800 MHz Post-Rebanding Interference – What You Need To Know


On November 6, 2017, the FCC held an Open Forum on Interference from broadband systems to public safety land mobile radio operations.  We were honored to have been asked to participate.

During the session, we were asked about our efforts to provide education to the public safety community about the issue.  We told the FCC about our half day interference workshops at the International Wireless Communications Expo (which we’ve done multiple times), presentations at numerous APCO meetings, and magazine articles.  The Commission urged us to keep getting the word out, and so this is the purpose of this blog post.

When we were part of the coalition that proposed what became known as the 800 MHz Consensus Plan, we repeatedly stated that rebanding would not totally “cure” interference, but rather would eliminate some levels of interference, but more importantly would allow for other steps to be implemented to assist in interference reduction.  For example, we said on May 6, 2002 in our FCC filing the following:

“However, the Commission must recognize that this re-banding will not result in 100%
interference-free operation. It will not be until manufacturers have developed a more “front end” limited radio, and public safety users have implemented new systems, that interference reduction can truly take hold. Even then, there is still potential IM interference to public safety and non-public safety users, although re-banding should lessen the incidences. The Commission must therefore make abundantly clear that carriers are responsible for resolving this interference, even after re-banding. Careful coordination of frequency use, such as that at the recent Winter Olympics, can
reduce the potential instances of 3rd and 5th Order IM products. Thus, in addition to re-banding (and limitation on cellularized systems as defined in the PWC 800 MHz proposal), the Commission should also make the following rule changes: (1) mandate IM ratings on mobile radios of greater than 75 dB for the band; (2) restrict the use of broadband hybrid combiners; (3) limit “power on the ground” in the band;
(4) require cellularized licensees to inform nearby Part 90 licensees which
may be impacted by 3rd and 5th Order IM products (which can be predicted prior to operation) of new operations.” (comments at page 29)
Thus, public safety entities must recognize that the rebanding effort is not the end of the story.  Rather, public safety licensees must be proactive to ensure that they proactively look for signs of interference, and properly report interference (as discussed below) when it is detected.
The FCC’s 800 MHz Interference Rules
The FCC ultimately adopted important interference rules for post-rebanding interference.  Specifically, Section 90.672 provides in sum that carriers must provide interference protection to Part 90 licensees that have a certain level of signal at a particular location, and the carrier may not degrade that signal more than 20 dB at 800 MHz, and 17 dB at 900 MHz.
When there is an unacceptable level of interference (as defined by the rule), there are specific steps that a Part 90 licensee must take in order to ensure that the carrier is obligated to remedy that interference.  Specifically, Section 90.674(a) provides that the land mobile licensee must report the interference to all carriers.  How does one do that?  The FCC required the carriers to set up a single point of contact for the interference problem to be report.  You MUST do so here: http://www.publicsafety800mhzinterference.com/CTIAWeb/
It is imperative that you use this website for the report, as using it entitles you to important protections, and imposes obligations upon the carriers.  Specifically, Section 90.674(b) provides that the carriers must conduct an interference analysis and take corrective action within 48 hours of notification.  Importantly, the section includes a list of affirmative corrective actions which carriers must take, including: (i) increasing the desired power of the public safety signal (note, this also applies to critical infrastructure licensees); (ii) decreasing the carrier signal; (iii) modifying the carrier’s antenna height; (iv) modifying the carrier’s antenna characteristics; (v) incorporating filtering by the carrier(s); (vii) changing carrier frequencies; and (VERY IMPORTANTLY)(vii) the carrier may need to supply “… interference-resistant receivers to the affected public safety licensee(s).  If this technique is used, in all circumstances, [carriers] shall be responsible for all costs thereof.”
Further, when the carrier cannot immediately eliminate the interference, the land mobile licensee may ask the FCC to order the carrier to shut down the interfering facilities where there is a clear and imminent danger, pursuant to Section 90.674(c)(3).
These provisions are incredibly powerful, but they are only available to a licensee if the licensee submits the interference report through the website.  Another important reason to take advantage of the reporting tool is that the “heavy lifting” of determining the source of the interference will be performed by the carriers.  This is important because there is no mechanism for cost recovery of your costs in resolving interference.
The Potential For Future Interference
As mentioned above, we cautioned that the FCC should limit “power on the ground” by carriers in 2002, and we did so again in 2015.  However, the FCC recently took the opposite action, allowing carriers to put more power on the ground.  The FCC’s Report & Order allows carriers additional flexibility with regard to power, and should be on the radar screen of public safety agencies.
FCC Seeks Comment On Technical Advisory Council Spectrum Policy Recomendations – ET Docket No. 17-340
The FCC is currently reviewing recommendations by the Technological Advisory Council (TAC) to the FCC in several white papers.  The TAC has recommended that the FCC adopt nine spectrum management principles that have the potential to significantly alter how interference is considered by the FCC.
What Should You Do?
Land mobile radio licensees in the 700, 800 and 900 MHz bands should be proactive in identifying potential interference.  The same goes for users in VHF and UHF.  Here is a list of proactive steps that you should take:
1.     Listen to your users.  When they report coverage problems in a particular location, do not assume that it’s something that you’ll have to “live with.”  Rather, document the location, date and time of the interference or coverage issues, and save it in a database.  You’ll be able to spot trends and problems, which will make later research easier;
2.     Use the reporting tool.  This imposes the requirements on carriers (as discussed above);
3.     Buy the most interference resistant radios.  As discussed above, one of the benefits of rebanding is that manufacturers are now able to make more bandwidth limited radios, which no longer cover what is now broadband spectrum.  While statistical information on interference rejection isn’t readily available, we are aware that Pericle Communications Company has performed multiple studies on typically available pubic safety radios.  Further, when issuing Requests for Proposals (RFPs), request information from proposers on this issue.  We’ve now worked on RFPs requesting this information, and it’s a powerful tool for comparative purposes;
4.     Urge your representative trade associations to get fully involved in ET Docket No. 17-340, and ensure that rules and regulations going forward protect public safety communications to the maximum extent possible.  Don’t be satisfied with mere comments, require active participation;
5.     Obtain as much education as you can on interference detection and prevention.  Viewing the FCC’s Open Forum On Interference video is an easy place to start.  We also perform educational seminars at IWCE every year, and when invited at other sessions around the country.
Interference is a dynamic, evolving area.  It requires everyone’s full attention.


2 thoughts on “800 MHz Post-Rebanding Interference – What You Need To Know

  1. 90.672 (b) does not permit 20 or 17 dB “degradation” of the performance of 800 or 900 MHz systems . Rather it requires that a 20 dB or 17 dB SNR performance be preserved for 800 and 900 KHz Public Safety and I/B operators respectivly.


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