Public Safety Advocate: Is LMR Old and Out of Date? LTE the Future?

For the past few weeks I have been talking with folks in D.C., states, and locally about FirstNet and if and when it will replace Land Mobile Radio (LMR) systems. I have found that among those not directly involved with public safety and do not have much, if any, technical background, there is a great deal of confusion surrounding LMR, FirstNet, and the limited amount of spectrum available to us.

These issues include but are not limited to the perception that LTE and 5G represents the only wireless future and land mobile radio is an antiquated technology that is no longer needed. Further, they believe all spectrum regardless of where it is located in the radio spectrum continuum is worth a fortune and therefore should be converted to broadband spectrum as soon as possible so it can be auctioned. It is interesting that these are the same issues the Public Safety Spectrum Trust (PSST) and Public Safety Alliance (PSA) faced when they were first engaging with those in the federal government to convince elected officials that public safety needed more broadband spectrum but needed to keep its LMR spectrum as well.

It took a while but public safety gained the support of the governors’ and mayors’ associations. However, when FirstNet was passed, Congress required a give-back of the T-Band spectrum. Part of the reason for this was the belief that the spectrum in these eleven major markets, once vacated by public safety (Congress forgot about business users also authorized in the T-Band), would be worth $billions of dollars and that funding could be used to relocate the T-Band public safety users and pay off a portion of the U.S. debt. However, it has not turned out that way. Now there is a bill in Congress to forgive the T-Band give-back but so far it has not progressed as quickly as we would have liked.

All of the above has convinced me that many of the staffers and those who served in Congress during the years preceding the law that created FirstNet in 2012 have left Congress or are not in the same committees they were. The new guard, as it were, grew up with cell phones. That is all they know, I don’t think any of them have been exposed to handheld radios with push-to-talk-only capabilities, even Family Service Radios (FSRs) that can be purchased for less than $20 in most stores. Nor do I think many, if any, have asked for a ride-along with police or sheriff personnel. Instead, they believe their smartphone can do anything and everything needed by public safety. And when they have a dropped call or cannot access the network it is an inconvenience and they complain, but they don’t seem to realize that it is not the same as a police officer being shot at and needing back-up. In that case, not being able to access the network or not being able to communicate with others can become a whole lot more than an inconvenience.

Even those in charge at FirstNet will tell you that both FirstNet and LMR networks are vital tools for public safety. Most recently, the head of AT&T’s FirstNet efforts was featured and quoted in an article in Urgent Communications and reposted on allthingsfirstnet.com saying the following:

“Push-to-talk over cellular (PoC) already is being used to replace LMR in non-mission-critical scenarios, but learning from those experiences eventually will impact acceptance of MCPTT-standard offerings, according to Chris Sambar, AT&T’s senior vice president for FirstNet.

It will start with extended primary [users] in public safety, and it will move to first responders, in time,” Sambar said last month during an event sponsored by Sonim Technologies. “I don’t know how long that will take. I think there will always be a place for LMR, because it’s a great tool. I think [LMR] will start slowly moving to a backup technology, though. But it will take time.””

Even AT&T understands that both FirstNet and LMR are needed today and into the future to ensure the safety of our first responders. As Mr. Sambar stated, it is possible today to move some administrative and other non-front-line public safety personnel off their LMR systems onto push-to-talk over FirstNet but it will take some time, if ever, for FirstNet to become the only communications platform for public safety.

Looking at the Other Concerns

Is LMR an antiquated technology or a proven technology? LMR was developed and deployed starting in the 1930s and push-to-talk communications were used by the military during World War II and in every conflict since. Some of today’s systems are based on digital technology (P-25) but there are still analog FM LMR systems in use, particularly in smaller agencies. LMR has evolved and now P25 PTT includes group PTT, one-to-one PTT, and the ability to be cross-connected with PTT on FirstNet.

One of the most significant advantages of LMR today is that many LMR systems are much closer to meeting the public safety-grade criteria than FirstNet. However, it is FirstNet’s (AT&T’s) goal to move FirstNet, over time, as close to a public safety-grade network as possible. While some new standards have been developed or are being developed to add even more redundancy to FirstNet, the results of these new standards remain untested.

LMR, on the other hand, has the real advantage of multiple modes of operation. If an LMR system is up and running using multiple sites in one of several modes that make that possible, and one or more sites fail, these sites, if still operational locally, switch to local access. If the site fails completely, units in the area can still communicate with each other using direct mode or off-network communications. This type of fallback is vital to the robustness of LMR. Further, if a site is in standalone operations mode, any unit in range will be able to communicate through the site. In the cellular world today, even if a site remains up but disconnected from the rest of the network, it is not clear whether devices will still be able to use the site because the device IDs and access rights are normally validated in the network core.

The most significant disadvantage FirstNet and all LTE networks have today when it comes to push-to-talk are that off-network PTT is not possible today with LTE. If two units or a group of units want to have a PTT conversation they must be in range of the network and the network must be operational. With LMR, neither of these is required. Off-network PTT can occur within the coverage of a network when one device is in network coverage and one is out of coverage, and if all units are out of coverage. This is a vital function of LMR that must be provided for FirstNet devices if FirstNet is ever to replace LMR PTT functions as well as network-related functions.

What Is Spectrum Worth?

This is an issue for which there are many answers. My answers are based on the following criteria:

  • In what portion of the RF spectrum is the subject spectrum?
  • How much of it is available?
  • What other services will need to be relocated out of this spectrum?
    1. To where will they move?
    2. Who will pay for the relocation?
  • Is the spectrum in a portion designed to cover LTE or 5G?
  • Is it possible to make this spectrum available nationwide?
  • Is the spectrum usable in mobile devices? (antenna size, battery life, device size)
  • Who are potential customers and is there more than one type of customer that might be interested enough in the spectrum to make it more valuable at auction?
  • What other factors might impact the cost of the spectrum?

Let’s start with LTE frequency allocations. According to Radio-Electronics.com, the issue with spectrum allocations for LTE using Frequency Division Duplex (FDD) where the cell site transmits on one part of the spectrum and the device transmits on another (what we are accustomed to), is that there must be sufficient separation between the two portions of spectrum to prevent the receiver from being blocked by the proximity of the transmitter. The FDD chart includes band 31 sets of spectrum at 452.5–457.5-MHz and 462.5–467.5-MHz, both of which are located in highly congested LTE public safety, business, paging, and other LMR systems in the United States. But this band is limited to 5 MHz of bandwidth, which means the value of this spectrum for broadband is very much diminished.

There are also LTE spectrum allocations for Time Division Duplex (TDD) (see some of Sprint’s 2-GHz spectrum holdings). In this case, the cell site and the device transmit on the same radio channel but in time slices so as not to interfere with each other. In TDD, the lowest spectrum supported is band 44, which is 100 MHz of spectrum in the 703–803-MHz range. Since Verizon and FirstNet broadband and LMR 700 are already in this spectrum in the United States, it is not practical to try to make use of it.

The T-Band 470–512-MHz is not included in any of the FDD or TDD LTE spectrum allocations. It does not offer enough spectrum in any given city (12 MHz total) for a reasonable FDD LTE transmit and receive split and the chances of it being used for TDD LTE in my estimation are slim to none. Add to this that this spectrum is only available in eleven major markets and the rest of the country is using this spectrum for its original purpose, which was to provide channels for TV stations, and there is yet another reason to limit the value of the T-Band spectrum.

The questions then boil down to who would want spectrum only in eleven major metro areas, who would then pay the estimated $billions in relocation fees for public safety (not including business users), and to where would these public safety systems be relocated? At one point the FCC was talking about using the T-Band for low-powered TV stations and translators but companies that do that are not inclined to pay much for spectrum. If the FCC were to offer the spectrum to them for nothing we would have more of a problem because there would be nowhere to move T-Band users to and no money with which to move them.

The value of spectrum varies widely based on the answers to my above questions. If you remember back to the AWS-3 auction (which funded the $7billion starter fund for FirstNet with the bulk of the $Billions coming from AT&T), it generated $44 billion in auction revenue. The price paid for this spectrum was more than had ever been paid for spectrum per-MHz in the United States. If you fast forward to the 600-MHz auction it was not nearly as successful for several reasons. First, carriers had all decided that 5G small cells were the be-all, end-all for capacity and speed increases in metro markets. The 600-MHz spectrum is great for more of the same LTE systems already on 700-MHz and other portions of the spectrum, but only spectrum above 2.5-GHz is really suitable for small cell. Many TV channels went unsold, and the price paid for the spectrum that was auctioned was much lower than expected. Verzion did not win a single piece of the spectrum even though it was registered to bid, and it stated beforehand that it really wanted 5G spectrum, not 600-MHz spectrum. As it turned out, Verizon did not bid on FirstNet either saying it simply did not need the spectrum. Not all of the spectrum was bid on and won and the bidding totaled $19.8billion, well below AWS-3 receipts.

Those who believe spectrum, regardless of where it is located in the RF spectrum, is worth a lot of money do not understand the issues. To raise money at an auction it needs to have nationwide availability and be in part of the spectrum where LTE or 5G spectrum is in demand. To try to convert 150–170-MHz from Land Mobile Radio to broadband mobile would end up with no one at the bidders’ table. Perhaps there are better future uses for this spectrum but not today and not with it encumbered with many different classes of license holders. The same goes for the 450–470-MHz and 800-MHz public safety bands.

The law that created FirstNet included a provision that the 12 MHz of 700-MHz spectrum used for LMR public safety communications could, at some future time, be converted to more broadband spectrum but only for public safety. That would not generate any revenue and would cause even more problems with LMR systems in the 700-MHz band that are deployed coast to coast including entire states such as Michigan. It appears as though those who are elected and can change the wireless landscape with their votes lose interest in converting a lot of spectrum to broadband when they come to understand that the highest and best use for spectrum in some portions of the RF spectrum is not for mobile broadband.

The AM broadcast band (525 KHz to 1705 KHz) is good for AM radio but at night local stations sometimes have to compete with interference from stations in other cities. As we move up the band into the MHz-region, we find long-distance ship-to-shore, country-to-country, amateur radio, and other forms of communications in spectrum that is not at all suited for broadband services. Then we reach VHF, UHF, and higher and some of this spectrum is great for broadband but some, such as 600-MHz and 700-MHz spectrum is better for larger cells with more coverage—the higher the spectrum the less range. 5G is based on the premise that there will be many small cells that are part of the network and users will move from one to another seamlessly as with cellular. However, since they are small cells with a lot of bandwidth, they will be able to deliver more capacity and data speeds.

Some people could have become very rich if they had realized four or five years ago that the real value for spectrum would shift to 2 GHz and above. However, until only a few years ago, the concept of cellular was the same: more towers closer together, and over time adding microcells. While 5G is a logical move forward, it was not widely considered viable until recently and now every carrier, cable tv company, and others want to play in this space.

The value of spectrum to the federal government depends on how many companies want access to the spectrum and for what purpose. 5G and the Internet of Things (IoT) seem to be the big drivers today, which leaves spectrum such as the T-Band and, thankfully, the rest of the public safety spectrum as spectrum having value to be sure, but not enough for elected officials to see visions of national debt dollars floating before their eyes.

The Last Word

The UK has come to understand that in order to move its public safety community over to LTE in the next two years or so it will have to use Tetra for off-network PTT since LTE won’t be anywhere close to providing this capability.

Sonim has announced it will be providing off-network PTT using licensed P-25 channels and Harris’s XP-200p has four bands of LMR and FirstNet, too (once approved by AT&T). There will be more products coming, and a larger variety of options. At some point, the technology will enable a single device with lots of LMR capability and FirstNet with long battery life. Until then, public safety needs to be able to use LMR and FirstNet through different devices: FirstNet for information, visual prompts, video of the scene, and more; LMR for normal day-to-day voice communications that have for years worked and saved lives.

When we were all working with Congress and I was presenting at APCO broadband summits, I had a set of PowerPoints that compared and contrasted LMR and LTE. Perhaps it is time to dust them off, update them, and hold a few Wireless Universities again!

Andrew M. Seybold
©2018 Andrew Seybold, Inc.

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