In petitions for reconsideration, wireless Internet service providers and car manufacturers go head to head over out-of-band emissions limits.

This was supposed to be a simple rule fix. Why are we still talking about it?

An unlicensed band at 5.8 GHz is heavily used for Wi-Fi, among other things. It is a particular favorite of Wireless Internet Service Providers, or WISPs, that provide point-to-point delivery of Internet services. Until recently the band was governed by two different technical rules, categorized respectively as “digital modulation” and Unlicensed National Information Infrastructure (U-NII). The rules varied in such essentials as frequency range, calculation of power limits, antenna focusing, and – importantly here – “out-of-band emissions” limits: a cap on energy produced outside the operating band.

An engineer could design a new device under one rule or the other, depending on her specific needs.

A change in 2002 made the rules more similar. Still, though, the digital modulation version allowed higher power in a focused beam, and also allowed higher out-of-band emissions, making it the favorite for many applications.

In 2013 the FCC proposed to combine the two rules into one. Following a lot of debate over individual technical requirements, it effected the combination in 2014. The new rule mostly retained the more stringent provisions of each predecessor, including the stricter U-NII out-of-band emissions limits. Done, the FCC dusted off its hands and turned to its next task.

Not so fast.

In came a boxload of petitions for reconsideration – seven, to be exact. Four of the petitioners, including WISPs, objected that the newly adopted out-of-band emissions limits were too low. In principle one can design a device for any out-of-band limit, but more stringent limits drive up the cost and weight, and may impair performance.

Also chiming in was an association of vehicle manufacturers and suppliers. Vehicle manufacturers? In 2004 the FCC had authorized a radio service for vehicles, including safety applications – Dedicated Short Range Communications (DSRC) – in the band immediately adjacent to the 5.8 GHz band. To date DSRC remains unused. With the band under pressure from the Wi-Fi industry, the vehicle industry promises to occupy it soon. The vehicle association asked the FCC to make sure it protected DSRC from nearby 5.8 GHz operations, but did not specifically challenge the new out-of-band limits.

The FCC responded last March by shrugging off the vehicle makers and relaxing the out-of-band limits, relative to the former U-NII rule, although not so far as the former less stringent digital modulation rule.

That order drew a strong objection from the same vehicle industry group, plus one other. Read it here. Concerned about out-of-band interference from 5.8 GHz into future DSRC receivers, they want the limits rolled back to the original U-NII values. They would make an exception, though, for the WISPs and other point-to-point users, who would be allowed the less stringent values adopted in March.

An association of WISPs also sought reconsideration of the March order, but with respect to a different U-NII band at 5.2 GHz. That pleading is here.

Both petitions are out for public comment. A recent Federal Register publication set the due dates at June 23 for comments and July 5 for replies. Interested? File your views at this website; use Proceeding Number 13-49.