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Everyone Should Support Receiver Standards

April 19, 2022

A few weeks ago, the FCC issued a Notice of Inquiry to kick off a program for regulating the receivers in wireless communications. This may sound like an arcane and meaningless action to some people. But I congratulate the FCC commissioners for starting this action, as I see this step as absolutely necessary to our 6G future.

For more than 80 years, the FCC has regulated spectrum in the United States by defining the limits on the transmitter. Every transmitter will send out signals in multiple frequency bands, with the strongest signals in the intended band and weaker signals emitted as “noise” in unintended bands, outside of the licensed spectrum. So, for 80 years the FCC has assumed that they can regulate transmitters to be ‘clean’ enough that the unintended emissions are not harmful to other users.  

However, we are now running into many examples where the simple ‘regulate the transmitter’ approach is not working. Lightsquared found out the hard way that having a license to use spectrum does not mean that other users are unaffected. In that case, Lightsquared transmitters were very clean, but millions of GPS receivers were not able to distinguish between Lightsquared transmitters and the GPS satellites…so the entire Lightsquared business plan was kaput.

The recent fight between the airlines and the mobile operators is another good example. The FCC has licensed the band for use, and the 5G radios meet all the standards. But the airlines are concerned that their receivers are not selective enough; in other words, they are concerned that their 30-year-old altimeter receivers might be impacted by signals in the 5G band.  

When an engineer designs a receiver, the best practice is to aim for the best possible sensitivity. That means that using a wideband filter is normal.   Wideband filters usually  have lower loss than narrowband filters. That’s why GPS receivers and altimeters and TV receivers and other devices use wide filters…the engineer looked at the interference environment and uses the widest filter that he can. Unfortunately, engineers are not prophets, so they cannot predict the interference of a new 5G or 6G service that doesn’t exist today. So, without some guidance, radio engineers in all industries are likely to keep doing things exactly the same way that they have for 80 years.

Take a close look at the spectrum chart, and you’ll see that adding new 5G or 6G bands will be adjacent to some other kind of radio system…there are very few ‘white spaces’ left on the spectrum. Does anybody think that we won’t be squeezing in a few more 5G or 6G bands?   

The only reasonable way to make radios work in the future will be to regulate both transmitters and receivers. This will add cost to some systems, and will reduce the sensitivity of some receivers. We may even need to plan for old radios to be replaced over time, which clearly carries serious costs.   The FCC must be extremely thoughtful and listen to public input here…because this decision will impact almost every radio that is used in thousands of different applications. We can’t be too strict, or we will kill our GPS and broadcast TV and long-haul microwave services.  We can’t be too loose, or we will create more conflicts that will become increasingly difficult to resolve.

Hats off to the FCC for starting this effort.  Now, the gauntlet has been thrown down and everyone in the radio business should submit their inputs to the FCC to make sure that this project reaches the right level of regulation:  not too much, not too little.