Another way of thinking about digital
For nearly a century, police, fire and other emergency responders have used powerful analog radios to deliver mobile communications over large coverage areas. These systems have worked well for communications between dispatch/command centers and field personnel within range. However, in cases where a first responder is inside a building, access to an RF signal often is limited or non-existent, which makes such systems less reliable or even useless. In the former case, voice communications are garbled and must be repeated, sometimes over and over. In the latter case, the radios simply fail to key up.
In such circumstances, would digital communications technology be superior to analog? In order to answer that question, let’s investigate the strengths and weaknesses of each technology.
Unlike analog radios, digital versions can share frequencies. The voice transmission is broken into time slices, with each slice sent in the form of a single digital packet. As long as there is no delay in the time it takes to deliver the packets, voice communications will be intelligible with minimal latency. However, all digital radios introduce some latency, which can be extremely uncomfortable to emergency responders who are used to the instantaneous communications provided by analog radios.
In addition, digital radios are able to tolerate weak signal strength or electromagnetic noise. Analog radios cannot do the same. But digital radios will fail abruptly when they reach the edge of the coverage area, which can put the lives of unsuspecting first responders at risk. In contrast, with analog radios there always is a chance that a garbled voice transmission will be understood, even in part. That can mean the difference between life and death for a first responder.
So, digital-voice enthusiasts should be realistic about the technology’s strengths and weaknesses. In addition to the above, digital radios are inherently less interoperable than analog radios. Two analog radios set to the same frequency generally can communicate. However, for digital radios to communicate, they must share a digital packet structure and understand each other’s digital encoding of the voice, e.g., the number of bits, data compression and encryption.
Before the Project 25 standard was adopted, there existed little hope of digital interoperability. However, even with P25, interoperability challenges will continue unless radio manufactures are forced to strictly conform to the standard. Spurred by profit incentives, manufacturers all too often add proprietary features that effectively make their P25 radios incompatible with those of their competitors.
Everyone assumes that their digital text messages eventually will be transmitted and when received will faithfully reproduce every letter. Even when no cellular connection exists when the message is sent, the message usually will be transmitted as soon the phone comes within range of a cell tower. If the message’s recipient isn’t currently connected, he will receive the message when he reconnects. The sender and recipient need not have the same carrier or phone.
Digital voice messaging works similarly. One’s voice is recorded to a file, forwarded as a multimedia text message and played back when the recipient is available. The message always gets through, and there are other important advantages:
- The fidelity is always perfect. Even when the communications channel is slow or temporarily non-existent, the message eventually gets through. Noise or weak signal strength introduces latency, but does not affect fidelity. Yet, digital voice messaging typically introduces no more delay than conventional digital voice.
- Digital voice messages are tagged with the person’s name and location; you know who yelled “Help!” and where they were.
- Digital voice messages are scalable; they can be sent one-to-many, just as an e-mail can be sent to many recipients.
- Messages can be played back during operations to avoid repeating them, or afterward for review purposes.
Reliable voice communication over limited spectrum by itself is sufficient justification for digital radios. But as the missions of emergency responders have expanded, along with the size of operations, voice alone is insufficient.
The Department of Homeland Security’s National Communications System states that operations involving more than 100 first responders and/or members of the public cannot be managed using voice alone. Such operations require the rich features that generally are available only on digital communications systems, including:
- Location tracking of emergency personnel and affected members of the public.
- Location tagging of pictures, video, voice and text messages.
- Advanced encryption, e.g., FIPS 140-2 (256- or 384-bit), which is required by federal agents.
- The ability to deliver enhanced situational awareness and command-and-control communications to field personnel.
Two methods exist to extend digital communications coverage: the use of powerful mobile transmitters, which increase interference and reduce battery life, or the addition of towers, which dramatically increases the system’s capital, operating and maintenance costs.
But what if every radio — and cell phone, for that matter — could have software installed that automatically, and securely, routes traffic to and from other devices that have similar software? What if any device or system that has communications capabilities — such as cameras, alarm systems and even drones — could participate in a communications mesh?
The Department of Defense tested “serial-bridging” software at the 2010 Coalition Warrior Interoperability Demonstrations that does this and more. Named a “Top Performing Technology,” this solution automatically bridges protocols. For example, a firefighter deep in a building might send a voice message to the phone of another firefighter in the building via Bluetooth; the message might then be relayed via Wi-Fi to the fire engine outside the building, which could route it to the command center over a cellular or satellite network. Because every device effectively is a repeater tower, emergency communications towers become movable and can be positioned by the emergency personnel where they are most needed.
Many believe that in the future police, fire, medical and other emergency personnel will carry two devices: an analog voice radio and a smartphone. The smartphone would be used 99% of the time, generally in situations when a small amount of latency is acceptable in voice communications. They also would be used and to provide situational awareness and command-and-control communications to field personnel. Such devices would still communicate if the commercial cellular network fails. Fourth-generation LTE and WiMAX systems now are being rolled out by commercial cellular carriers that eventually will provide emergency responders with guaranteed priority communications, even when the cellular network is overloaded, as is likely during large-scale emergencies.
A compelling use case for existing high-power analog voice radios continues to be when a police officer or firefighter is trapped inside a large building and is calling for help. If the radio only is used on such rare occasions, it can be very powerful without requiring a large battery. Moreover, if radios only are used in rare emergencies, rather than routinely, interference with neighboring agencies becomes less of an issue. It might even make sense to have all agencies use the same analog frequency to increase the chance that someone would hear the call for help.
So, first responders then would use their commercial cellular devices, based on digital technology, for the vast majority of their day-to-day communications needs, and point-to-point analog radios only in rare cases. This would significantly reduce — and potentially eliminate — the need for public-safety agencies to erect and maintain their own communications infrastructure. Given federal state and local budget constraints, serious consideration must be given to alternative ways of designing effective robust emergency communications systems.
David Kahn is the CEO of Covia Labs, a Mountain View, Calif.–based vendor of wireless push-to-talk and command-and-control solutions.
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