What is the 3.5 GHz Citizens Broadband Radio Service?
Last year, the U.S. allocated 150 MHz of spectrum for fixed and mobile broadband use under the newly-created Citizens Broadband Radio Service (CBRS) in the 3550-3700 MHz band. To put 150 MHz of bandwidth into perspective, this is roughly equivalent to the total spectrum that each of the Big 4 U.S. wireless operators have licensed to date.  With 10 MHz channels, this is ideal for LTE TDD and small cells with transmitter powers of 1W/10 MHz EIRP for indoor use and as high as 50W/10 MHz EIRP in rural locations. This is great for MSOs who have the key locations, backhaul and power where people use data, either inside buildings or outside via their external cable infrastructure. For example, in metro areas, MSOs can place 10W/10MHz EIRP small cells on cable strands for great coverage. It is the first time that fixed operators will be allowed to use LTE in unlicensed spectrum.

CBRS is the world’s first three-tier spectrum sharing framework in which one or more Spectrum Access Systems (SASs) will actively manage 1) incumbents, 2) priority access licensed (PAL) users, and 3) general authorized access (GAA) users. Basically, the SAS will tell the Access Points, called CBRS Devices (CBRDs), which channels to use to avoid interference to other users in a given geographical area. CBRS contains both licensed spectrum, with seven PAL channels, and unlicensed spectrum, with eight GAA channels, in over 73K census tract areas across the US. The PAL license period is three years with an initial right to renew for a further three years. In areas where the auction for PAL is unsuccessful, all this spectrum becomes available as unlicensed (GAA).

Incumbents in the band include shipborne radars operated by the Department of Defense and receive-only fixed-satellite service earth stations. Wireless Internet Service Providers (WISPs), utilities, and other terrestrial users currently in the 3650-3700 MHz segment are required to transition from 50 MHz of spectrum to 150 MHz of CBRS. The main issue for use of 3.5 GHz in the coastal regions of the U.S. is the detection of shipborne radars used by approximately 30 U.S. naval carriers. However, these ships are normally stationed globally. To detect the arrival of one of these ships on either the East or West coasts of the U.S. requires building an Environmental Sensing Capacity (ESC) – a radar detection network. The ESC will inform the SAS which channels the radar is located on in a given area so that current users are moved to adjacent channels. Normally, the radars will only occupy one or two channels over a relativity small geographical area containing the current location of the ship. The rest of the spectrum is available to all.

Momentum for 3.5 GHz

The U.S. wide commercial timeline for 3.5 GHz use is dictated by the availability of the SASs, ESCs, commercial grade network equipment, and capable end-user devices. The recent Mobile World Congress (MWC 2017) in Barcelona, Spain showcased  the status of many of these time critical components. CableLabs hosted its own workshop there, inviting several of the key players in the 3.5 GHz space.  Many companies on the show floor demonstrated their readiness for 3.5 GHz.

Of course, the guarantee of success is not only the availability of technology but also the willingness of key players to adopt and bring consensus support for the opportunity - particularly for a U.S. specific band where wide adoption is key. In particular, this is key for the most important component of the technology – the smart phone. Recently, Verizon committed to 3.5 GHz in an interview with FierceWireless.

Equally, T-Mobile, Sprint and AT&T are eyeing LTE deployment in the 3.5 GHz band. All four of the US mobile network operators are members of the CBRS Alliance which is driving the LTE TDD use of this band for mobile.  CableLabs was one of the first organizations to join to help set the direction of CBRS for our members. Charter and Comcast are now also members bringing key MSO support.

The collection of these mobile operators and the larger MSOs with interest in 3.5 GHz will help create the interest among the tier one handset vendors, such as Apple and Samsung, to support this band. Actually, at MWC 2017, Sony has already announced the support of band 42 in their new handset for Asia which supports the first 50 MHz of the CBRS band. One terminal research web site, The Global Mobile Suppliers Association (gsacom.com), claims that the new Samsung Galaxy 8 in April will also support band 42 at its launch. This is compelling since it means the engineering “tweaking” of the handset antennas has largely been solved. Beside these antennas, the silicon support of 3.5 GHz has already been achieved by Qualcomm in their latest Snapdragon modem released in October of last year. All of this bodes well for 2018 and handset support of the new CBRS band 48.

Outside the key handset issue, it is expected that the SASs and ESCs will be up and running at the end of 2017, promising full spectrum availability across the U.S. in 2018. The PAL auctions are expected towards the middle to end of 2018, but in the meantime operators will have access to all the spectrum as GAA.

Again, there was no shortage at MWC 2017 of the availability of Access Points (CBRDs) both for indoor and external use from the likes of AirSpan, Accelleran, Juni, Nokia and Sercom. And, I am sure I missed others there as well.

On the SAS side, Federated Wireless and Google are probably the leading SAS providers at the moment. However, besides Federated and Google, other WinnForum members which were successful in gaining licenses from the FCC in the first phase include Amdocs, Comsearch, CTIA, Keybridge and Sony. The WinnForum is driving the standards for the SAS and SAS to SAS interconnections. Again, here CableLabs is also a member.

Customer Propositions

BGR found last year that the average speed of LTE in the U.S. was only 10 Mbps, placing us at number 55 in the World with Singapore at number one with an average speed of 37 Mbps according to OpenSignal’s data. Here the customers needs are met by external macro-cellular networks which lose speed as they pass thru walls. However, locating small cells inside buildings, where 80% of mobile data is consumed today, can offer speeds as high as 570 Mbps if all of the GAA spectrum (80 MHz) is used with 4x4 MIMO. Even with access to just two channels, 20 MHz, this will offer 7 times faster than the average LTE network here according to CableLabs testing with 2x2 MIMO. But why stop there? We can aggregate 3.5 GHz and WiFi to reach a potential 1.4 Gbps.

CableLabs’ UpRamp Fiterator® has already identified one company, Trinity Mobile Networks, which uses Multipath TCP to aggregate both WiFi and Macro cell LTE networks to combine the speed of both. While in 2015, SK Telecom in Korea launched “Giga cells” which combines their WiFi network with LTE to reach 1.17 Gbps speeds in Android phones.

And Finally, One Last Thought

3.5 GHz offers the potential for US operators to offer 5G connection speeds years before 5G! All of this bodes well for an exciting 2018 for 3.5 GHz and for our members to take advantage of this spectrum for both mobile and fixed plays. Remember everything is wireless and wireless is everything!