3.5GHz Spectrum Sharing: Playing Together in the Sandbox

Wireless Wonk

3.5GHz Spectrum Sharing: Playing Together in the Sandbox

By Barlow Keener, Attorney  |  June 10, 2013

Spectrum (News - Alert) sharing is in; exclusive licensing is out. 

On Dec. 19, 2012, the FCC issued a Notice of Proposed Rulemaking opening the gates for spectrum sharing for the 3.5gHz spectrum. The FCC (News - Alert) proposed to use a database system, developed for unlicensed TV White Spaces, as the method for sharing. A total of 100mHz of spectrum will be available from 3550-3650mHz.  The FCC called the new 3.5gHz sharing proposal “Citizens Broadband Service.”  The focus being on the use of the spectrum by citizens.  

The FCC OET Chief Julius Knapp and FCC Chairman Julius Genachowski have been evangelical in their promotion of innovative spectrum sharing and encouraging sharing technology innovation. The FCC’s White Spaces 2008 and 2010 orders laid the groundwork for spectrum sharing, creating a new spectrum access system to help everyone play fairly with unlicensed spectrum. The spectrum sharing system is predicted by some to eventually be incorporated in all wireless networks, mobile and fixed, licensed and unlicensed consisting of a database that gives radios notice of spectrum ownership rights, and requirements that radios use information such as location and regular communication with the database. 

White Space database providers iConectiv (formerly Telcordia (News - Alert)), SpectrumBridge, and Google have an opportunity to provide sharing technology to mobile carriers – moving beyond White Spaces. Additionally, new receiver requirements with power limitations, strict masks to prevent interference spillover into other channels, were required for White Spaces. The FCC

White Spaces methodology was copied by other regulators in Europe, Africa, and Asia. Then, the White House issued the 2012 PCAST spectrum sharing report, supported by the Department of Defense. PCAST strongly encouraged sharing of 1000mHz of federal spectrum using LSA, ASA, and unlicensed methods. With the December 2012 3.5gHz NRPM, the FCC took the White Spaces spectrum sharing concept upstream from the TV UHF channel to 3.5gHz.   

The FCC 3.5gHz NPRM proposes three tiers of sharing: tier 1 for incumbents such as DOD (Department of Defense) radar and satellite ground station receivers; tier 2 is for protected access and includes critical use facilities, such as hospitals, utilities, government, and public safety; and tier 3 is for general authorized access for carriers using small cells and others.   

The FCC named small cells as the primary application for 3.5gHz spectrum sharing. Carriers are planning to deploy small cells, also known as femtocells, picocells, and microcells, in the mobile carriers’ radio access networks. The 3.5gHz spectrum is ideal for high-capacity, short-range propagation. The small cells are lower powered than larger mobile macrocells and cover a smaller geographical area. LTE release standards have incorporated small cells and RAN cellco engineers have named the combined use of small cells and macrocells, a hetrogenous network or hetnet.    

The hope is the small cells will more effectively handle the huge data demands of smartphones using LTE in the small cells at 3.5gHz. Most of the data is now being delivered using unlicensed 2.4gHz Wi-Fi. With LTE and small cells, the carriers can begin to meet this demand carried on Wi-Fi on their own networks rather than having the customers supplying Wi-Fi equipment and backhaul. The new small cell access can also eliminate or lower the restrictive cell phone data caps.

The 3550-3650mHz spectrum is currently used by DOD radars and fixed satellite service earth stations. The Navy radars cover 60 percent of the U.S. population. The radar is not used all of the time and therefore the concept is that when it is not in use, other private users can share the spectrum. DOD experts contend that in order to implement spectrum sharing, the radios will be required to perform spectrum sensing and the installed radars will need to be removed. Both of these requirements are technical hurdles that may be years away from feasibility. The FCC points out that small cells are short range and low powered and can effectively share spectrum with the radar. One proposal is to add 50mHz more, from 3650-3700mHz, currently used by fixed broadband wireless internet providers, thereby creating a contiguous 150mHz band for fixed wireless use.

Spectrum sharing was initially developed in 2008 by the FCC for White Spaces in the unused, cleared TV channels. The FCC’s White Spaces spectrum sharing methodology has since spread to other countries including the U.K., Ofcom, and the E.U. Regulators in other countries have developed various methods of priority use spectrum sharing such as Authorized Shared Access  and Licensed Shared Access. Now, for the first time, the FCC is going to wrestle through the new priority-based, second generation, spectrum sharing like ASA and LSA in the U.S.

The goal of spectrum sharing is to more efficiently use an increasingly valuable public asset. The 20-year-old method of allocating spectrum for mobile carriers is to auction exclusive licenses for the public’s spectrum. The carriers argue that the primary reason they have invested $10 billion annually in mobile RAN infrastructure over the past 10 years is that the exclusive spectrum license system gives carriers the assurance that mobile customers will experience a higher quality of service. Others argue that the exclusive licensed mobile spectrum is not used efficiently, that much of it is fallow and not built out, and that even at peak times in urban areas only 25 percent of the licensed spectrum is used. Spectrum sharing, they say, will solve the inefficient use problem.

Some advocates in the spectrum sharing debate support full unlicensed use of the spectrum just like 2.4gHz Wi-Fi. The proof of Wi-Fi success, they point out, is the large percentage of Wi-Fi data use by smartphones and the data cap limits required by carriers. Wi-Fi works for almost all businesses and home users. Each of these home or business locations installs and maintains a micro-RAN consisting of a Wi-Fi router connected to cable or DSL Internet using unlicensed spectrum without noticeable interference from neighbors. The argument is that if Wi-Fi, 2.4gHz and 5gHz unlicensed spectrum has been proven so effective, 3.5gHz spectrum should also remain very lightly licensed, or unlicensed.   

LSA and ASA sharing allow for efficient use of spectrum somewhere on the spectrum between exclusive licensing and completely unlicensed. For example, with LSA, a carrier licensee may be authorized for a higher, licensed priority service than other carrier licensees. If the carrier is not using the LSA spectrum in a particular geography, then other carriers licensed for a lower priority use of the spectrum are authorized by the database, in that moment of time and place, to use the service. The database informs the carrier licensees which spectrum is available in a particular geography and when that spectrum is available. LSA achieves the goal of spectrum efficiency by ensuring that the spectrum is always in its fullest use by all the licensed carriers.  

Mobile carriers, like Verizon (News - Alert), are contenting that a large portion of the 3.5gHz spectrum should be exclusively licensed through auctions to carriers for small cell LTE use. The mobile carriers concede, however, that a portion of the uncleared band now occupied by DOD radar and other incumbents should be shared using a database.   

Everyone is weighing in on the spectrum sharing including NAB, National Public Radio, MIT professors, the Satellite Industry Association, Google, Verizon, AT&T, T-Mobile (News - Alert), New America, TIA, CTIA, and the White Spaces Alliance. The issues are complex. It does not look like there are simple answers. However, the outcome will be significant because the proceeding outcome should create a new foundational methodology for assigning or licensing spectrum for the next two decades. Exclusive licensing of blocks of spectrum for single carrier use, may, it seems, become a thing of the past. 

The spectrum sharing questions are now open for resolution: Should auctions be used for exclusive licensing of spectrum? Should White Spaces database technology be used? What about spectrum sensing receivers, are they technically feasible in the near future in mobile phones? How should federal spectrum use be diminished or cleared for private users? Can the spectrum be shared effectively like Wi-Fi 2.4gHz /5gHz as unlicensed? And how can the new users of spectrum – whether exclusive, LSA, ASA, or unlicensed ­– prevent interference with the incumbent federal users like satellite ground stations?  

The 3.5gHz spectrum sharing proceeding may take years before an order is implemented, but the spectrum sharing policy issues are new and exciting for the wireless innovators and regulators.

Edited by Stefania Viscusi