There has been a lot of activity over the last few weeks around both Land Mobile Radio Push-To-Talk (LMR PTT) and FirstNet/LTE PTT with the introduction of the first two flavors of what the 3GPP continues to call “Mission-Critical PTT” (MCPTT), which is a set of 3GPP specifications having nothing to do with being mission-critical. Ericsson claims the PTT it sold to Southern Linc meets all MCPTT specifications, and the PTT reportedly developed by Samsung and introduced by FirstNet (FirstNet PTT) also claims to be fully 3GPP-compliant.
The introduction of these first two MCPTT-compliant PTTs in the United States has people once again discussing the migration of LMR systems to FirstNet-only systems and doing away with LMR. As far as I am concerned, these discussions are premature. We have a very long way to go before LMR systems are no longer needed by the public-safety community, if ever, and while we have two vendors claiming their products meet all 3GPTT specifications, they are not in service and not being use by the first-responder community so we do not have any feedback from the public-safety community concerning how these products work in the field.
We don’t have any information about MCPTT-to-LMR integration for analog FM, P-25 conventional, and P-25 trunked, either. We don’t know if the FirstNet product is fully compatible with all existing approved devices or if new devices will be compatible with it. Because these are brand new offerings, there are other questions to be answered but I am sure we will learn a lot more over the next few months as products supporting MCPTT are rolled out and we hear what the public-safety community has to say. I am also certain some who write articles for a living will start building feature and function charts comparing these first MCPTT offerings with PTT offerings already approved and running on FirstNet. I am confident these questions and more will be answered in a matter of months.
However, there remains a substantial discrepancy between what is required by public safety and what MCPTT delivers. As far as I am concerned, LMR PTT will be indispensable for a long time to come. The holdup is off-network PTT, which is vital to the public-safety community in many types of incidents and as a fallback mode when one or more networks are out of service due to weather or other unplanned circumstances. Yet in the past few weeks, I have seen posts on LinkedIn and in an opinion piece (They have also published opinion and feature pieces which point out the need for true off-network PTT) in Mission Critical Communications magazine stating PTT over broadband does not really need off-network communications capabilities and, if needed, MCPTT specifications do include off-network communications with a feature known as ProSe.
What, exactly, is ProSe and how does it work? ProSe is talk-around over LTE and in my estimation, the current version of ProSe is absolutely useless for public safety and its needs. I will come back to ProSe in a moment, but first I want to comment on the Mission Critical article written by Tero Personen who is chair of The Critical Communications Association’s (TCCA) Critical Communications Broadband Group and vice-chair of its board representing Finland. The article starts out this way:
“Direct mode, also called device-to-device (D2D) communications — or more precisely, the lack of it — is seen to be one of the main risks in moving from narrowband professional mobile radio (PMR) technologies exclusively to broadband Third Generation Partnership Project (3GPP)-based solutions. However, at times, the root cause is lost in the discussion.
Why is the public-safety and wider critical communications sector so keen on direct mode in the first place? Their fundamental requirement is to have a connection at all times in all locations. Direct mode as we know it from the narrowband world has on one side enabled communications outside the network coverage area, be it rural or inside buildings, and on the other provided redundancy in case the network wasn’t available. Direct mode has offered the core group voice, some messaging, and via a gateway, network access. Despite offering inferior service compared to the network mode, at least in digital technologies such as TETRA and Project 25 (P25), the service has been acceptable, and the operational mode has been adapted to use it when needed.”
Fair enough, LMR PTT is about voice—lifesaving, always-available voice—and yes, it would be nice to have data and video unit-to-unit, but off-network cannot be replaced with the suggestions made in this article. For example:
“On a philosophical level, how the connection is established is irrelevant as long as the users on the field can rely on it, it does its job, and it is affordable. So, what are the options for providing connections to places without critical 4G/5G network coverage?
One category is to bring the network to the users. The normal solution is to extend the network coverage permanently by building new sites and introducing leaky feeders and other solutions for indoor coverage. More temporary solutions include the traditional cell on wheels or more advanced cell on wings (both known as COW). 5G introduces promising integrated access backhaul (IAB) for extending backhaul. Private Long-Term Evolution (LTE)/5G networks and isolated E-Utran operation for public safety (IOPS) essentially provide a private local network at the scene.
Another category is to look for alternative access methods. For rural areas beyond financially viable network coverage, an interesting option is 5G satellite connectivity, albeit with limited bandwidth but potentially large coverage areas. However, there are challenges to provide coverage to locations where satellite is not viable, such as in-building and underground.
For local area coverage, especially indoors, direct mode remains the last lifeline. The work is ongoing in 3GPP using vehicle to everything (V2X) new radio (NR) sidelink capability for D2D communications. This includes potential for network gateways and D2D repeaters (sidelink relay). By reusing V2X capability, the goal is to benefit from the economies of scale provided by the vehicle industry and thus catalyze the interest of industry to produce the required components and products.”
This article misses the point of off-network PTT by a mile. I wonder if the author has any real public-safety experience or has participated in any ride-alongs with first responders. He stated that public-safety networks can continue to be built out to cover what, the entire world or in this case the Untied States? Or when needed, public safety can wait for Cells On Wheels (COWs) or flying cells to arrive while a person is 100 feet down a well, deep in a cave, a sub-basement, or an underground parking garage. How about when the commander on the street is within network range and the fire fighter, EMS, or law enforcement officer is out of range inside a building?
This article and the postings on LinkedIn appear to have been written from a broadband-only perspective, not from the perspective of what public safety wants and needs. In 2004, FDNY was upgrading its communications systems after issues arose during 9/11. One upgrade was to join the New York City Wireless Network (NYCWiN), a broadband system operating on 2.5 GHz with 377 network sites designed to ensure reliable and secure access for first responders during multijurisdictional emergencies. The system did not cover much in the way of in-building communications and in one trial, fire department personnel were to drop a small repeater inside the structure as they entered. You won’t be surprised to learn that this still did not provide in-building coverage. When FDNY arrives on scene today, it switches to off-network communications for the entire operation and uses LMR. Moving to a FirstNet-only system and ProSe would not begin to provide the needed in-building coverage.
As mentioned, ProSe is in the 3GPP specs but today’s version of ProSe is not ready for prime time. It might be of value to teens inside a mall who can see each other and want to exchange pictures, but as I have said before, two people can yell farther than today’s ProSe will cover. ProSe is transmitted at ¼ watt, the same power as the smartphone, and on most devices the antenna is internal to the smartphone so the radiated power is below ¼ watt. Compare this to 5-watt, 3-watt, and 2-watt handheld LMR radios with external antennas. Which system do you think will pass the following off-network tests I developed for comparing LMR off-network to ProSe systems?
Test One: Street-Level
- expected range, 2-4 miles flat terrain, semi-urban areas
Test Two: In-Building
- street-level to sub-basement
- street-level to top floor rear
- street-level to middle floor rear
- street-level to street level around entire building perimeter
Test Three: Industrial Fire
- device to device
- fire IC to staff (anywhere on fire ground)
- staff to firefighters
- law to law
- law to Incident Command (IC)
Test Four: Wildland Fire
- air boss airborne to IC on the ground
- finance (ECC)
- base camps
FirstNet High-Power Devices
Except for Sprint’s 2.5-GHz spectrum, FirstNet is the only LTE network in the United States that has been granted permission to increase device transmit power to 1.25 watts but ONLY in public-safety Band 14. This restriction is included in the 3GPP specification and has been approved by the FCC. Perhaps at some point handheld devices could be developed to enable this higher power with an external antenna. Today the issue is that running a handheld LTE device at 1.25 watts would dramatically reduce the device’s battery life or the device would have to be far heavier and bulkier than today’s smartphones.
The term “migration” is being used more and more in reference to land mobile radio and this is not helping the public-safety community. Elected officials don’t think about LMR migration in technical terms or even whether it is viable, they think about cutting funds for LMR support, systems, and device upgrades, or that their jurisdiction will not have to spend the money requested to replace existing and aging LMR systems. This leads to frustration within the public-safety community and requires someone to gently explain to these elected officials that such a migration does not relate to today, or even to their term in office. Instead, LMR migration might happen someday or not at all, depending on what technologists can accomplish within what time period.
Public safety will continue to use both FirstNet and LMR until fire, EMS, and law enforcement chiefs are convinced they can trust FirstNet with the lives of responders answering calls in the field and when and if Talk-around or off-network communications on LTE can pass the above tests. I request that everyone writing about MCPTT and future additions to enable video, pictures, and data (currently called “Push-to-X”) discontinue use of the term “migration,” which is creating issues for those who have to fight for funding for their communications systems year after year.
Let’s instead spend the time and effort to figure out how to connect LMR to FirstNet PTT, how to ensure all approved PTT systems on FirstNet are fully interoperable, and to ensure the dwindling number of agencies not yet on FirstNet have an over-the-top PTT solution that is compatible with the flavor of MCPTT running on FirstNet and other PTT applications in use. PTT has to be totally seamless and work on LMR and FirstNet and it must enable agencies that have not joined FirstNet to access PTT services during multi-agency incidents. I don’t care what you call this type of PTT as long as it is not “Mission Critical Push-to-Talk.” I prefer “Public-Safety Grade,” a term the National Public-Safety Telecommunications Council (NPSTC) began using many years ago.
One comment I received about last week’s Advocate was that there are not many 4.9-GHz products for public safety to use. I have found that companies such as Ubiquiti (UniFi product line), Mimosa Networks, and others make a number of products capable of 4.9-GHz operation but in order to buy their point-to-point and other products set up for 4.9-GHz, customers must submit a copy of a valid 4.9-GHz license issued by the FCC.
I have used Ubiquiti products for a number of years on 4.9 GHz for clients and they work well. My favorite is its “bullet,” which can be attached to any antenna, dish, or other point-to-point antenna. After it is plugged into an Ethernet cable, programmed for 5, 10, or 20-MHz bandwidth using a PC or laptop, you are off and running. (Ubiquiti is not and has never been a client.)
In the same post I was informed that high-power LTE has been available in Sprint’s 2.5-GHz spectrum for some time, so perhaps I should amend my comment about High-Power User Equipment (HPUE) to state that 1.25 watts of power may be legally used in the 700-MHz Band 14 public-safety spectrum since the rules state commercial users can use this spectrum on a secondary basis when it is not used for public-safety in a given area or is only lightly used by public safety. There is, of course, a significant difference in coverage between high-power use on 2.5 GHz and high-power use on the 700-MHz band, with the public-safety band providing better coverage and higher data rates farther from the cell center.
NPSTC has sent letters to the U.S. House and Senate about the repeal of the T-Band giveback. You might recall that NPSTC provided two detailed reports addressing the T-Band issues, one in 2013 with an update in 2016. NPSTC dove into the issues of how many licenses had been granted for T-Band use in the eleven major metro areas and their surrounding areas, how many if any existing public-safety channels outside the T-Band might be available in each area, and costs involved in moving users and their systems to other spectrum if any other spectrum was available. The reports reveal that there are no appreciable public-safety channels that could be used to relocate T-Band users and if there were, the costs would be astronomical. Further, even if channels were available, existing T-Band systems would have to remain in place and operational until the new systems were fully proven, thus increasing system cost and time required to move existing users.
We are coming close to the deadline for public safety to begin moving off this spectrum but, as NPSTC has reported and others including the Government Accountability Office (GAO), the Chairman of the FCC, the IAFC, IACP, APCO, and others have reiterated, the right thing to do for public safety is to repeal the giveback of the T-Band and open it up for system upgrades and expansions that have not been permitted for some time.
As a follow-up to the NPSTC letters, members of the public-safety community need to let their Representatives and Senators know that the repeal needs to happen soon. Especially during this current nationwide crisis, agencies relying on the T-Band need assurance they will not have to scramble for spectrum in the near future. Many of you are familiar with my articles on this topic and if you would like to read more, recent and past articles on this subject can be found in the archives of the Public Safety Advocate that are maintained at AllThingFirstNet.com.
A final note. The National Association of State EMS Officials (NASEMSO) has published a COVID-19 policy guidance checklist for EMS agencies. This set of guidelines, including sanitizing instructions from the major LMR radio companies, is a must-read for all involved in Fire/EMS work during the virus crisis. NPSTC has posted this as a download on its website. I think it should be a must-read for everyone within the public-safety community.
Until next week…
Andrew M. Seybold
©2020, Andrew Seybold, Inc.