FCC Shifts The Interference Paradigm

The FCC has released a Policy Statement that contains spectrum management principles for transmitters and receivers.

Why should you care?

This document represents a seismic shift in how the FCC has assigned responsibility for curing interference. In this regard, we started long ago with a standard of “last-in, fix it.” Accompanying that was the concept that the interference had to be “harmful.”  Unfortunately, defining harmful became quite difficult, with some believing ANY interference was harmful.  However, remember even in Part 90 we have for many decades separated systems based upon a desired signal being heard at 50 percent of the locations in the licensed area 50 percent of the time, having a non-overlap with a signal heard at 50 percent of the locations, 10 percent of the time (using the TV R-6602 curves).  Thus, there’s an assumption from the start that there are SOME locations within a licensee’s service area where interference will occur.

But then came Nextel, and its interference to public safety.  We determined that we needed to better define what interference was, and that determination resulted in the adoption of Sections 90.672-675.  But those sections were created at the end of the analog era, without sufficient consideration of the changes that the digital era would create.

While we’ve refined the protocols that we used to determine what signals are out there, we really haven’t changed much of anything in terms of responsibility for curing it (other than Sections 90.672-675).  With the FCC’s decision to allow spectrum sharing between 6 GHz microwave systems and unlicensed devices, and the interference that will no doubt result in the field (all representations from unlicensed interests to the contrary), the FCC is now creating a shift in the responsibility quotient.

Before, an incumbent experiencing true interference could point to the interferor and force them to “fix-it.”  But we made a slight change in that dynamic in Section 90.672(1)(i), where the FCC set a minimum signal level that the 800 MHz licensee must be receiving at the location in order to be entitled to protection.  At the time we (meaning my office and Jay Jacobsmeyer of Pericle Communications) encouraged public safety entities issuing RFPs for new portable and mobile radios to get from responding manufacturers information sufficient to determine the ability of the proposed radios to reject unwanted signals.  This came on the heels of Pericle’s work in evaluating then-available equipment, which showed a huge variation amongst Part 90 equipment, a variance that didn’t necessarily correspond with the relative cost of the radio.

Now, more than 15 years later, the FCC is taking that to the next level.  Specifically, the FCC is talking about “shared responsibilities” between licensees, which the FCC says should include:

(1) transmitters should be designed to minimize the amount of transmitted energy outside of their assigned frequencies; (2) receivers should be designed to mitigate interference from emissions outside of their service’s assigned frequencies and channels; and (3) radio systems should use good engineering practices to mitigate degradation from interference.

What this tells us is that the FCC is going to start looking at your radios and your system design when you have an interference problem, and your system ought to be “up to snuff” if you wish to be protected (or even if you’re the one causing).

While this is a policy document, and not new rules (yet), it is a significant paradigm shift, one to which wireless operators should pay much attention.  At the recent Annual Meeting of the National Wireless Communications Council (“NWCC”, the successor to the Land Mobile Communications Council a/k/a LMCC) of which we (the Government Wireless Technology & Communications Association or GWTCA) are a member, I asked Ira Keltz of the FCC’s Office of Engineering and Technology whether the FCC recognized that land mobile operators needed time to adapt their systems to this new responsibility, with equipment often being used for twenty years or more, and the significant costs that would entail.  He said that the FCC was well aware of these factors.  But be aware that while legacy Part 90 systems may still have a little runway left before interference and sharing decisions directly impact system operations and design, that runway isn’t endless.  And the sooner that system operators review their equipment and designs, and start make plans for the next stage, the better.

Public Notice:

Policy Statement (Original Draft):

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