Public Safety Advocate: FCC Receiver NOI; Will Broadband Replace LMR? (Yet Again)

Welcome to the last Advocate for the month of April 2022. This month’s FirstNet (Built with AT&T) statistics as of the 22nd show two significant milestones have been reached: There are now 3.3M FirstNet connections and 20.5K+ agency subscribers.

The first topic that warrants a discussion this week is the FCC release of a Notice of Inquiry (NOI) for Receiver specifications. As you may know, there have been FCC rules for transmitters used in Land Mobile Radio (LMR) for many years. The purpose of these rules is to assure transmitters stay on their assigned channel and do not put out spurious emissions. Spurious emissions occur when the transmitted signal drifts from its licensed channel and spews out noise on either side of the channel.

This NOI has some interesting implications for both LMR vendors and users. Prior to this NOI, many LMR receivers were designed to receive channels that are far apart. For example, in days gone by, LMR spectrum bands between 150 MHz and 174 MHz VHF were assigned to public safety, businesses, some paging, and other narrowband uses, with about 170 MHz of the band reserved for federal government use. Due to engineering constraints, early receivers and transmitters could not be built to cover the entire spread of spectrum so they were ordered for specific portions of the band. To change radios to different band segments, some only needed to be retuned but some required new components.

As engineers gained knowledge and became better at their craft, we began to see LMR devices capable of covering the entire band. An example of this was when the FCC added the T-Band above the 450–470-MHz UHF band. The T-Band provided eleven metro areas with some additional spectrum above the UHF radio band. This spectrum was dubbed the “T-Band” because in each of the eleven metro areas this new LMR spectrum was designated for TV stations. Even so, public safety and some business users were permitted to use this spectrum for LMR in these metro areas.

Thanks to Los Angeles County’s efforts, the T-Band was opened up to public safety. While based on radios used in the 450–470-MHz band, both mobile and handheld LMR units for the T-Band required different frequency-sensitive components.

Today, a single radio can cover the entire 450–512-MHz band with ease. Those designing LMR units learned how to build radios so both the transmitters and the receivers can be spread over an entire public-safety radio band. Remember that the transmitters still have to meet FCC specifications and be certified but there are no such specifications for the receivers. 

Receiver Issues 

Everything was fine until it wasn’t. As more, different types of radio systems with different types of modulation went into use, reports began coming in that there were instances when public-safety radios, mostly handhelds, entered certain areas officers were no longer able to hear dispatches or other radio traffic on the channel they were listening to. 

The most significant and most costly occurrence was in the 800-MHz band that was widely used by public safety and others. Nextel had convinced the FCC to convert some of this spectrum so Nextel could use some of the channels and turn them into another cellular radio system. The rationale for rearranging the radio channels in the 800-MHz band was to stop Nextel cell sites from interfering with public-safety radios. 

The cause of this interference was that cellular providers had placed their towers on high peaks (on tops of buildings) and Nextel built its towers much lower. The result of this was that when a police officer, for example, was near a low Nextel cell site, the officer was not able to hear any radio traffic on his/her radio due to interference from the Nextel system. The FCC ordered rebanding of the spectrum and Nextel was required to reimburse public safety for the costs. This rebanding effort went on for years and cost Nextel $billions. Rebanding also took careful planning—it is not possible to convert a fleet of hundreds of radios overnight. 

The next issue to have an impact on receivers was when the FCC required all LMR users in VHF frequencies (150-170 MHz, UHF 450 MHz) and some other segments of spectrum to use these frequencies primarily for narrowband voice communications. This time there was ample notice from the FCC and a firm date for completion of narrowbanding and many vendors started developing radios that would work on the existing 25-KHz channels. These radios were being designed to be reprogramed to move to narrowband channels (12.5 KHz) when it was time. Some agencies, LA Country Fire, for example, had to replace all its mobile radios because they were too old to be converted to the narrowband channels. There were some delays and some waivers were granted but in the end, everyone settled into this new narrowband LMR world. 

Wide-Band Receivers

LMR devices kept improving and receivers became capable of handling larger frequency spreads so they could move almost anywhere in a specific band. Then reports starting coming in that, for example, the Oakland Police Department (Calif.) was being interfered with by at least one cellular system in the area. It took a lot of testing and money on both sides of the discussion and I believe the issue was resolved when Oakland’s radios were replaced with a newer version of the same radio with better noise rejection. It is difficult to trace most interference issues and have them corrected. In Florida, communications agencies complained that a FirstNet temporary cell site was interfering with its 700-MHz LMR system. That, too, turned out to be caused by older radios in the system, not the public-safety FirstNet system.

Notice of Inquiry (NOI) 

I think receivers need to be tightened to better ward off interference from other systems, but they still need the flexibility to be usable over wide portions of spectrum. 

For example, in the 450–470-MHz band, all base station repeaters transmit on the low portion of the band and receive at 5 MHz higher. However, we also need these radios to work in off-network (simplex) mode. To provide off-network communications, the repeater will transmit on either the output of the repeater or the repeater will have dedicated off-network channels, which means the receiver must be able to receive channels over the entire band.

We are just entering this NOI period so we will have to wait and see what happens. This is an issue that affects both public safety and other narrowband users so there should be many responses. I am hopeful that we will see ideas from design engineers who know how receivers work and what can be done to make them less prone to external interference, and not executives from companies that sell radios and are looking for ways to increase sales.

We need to keep our eyes on what happens with this NOI. Hopefully, the results will help solve some interference issues without putting back limitations that could interfere with how public safety has been managing its narrowband LMR systems.

Will Broadband Replace LMR?

It seems like once a year or more we hear about how LMR radio channels will no longer be needed because broadband will be able to fully replace LMR. This year it started anew during IWCE 2022. Since then, I have read a number of articles and reports saying LMR will simply fade away because it will no longer be needed. 

Last week I reported on the FirstNet (Built with AT&T) announcement that it will be adding eMBS to the network. eMBS provides one-to-many capabilities, a feature of LMR that has been used for many years though it is new to FirstNet. We still don’t have any information on how eMBS will work or when it will be available. In talking with a number of savvy LTE folks, it appears as though a portion of Band 14 will have to be set aside a for eMBS. If eMBS is to be used only for PTT, the amount of spectrum would be in the neighborhood of 0.5 or perhaps 1 MHz in both directions, meaning it will reduce Band 14 from the 10X10 MHz it is now to 9X9 MHz. However, if FirstNet plans to provide eMBS that is capable of sending high-definition video, a lot more of Band 14 will have to be set aside.

One source told me that perhaps eMBS will require as much as 4 MHz in both directions, reducing Band 14 to a 6X6 MHz band, which might have some implications for network capacity. To be fair, we have no information from FirstNet on how eMBS will be configured so what I have been told may or may not be factual in all respects. The bottom line is that for the first time, FirstNet will be capable of sending information over FirstNet on a one-to-many basis. This would mean, for example, a video of a major incident could be broadcast using eMBS to scores of people simultaneously in real time. This would be important if, for example, there is a major wildfire and several people need to see the current condition so they can discuss the appropriate approach for dealing with the fire. 

Think of how useful this would have been during the Boston Marathon bombing. The police were able to send pictures of the bombers, but if they could have broadcast the pictures to everyone in every jurisdiction that touched Boston, they may have been able to capture the bombers more quickly. There will be many uses for eMBS, but just after the eMBS for FirstNet announcement, the talk started up again. “Wow, now FirstNet really does all of the same things as LMR does, so why do we need both?”

Neither the question nor the answers have changed. Some are restated below:

  • Having two networks provides an additional level of redundancy.
  • LMR systems have been built over the years to cover jurisdictions. While FirstNet may provide the same coverage, LMR’s higher-power base stations, repeaters, and higher-power mobile and portable radios are important additions.
  • Currently, no broadband network can provide talk-around or off-network push-to-talk, and indications are that broadband systems will not solve the off-network issue anytime soon. If broadband does solve this issue, will it provide the same level of off-network communications as LMR systems do today?
  • Graceful Degradation: Today, if an LMR system fails it will fall back to a trunked system then to repeaters. The last fallback communications capability is off-network or simplex. 
  • A broadband network, even if hardened, does not have a fallback.
  • FirstNet and other broadband networks do provide transmission for pictures, video, data streams, and more that cannot be duplicated on LMR. FirstNet has added a host of capabilities to make first-responder’s jobs easier and safer. 

The items above explain why I am pro-LMR/LTE coordination with the ability to use PTT over both. I would further like to see FirstNet become the true nationwide PTT network with LMR remaining local except for LMR systems that are tied to FirstNet for cross-system communications.

Will broadband replace LMR at some point in the future? Perhaps. When will that be? No one knows when or even if. Smart agencies continue to use both LMR and FirstNet in the field. As I have written before, I would like to see more integration of the two networks and when Next-Generation 9-1-1 (NG911) is ready, I hope it will be blended into the mix as well. 

Winding Down

This may be the end of April, yet if you follow the news, you will see reports of wildfires currently in New Mexico, Arizona, Colorado, and California. This is not even close to the start of what used to be a “normal” fire season. The west is in this situation because we are short on rain, snowpack is very light, winds continue to pick up speed, and humidity levels are low (as I write this, the humidity is 5-percent in Phoenix). All this means it doesn’t take much to ignite a wildland fire and once it starts, it often creates its own weather. High winds mean three things to firefighters: a faster rate of spread, fire hopping, and if winds are strong enough, helos and fixed-wing aircraft cannot fly to help personnel on the ground. 

There are reasons we now face fire season all year around but that is not a subject for the Advocate. I am mentioning the fires here because it appears this will be a busy year for first responders. I am writing this portion of the Advocate to acknowledge how hard firefighters work and how they head into danger while others are evacuating. Firefighters don’t often receive the recognition they deserve and it looks like this will be a very busy year for them. If you happen to see firefighters that are battling a fire in your neighborhood or working in the aftermath of a storm or flood, thank them even if there is only time for a thumbs up. 

First responders, each time you use your FirstNet device while you are on an incident, remember that FirstNet will also be busy as they deploy a variety of temporary cell sites when and where they are needed while they do what they can to keep existing cell sites up and running. FirstNet personnel report to incidents, deliver and set up FirstNet deployables to maintain emergency communications, and then stay to monitor the equipment. These FirstNet crews also deserve thanks for the support they provide. 

Until next week, 

Andrew M. Seybold
©2022, Andrew Seybold, Inc.


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