Public safety personnel concerned about digital radio transition
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Public safety personnel concerned about digital...
Like here at WSLS, many fire and other public safety departments across our area are being pushed to switch to new systems. That's because just like TV's and cell phones it is supposed to be clearer,...Published: October 30, 2008
Updated: October 31, 2008
In an emergency, Roanoke City Deputy Fire Chief Billy Altman says good communication is key.
“We don’t want to be on the news for having a line of duty death,” Altman said. “That’s nothing anybody wants, and the radio system is a big key with preventing that.“
Franklin County Fire Marshall Bennie Russell agrees.
“Communications is a life or death situation—especially in fire and rescue when you’re dealing with the unknowns,” Russell said.
Virginia firefighter Kyle Wilson, 24, found himself right in the middle those unknowns back on April 16, 2007.
That morning, Wilson and his crew were called to a house fire. Not long after Wilson went in, he used his radio to call for help. Those were his very last words.
Hundreds turned out for Wilson’s funeral, and the Prince William County Fire Department vowed to figure out what went wrong.
A 382 page report details many different things that contributed to Wilson’s death including communication –- specifically problems with the county’s digital radio system.
Like here at WSLS, many fire and other public safety departments across our area are being pushed to switch to new systems. That’s because just like TV’s and cell phones it is supposed to be clearer, can transmit more information, and eventually will be less expensive.
By 2013, the FCC is requiring all public safety radios to do use less bandwidth and the best way to do that is by going digital.
Dr. Charles Bostian is a Virginia Tech researcher who’s working with his students to develop cutting edge radio technology.
“Digital transmission saves a lot of radio spectrum,“ Bostian said.
Franklin County’s 911 coordinator says they recently switched to digital.
“There’s a lot of things we can do with a digital system that you could not do with an analog,“ Bill Agee said.
But they’ve also run into some problems.
“We have found holes in our system where we can’t talk very well. There are different holes than we had with the analog signal and we don’t know why,“ Agee said.
That’s one of the reasons Roanoke City is still carrying the old analog radios.
Money is a big factor, but talk of problems with the new technology has held the city back as well.
“There’s still that doubt in everyone’s mind about the digital,“ Altman said.
One of the doubts has to do with the digital signal. Basically, when you’re using an analog radio the signal fades as it gets weak. But just like your TV, a digital signal is either 100 percent there, or it is not.
“That’s an inherent problem with digital systems. They either work very well or they don’t work at all,“ Bostian said.
Bostian says background noise is another problem with digital radios leading to garbled messages and miscommunication.
“If a person listens to somebody talk while they’re standing next to a pump truck, the human brain can identify the voice and can understand what’s being said. Digital electronics isn’t quite as good at doing that,“ he said.
“That can cause a big problem, because the guys if they’re inside a house and they have an emergency and they call mayday firefighter down, you may only have one chance to answer that or hear that,“ Altman said.
The International Association of Fire Chiefs (IAFC) formed a group to investigate digital radio problems. Ten On Your Side asked the group whether our public safety people are putting their live sin danger by using digital radios.
“That’s a very difficult question to answer with specifics,” Charlottesville Fire Chief Charles Werner, chair of IAFC group, said. “Let me say this, there is no question the future of public safety communications is going to be digital communications.“
But if problems exist, is the transition premature? The FCC says no.
“We believe that is ample time for the transition to occur,“ FCC spokesperson Robert Kenny said.
But the FCC admits firefighters have been concerned about the requirements.
“We understanding there are some concerns,” he said. “We are working with them to resolve it.“
In the meantime, digital radio experts in our area continue to trouble-shoot problems with the new radios before the deadline.
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While it’s a given that PS radio will eventually go digital, the transistion is too soon.
The 2013 date is not the drop dead date to go digital. It is only to make sure that everyone is operating with 12.5khz bandwidth radios instead of the earlier
standard of 25khz bandwidth.
Radios using 12.5khz bandwidths do not need to be digital to operate well.
Analog 12.5khz radios abound in both PS & business enterprises & they work well.
It won’t be until the FCC mandates 6.25khz bandwidths that a radio will need to use digital techniques to send a voice.
At present the FCC has only eluded to mandating a shift to 6.25khz technologies & no date has been set to force that move.
Under most circumstances, digital technologies work fine. It’s not until you get into mission critical, especially life saving scenarios, where digital can & has let users down.
There’s at least a couple reasons that digital fails the user. One reason would be a well known shortcoming of digital technologies as applied to present PS radios. The choice of vocoder.
Vocoders are the circuits that convert human speech into the digital realm for transmission & reconverts that digital signal back into a voice in the speaker.
The trouble is that PS’s vocoders can only deliver a rough representation of a human voice; What it “thinks” the digital numbers “should” sound like based on an internal “lookup table” of sounds.
The vocoders in use now, don’t have a way of truly replicating a voice masked by “noises” such as those mentioned as loud background noise. The best they can do now is attempt to filter out loud, non-speech sounds before transmission & during reception.
This doesn’t usually lend itself to an understandable sound from the speaker when the transmitting user is next to a loud machine, in a moderate breeze or talking thru a respirator.
Newer, much improved, vocoders are available but cannot be retrofitted into the present radios. The present batch of radios will need to reach their end-of-life before replacement brings the newer vocoder equipped units.
Many of the existing units are only part way thru their expected life-cycle with some being only a year or so old.
It’s difficult to justify dumping only partially used $5k units for new $5k units. Albeit, the price of radios is coming down as long as you’re not stuck in a proprietary system from one of the major manufacturers.
Another caveat to digital is the way a signal propagates in, thru, around & off of various terrain & physical surfaces.
It’s commonplace for a receiver to hear the same signal coming from multiple directions. This is known as Multipath.
When a signal bounces from an object,or several, it will take longer for that reflected signal to reach a receiver than the part of the signal that went directly to the receiver. When each of these signals arrive at a particular receiver, they can add together or subtract from each other in many ways. This results in distortions & sometimes less signal available for the vocoder to work with.
Again, the vocoder doesn’t know what to do with this type of interference & may block the speaker audio.
Where analog signals are received with multipath interference or interfered with in other ways, the human brain can usually “filter” the noise & recover a usable voice.
Digital signals suffering interference have only the error corrections built into the radio to act as those filters.
The digital “filters” are nowhere as good as the human brain at deciphering a voice from the noise. When the digital filtering gives up, the sound stops emanating from the speaker. The user is not given the opportunity to use his/her own ears to discern the voice in the noise.
Along the same lines of interference issues, if two units transmit at the same time using a digital modulation, there’s the excellent chance that no ones receiver will “open up” to make anyone aware that this happened.
In standard analog fm, you may not understand what’s been said due to the inherent distortion but, you’ll know that someone tried to send a message alongside another unit & can ask for it to be repeated.
This is not to say all digital is bad, it just has a place & time for use.
On a fireground it has no place when firefighters are inside a building.
I’ve been collecting information about problems with digital trunked radio systems for several years. A summary of my research is available at http://blog.tcomeng.com/.
The problem is extremely serious and widespread.
The issue of digital radios is complex. To fully understand this critical issue, please visit the International Association of Fire Chiefs website for the full report and best practices presentation at:
http://www.iafc.org/digitalproblem
Thanks,
Charles Werner, IAFC Digital Project Workiing Group Chair
As the telecommunications specialist for a federal disaster response team, I as well have concerns over digital radios. I have no plans of changing my team from the radios that we already have. While it is true that digital radios require less spectrum and because they are digital can be encrypted for security, they come with a cost both financially and in a lack of fidelity. I can buy 10 standard high quality radios for the cost of ONE of the new “Project 25” compliant units. Also, I personally find digital radios harder for me to understand because there is not as much of the voice quality that is transmitted. While I do think there are areas where digital transmissions can be of great value, especially for sending data, I will be slow to consider it for voice.
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