Public Safety LTE Deployments

Several weeks ago I gave a talk to the Northern California Chapter of APCO and I am currently preparing for my LTE 101 speech at the APCO Broadband Summit in Washington, DC next month. As I review my presentation and plan for the new one, I think it would be appropriate to share some of my observations about LTE broadband and how it differs from traditional conventional, trunked, and P-25 Land Mobile Radio (LMR) systems. We all use cell phones every day to make phone calls, send text messages, and for data applications, and some of us use commercial PTT services for administrative but not mission-critical PTT services. However, there are big differences between LMR systems and commercial wireless systems.

Some of you have used 3G data services from commercial operators so you already know the advantages of having wireless broadband capabilities available to you, even though you also learned that during incidents it is not always possible to make use of broadband due to network demand from civilians and the press. Those who have not yet tried wireless broadband will also find how valuable a tool it can be. For all branches of Public Safety, it is like giving sight to the blind (video) and providing better information to those responding to and at an incident. The idea of having a common broadband network available to Public Safety on a nationwide basis will change the way Public Safety responds to and handles incidents. It will end up saving first responders and citizens lives, and can even help keep an incident in check that could easily have escalated into a larger one.

Public Safety Broadband Spectrum

At the moment, Public Safety has access to 10 MHz of broadband spectrum in the 700-MHz band and the Public Safety community is lobbying hard to have an additional 10 MHz of spectrum allocated to Public Safety in order to have enough broadband spectrum to meet its needs. This additional spectrum will only be made available if Congress and the Executive Branch can pass and sign into law, a bill that will take the D Block (the 10 MHz of spectrum adjacent to the Public Safety spectrum) off the auction block and make it part of the Public Safety-only spectrum allocation. A lot of hard work is going into making this happen and the Executive Branch as well as many in Congress are headed in this direction but it will still take additional effort to ensure that a bill passes in both houses of Congress and is sent to the President for signature.

Meanwhile, some in the commercial community, and within the FCC, still maintain that the D Block should be auctioned to the highest commercial bidder and that this bidder should work with Public Safety to build out a nationwide system that would be shared between the commercial auction winner(s) and the Public Safety community. This is not practical for a number of reasons including the fact that during incidents demand for broadband services peaks for both Public Safety and commercial customers.

In the meantime, the FCC has granted waivers to some jurisdictions to begin building out portions of the nationwide broadband network in the existing 10 MHz of spectrum already allocated. Recently, we ran exhaustive tests on one such system in the San Francisco Bay area and determined, as was predicted by ourselves and many others, that 10 MHz of spectrum is not sufficient to provide Public Safety the broadband capabilities it needs at most incidents, and certainly not enough for a major, localized incident. I say “localized” because during these types of incidents the resources of Public Safety responders are usually confined to small geographic areas and the need for broadband services within and around the incident will be high, especially if video is used to help manage the incident. While we are not prepared to release our test results at this time, I will state that we found that within one-quarter to one-half mile from the center of a cell site, the maximum data rates available were in the order of 10 Mbps down to devices in the field and 6 Mbps from the devices back to a command center. When we moved one to two miles from the cell center, the data rate dropped to 6 Mbps down and 4 Mbps up, and by the time we were three-and-one-half to four miles from the center, the data rates had dropped to 4 Mbps down and 2 Mbps or less up.

This is lesson one for Public Safety: The further you are from a cell site, the slower the data rate, and at the edge of a cell, the data rates drop off dramatically. Another lesson from these tests is that when the network was overloaded, that is, we tried to push more data and video over the system than it could handle, not only was the last data or video unusable, it also rendered existing data and video transmissions that were already in use unusable or at least unstable.

LMR and LTE: Some Differences

LMR systems for Public Safety are designed to be one-to-many voice systems (some slow-speed data), usually with high-powered tower or mountain-mounted base stations, high-power mobiles for vehicles and even HT’s have what, by cellular standards, is considered to be high power. In addition, simplex, talk-around, or tactile channels are widely used and the HT to HT range is sufficient to penetrate into buildings or talk over distances of several miles. A typical HT has a power output of about 5 watts. Now compare that to an LTE device with a power output of 200 milliwatts. That is a BIG difference in power and therefore, LTE systems cannot be designed in the same way as LMR systems.

Let’s look at some of the differences:

LMR Base Station   / LTE Broadband Cell Site

  • High-level sites   /   Low-level sites
  • High-power transmit   /   Low-power transmit
  • Transmit as needed   /   Transmits 24/7 (all the time)
  • Coverage 20-40 miles   /   Coverage 1-3 miles
  • Omni-direction antennas   /   Sectored antennas (3 sectors per site)

Obviously, there are many different types of LMR configurations; I have chosen to use a plain vanilla configuration for the example here. One way to visualize the LTE system is that each tower and each sector on the tower transmits on the same portion of the spectrum and receives on another portion of the spectrum (FDD), and every cell site uses the same spectrum. This might equate to a sophisticated simulcast system with many different sites, and since all cell sites are using the same spectrum, there can be interference between two or more cell sites and this interference has to be managed. This is done in both the design and operational phases of building a network and this has to be factored in when building adjacent to Public Safety systems. Say, for example, City A built out a system and then the County built out its own. The areas of concern would be the overlap areas where the cell sites of the County system and the City system both cover the same area. Careful engineering is required to minimize this interference because it will result in even less data throughput.

Something that must be considered in the budget process is the fact that the electric bill for each site will be $200-$500 per month depending on the complexity of the installation. So if your system is to make use of 50 sites, you should expect to see electric charges in the area of $10,000 to $25,000 per month.

LMR Mobile   /   HT LTE Devices

  • High power (5 to 100 watts)   /   Low power (200 milliwatts)
  • External antennas   /   Mobiles external, handheld built-in antennas
  • Talk around/simplex   /   Must be in range of a cell site
  • Battery life: at least one shift   /   Depends on data usage
  • Channel change by user   /   Channel change by network
  • External spkr/mic   /   Built-in screen/display

You can already compare LMR and LTE-like devices by comparing your own HT to your own cell phone. Your HT has a large battery, an external antenna, and speaker and microphone. Your cell phone’s antennas (multiple) are built in, the battery is very small compared to your HT, and while most commercial devices have speakerphone capabilities, they do not have the same audio output as your HT since they are designed to be held up to your ear when talking.

Other Differences:

LMR /   LTE Broadband Backhaul

  • Wireline/control station   /   Fiber/microwave
  • Low capacity (voice slow-speed data)   /   High capacity (+30 Mbps per site)
  • Dumb networks (exception: trunked)   /   Smart cell sites/smart network core
  • Set and forget (routine maintenance)   /   Modify network perimeters on a real-time basis

There are many more differences but I have included the major ones here. In more urban areas where data capacity requirements will be heavier, more cell sites, closer together will be required.

One example of this is Santa Barbara County, which uses six high-level sites on VHF and simulcast for the County Fire Department. Verizon covers the same area with sixty to eighty cell sites, some of which are used to increase capacity in the City of Santa Barbara. My estimation is that an LTE system for Santa Barbara County will require between fifty and sixty cell sites in order to provide the required broadband coverage.

LTE broadband networks will cost more to build and to operate than LMR systems covering the same areas. However, these added costs will prove to be worthwhile by opening up a whole new way of sending information to and from the field and incidents. Video cameras will be an important tool for Public Safety as well as building plan downloads, and even routine license plate checks. In addition, field personnel will respond to incidents better prepared for what they are heading into, and more resources can be more quickly added to an incident, preventing it from escalating. Another advantage will be the ability to bring in outside expertise by sending video and audio to experts remotely from a scene. For example, suppose you are faced with a device that could be or is a bomb and your bomb squad has no experience with the type of device. There are bomb experts around the country and around the world that could be added to a live video feed and perhaps recognize the bomb type and assist your bomb squad in the proper way to handle the device.

LTE broadband will change the way Public Safety does business. The changes won’t be instantaneous; they will be gradual over time. The Public Safety community will also have to learn how to manage the bandwidth available during an incident. There will be plenty of applications available to assist, but no matter how much spectrum is available, it is still shared spectrum and priorities as to the type and amounts of data that can be used will have to be managed on an incident-by-incident basis.

I expect initial deployments to become overloaded at first as departments try using lots of video and data services over the network. There will be a learning curve, and it will take some time. However, just as using our smartphones for Internet access, texting, and voice are second nature to us (with others managing the network resources on our behalf), so, too, will Public Safety’s use of LTE. In my presentation, I showed several pictures of today’s command centers and mobile command vehicles and then pictures of what these centers and mobile command posts will look like in the future. To get an idea, visualize a TV studio or an ESPN vehicle parked next to a stadium where there is a ball game in process. The operators are constantly choosing which camera angle to provide the viewers, cueing up other scenes and even having instant replays available for viewers. The difference here is that the viewers will be those involved in the incident command structure who will want to see what is going on in real time to help them make better decisions faster.

Wireless broadband services for Public Safety will transform many things, giving personnel more information than they have ever had before. However, broadband will not replace voice. Voice is and will remain the mission-critical lifeblood of the Public Safety community. There is a truism that a picture is better than a thousand words and this will be the case in our LTE broadband future, but LTE broadband will not replace a voice radio when the message to be transmitted is, “Officer needs assistance!”

Andrew M. Seybold

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3 Comments on "Public Safety LTE Deployments"

  1. Very informative. Are you currently retained by any LMR, Carrier providers or jurisdictions who are working on LTE projects?

  2. My company was hired by the Cornerstone project to complete the capacity tests which are still in progress. As for LMR, carrier providers or jurisdications we have some RFPs in house which we are evaluating, what what the reason for your question? Our tests have been veteed by many different organizations and companies.
    Andy

  3. Any thought on the “range” with a 2-watt mobile 700mHz radio feeding a 3-6 db antenna on the roof???

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