Public Safety Advocate: Wireless Coverage Extension

It is often desirable to extend wireless coverage into areas that are not well covered. Those with experience in the Land Mobile Radio (LMR) world are familiar with communications range extenders, while FirstNet offers MegaRange ™ for extending public-safety spectrum coverage (Band 14 only).

Range Extension 

There are a number of reasons for extending both mobile and portable coverage and a variety of ways to increase coverage. One way to enlarge a coverage area is to use a range extender. These devices have been used for many years in LMR public-safety communications and more ways to achieve similar results are described below.

One of the first inventions started out as a Motorola PAC-RT (Portable Area Communication Repeater) , now called a “PAC-RAT.” Today, they are made by Pyramid and sold by several vendors. The PAC-RAT is a separate transceiver that mounts in a vehicle and is attached to the main radio used for voice communications. Generally considered to be a “dumbed down” mobile radio, the PAC-RAT receiver is not nearly as sensitive as a typical mobile radio and its transmit power is very low. PAC-RATs enable first responders with handheld radios to communicate over longer distances. Handhelds that need to talk back to the nearest base station talk to the PAC-RAT which, in turn, re-transmits radio traffic in both directions. With this configuration, the portable radio now has the same range as the mobile radio with its higher power and external antenna. 

Over the years, other ways were developed to extend an LMR system’s range and satellite receivers are often used. These are not satellites flying around the sky, they are receivers located in coverage areas where the handhelds and mobile devices can hear the base station but may not be able to transmit to it. By installing a remote (satellite) receiver as part of the network, the mobile devices’ range is also extended. Over time, agencies deployed many multiple receivers and among these receivers is a device known as a “voting” system. With this device, all of the receivers including the primary receiver are routed to the main radio site. The “voter” or “comparator” measures incoming receiver signals and selects the receiver with the best signal to switch to the network. 

LMR vendors later developed “trunked” radio systems and simulcast. Trunking is as close to cellular topology as a radio system gets. In a trunked system, all of the mobiles usually listen to a command channel. When one mobile or the dispatcher wants to reach a group of users, their radios are automatically moved to a different radio channel and they can then hold a normal Push-To-Talk (PTT) voice conversation.

When simulcast is added to this or other types of systems, all the radio sites in the system transmit on the same channel every time there is a call. This is tricky to set up and keep running since each transmitter must be synchronized with the others. When deploying the system, it is important that transmitter coverages do not overlap with other base stations’ coverage. Years ago, we built this type of system for the California Highway Patrol (CHP) in Los Angeles. After the system was set up and during optimization and synchronizing, we found a dead zone at one major intersection and none of the vehicles could hear the network. We learned the hard way that there were a number of overlapping transmitters at the intersection that cancelled each other out. 

At least one vendor builds in a vehicle technology that also extends the range of LMR systems and, for that matter, FirstNet/broadband systems as well. Cinetcomm systems are constantly monitoring both the LMR and FirstNet signals. If the vehicle is out of range of the LMR system but in FirstNet range, the LMR traffic is automatically routed over the FirstNet network where it is rejoined to the LMR system. If the vehicle is out of range of both the LMR and FirstNet systems, Cinetcomm can take this one step further by adding mobile satellite capability. In this case, the LMR and FirstNet connections can be set over satellite. Today, simulcast, satellite receivers, PAC-RATs and, of course, network extenders, all extend the range of LMR systems into buildings. However, these range extenders cannot turn a local LMR system into a statewide or any kind of nationwide LMR system. They are designed to add coverage within an agency’s primary coverage area.

Over the years, there have been other ways to extend LMR systems. These include use of passive antennas with one pointing at a base station and one pointing toward a dead spot. However, for the most part, extending range on FirstNet is totally different from extending range for LMR.

FirstNet Range Extension

There are a number of reasons people want to extend the range of the FirstNet network. First, cell sites are expensive and if there is not enough demand for service in a rural area it is a costly undertaking. Even so, FirstNet (Built with AT&T) has been addressing these problems and has accepted this challenge. Another major reason for extending FirstNet’s range is because as you move farther from a cell site, data speeds become slower in both directions. If the field device cannot hear or be heard by the cell site, all types of communications stop. There are other reasons as well and some parallel reasons for LMR range extensions. These include filling in gaps in coverage, improving or establishing inbuilding coverage, and more. 

There are also several ways to extend FirstNet range. For one, the Federal Communications Commission (FCC) and the 3GPP allow public safety to use higher-power field devices but ONLY when transmitting and receiving in 20 MHz of the 700-MHz spectrum reserved for public safety (Band 14). The permissible power level on Band 14 is 1.25 watts while typical wireless broadband networks are limited to a mere 0.25 watts. Band-14 devices are called “High Power User Equipment” (HPUE) but FirstNet (Built with AT&T) trademarked the term “MegaRange ™” to designate high-power-capable devices for Band 14. 

At present, only two companies have been certified by FirstNet to build and sell MegaRange devices. The first is Assured Wireless, the company that developed the high-power Band-14-capable chipset and makes and sells its own version of HPUE devices. The second is Airgain, which embeds the Assured Wireless high-power chipset directly into a roof-mounted antenna. More HPUE devices will be certified over time, and some vendors may be looking for ways to incorporate this high-power chipset directly into a smartphone and/or tablet. In the meantime, a sufficient number of tests have been run and enough agencies have been purchasing HPUE devices that we have a host of data verifying HPUE effectiveness and edge-of-cell performance levels. Basically, HPUE devices mounted on a vehicle with an external antenna will add as much as 80-percent to the coverage area of a Band-14 cell site. 

HPUE devices mounted in a vehicle and connected to a router could be considered a PAC-RAT-like device since most vehicular routers can form a “Wi-Fi bubble” around the vehicle. When set to Wi-Fi mode, this bubble enables communications using any smartphone or tablet within Wi-Fi range of the vehicle. FirstNet transmission and reception are handled by the vehicle with its MegaRange device and external antenna. 

There are other ways to extend FirstNet coverage and/or add capacity to the network in congested areas. One of these is the ability to alter the size and coverage area of a given cell site by electronically changing the angle of the antennas and/or expanding or contracting the area a cell site covers. 

Then there are the deployables that are staged across the United States. These include Cells On Wheels (COWs); Cells On Light Trucks (COLTs); airborne devices; small, easily-towed mini-cell sites; carry- in backpacks; and other packaged portable cell sites. These are designed to be used when FirstNet service is not available because of a major incident that disrupts service, and when a planned event is expected to draw large crowds and require extra capacity. 

There are also ways to extend coverage range using HPUE devices mounted in a vehicle or in certain fixed situations. Some Emergency Communications Centers (ECCs), Public Safety Answering Points (PSAPs), and Emergency Operations Centers (EOCs) have already installed HPUE devices as a fallback for fiber or other backend services. If the main incoming connection(s) fail, the HPUE installation will kick in automatically and the center will remain connected. This will also work when dispatch and other personnel must work remotely as many did during the Covid pandemic. Connecting home workers to FirstNet with an HPUE device will result in better connectivity and higher data rates.

Fixed HPUE installations could be used in a number of ways. Suppose, for example, you have one or more areas where your FirstNet coverage is blocked by a hill or some other obstacle. An HPUE device could be set up in the affected area to provide or expand coverage. If the HPUE is also attached to a Wi-Fi network in the area it will, again like the vehicle router, be able to provide FirstNet coverage to handheld devices by using Wi-Fi to the HPUE device. 

Conclusions

While there are ways to extend both LMR and FirstNet/broadband coverage, there will always be areas where it is not financially feasible or access issues prohibit building a new LMR or cell site. However, by using some of the techniques described above, these networks can be extended. Newer methods will hopefully provide much more effective ways to expand coverage in areas where needed. 

One more thing. I did not mention that LMR also provides off-network or simplex, unit-to-unit communications over a few miles, into basements and parking garages, and should be considered as yet another way to extend communications into areas where they are lacking. 

It took the LMR community many years to develop a variety of techniques to expand and/or add coverage through network expansion. I suspect that over time, FirstNet will also find more ways to increase coverage and capacity without having to spend $250K or more developing a site and then having to foot the bill for ongoing monthly costs for insurance, power, backhaul, and more. I will share further developments in coverage expansion with you as I hear about them.

Winding Down

This is the last Advocate of the first half of 2022, so I thought it might be a good time to look at what we have and have not accomplished so far this year. 

There are new board of directors and an acting CEO to serve while the search is on for a new CEO. My vote is for someone who knows his/her way around finances and administrative duties that has also served in frontline first-responder positions. A number of retired or ex-public-safety professionals currently hold positions with the Authority or FirstNet (Built with AT&T). I cannot help feeling that if this is, indeed, the Nationwide Public Safety Broadband Network, we could use some people in upper management who have all the skills necessary for serving on the Authority board. And to be effective, they need to have been there, done that!

There are some areas where I expected to see more progress than we have so far in 2022. Many readers can guess that the biggest “not met” goal is that of finally having a nationwide push-to-talk system that includes inexpensive, easy-to-build interfaces to local-area networks. 

FirstNet (Built with AT&T) has continued to turn on more public-safety Band-14 cell sites; add more certified devices and applications; formed an alliance with the Safer Buildings Coalition to work together to provide indoor coverage; and is adding to its user base and the number of agencies moving over to FirstNet month over month. 

This is particularly disappointing to me since those who keep touting the 3GPP standard for PTT over broadband have yet to show us a complete and cohesive approach to providing the nationwide coverage that should have been in place years ago. There are no provisions for priority in the 3GPP standard, and we are no closer to PTT over FirstNet, which should have been the very first nationwide, common, application. 

I have been hearing how this issue is being viewed and handled and it looks like whatever is put on the table will cost first responders more per-device, per-month than it should. When FirstNet was envisioned, there were two main objectives: The first was to build a true nationwide public-safety broadband network that includes metro, suburban, and rural areas. The other objective was to be able to offer services to public safety at a per-unit price that would prove to be both reasonable and obtainable. However, from the printed material I have seen for moving forward with nationwide PTT over FirstNet, it appears that in most cases the per-month, per-device price for PTT will be almost double or possibly more. 

Here are a few examples at various price levels. 

Today, from what I can surmise from talking to first responders and the vendor community, the average per-unit price for PTT is in the $5 range. 

If the pricing I have seen both in writing and in discussions holds, the per-unit price will almost double. A little math here: The following PTT charges are based on the number of first responders in an agency.

50 users          Today $250 per month. 
Proposed $450 per month ($9 per month per unit).

100 users:       Today $500 per month.
Proposed $900 per month.

1,000 users:      Today $5,000 per month.
Proposed $9,000 per month.

Note: These are NOT yearly prices, they have been calculated as per unit, per month. For total yearly cost for today and tomorrow’s PTT, multiply by 12. 

If these new prices are real and some are even higher, nationwide PTT pricing will probably be out of reach for most volunteer, small, medium, and large agencies

The combination of these proposed price increases and what appears to be a very complex method of setting up PTT interoperability makes me think there must be a better way. We already have several solutions that can be melded into an offering that includes the 3GPP standard PTT, if necessary. We could have a simpler nationwide PTT for about the same the per-unit prices being paid today.

I have to wonder if there will be any more progress during the rest of 2022. Judging from all of today’s activity, I think we will move ahead with network build-out; devices and applications development; and the addition of 5G. On the administrative side, the FirstNet Authority will hire a new CEO and begin planning for its next investment in the public-safety network. 

Still, my guess is that nationwide or Unified PTT still won’t be available though some progress might have been made. The holdup is not the technology, there need for discussions and agreements before Unified PTT is a reality. I would love to be proven wrong!

Until next week…

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