a Spectrum Inquiry, it can request access to the spectrum by sending a Grant Request to the SAS. This request typically includes the CBSD's unique identifier (cbsdId), the desired frequency range, maximum transmit power, and other operational parameters.
- Grant Evaluation: The SAS receives the Grant Request and evaluates it. This involves checking if the requested spectrum is available, ensuring there are no conflicts with other users (including incumbent users, Priority Access Licenses (PALs), and other General Authorized Access (GAA) users), and potentially deconflicting any overlaps.
- Grant Response: After completing its evaluation, the SAS sends a Grant Response back to the CBSD. If the Grant Request is approved, the response will contain a grant identifier (grantId), the grant expiry time, and possibly other operational parameters. If the request is not approved, the response will indicate why the grant was not issued.
- Heartbeat Procedure: If the Grant Request is approved, the CBSD will then begin the Heartbeat procedure, periodically sending Heartbeat Requests to the SAS to maintain its grant and confirm its operational status.
See “WINNF-TS-0016, 8.5 CBSD Grant Procedure”.
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The Heartbeat procedure in the Citizens Broadband Radio Service (CBRS) is a process that allows a Citizens Broadband Service Device (CBSD) to maintain its grant, confirm its operational status, and synchronize with the Spectrum Access System (SAS). Here's a high-level overview of this process:
- Heartbeat Request: Once the CBSD has been granted access to a specific portion of the spectrum by the SAS (i.e., it is in the "Granted" or "Authorized" state), it needs to periodically send a Heartbeat Request to the SAS. This request typically includes the CBSD's unique identifier (cbsdId) and the grant identifier (grantId).
- Heartbeat Verification: Upon receiving the Heartbeat Request, the SAS verifies the status of the CBSD and its grant. This could involve checking if the grant is valid, if the CBSD is still authorized to use the spectrum, or if there have been any spectrum availability or usage rules changes.
- Heartbeat Response: After completing its verification process, the SAS sends a Heartbeat Response back to the CBSD. This response confirms whether the CBSD can continue operating under its current grant. If there's any issue (e.g., the grant has expired or the spectrum is no longer available), the response will indicate that the CBSD needs to take further action, such as requesting a new grant or ceasing transmission.
The Heartbeat procedure is essential for maintaining the dynamic sharing of the CBRS spectrum and ensuring that all users can coexist without causing harmful interference to each other.
See “WINNF-TS-0016, 8.6 CBSD Heartbeat Procedure”.
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A CBSD may relinquish a grant if it no longer needs the granted spectrum, wants to request a new grant with different operational parameters, or when the device is being repurposed or temporarily taken out of service. This allows the SAS to manage spectrum usage effectively and reassign relinquished spectrum as needed.
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A CBSD may choose to de-register with the SAS in situations where it is being decommissioned, moved to a new location, or taken offline for a prolonged period. De-registration enables the SAS to effectively manage spectrum allocation and uphold regulatory requirements without factoring in inactive CBSDs.
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Yes, A CBSD can indeed register with multiple SASs for redundancy or failover purposes, but it can only receive grants and perform heartbeat exchanges with one SAS at a time. When operating, the CBSD must select a single SAS to interact with for spectrum access and ongoing grant management. This ensures that the CBSD is compliant with the operational constraints imposed by the SAS, which helps in maintaining spectrum efficiency and minimizing interference among various CBRS users.
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The role of a Certified Professional Installer (CPI) is crucial in the proper installation and maintenance of CBSDs. They are responsible for adhering to regulatory and technical requirements, accurately determining CBSD locations, and configuring operational parameters to minimize interference and optimize spectrum usage. Some of the key functions of a CPI defines include:
- Location: The CPI determines the accurate geolocation of the CBSD, which is essential for the Spectrum Access System (SAS) to manage spectrum allocation and prevent interference with incumbent users and other CBSDs.
- Antenna height: The height of the antenna above ground level is an important parameter that affects the coverage area and potential interference with other users. A CPI ensures the correct height is specified during the registration process.
- Antenna azimuth: The azimuth of the antenna, or its orientation in the horizontal plane, is critical for directing the signal towards the intended coverage area and avoiding interference with other users. The CPI is responsible for correctly specifying this parameter.
- Antenna gain and radiation pattern: A CPI must accurately define the antenna gain and radiation pattern, which are essential for determining the coverage area and potential interference with other users.
- Category: The CPI must correctly identify the CBSD's category (either Category A or Category B). The device category has implications on the operational parameters offered by the SAS.
- Frequency range and channel bandwidth: The CPI may provide input on the desired frequency range and channel bandwidth during the spectrum inquiry and grant request processes, depending on the specific deployment scenario and requirements.
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Additional Resources
