Analysis: Unlicensed Devices Can Coexist in 6 GHz Band
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Friday, January 26, 2018

Analysis: Unlicensed Devices Can Coexist in 6 GHz Band

Unlicensed devices can share the 6 gigahertz band without causing harmful interference to primary incumbent operations, according to an analysis submitted to the FCC by 10 companies that want the FCC to approve such sharing.

The “findings are clear: unlicensed devices can successfully coexist with the primary services present in the 6 GHz band,” said an ex parte filing in GN docket 17-183 reporting on meetings that representatives of the companies had yesterday with FCC Chairman Ajit Pai; Commissioners Jessica Rosenworcel, Mike O’Rielly, and Brendan Carr; and Louis Peraertz, a senior legal adviser to Commissioner Mignon L. Clyburn.

“New RKF Engineering report answers many technical interference issues re: unlicensed use in 6 GHz band,” Mr. O’Rielly tweeted yesterday. “Certainly work ahead but this needs to be a Summer @FCC NPRM!”

The analysis was done by RKF Engineering Services LLC and submitted to the Commission by Apple, Inc., Broadcom Corp., Cisco Systems, Inc., Hewlett Packard Enterprise, Facebook, Inc., Google LLC, Intel Corp., MediaTek, Inc., Microsoft Corp., and Qualcomm, Inc.

Last year, the FCC adopted a notice of inquiry to explore freeing up frequencies between 3.7 GHz and 24 GHz for 5G services (TR Daily, Aug. 3, 2017).

The NOI solicited comment on three specific bands: the 3.7-4.2 GHz and 5.925-6.425 GHz bands (which are known as the conventional C-band), and the 6.425-7.125 GHz band. It also sought views on other non-federal mid-band frequencies.

In response to the NOI, representatives of a number of 6 GHz band incumbents and those that rely on the spectrum, including public safety entities, utilities, broadcasters, fixed service operators, and fixed-satellite service providers, complained that authorizing proposed unlicensed or licensed devices in the frequencies would result in harmful interference to their operations (TR Daily, Oct. 3, 2017). At the very least, some said, it must be proven that such interference will not occur before the new devices should be permitted.

In its analysis, RKF Engineering Services noted that in the U.S., “the 5.925 to 7.125 GHz band (6 GHz band) is shared primarily by two services: Fixed Satellite Service (FSS) uplinks and fixed microwave (Fixed Service or FS) links. Portions of this band are also used by the Mobile Service (MS) for public safety and electronic news gathering applications such as TV Broadcast Auxiliary and Cable Relay Services. … The results of this analysis show that a national deployment of RLAN [radio local area network] devices (RLANs) in the 6 GHz band, using established RLAN mitigation techniques and regulatory constraints similar to those applied in the neighboring 5 GHz band, will be complementary in spectrum utilization to these primary services and will not cause harmful interference.”

“Unlicensed services will not cause harmful interference to Fixed Satellite Services (FSS) because the power levels of unlicensed devices at the satellite receivers are so low,” said yesterday’s ex parte filing from the 10 companies, summarizing the analysis’ findings. “Interference from existing Fixed Service (FS) transmissions significantly exceeds any potential interference that might be caused by unlicensed operations. RKF’s findings also demonstrate that unlicensed services can successfully coexist with the 6 GHz band’s FS incumbents. RKF directly addressed concerns that individual unlicensed devices situated on high floors, at close range, through a window, or other corner-case geometries may pose an unacceptable risk to FS receivers, and it concluded that these corner cases are extremely rare. And even when they occurred in the study, their impact was exceedingly small: in no case did the interference cause any FS link to fall below its availability design criteria.

“For mobile services, RKF’s study showed that a small impact to incumbent links is possible,” the ex parte filing added. “The study evaluated the introduction of unlicensed devices in a mobile services deployment scenario where the likelihood of interference impact was highest (i.e., in an urban environment with high population density, in the presence of Broadcast Auxiliary Service base stations and mobile, truck-mounted transmitters). Even in that worst-case scenario, unlicensed operations did not cause a degradation in service approximately 99 percent of the time, and in the remaining 1 percent of the time, the link margin could be maintained by the mobile operator in a manner consistent with the current operating and setup practices for these highly variable ad hoc deployments.”

The filing continued, “Unlicensed services like Wi-Fi have proven to be highly complementary to licensed wireless broadband services. RKF’s study demonstrates that unlicensed services can similarly coexist successfully with the range of licensed services present in the 6 GHz band. We believe that the need for new unlicensed spectrum is urgent, and we hope that providing a detailed and thorough engineering analysis unusually early in the process, before the NPRM stage, will aid the Commission in working quickly to meet that need.”

The companies that submitted the analysis were among 30 that joined in comments supporting FCC action to provide unlicensed access to the entire 5925-7125 MHz band, saying that such a step “is essential to meeting demand for the next generation of wireless broadband services. By opening this entire band to unlicensed radio local access network operations, the Commission will allow us to bring consumers faster service, lower latency, and more pervasive coverage, and allow the nation to reap the economic and public safety benefits that are associated with unlicensed technologies.”

Most of the companies that submitted the analysis are also members of an ad hoc coalition called the Mid-Band Spectrum Coalition that is seeking access to the 3.7-4.2 GHz band for licensed mobile services and to the 6 GHz band spectrum for unlicensed usage.

The ad hoc coalition’s members include Intel, Verizon Communications, Inc., T-Mobile US, Inc., Apple, Broadcom, Cisco, CTIA, Comsearch, Ericsson, Google, Alphabet Access, Nokia, Samsung, the Information Technology Industry Council, HP, and the Wi-Fi Alliance. —Paul Kirby, paul.kirby@wolterskluwer.com

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