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As the FirstNet board moves forward to get the public safety broadband network under way, there is still a lot of confusion within the public safety community regarding use of this network for voice. One commercial network (so far), MetroPCS, has started to offer voice over LTE or VoLTE as it is called, however, what MetroPCS is offering is dial-up or phone voice and not push-to-talk voice over LTE. Network operators will be adding dial-up voice to their networks as soon as they can so that they can shut down their 2G networks and re-purpose the spectrum for the much more efficient LTE service.
However, dial-up voice is a very long way from what is needed by the first responder community. Dial-up voice supports one-to-one calling and conference calling (using a conference bridge service) but does not support one-to-many voice communications nor does it support PTT services. Dial-up voice is important for non-emergency communications but does not provide the features and functionality needed for dispatch and operational voice services. Several commercial networks say they are ready to offer PTT services over their LTE networks, and several traditional land mobile radio companies are also showing off PTT over LTE. The issue here is that for each vendor PTT is proprietary and not compatible with any other PTT services. Permitting non-standard or proprietary PTT services on the public safety broadband network defeats the purpose of this network being a fully interoperable network from coast-to-coast.
While the commercial PTT services include group call and functions which make them pretty equivalent to LMR PTT services, the fact that none of them are compatible with the others means that if an agency decides to launch a PTT application (and yes on LTE, PTT is an application), then they will be incompatible with their neighbors who might use another vendor’s PTT service. It is going to be possible to combine or bridge LMR PTT with LTE PTT services; however, there still won’t be compatibility between PTT services.
What needs to happen is that a common PTT technology needs to be made available for the public safety LTE network and the Public Safety Communications Research Group in Boulder, Colo., which is a government funded and run organization for testing LTE for public safety, has introduced into the LTE standards body (3GPP) a request for work on VoLTE as well as for off-network (simplex) LTE voice. It is unknown at this point in time if the 3GPP will accept these items to be included in a future release of LTE and if they do what release it might be included in. In the meantime public safety has enough work to do getting the network up and running for data and voice services to augment the existing LMR systems.
The issue of voice over LTE or VoLTE is more complex in the public safety world than it is in the commercial environment. Public safety requirements for voice are significantly different than just dial-up voice and need to include:
Dial-up voice: This should be handled by partnering with existing commercial network operators, since the additional network cost to implement dial-up voice will hamper the FirstNet efforts to build out as much of this network as is possible with the money that is available. Most devices will or should include access to at least one commercial network in addition to the Public Safety network so dial-up voice can easily be handled on the commercial side.
Push-to-talk over LTE: My belief is that while some vendors are pushing the availability of PTT over LTE, at least for now each vendor offers their own solution, not compatible with others, and to count on PTT over LTE from the outset would be a mistake. In reality we need to move slowly in this area, not only do we want PTT over LTE at some point but we want it to be one-to-many and have all of the capabilities we are used to on our LMR voice systems. Further, there is a difference between PTT, as defined by commercial operators, and mission-critical PTT which is absolutely a requirement of the public safety community.
Off-network PTT: The commercial network operators refer to this as off-network, in the public safety community we refer to it as simplex, or talk-around communications. This is perhaps the hardest form of voice communications over LTE. First of all, LTE devices run about one-quarter of a watt of power with internal and very inefficient antennas so expecting them to be able to cover the same distance as a 5 watt handheld radio with an external antenna is not realistic. Next is the fact that we do not know, today, if off-network PTT will work when the device is in range of the network, a large portion of the off-network requirement, and we don’t know how many simultaneous conversations can be held in the same area, nor do we know what type of in-building coverage we can expect. Add to this that we need 3GPP to come up with a standard based on the requirements submitted by the PSCR on behalf of public safety and you can see that we cannot count on off-network PTT services or even off-network data and video services, at least for now.
Below is my own road map for mission critical voice over LTE and off-network PTT voice. There are those both within the wireless industry and even within the PSCR and other organizations who believe that I am being way too conservative. However from my perspective, until we have proven the technology, developed the devices and tested and retested them and their capabilities, it is never wise to assume that they will be available when the engineers believe that they will be. Further, we do not know how long it will take 3GPP, if they agree to look at the off-network requirements, to get to including off-network into the 3GPP specifications. The 3GPP is made up of thousands of members, vendors, and network operators, and most of the network operators I have had a chance to talk to either don’t want their customers to have the ability to do off-network communications or are concerned about how it will work. Commercial network operators want to know and manage all of the devices on their network.
LTE mission-critical voice timeline
Understanding the timeline and the risks involved in counting on a technology which has not yet been developed or proven, and which is still in production is dangerous because it could lead to cities, counties, and states, withdrawing needed funding to keep their existing land mobile radio voice networks up and operating or even expanding them to provide better coverage. It is better to be skeptical in this case rather than to plan on LMR systems being replaced with the public safety broadband system in the near term.
We will see LTE-only devices with both the public safety network and commercial network capabilities and we will also see combination LMR/LTE devices which will provide the public safety community with both broadband and mission critical on and off-network voice capabilities in the next few years. Let’s learn about and use the data and video capabilities of this new nationwide network first. Let’s find out what applications we want and need, what types of devices will be available and work with the LTE system as an adjunct to our existing LMR voice systems and not a replacement for them. This is the safest course of action and one that will prove the most beneficial for all concerned. When and if mission critical on and off-network LTE voice becomes available, departments can transition their voice communications in stages.
Andrew Seybold has been involved in public safety and public safety communications for more than 40 years, starting as a first responder and then working with RCA Mobile Communications, General Electric Communications, Biocom (where he helped develop the first paramedic radio for sending voice and EKG from an incident to a hospital) and Motorola. In 1981, he began his career as a consultant, educator and writer. For the past four years, Seybold has been volunteering his time and efforts to the public safety community in its quest to build a nationwide, interoperable broadband communications network, and has worked closely with the Public Safety Spectrum Trust, The Public Safety Alliance, the Major City Chiefs Association, APCO, The International Chiefs of Police, the National Sheriff’s Association and other organizations.
