Public Safety Advocate: Translating for LMR and LTE Worlds

Thu May 11 18:14:07 2017

A number of vastly different languages are spoken within the wireless industry. I don’t mean different languages such as English and French, I mean different groups within the same profession having their own way of describing their particular specialty.

This is particularly true with the LMR Public Safety and LTE/broadband worlds. As broadband comes to Public Safety there is often confusion about the meaning of a term. It is, perhaps, helpful to remember that Land Mobile Radio (LMR) was developed as two-way radio and put into use by Public Safety in the 1930s. LTE is still the new kid on the block having been designed as the fourth generation of cellular primarily for data and video. Voice services were added much later and are, in essence, using the LTE data technology since voice is converted to digital packets, transmitted, and then put back into understandable voice at the other end.

Although there are some statewide systems up and running, LMR systems are local in nature. They are usually designed to cover a local jurisdiction very well and they have been added to and enhanced over time. In many places today LMR systems have an advantage over commercial LTE networks covering the same geography in counties and cities, but LTE has better coverage over much wider areas including Interstates and major state highways. Currently, the greatest difference is that many LMR systems have evolved over time to provide coverage where it is needed by Public Safety including inbuilding coverage, while commercial LTE covers a much broader area. In many places inbuilding communications is handled via Wi-Fi off-loading rather than inbuilding LTE extensions although there are a number of LTE extensions or Distributed Antenna Systems (DAS) in major venues.

The premise of FirstNet is that Public Safety will be supported where needed. It is to Public Safety’s benefit that AT&T is making its entire existing network available as it builds out the FirstNet spectrum. This will enable users to experience the coverage that now exists and perhaps be able to assist in helping FirstNet and AT&T provide coverage where it is needed but not available today.

While all this is happening, it is important that the LMR and LTE communities be able to communicate effectively. It is also important that the LMR community becomes more conversant with the LTE/broadband world and that the LTE/broadband world understands the fundamentals of Land Mobile Radio. LMR is not going away anytime soon. Those claiming it will are giving Public Safety personnel serious problems as they submit their budgets for LMR systems to elected officials who see FirstNet/AT&T as a way to save money for their jurisdictions and don’t understand the differences between FirstNet and LMR. The elected officials are not steeped in wireless technology, most them only know wireless as in smartphones and tablets.

It is, therefore, important that the LMR and broadband communities speak with a common voice, understand each other, and are able to convey to those who hold the purse strings that these networks are complementary and will remain so for many years. This in turn means that both groups understand what the other brings to the party and they understand each other rather than speak over each other.

Some examples of terms meaning different things to different people come to mind right off the top. My least favorite concerns the term “Mission Critical Push-To-Talk over LTE.” Mission-critical implies that those within the Public Safety community can trust their lives to PTT voice over LTE. This is simply not true and won’t be true until AT&T can harden portions of its network and the FirstNet network, which will take time. Even PTT over LMR is not always on a mission-critical network, but the network is more mission-critical than today’s commercial LTE networks. Further, LMR networks offer fall-over or fallback modes. The number of modes differs depending on the type of LMR network but the final fallback mode is “simplex” or “talk-around.”

Most LTE-speak people’s eyes will glaze over when they hear the term “simplex” or “talk-around.” I have found that saying “peer-to-peer” and “one-to-many peer-to-peer” helps them better understand. However, they still have an issue when the LMR community talks about off-network and in-coverage of the network simplex communications. If, in LTE-speak, you are in range of a network your phone works. However, if you are not in range of the network it won’t work. If you are in range of the network, why in the world would you need to talk unit-to-unit without the network?

It takes a while to explain why organizations such as FDNY use simplex on a daily basis even when they are in range of their LMR system. First, it moves traffic off the network and second, if the incident is deep inside a building or sub-basement, simplex may be the only way to talk from the street to those inside. In that case you would have one handheld within network coverage and one out of coverage but still be able to communicate. Simplex or talk-around is one of the most difficult things for those in the broadband world to comprehend. The standards body for LTE is working on a technology called ProSe that is supposed to be the answer for off-network communications using LTE devices but so far it does not appear as though even the standards body truly understands unit-to-unit requirements.

If for no other reason, the use of simplex or talk-around should be enough to justify keeping an LMR system in place at least for the foreseeable future. What will happen in years to come no one knows, but in the meantime I see numerous vendors working on combination LTE and LMR devices to try to solve the two-device-per-person issue. It will be interesting to see how this plays out over time.

Other terms that are confusing to both groups include LMR base stations, repeaters, simulcast system, trunked systems, P-25 digital systems, talk-groups, time-out-timers, and many more. On the LTE side of things are the Radio Access Network(RAN), the Evolved Packet Core (EPC), IP, Asynchronous Balanced Mode (ABM), Access Class (AC), Quality of Services (QoS), and priority, pre-emption, and ruthless pre-emption, which seem to be used interchangeably even though each carries a different set of implications. For antennas, the term MIMO is confusing to LMR folks. Multiple Input, Multiple Output antenna technology has an impact on the number of antennas needed on a tower, on a vehicle, and in a handheld device. Today there is 2X2 MIMO and 3X3 MIMO, each offering more throughput and capacity, and work continues on adding even more antennas to an antenna array.

I spend a lot of time talking to both LTE and LMR folks and sometimes feel like many of us who understand both are becoming interpreters between the two disciplines. I have been in meetings where a commercial company’s field people and Public Safety communications people have been trying to understand the advantages and disadvantages of both as well as how to translate LMR operational requirements into LTE-speak.

Those in the LMR Public Safety world grew up in it and understand it so have somewhat of an advantage over the LTE folks because in addition to LMR, almost everyone in the LMR community is carrying a smartphone and even a tablet and understands a little more about broadband services than the other way around. Years ago those within the commercial industry would be able to relate because they would have used walkie-talkies as kids or what is now known as Family Radio Service (FRS) two-way radios.

Before FirstNet can replace LMR (if it ever does), a convergence will have to occur. LMR PTT will be bridged to FirstNet/AT&T PTT for both administrative and incident communications. PTT over LMR that is not mission-critical can still be a powerful tool to help disparate agencies or jurisdictions communicate over a common network. Top-level officials will be able to follow incidents using only their LTE device when out of their area or when not in uniform but out and about at meetings and other functions.

As AT&T and FirstNet put the broadband network in place there will be many opportunities for LMR and LTE folks to work together to provide gateways between LMR and LTE, and there will be opportunities to provide many different ways of assisting the Public Safety community. In order to do this efficiently, both groups need to understand each other.

I have seen no arrogance from within one group or the other nor have I seen any distain for the other group. What I have seen is a real desire for both groups to be able to fully understand each other and to work together to make Public Safety communications the best it can be. LMR and broadband or LTE complement each other and will be used differently to accomplish a unified goal: To provide the best possible communications for the Public Safety community no matter where or when.

Andrew M Seybold


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