Spectrum Sharing in
3.5 GHz Band
Citizens Broadband Radio
Service
Report and Order Issued
April 2015: FCC adopts rules for innovative spectrum sharing
techniques to create a new three-tiered commercial radio service
spanning 3550 MHz to 3700 MHz (3.5 GHz Band).
• The 3550-3650 MHz band segment is currently allocated for use by
Department of Defense (DoD) radar systems. The National
Telecommunications and Information Administration (NTIA) first
proposed making the band available for shared use in its 2010 “Fast
Track Report.”
• On March 24, 2015, NTIA filed a letter recommending a framework
that would reduce the geographic area of the zones by approximately
77 percent. NTIA’s letter also recommended the use of sensor
technology to permit commercial use inside the zones, providing a
roadmap to full nationwide commercial use of the band.
• Smart grid, rural broadband, small cell backhaul, and other point-tomultipoint networks can potentially access three times more
bandwidth than was available under our previous 3650-3700 MHz
band rules.
Facilitating More Spectrum Sharing
With the new rules, the Commission enables a new model that
uses modern technologies – spectrum sensing, cloud computing,
and others – to break down some of the old categories:
Federal vs. NonFederal
Allocation.
Carrier vs.
Private
Networks.
Licensed vs.
Unlicensed
Authorization.
Spectrum Access System (SAS)
• This federal/non-federal sharing arrangement is part of a
broader three-tiered sharing framework enabled by a Spectrum
Access System (SAS).
• The NPRM proposed that the SAS would accommodate three
service tiers:
Incumbent Access
Priority Access
General Authorized Access
Spectrum Access System (SAS)
The core functions that an SAS must perform:
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Determine the available frequencies at a given geographic location and assign them to CBSDs;
Determine the maximum permissible transmission power level for CBSDs at a given location and communicate that
information to the CBSDs;
Register and authenticate the identification information and location of CBSDs;
Enforce Exclusion and Protection Zones, including any future changes to such Zones, to ensure compatibility
between Citizens Broadband Radio Service users and incumbent federal operations;
Communicate with the ESC and ensure that CBSDs operate in a manner that does not interfere with federal users;
Ensure that CBSDs protect non-federal incumbent users consistent with the rules;
Protect Priority Access Licensees from impermissible interference from other Citizens Broadband Radio Service
users;
Facilitate coordination between GAA users to promote a stable spectral environment;
Ensure secure and reliable transmission of information between the SAS, ESC, and CBSDs;
Provide an approved ESC with any sensing information reported by CBSDs if available;
Protect Grandfathered Wireless Broadband Licensees until the end of the grandfather period; and
Facilitate coordination and information exchange between SASs.
Tier 1: Incumbent Access
Incumbent users represent the HIGHEST TIER in this framework and receive
interference protection from Citizens Broadband Radio Service users.
Protected incumbents include the federal operations, as well as Fixed Satellite
Service (FSS) and, for a finite period, grandfathered terrestrial wireless operations in
the 3650-3700 MHz portion of the band.
Phased in approach: During phase one, a large portion of the country will be
available for Citizens Broadband Radio Service use as soon as a commercial SAS is
approved and made commercially available.
During phase two, much of the rest of the country – including major coastal cities –
will be made available for commercial use when no federal incumbent use is
detected in a given area
Environmental Sensing Capability (ESC) will have to be developed, authorized and
deployed. ESC will involve systems of sensors that detect federal uses in and
adjacent to the 3.5 GHz band.
Tiers 2 (Priority) and 3 (General Authorized)
The Citizens Broadband Radio Service itself consists of two
tiers—Priority Access and General Authorized Access (GAA)—
both authorized in any given location and frequency by an SAS.
• As the name suggests, Priority Access operations receive protection from
GAA operations. Priority Access Licenses (PALs), defined as an authorization
to use a 10 megahertz channel in a single census tract for three years, will be
assigned in up to 70 megahertz of the 3550-3650 MHz portion of the band.
• GAA use will be allowed, by rule, throughout the 150 megahertz band. GAA
users will receive no interference protection from other Citizens Broadband
Radio Service users.
Tier 2: Priority Access
In the Priority Access tier, the Commission authorizes certain
users with critical quality-of-service needs (such as hospitals,
utilities, and public safety entities) to operate with some
interference protection in portions of the 3.5 GHz Band at
specific locations.
• A maximum of 70 megahertz may be reserved for PALs in any given license
area at any time and the remainder of the available frequencies should be
made available for GAA use.
• Priority Access Licensees will have more predictable access to spectrum.
• 10 MHz channel of unpaired spectrum, with census tract-level licensing
Tier 3: General Authorized Access
In the GAA tier, users are authorized to use the 3.5 GHz Band
opportunistically within designated geographic areas. GAA users
would be required to not cause interference to, and accept
interference from Incumbent and Priority Access tier users.
• GAA users will potentially have access to all 150 megahertz in the band in
areas where there are no PALs issued or in use and up to 80 megahertz
where all PALs are in use
• Under the license-by-rule framework, GAA users may use only certified,
Commission-approved CBSDs and must register with the SAS.
• Devices operating on a GAA basis must provide the SAS with all information
required by the rules – including operator identification, device
identification, and geo-location information.
Potential Bandplan
-13 dBm/MHz from 0 to 10
megahertz from the SAS assigned
channel edge
-25 dBm/MHz beyond 10
megahertz from the SAS assigned
channel edge down to 3530 MHz
and up to 3720 MHz
-40 dBm/MHz below 3530 MHz
and above 3720 MHz
Future Work
April 2015, FCC proposes further study:
Protection Criteria for in-band and out-of-band Fixed Satellite Service
Earth Stations
Appropriate Secondary Market Rules
How to define whether PALs are in “use” at a particular location
Future Work
May 2015, FCC issues a Public Notice:
• The wireless industry is developing a version of commercial wireless
LTE technology called LTE-Unlicensed (LTE-U) that is intended for
operations in certain unlicensed frequency bands. LTE-U could
operate in conjunction with licensed commercial wireless services
using a technique called Licensed Assisted Access (LAA) whereby a
channel in an operator’s licensed spectrum is used as the primary
channel for devices operating on an unlicensed basis.
• The FCC seeks information on these technologies and the techniques
they will implement to share spectrum with existing unlicensed
operations and technologies such as Wi-Fi that are widely used by the
public.
• A number of organizations have approached the Commission about
the development of LTE-U and LAA in the context of the 3.5 GHz and
5 GHz proceedings, which would make spectrum available for general
access and unlicensed use, respectively.
Links
Report and Order and Second Further Notice of Proposed
Rulemaking: https://www.fcc.gov/document/citizens-broadbandradio-service-ro
Public Notice: https://www.fcc.gov/document/oet-and-wtb-seekinformation-trends-lte-u-and-laa-technology