Public Safety Advocate: Part 1 – Wireless Networks and Devices for Public Safety, Even PTT

Now for something different… This Advocate will be published in two parts starting this week and finishing next week. This first part features some history of LMR, other forms of wireless data, and a little about FirstNet. Next week we will be taking a deeper dive into where we are today and where we hopefully will be providing public safety professionals with increasingly better was to communicate, including true nationwide PTT.

A Little History

Today, the public safety community enjoys a variety of wireless networks, devices, and applications. Most jurisdictions use their own Land Mobile Radio (LMR) system or a system that is shared with a city, county or, in some cases, an entire state. For this discussion, it is assumed that all broadband devices and some LMR devices will be equipped with Bluetooth and WiFi.

FirstNet (Built with AT&T) enables public safety professionals to access the nationwide public safety broadband network or one of the commercial broadband networks deployed in the United States. If you had been a beat cop in the 1920s, you would either be at your station waiting for a phone call or walking a beat and checking in at every police telephone mounted strategically across the city.

Then in the early days you might have been lucky enough to ride in a vehicle equipped first with a one-way radio and then a two-way radio. In the 1930s so you could acknowledge calls coming to you from the radio’s dispatch point. Compared to what we have today, these first systems were crude and, in most cases, they operated on a single radio channel.

Starting in the 1930s, Land Mobile Radio (LMR) has been the mainstay for public safety communications. These systems have grown from single-channel citywide systems to complex multichannel, trunked, and simulcast radio systems. Even so, their main function remains the same today. They provide voice using Push-To-Talk (PTT) over dedicated and licensed FCC spectrum.

Then came Motorola’s first 16-channel, analog FM handheld radio. A handheld capable of operating on any one of sixteen radio channels within a segment of licensed public safety spectrum was a giant move forward.

Today, both LMR mobile and handheld devices are basically built around a computer system and are capable of being used on hundreds if not thousands of radio channels. Since they are no longer single-band radios, they can accommodate all of the public safety LMR spectrum and they will include FirstNet broadband spectrum in the future.

I wonder if all this new technology is really needed in the field. These multiband, multichannel, and/or multigroup radios are complex and many users in the field are still not comfortable with so many features and functions on their belt or in their car. What if FirstNet could be used by all agencies and personnel, and LMR for use in the field could be redesigned with fewer bells and whistles to make them easier to use in the field.

Cellular communications was invented in the late 1940s by Bell Labs and was first deployed within the United States in (TK ) as channelized analog radios. Control of these devices was not necessarily left to users in the field. We have also gone from 1G to 5G technologies in a very short period of time and from only a few radio frequencies built into the devices to many different built-in segments of spectrum along with digital information that rides across the networks.

Today’s World

Today, LMR devices still operate in small segments within a wide portion of available radio spectrum. On the other hand, cellular systems using fourth- and fifth-generation technologies are almost spectrum agnostic as many of the devices used in the field are crammed full of radio spectrum and different digital technologies.

Moving Toward Convergence?

There were some interesting developments along the way. First, the Nextel cellular network included PTT between users from day one and PTT provided a different way of communicating with others in the field. They were not on the public safety network so, for example, detectives could work in the field without having to worry about citizens listening to their conversations. Others within the law enforcement community used the Nextel PTT system to communicate during the day or their shift without being recorded by the department’s audio recorders. When Nextel closed its doors and handed the key to Sprint, there were a lot of unhappy nonbusiness users who really wanted Nextel to stay in business

During this time, we also saw the introduction of Cellular Digital Packet Data (CDPD), a technology invented by IBM that enabled cellular operators to use their voice channels for packet data transmission and reception. The speeds promised by cellular carriers were less than 20 Kilobits per second (Kbps), but that was 20 Kbps more data than users could send and receive before.

Motorola entered into an agreement with IBM to provide packet data devices to all IBM service personnel. Motorola then purchased this network and turned it into what was then known as Ardis.

Research In Motion, home to the BlackBerry, was rolling out its product on the RAM Mobile Data nationwide network. Of the three, this was the slowest network with data speeds of about 8 Kbps. This network was 50-percent owned by BellSouth.

Motorola was installing Mobile Data Terminals (MDT) in vehicles to transmit and receive text messages. The Panasonic Toughbook was another front-runner in packet data because many companies built Personal Computer Memory Cards [international Association] (PCMCIA) plug-in telecommunications modems for the Toughbook. Panasonic later included the modem in the laptop.

Needless to say, the public safety community was scouting for ways to send and receive more than plain-old PTT. (When Nextel was purchased by Sprint, I had an engagement with Verizon and tried to convince the company to find a PTT solution for its network. I was told by a high-ranking executive that there was no market for PTT and they had more important things on their plate.)

It is interesting that that Verizon, AT&T, and newer cellular providers were chasing CDPD but saw no value in PTT.

While the LMR community (public safety) was interested in sending and receiving data, and several companies were already selling bits of data, it is curious that no one combined digital data and PTT.

Broadband and Public Safety

Meanwhile, the cellular community was not standing still. It went from GSM (1G) to 2G, which basically added data capabilities to 1G to became 3G. This is where network operators and the public safety community became interested in wireless broadband data. Since 3G wasn’t all-IP-based, a few companies were already using 3G for PTT services. My consulting company was hired by a group of PTT providers to compare and contrast what was available at the time. We decided to measure “attack time” and “volley time.” Over the years, attack times have changed depending on the type of system. Analog radio PTT attack time is based on the time it takes for your transmitter to come up to power so the network can receive the signal and decode private line or some other code and when you can talk. Volley time is the time between when the talker lets go of the PTT switch and the recipient pushes his/her PTT switch and responds.

Push-to-talk over 3G cellular was not great. Typical LMR analog PTT attack time was in the 500 to 750 micro second range. With 3G, this time was doubled or even tripled.

It wasn’t until 4G that there were some serious solutions for PTT over cellular that rivaled speeds for PTT over various forms of LMR. The longest attack time for LMR has to do with how a trunked radio system allocates spectrum to a user requesting the channel to when it is ready to talk.

A Convergence of Technologies?

Today we have sophisticated, expensive PTT LMR devices and simpler-to-use, less functional PTT radios for LMR. Attack and volley times vary depending on several factors including the type of analog digital trunked network and a trunked simulcast network. The set-up or attack time within the volley time on some of these networks is more dependent on network set-up times than anything else.

FirstNet (Built with AT&T)

As FirstNet was being rolled out, AT&T and the FirstNet Authority spent a great deal of time working out access and timing details for the network, e.g., how much time priority and/or preemption added and how long it took for the cell site to recognize a request for service.

These and many other questions have been answered and today, PTT over FirstNet/broadband can be compared favorably to PTT over LMR.

This presents some interesting ideas. FirstNet has been designed to be a true public safety broadband network dedicated to serving the public safety community. However, there is no commonality between the many PT vendors certified for FirstNet. So, while we have a nationwide broadband network capable of being used for nationwide PTT, PTT interoperability has not been realized.

Winding Down

First, the Public Safety Advocate would like to congratulate Jim Bugal who has just been promoted from Vice President of FirstNet at AT&T to President of FirstNet at AT&T. Jim has worked on behalf of public safety within AT&T for many years. He is truly an advocate for the public safety community and he understands the differences between the commercial side of AT&T and the FirstNet (Built with AT&T) side. We are fortunate that Jim has been the driving force within AT&T and I look forward to his continued leadership as we implement the AT&T FirstNet next generation of services, devices, and applications.

Finally, this week I want to complain or make it obvious that I’m not an expert when it comes to the iPhone. As many of you know, I have a vision impairment and over the last two years I have been learning new ways to communicate through my computer using a software application known as Dragon. I have also used my iPhone with larger type provided by iPhone accessibility applications but I recently found that I either don’t understand how to make the iPhone do what I want it to do, or perhaps Apple didn’t quite get it right for those of us who have trouble reading the screen. My iPhone is a 12 so it’s new and it has the latest ILS installed on it. I was told I could have the iPhone talk to me and read my email, texts, and news items that I receive.

I set out to do this with some help and turn my phone into a useless brick. At that point, I decided to call in the experts at a local computer store where they really know Apple products. It took them about twenty minutes to return my iPhone back to where it was before I tried to add voice services.

What I think I found out, although I’m not sure, is that when you invoke the voice mode the iPhone will in fact read content to you. However, it also puts the phone in doing mode were swiping and all the normal ways of accessing information and data no longer work. Instead, you have to double-tap everything you want to access. For example, if my passcode was “1234,” I would have to click on “1” then very quickly double-tap “2” and so on until all four digits of my passcode are accepted by the iPhone. I found this very annoying, especially when using ESChat on the phone.

Furthermore, since my phone talks to my hearing aids and I can use my hearing aids on phone calls, I expected to be able to choose the content I wanted the iPhone to speak to me. Instead, in the mode I ended up with, the iPhone became way too chatty and every time I received an email, text message, or other input such as my news feeds, the voice would automatically start reading them to me. Perhaps this is because my iPhone is connected via Bluetooth to my hearing aids, but I found it very disconcerting to have a conversation with someone and the iPhone rudely interrupt me because it had received a text message.

Perhaps there is a way to do what I want but I have yet to find it. I want to be able to listen to the various content on my iPhone but I want to be able to select what I am hearing with a simple tap or some other way of saying “readme this email,” which Seri is supposed to do but so far, Siri does not like my voice. I am still an iPhone fan but perhaps there is someone out there who knows enough about how to set up accessibility features that they could guide me through what I am trying to do. In the meantime, have a great week and we will be back Part 2 next week.

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


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