We’ve Seen This Interference Movie Before


Science projects can be so much fun. We all remember the science fairs when we were in school with volcanos, homemade playdoh, and a million other things. Science projects are also so important to life. Marie Curie, Jonas Salk and hopefully someone developing a COVID-19 vaccine soon come to mind.

However, public-safety communications should not be a science project. Mistakes in this instance can prove costly. If risks are to be taken, they shouldn’t be taken without adequate testing.

Unfortunately, that’s exactly what the FCC has permitted in its decision to allow unlicensed devices to share the 6 GHz band with public-safety and critical infrastructure industries (CII) microwave systems. By permitting such sharing without first demonstrating that co-existence can work in the field, there is a dangerous risk that this science project can have disastrous consequences.

We’ve seen this movie before. In 1981, WVEU-TV’s operations on channel 69 in Atlanta caused interference to adjacent land mobile operations. Years of work and incredible expenditures on the part of land mobile licensees ultimately led to an unsatisfactory outcome. Later, public-safety licensees were promised that Nextel’s conversion from MIRS technology to iDEN wouldn’t result in interference. This year, we will complete 800 MHz rebanding, a project that started in 2004 and was supposed to last three years to cure the interference that wasn’t going to happen.

The costs to public safety in attempting to detect and then mitigate interference are huge. Several years ago, it cost the city of Oakland, California, more than $100,000 (not counting internal staff costs) to prove to a cellular carrier that the carrier was causing interference, and even then the FCC had to become involved and threaten to shut down the carrier’s offending operations. Today multiple T-band licensees are fighting with recalcitrant TV stations over interference, even when it is clear that the TV station’s operations are secondary.

The FCC’s response to interference concerns in the 6 GHz report and order was to “encourage” a voluntary multistakeholder group. Unfortunately, this is another re-run. When carriers wanted to use power spectral density (PSD) instead of effective radiated power (ERP) for their power limitation measurement standard, the commission directed its bureaus to convene a forum to foster the conversation and further good-faith efforts among stakeholders. I was one of the participants in that forum, which the FCC held Nov. 7, 2017.

At the end of the forum, David Furth, deputy chief of the FCCs Public Safety and Homeland Security Bureau (PSHSB), summed up the discussions. Among Furth’s takeaways were the inability of agencies to afford the costs for detecting and dealing with interference; the need to continue the discussions, including development of standards for detecting and dealing with interference to reduce costs for these agencies; and the need to reconvene the forum group “on a semiregular basis.”

What has happened since the forum? Nothing. I invited the forum carrier participants to participate in another working session to be held at IWCE 2018. The few who responded declined. There have been no follow-up forums by the commission either.

It is abundantly clear that “voluntary” efforts such as recommended in the 6 GHz order do not work. What is also abundantly clear is that clearly delineated rules with consequences work extremely well. The best example is what we proposed in the 800 MHz rebanding proceeding and is codified at 47 C.F.R. §§22.972 and 90.674. This is what I call the “what if” rule. In other words, “what if” all of the things that we do to prevent interference don’t work, and we have a case of interference? How do we define interference, and what are the procedures and responsibilities with regard to fixing it?

The success of this rule has been terrific. Unfortunately, we failed in two areas in crafting this rule: identifying a bit error rate (BER) threshold (as we were then still mostly dealing in a public-safety analog world); and making carriers responsible for LMR licensee costs in going through this potentially expensive back-and-forth. But when used properly by licensees experiencing interference, the rule provides clear definitions and responsibilities, properly incenting carriers to cooperate.

The rule has been extremely successful in ensuring timely action by carriers, and the commission has rarely had to be involved — even then on a “light touch” basis. During the 2017 800 MHz Interference Forum, Furth said that the “what if” rule provides “important lessons for legislators.” Despite these important lessons, the FCC failed to include any such provisions in the 6 GHz order.

There are no urgent circumstances that necessitated the commission’s 6 GHz order. No delays in public access to 6 GHz would have occurred had the FCC required, not suggested, testing before deployment. Had procedures and responsibilities for interference detection and resolution been incorporated into the order, problems that we know will arise could have been handled efficiently and comprehensively. In short, there is simply no excuse for failing to deal with this important and known issue.

It is not enough to suggest that the commission’s rules will be updated based on the work of the voluntary working group or after experience is gained in the field. We are still waiting for the FCC’s rulemaking on ducting interference, which was promised in 1984, for which a study was launched in 1978 and was supposed to be completed by 1982 [Private Land Mobile Radio Service (Los Angeles ERP Limits), Report & Order, PR Docket No. 82-244, FCC 84-415, 56 RR2d 1352 (1984)].

APCO submitted a petition for reconsideration of the commission’s 6 GHz order. The Government Wireless Technology & Communications Association (GWTCA), in conjunction with five municipalities as well as other parties filed in support of the APCO petition. It is imperative that the commission reconsider this decision, view the potential consequences of public-safety interference through the lens of history and act accordingly

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