Voice over Public Safety Broadband

The Politics and the Technology

As the FirstNet board addresses the architecture for the Nationwide Public Safety Broadband Network using LTE (Long Term Evolution), one of the issues concerns voice: what to include when. The different types of voice include dial-up for making phone calls, non-mission-critical push-to-talk, and mission-critical push-to-talk (PTT). Then there is off-network, or as the first responder community is accustomed to saying, simplex or talk-around, which is the ability to talk to multiple units without having to be connected to a network. Each of these is important for the Public Safety community, some more than others, and each presents its own technological challenges that will be discussed in more detail later. First, I want to concentrate on the politics of voice on this network.

If the various levels of government believe that the new Public Safety broadband network will be able to satisfy Public Safety’s requirements for voice as well as data services, local and state jurisdictions will stop spending money on their existing Public Safety voice networks that are and will continue to be critical to Public Safety. On a federal level, if Congressional leaders believe that the new network will be able to replace Public Safety voice networks they could convince Congress to require the Public Safety community to return their existing voice spectrum to the FCC so it can be used for other broadband networks. In point of fact, the law that provided Public Safety with the spectrum and the funding for the nationwide broadband network already takes the first step in spectrum give-back requiring agencies in the top eleven municipalities to vacate the T-Band spectrum they have been sharing with TV stations for many years—spectrum that is vital to their ability to serve the public in those areas.

With each level of government, the reasons for wanting to believe that this new network will replace today’s Public Safety voice networks are different but the results would be the same: Public Safety would lose vital spectrum, which would seriously harm their effectiveness and endanger them and the citizens they are sworn to protect.

The Local Level

Currently, the municipalities and counties of America are strapped for funding. Many Public Safety agencies have already seen their budgets cut. Some police and fire departments have lost personnel to these cuts, others have lost new and much needed equipment, and some both. Many municipalities and counties are funding the FCC’s unfunded mandate requiring some land mobile radio users, including the Public Safety community, to narrowband their radios. That is, they have to use less spectrum for voice—half as much per channel—than they had been using. While this mandate has been on the books for more than ten years, many departments have not yet upgraded or replaced their existing Public Safety radio equipment. Some of these upgrades require only software changes to each and every radio in a given system, but departments with older radios are facing the expense of having to replace these radios at an average per-unit cost of about $2,000.

Next the municipalities and counties are faced with having to continue to spend funds on their existing land mobile radio systems because their equipment is outdated, and in some cases update them for better coverage or join a regional system. Yearly costs include radio site rental, electrical power, and microwave, and other items need to be covered each month in municipal and county budgets, as well as communications personnel or two-way radio service shops needed to keep this equipment operational 24/7 no matter what. All of these items are a drain on dwindling budgets and we are already seeing that some elected officials who are finding out about this new nationwide broadband system are jumping to the conclusion that this new network will enable them to do away with their own voice networks, eliminate personnel needed to operate and maintain them, and save the municipality or county a significant amount of money. Therefore if voice, even if it were available on the LTE network from day one, is part of the initial roll-out requirements put forth by FirstNet, the result will be the deterioration of the existing mission-critical Public Safety voice networks, something first responders cannot afford to have happen.

The States

Many states are also faced with having to spend money to narrowband and many of them are in a position where they will have to upgrade or replace their existing statewide Public Safety radio systems within the next five years. In California, for example, the Highway Patrol is still operating in the 42 MHz portion of the spectrum. The good news is that radio waves carry further at this frequency, so the nationwide system will use a lot fewer radio sites than would be required to replace the system, which it is currently planning to do. The object is to combine the Highway Patrol and other Public Safety and state agencies on a single statewide voice system so that a single statewide radio system will replace the multiple systems in operation today, effectively saving the state considerable money. But first it will have to spend a lot of money it doesn’t have today. To replace the existing Highway Patrol radio system will require more than three times the number of radio sites and a smarter radio system, which will cost millions of dollars. At the moment, this project is moving ahead slowly. California is not the only state in this position.

Once again, if voice is named as a component for the first deployment of the Public Safety broadband system, I am sure that those who run the state governments will cancel any plans for radio system upgrades believing that this one new broadband system, partially funded by federal dollars, will solve their problem for them and significantly reduce their own need to spend money. This is a mistake that would also jeopardize the lives of our first responders, the citizens and, by the way, those within the state government who also rely on Public Safety protection on both a local and state level.

On the Federal Level

When we were working with the FCC, Congress, and the Executive Branch to obtain the spectrum, funding, and governance needed to build this nationwide, fully interoperable network, some of the obstacles we ran up against were:

1)     False claims that Public Safety already has a lot of unneeded, valuable spectrum that could be auctioned to help reduce the national debt.

2)     A claim that the spectrum Public Safety was asking for (worth about $3 billion) and the funding Public Safety was asking for ($12 billion) should both be used to help reduce the national debt.

Public Safety had to overcome other objections but these are two of the primary ones that required responses. Even so, during the process, various bills either being floated or introduced in Congress required Public Safety to give back some of its voice spectrum. Public Safety and its supporters fought this give-back successfully until the last few days when the compromise bill included the spectrum Public Safety wanted, $7 billion in funding, and a governance organization but also included the provision that within nine years the top eleven municipalities and surrounding areas would have to vacate the spectrum they have been sharing for years with the TV industry. This spectrum is vital to municipalities such as New York, Chicago, Boston, and LA, but the give-back is part of the law and the rationale for this was that the new network would be able to replace the spectrum Public Safety has to give back. At the time the law was passed, not even the experts in the LTE technology knew whether mission-critical voice could or would be supported on the new network. However, some of those in power within the federal government had been told that the network would support voice so Public Safety has effectively already lost valuable voice spectrum.

If those in power next term see that the Public Safety broadband network will support voice, or that voice is included in the specification for the first generation of the network, they could easily put more pressure on the Public Safety community to give back even more of its current voice spectrum allocations—allocations Public Safety cannot afford to lose for many years to come. The other issue that is not well understood in Washington is that most of the spectrum now occupied by Public Safety for voice is intermingled with other users including businesses, industry, taxi cabs, and alarm companies, and the spectrum in question is not well suited for conversion to broadband use. Yet because the laws and rules are made by those with little or no understanding of the technical reasons that converting the spectrum to broadband use is neither feasible nor cost effective, that won’t stop them from trying to take it back from the Public Safety community.

So to me the political dangers of declaring the Nationwide Public Safety Broadband Network (NPSBN) capable of voice services for Public Safety are many as are the risks. Public Safety cannot afford to lose any more of its voice spectrum. There are those within the technology community who believe that voice over LTE is possible very soon, while others, including me, are a lot more cautious. I would never say “never” in a debate about voice over LTE and its capabilities, but I am saying that until we have it, it works, and it is proven to provide 100% of the requirements of the Public Safety community, to include it as though it were real today would be a costly mistake for the Public Safety community at all three levels of government: municipalities/counties, states, and federal.

The Technology Reasons

In order to fully understand the issue of voice over LTE it is important to break voice down into three different components or types, and then add the term “mission-critical” to at least two of these. Mission-critical voice is what Public Safety uses today. It is vital to its operations, it is vital to its safety, and it is vital to the safety of those they protect. Mission-critical means everywhere, all of the time. It does not mean best effort, which is how commercial networks’ services are described. A commercial network’s best effort is NOT good enough.

Dial-Up Voice

Commercial operators provide wireless telephone service. That is, with your device you can receive a call or call a phone number anywhere in the world. You dial a number and if you are in range of the commercial network, you hear it ring and are connected to the number or to voice mail. Dial-up voice is the main function of voice over commercial networks but it is NOT the mainstay of voice over Public Safety networks. Today, Public Safety uses dial-up voice for non-essential communications between two people. Normal, essential voice communications is handled by Push-To-Talk or PTT services (see below). Today the only voice over LTE network provider in the world is Metro PCS, the rest of the networks are still relying on their 2G and 3G networks for voice services. Voice over LTE (VoLTE) is Voice over IP (VoIP). It is coming to LTE for certain, but even Verizon recently decided to delay its own voice over LTE service until 2014. To me this means that VoLTE is not yet ready for prime time or Verizon, the world leader when it comes to LTE deployment, would not have delayed its launch of VoLTE by eighteen months.

Public Safety networks do not include dial-up voice services. The Public Safety voice networks make use of push-to-talk voice and when they need dial-up voice they reach for a commercial cell phone. Unless they are involved in a major incident when commercial networks are overloaded, they make their voice call the same way you and I do every day. So while dial-up for Public Safety is an important form of voice communications, it is my belief that it should continue to be left to the commercial network operators that have been doing it for years and who have all of the roaming and billing platforms in place to make it seamless no matter where in the world we are.


The first type of push-to-talk is on-network, which means that the radios all talk through the network just as our cellular phones do. The network relays the voice to the dispatch center as well as other units on the same radio channel. Push-to-talk is the workhorse of voice for Public Safety and will continue to be of key importance in the future. PTT is faster than dial-up—push a button and talk. PTT is one-to-many, vital for Public Safety. Voice traffic on a Public Safety network is managed by real people in a dispatch center. Their job is to dispatch a call, again one-to-many so even if a single patrol car is to respond, nearby cars hear the call and the response. If additional assistance is required cars might start making their way closer to the incident location so they will be available to respond more quickly. Dispatchers mange the traffic on the network and assure that responding and other units are heard and information is passed. During times of heavy network usage, they are called upon to manage multiple incidents including routine patrols and other voice information by taking control of the radio channel and maintaining a military-type discipline when running the radio channels.

Off-Network Push-To-Talk (Simplex, Direct Mode, or Talk-Around)

One of the most important forms of voice communications for Public Safety is off-network or simplex push-to-talk. Today this usually occurs on separate channels that are not part of the network. This type of communications is used in the following scenarios:

1)     When units are together at an incident, they switch to off-network and are able to talk directly to others at the incident. This accomplishes two things. First, it moves this traffic off the network so the dispatch channel is available for other dispatches and radio traffic.

2)     Next, it enables the units on the scene to talk directly to each other, even when they are deep inside buildings or sub-basements where they might not be able to contact the network.

3)     If the incident involves multiple groups (e.g., police, swat, detectives, fire, and EMS personnel), each group usually has its own channel to coordinate its own activities without causing interference with the other groups.

4)     If the units are out of range of the network, they can still communicate with each other—perhaps not with the dispatcher, but with each other. This serves them well because they are still in communications and if a first responder needs help, he/she can communicate with others in the area. This is a mission-critical Public Safety requirement because if the Public Safety radio cannot reach the network it is a worthless tool. A fire fighter trapped deep inside a building who needs help and cannot reach a network must have off network/direct mode capability to call for help or could be doomed to death or serious injury.

Today Public Safety voice communications is channelized. That is, each department has certain channels for their use. Some are assigned for on-network dispatch, some for municipality-wide on-network communications, and some for off-network, incident-type communications, but all are vital to the Public Safety community and each of these serves a distinct and specific purpose. If a network fails, and even Public Safety networks fail, the Public Safety community can still communicate unit to unit. Usually the dispatch center can transmit both on and off-network and while off-network communications is not usually designed for wide areas, it does provide a back-up in case of network failure. In a commercial network or using the Public Safety broadband network today, if you are out of range or if the network fails or is congested, your wireless device is basically useless. This is not acceptable in the world of Public Safety.

One final point about Public Safety push-to-talk systems. Larger municipalities are usually divided into multiple dispatch zones and each has its own dispatcher or two assigned to it. In addition, there are usually several municipality-wide channels used for municipality-wide incidents (storms, snow, etc.), and for the Public Safety Brass to be able to travel municipality wide and still be in touch. As for off-network channels, it depends on what is available in the area. On the various radio bands (there are six different bands today), there are interoperability channels. These are different for fire, EMS, and law enforcement, but there are statewide and nationwide interoperability channels. They are not designed to handle the volume of communications needed in a major disaster such as 9/11 or Katrina, but they are designed so that units traveling to another jurisdiction can always have a radio channel available for emergency traffic or to be contacted while in route.

How many discreet radio channels are needed in any given area? That will depend on each area and how many channels are available for use. For example, in Santa Barbara County, the county fire department has six countywide dispatch channels and six additional off-network channels and the city fire department has three municipality-wide channels and two off-network channels. However, during our recent wildfires we ended up using eighteen on-network channels (county, city, forestry, and state), and 78 off-network channels—virtually every off-network channel available in the Southern California region. It is unknown at this point whether PTT over LTE can begin to support this number of discreet voice channels.

Voice Over LTE

Let’s start this section with the commercial operators. First, as mentioned previously, Metro PCS is the only U.S. network operator offering voice over LTE today and Verizon has delayed its launch by eighteen months to a projected date of 2014. Today your LTE phone, unless you are on Metro PCS, uses the network operator’s 2G or 3G networks for voice services and this will continue for some time. There are several reasons I do not believe the Public Safety network should include dial-up voice. The first is that it is in its infancy at the moment. Next, the commercial operators provide excellent dial-up voice services at very good prices. Since the FirstNet architecture includes multiple commercial networks in each device, the dial-up voice functions of the network, which are non-mission-critical in nature, would best be left to the commercial operators. Lastly, I am told by some very smart LTE engineers that adding dial-up voice to the Public Safety network will increase the cost of the network by up to 30% and the number of sites required by as much as 10%. Public Safety doesn’t have enough money to build the network it really needs so it does not make sense to me to use the extra money to add dial-up voice when it is available on at least four other networks.

Push-To-Talk over Commercial Networks

AT&TSprint, and Verizon all offer push-to-talk over their networks. Moreover, their PTT mimics a lot of the same functionality required by Public Safety. However, theirs are best-effort networks and not mission-critical networks, so during times of heavy congestion due to incidents there is no guarantee that Public Safety could even access a commercial network let alone its PTT capabilities. Now add to that the fact that each network is using a different PTT technology, which is NOT cross network compatible, and you can easily see that PTT over commercial networks is neither mission-critical nor interoperable across the networks. Sometime in the future I believe that this will change just as it did for voice, text messaging, and MMS, but for now this remains a problem for the Public Safety community. The off-network capabilities of the commercial networks today can be answered with two words: NOT AVAILABLE. When you are out of range, your wireless device is merely a paperweight!

Voice on the Public Safety LTE Broadband Network

As you can see, even dial-up voice is in its infancy on commercial LTE networks and it will be many more years before it is available on top tier networks. PTT is in disarray since each network has its own version of PTT and these systems are not compatible. While there is work being conducted by the Public Safety Communications Research (PSCR) organization in Boulder, Colorado, part of the National Institute of Science and Technology, and the NTIA within the Commerce Department, so far, we do not have any definitive solutions for Public Safety-grade PTT over LTE.

Many vendors in the Public Safety community have already been touting PTT over the Public Safety network and PTT bridges between the LTE network and the voice networks (usually the P25 digital technology for voice used by Public Safety). Harris, Alcatel LucentMotorola, Cassidian, and others have been demonstrating PTT over LTE and cross network LTE for the past year. However, once again, each vendor is using a different technology for its PTT solution. These solutions are not compatible with each other and it does not appear that there is any effort underway to come up with a common air-interface for PTT over the Public Safety LTE broadband network. Until that work is completed, if it is ever started, and a common interface is decided upon, the use of PTT over LTE will remain proprietary to each vendor.

At least in the world of Public Safety narrowband voice, there are only two standards: FM analog (the older technology) and P25, the new digital technology. Most land mobile radios on the market are capable of running both technologies. This is not an ideal world for sure, but it is better than four or five vendors offering PTT over LTE, none of which are compatible with the other. So if you look at the timeline I have developed below, you will see that I am convinced that a common PTT air interface for Public Safety LTE will not be available until at least mid-2015, and it will be 2018 before we see on-network mission-critical PTT voice services. Therefore, to include voice over LTE for Public Safety as a requirement for the initial nationwide Public Safety broadband network at this juncture is premature. I will admit that a few within the Public Safety community do not share my pessimistic view of this, but until voice over LTE is demonstrated, and until it has been tested and accepted by the Public Safety community, it is not real as far as I am concerned. I learned a very long time ago that engineers always believe they can bring technology to market faster than they really can and that the marketers of the world are prone to reducing the time to market even further.





The last and most important form of PTT voice over LTE is the off-network component. Here the PSCR is working diligently with the 3GPP to have a standard introduced and approved, but since the 3GPP is made up of thousands of members, some of which just plain don’t support off-network communications where the network cannot see what the device is doing, I am not all that optimistic. In this case, I am hoping that I am the one who is wrong but I have learned over time to err on the side of caution. If Public Safety loses its voice spectrum because of the expectations that LTE voice will be able to provide all of the benefits Public Safety needs today, then the Public Safety community will be in danger of not being able to protect each other or perform its duties properly. I would rather see it, kick the tires, and make sure it meets all of the requirements than to be optimistic that the engineers will be able to make it happen in a short timeframe.

These are my issues with off-network PTT over LTE:

1)     Today’s Public Safety voice radios use a transmit power of 5 watts for handhelds and 30-100 watts in the mobile. LTE devices have a transmit power of ½ watt.

  1. There will be a big coverage difference when communicating device to device.

2)     LTE devices are designed so that part of the “smarts” is in the network and part is in the devices. Using these devices off-network will mean moving more of the “smarts” to the device.

3)     Can a device that is controlled by a network be used off-network when within network coverage?

4)     How many off-network voice channels or groups will be supported by off-network voice? What is the correct number? One is not enough, we used 78 during our Tea Fire but spread out over ten miles. Could we manage with less if the coverage is not as good?

5)     What will off-network voice communications cost? Will it be comparable to a device that includes both land mobile radio off-network channels and LTE on-network PTT?

6)     Will commercial operators really support off-network voice and data services within the 3GPP?

7)     Is voice over IP on the 4.9 GHz licensed Public Safety band an option?

I am sure there are other issues as well but I believe we need answers to at least those posed above to determine whether off-network PTT voice will be viable over the LTE broadband network. As I have said, I don’t believe that based on all of the above political and technological questions that remain unanswered that we should consider including voice communications in the first iteration of the Nationwide Public Safety Broadband Network. There are too many unknowns and too many differences in opinions about when the technology will be available to support the requirements of Public Safety voice in a mission-critical situation to trust those who are, I believe, overly optimistic about when these capabilities are coming to LTE.

I may be too conservative in my timeline, as others are quick to point out, but I believe that in this case we need to err on the side of caution rather than the side of optimism. Too many times in this world of technology we have been promised the commercialization of technology that has taken years longer to become a reality than we were originally told. I do not believe that Public Safety can take chances with a new technology that is unproven and broadcast to the politicians that we are willing to do so before we even have a technology that is proven and available.

Let’s launch the new and important Nationwide Public Safety Broadband Network and make sure it does what we expect of it for data and video, get it up and running and learn how to take full advantage of it first, and THEN let’s work on the voice component. To do otherwise will put Public Safety voice communications at risk. At the end of the day, voice will still be the most important component of the communications tools we make available for Public Safety and we cannot afford to take any chances.

Andrew M. Seybold


1 Comment on "Voice over Public Safety Broadband"

  1. Now that it has been a year since the post, do you see any changes in the timeline

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