The APCO International Annual Conference & Expo — being held this week — holds a special place in my heart. So, if you’re still reading, you’ll have to indulge me as I share a small rant, or a detailed reflective appreciation for the public safety wireless communications industry. It all depends on your perspective.
The public safety wireless communications industry has never pushed the technology envelope. Back in the day, it was a non-encrypted FM channel that was 25 kHz wide. That means almost anyone, including so-called radio hackers, could listen to the local public safety dispatch communications. You might think such listening would pose a safety problem; however, almost all public safety wireless communications avoided using identifying information that would violate personal privacy. In many ways, the ability to listen in this way was helpful because the non-encrypted dispatch communications allowed volunteers to learn of an incident and respond appropriately. All it took was a $100 scanner from Radio Shack. These days were good for us tower folks because the public safety wireless networks were technically interchangeable with land mobile radio systems. They had good outdoor coverage that was designed to work with a 50-watt transceiver in a truck. That made for a nice RF link budget.
As times changed, the FCC mandated the use of narrowband radio channels with a 12.5- kHz bandwidth instead of a proper FM channel. Maybe it wasn’t such a big deal, technically, but as the need to move to digital modulations became clear, APCO Project 25 (P25) was born. The first cries for financial assistance were raised. For non-geeks, a voice channel is about 6 kHz wide, and the analog spectrum required is about twice the desired modulation (FM) bandwidth. That relationship changes with digital modulation. It was easy to deduce from proposed FCC rules during the creation of P25 that even with more narrow channels, more spectral efficiency would be required, essentially mandating digital modulation. All would still be good in our world. All of the radio equipment and antennas still look like the same stuff we’ve had for years.
Many smaller jurisdictions, and many big ones, too, became frustrated and confused by the digital revolution. Some still are. For many municipalities, not much has changed in 15 or 20 years, except they spent a lot of money on wireless equipment with digital modulation without obtaining much additional functionality. The radio link budget is not much different (although it’s better by 10 to 15 dB), so P25 extends much better coverage into buildings and other places where analog FM systems were not intended to work. FM systems typically were designed to work only outdoors.
Now, the promise of public safety LTE is a reality. LTE is a much more efficient modulation, allowing about five bits of data for each hertz of spectrum. So, roughly, 10 MHz can carry about 50 megabits of data. And wider the RF channel, (5 MHz, 10 MHz or 20 MHz or more) the more efficient LTE becomes. For video, voice and file transmission, the bandwidth needs are dynamic. With digital modulation, a much weaker signal can cover a lot more area and extend signals more effectively into previously difficult-to-reach areas, such as parking garages, malls and home basements.
Many challenges abound for LTE in the public safety space. What will the bandwidth be used for? If not a dispatcher, who will decide what video should be shown? And how will the access to the bandwidth be prioritized — on dedicated networks, or on commercial networks with the dollar-meter running? Technology is offering a delivery mode with some impressive capabilities. The question is: How efficiently will it be used?
With my infrastructure industry hat on, I remain optimistic about the future antenna site needs of the public safety wireless communications community’s LTE deployment. The way the FirstNet network is being designed and built, it should look like nothing more than an additional carrier with a lot more security and reliability requirements.
One thing is for sure: Our public safety partners are not going to be a decreasing line item on the old income sheet. It all evolves. Usually for the better. And this future seems a lot better.