Public Safety Advocate: HPUE—What It Does, How It Works, What Is Available

How much and where will High-Power User Equipment (HPUE) devices provide additional coverage?

This week’s Advocate about HPUE is divided into sections. The first discusses the impact of using high-power user devices for Band 14 FirstNet in terms of coverage and data speeds, the middle section presents a little history and then explains some of the technology that goes into FirstNet and other LTE-based networks in non-technical terms, and the last section gives use cases for HPUE followed by a more in-depth discussion of some interesting products entering the market that are designed to enable FirstNet to support higher-power end-user devices. 

Impact of HPUE

First, we need to understand that high-power handheld devices will not be coming to FirstNet anytime soon, though I believe battery power issues including size, weight, and other considerations will be addressed and high power will be included in future handheld devices. HPUE draws a lot of battery power and is more suited for mobile devices that are not dependent on a self-contained battery. Several different types of mobile high-power devices have passed the rigorous testing required by FirstNet and conducted by AT&T and we will be able to use mobile HPUE this year.  

The next question is what types of FirstNet users will find this additional power to be of benefit and in what circumstances? Most obvious are FirstNet users in rural areas where cell towers tend to be further apart and data speeds are less consistent than in suburban, metro, and urban areas. HPUE could go a long way toward erasing some digital divide issues, which have become more serious since the pandemic. HPUE tethered to a home WiFi access point would provide great LTE coverage to the home. While use of Band 14 by non-first responders is secondary, once you understand that especially in rural areas, the amount of Band 14 bandwidth needed by public safety will not normally necessitate closing Band 14 to non-first responders. If Band 14 does need to be closed down due to a serious incident, the closure will impact only a limited number of cell sites in the affected area, not all of rural America. 

High-power devices installed in emergency vehicles will also increase coverage and provide higher data speeds in suburban areas, metro areas, and urban centers, especially in hilly terrain. If a vehicle is equipped with HPUE as part of a mobile gateway, and a WiFi hotspot is available from the mobile gateway, which is typically the case, the added range will mean better coverage and higher data rates for those within the secured WiFi range of the vehicle.

The closer a vehicle with high-power capabilities is, the better the coverage is inside a building or structure. While I do not believe using HPUE on FirstNet will negate the need for off-network voice communications, it can be a valuable asset for other types of communications. A high-power device with a hefty contingent of batteries packed into a portable briefcase for remote incidents would serve as a portable range extender, again to WiFi or perhaps even 5G services. While today’s mobile high-power devices are designed to extend the range of a single FirstNet device, we are in the very early stages of other devices coming to market in other forms. 

Many on the Land Mobile Radio (LMR) side of things are familiar with PAC-RT, a product first developed by Motorola that soon became known as pack-rat. This device is a separate radio mounted in a vehicle that is interconnected with the vehicle’s mobile radio. The object is to provide mobile transmit and receive capabilities to handheld devices in and around the vehicle. Users take the handheld with them when they leave the vehicle, which starts the pack-rat operation and provides handheld users with the same range and capabilities as when they are sitting in their vehicles using the high-power mobile radio.

PC-RAT systems are still popular with both law enforcement and fire service. The California Highway Patrol (CHP) has been using these devices for many years and recently upgraded to 700-MHz LMR pack-rats, and Nevada, Ohio, and many other states still use these range extenders. It doesn’t take much to imagine turning high-power devices into range extenders. If the FCC ever stops trying to usurp the public-safety 4.9-GHz band, this band could play a significant role in increasing coverage from a public-safety vehicle at an incident. 

High-power user equipment is a game changer. What excites me most is that while we have a few great products coming to market in this class, this is only the beginning of what HPUE will add to FirstNet Band 14. I expect to see a host of products in the next few years, including devices with more mobility, devices that are similar to LMR pack-rats, and some we cannot yet envision but which, I am sure, will be developed once the need is made clear.

Brief History and Not-Too-Technical Explanation 

Band 14 within the 700-MHz band was assigned to FirstNet when it was created in 2012. In September 2012, the FCC issued a report and order (PS Docket no. 12-94, 06-229, and 06-150) assigning the 700-MHz spectrum (763-788 MHz and 793-799 MHz), better known as the “D Block,” to the public-safety community. Along with spectrum already assigned to public safety (758-763MHz and 788-793 MHz), this created a total of 20 MHz of spectrum (10 MHz X 10 MHz) known as Band 14 to be allocated to FirstNet. If you are good at math, you will note that combining these two portions of spectrum results in more than 10X10. The FCC further created two “guard bands” of 1 MHz each between narrowband (LMR) and broadband (LTE) public-safety spectrum and license holders on either side. After the FCC reconfiguration of the upper 700-MHz band, this left 20 MHz of broadband spectrum that was then licensed to The FirstNet Authority.

There are some other twists in the FCC report and order, one of which is that this spectrum falls under FCC Part 90 rules (90.18 and 90.258) and not under commercial cellular rules (Part 22). This report and order issued by the then chief of the Public Safety and Homeland Security Bureau established the Band 14 power limit at 1.25 watts (31 dBm) even though the limitation for commercial cellular systems is 0.25 watts (23 dBm). The 3GPP standards body states it this way: “Commercial User Equipment on all bands approved for LTE will operate in power class 3 (+23 dBm). Devices operating in band 14 only may operate in power class 1 which is +31 dBm or 1.25 Watts and band class 2 which is for Time Division Duplex (TDD) as used in Sprint’s 2.5 GHz spectrum is limited to +26 dBm or 0.400 watts.” As a result of the 3GPP standards and FCC ruling that permits 1.25 watts on Band 14 only, FirstNet users enjoy a number of advantages over commercial users.

It has taken a number of years for the first vendors to develop products, have them certified by AT&T for FirstNet, and begin bringing them to market. I have mentioned Assured Wireless and its HPUE devices several times now. These devices, approved by FirstNet, are becoming available and have found their way into other products that offer further advantages. Before we delve into the products and what they provide, it would probably be helpful to look at how LTE networks work.

Let’s start at the cell site, or at the base station if you are an LMR person. Typically, the power output of each cell site can vary from 20 watts (43 dBm) to 69 watts (48 dBm) at the antenna connector. There are power loses in every cell site and transmit power loss is dependent on the type of site. A very helpful set of articles about transmit power loss can be found in the LTE Encyclopedia on the web. 

Next, most cell sites, unlike LMR sites, divide 360-degree coverage into three sectors of 120 degrees each. This is important not only for transmit power but because each sector has the same data send and receive capacity. In reality, each site provides the total of the capacity and data speed available in each of the three sectors. 

The cell site transmits at a much higher power than a smartphone or tablet. If the site transmits at 30 watts, for example, and a smartphone in range of that site is sending back information at 0.25 watts, it is easy to understand there can be issues between cell site transmitter range and handheld range. Most cellular systems are carefully engineered to minimize differences noticed by users. One reason for the differences is to provide better data speeds to the edge of the cell. Still, the best possible data speeds are available closer to the center of the cell’s coverage, speeds are still good mid-range, but speeds drop off toward the edge. 

Most cellular systems are designed so by the time you reach the edge of one cell you are moved to another, closer cell, except when you are in an area not built out with the number of cell sites found in metro and urban areas. Most people do not notice differences in signal strength as they move around simply because, unlike LMR systems, both the cell site and handheld device are constantly communicating with each other so the cell site knows the phone is in range before sending it a message. In the LMR world, it is not unusual for a handheld to hear a base station when it cannot talk to it. Over the years, this has been mitigated fairly well with satellite receivers, antenna patterns, and more black magic. LMR trunking systems are the one exception since the handheld or mobile device and the trunked radio system communicate with each other. 

LTE experts have spent years perfecting LTE systems based on limited-use device power. You might have heard the term “MIMO” and other LTE jargon. Basically, Multiple-Input and Multiple-Output (MIMO) is the art of using multiple antennas to pick up receive signals at the cell site that a single antenna might not hear. Other unfamiliar terms are used to describe advances but they are all based on extending the range to and from cell sites and increasing data rates and capacity of each cell sector. As mentioned, cell site and user devices are constantly chatting with each other so the cell system knows what user devices are in range and which cell site they are currently connected to, but there is another reason for this chatting. The cell site actually adjusts the transmit power in the user device up and down depending on where the user device is located and how much signal is being received by the cell site, and also to keep transmit power as low as possible to save user-equipment battery life. 

The cellular community is required to stay within the approved device transmit maximum power level of approximately 0.25 watts. FirstNet users on AT&T’s existing LTE spectrum also must abide by the 0.25 watts power limit. However, on FirstNet Band 14, the power limit is 1.25 watts which is, as several AT&T executives at have said, a game changer. One final point, the network still varies transmit output power of a high-power device when it is used on Band 14. In other words, these devices do not always operate at 1.25 watts. They only use maximum power output when needed, e.g., at the edge of a cell or when inside a building.  

Approved HPUE Devices and Availability

The first two HPUE devices approved for use on FirstNet are from Assured Wireless and they have been in development for many years. On its website, Assured Wireless describes its devices as having six times the power of standard LTE broadband devices, enabling three times the coverage area of traditional devices and an 80% reduction in Radio Link Failures (RLF), or the ability to remain connected to a cell site. 

The Assured Wireless website illustration shows a complete wireless modem with high power on Band 14 that connects to devices via a USB port. This modem can be used with existing mobile gateways such as the Cradlepoint and Sierra Wireless units, or it can be attached to a notebook or tablet mounted in a vehicle to provide additional power on Band 14.

This product will also show up in other devices. Airgain, Inc. has packaged the Assured Wireless modem directly into an antenna. This product, called AirgainConnect, is described as an HPUE Band 14 antenna-modem platform and it should be available in the second half of this year. This new antenna/modem combination was developed to eliminate some of the loss usually associated with a modem mounted inside a vehicle with antenna cables running from the modem to the antenna, which is typically 2 dBm on 16-foot cables according to Airgain. There is virtually no loss when the modem is mounted in the antenna. Combining modem and antenna in the same enclosure promises to provide the best possible performance. It should also be noted that since the antenna/modem combination also holds the other bands, FirstNet users can operate at the 0.25-watt power level on the rest of the AT&T LTE spectrum and still see additional coverage and data rates since there will be no loss due to antenna cables. 

Cell site transmitter/receivers had previously been housed in blockhouses at the base of towers with coaxial cable run to connect them to antennas at the top of the tower and transmit power loss was a fact of life. For a number of years now, antennas with built-in transmitter/receivers have been available and coax feed lines are being replaced with Ethernet cables, further reducing transmit power and receive losses.

The Airgain antenna connects to the vehicle router or modem using the Wide-Area Network (WAN) port via standard Ethernet cable. Since most routers/mobile gateways also need to be connected to a WiFi and a GPS/GNSS antenna, AirgainConnect provides the antennas and cables so the router/gateway continues to operate as designed while providing high transmit power on Band 14 and standard 0.25-watt transmit power on the other FirstNet LTE bands. Since the receiver is mounted in the antenna housing, there is some benefit in signal strength on the receive end as well. Airgain claims on its website that this combination of modem and antennas can provide up to two times the coverage radius available using a standard 0.25-watt router/gateway on Band 14 as well as additional performance gains on the balance of the FirstNet LTE bands. If it works as well as claimed, this is a significant advance in coverage and data throughput.

Vehicular Routers/Mobile Gateways

There will be demand for Assured Wireless and AirgainConnect devices from many agencies that are already using FirstNet and these products might even win over some agencies that have not yet made the switch to FirstNet. I also expect to see a number of other related products coming to market soon. As mentioned, mobile HPUE devices can be used as vehicular repeaters, high-power devices can be packaged in portable travel cases with batteries/solar cells, and many other configurations are possible.

The public-safety community will welcome the additional power and the way Assured Wireless and AirgainConnect devices are being configured to interface with existing routers/mobile gateways will certainly help first responders. Once we have completed our almost street-by-street coverage test drives described in a recent Advocate in which we are measuring FirstNet coverage in Phoenix and surrounding areas, we are hopeful of redriving many of the shaded spots or spots where coverage is less consistent due to terrain to compare our initial findings to coverage after installing HPUE devices. 

It appears one function of a Cradlepoint or Sierra Wireless router/gateway is that the captured data is kept in a cloud as we drive our route. We can download the results and see exactly where there are coverage issues. From what I understand at the moment, it appears we will not be able to measure the increase in coverage with HPUE devices for this generation of routers/gateways because HPUE and, in fact, all transmit and receive functions will be provided by the Assured Wireless device and the router/gateway will not be able to track coverage in the same way as a standalone router does today.

Having high-power devices will be a great benefit, especially when there needs to be a decision about which direction to take and having conclusive proof of coverage with and without high-power capabilities might help. You may recall my saying that public-safety professionals were all born in Missouri, the Show Me state! 

Assured Wireless and Airgain devices will change the way public-safety will use Band 14 not only in rural areas but in rough terrain, suburban, metro, and urban areas and will provide better inbuilding penetration when high-power devices become more portable. I believe this is the start of what should be some very exciting times and it will help make FirstNet even better, faster, and more compelling.

Winding Down

Loony Tunes Now in Serious Deployment

For ten years, Alphabet (which owns Google) has been working on a pet project to launch a constellation of radio-equipped balloons into the stratosphere to provide Internet access where it is not available on a regular basis. Project Loon, the plan to float balloons equipped with cell sites miles in the air, was not met with much enthusiasm and the idea has not caught on. However, in cooperation with AT&T, Loon LLC launched one of Google’s Loon balloons in Puerto Rico after the hurricane devastation there.

As FirstNet (Built with AT&T) continues to provide outstanding services across the United States using mobile Cells On Wheels (COWs), Cells On Light Trucks (COLTs), and airborne drones, it seems to makes sense to add Loon balloons to the mix. Loons are huge balloons with a solar-powered cell site payload that are designed to stay aloft for up to one-hundred days. After they are launched, their movement is calculated to follow a wind pattern or sometimes to remain in the vicinity of an incident.

It is easy to imagine how helpful Loons could be during major incidents where terrestrial systems have been affected. Given today’s situation with a nationwide pandemic, tornadoes, heavy rains in the Midwest, West Coast fire season fast approaching, and predictions of a severe hurricane season, it makes sense for FirstNet to be prepared with a variety of emergency systems that can be deployed on land and in the air. It is not unreasonable to expect the pandemic to still be with us through this summer and into the fall while we also face these other elements. 

This week is National Police Week. I congratulate all our first responders as well as those who should be considered first responders during this pandemic including nurses, doctors, hospital workers, truck drivers, store clerks, and so many more. Our military, including National Guard troops, is also in the battle with all the other people trying to keep us safe.

I suspect the high-power capabilities now available to growing numbers of FirstNet users will morph into a wide variety of devices that will, as others have said, be a game changer. I believe HPUE checks off one more of the many important pieces that need to find their way into FirstNet and the public-safety community’s arsenal of products and services available to our first responders.

Until next week…

Andrew M. Seybold
©2020, Andrew Seybold, Inc.