Adventures in Trunked Radio…and Beyond

Last month I wrote about the transition of Mesa County’s public safety and other government agencies to the state’s Digital Trunked Radio system (DTRS). Most of the county’s law enforcement agencies, as well as the Grand Junction Fire Department, were slated to be operating completely on the new system yesterday. Other area fire departments will remain on the existing VHF radio network; according to a memo issued last week, a transition date for them “has not been determined”.

Digital Trunked Radio Systems are not new technology. They have been put to the test in much larger urban environments, and dependent upon their configuration have proven to be a largely reliable, robust, and reasonably secure method of maintaining communications and establishing interoperability between large and diverse groups of radio users. As with many technological advances, adjustments and updates are almost a constant process, and a complex system such as trunked radio is no exception.

I thought that I would expand on how these technologies are developed, marketed, procured, and implemented, in hopes of fostering some understanding of the complexities involved.

Warning: Fairly exhaustive late-night techie diatribe follows.

A Brief History of Trunked Radio.

Trunking is the use of several repeaters, on different frequencies in the same band, operating together under computer control to allow for the pooling of resources.1 The first trunked radio systems started to become operational in the late 1970’s. By the early 80’s it became apparent to many in public safety that a standard group of capabilities were necessary, such as a mode for operation in the event of computer problems, or a transmitter site becoming isolated from its computer controller, priority access to the system, and emergency alerting.

The Association of Public Safety Communications Officials (APCO), made up of members from both public safety and the commercial sectors that provide radio equipment, established a project group within its membership to develop such a standard. This Project 16 group was successful in putting forth standard capabilities that were adopted by several of the ‘big players’ in the industry, such as Motorola and General Electric.

The standards list dovetailed with the Federal Communications Commission‘s first issuance of licenses to operate public safety radio systems in the 800 Megahertz frequency band. While trunked radio systems can effectively operate in the VHF (150-170 MHz) or UHF (450-512 MHz) bands, they are most frequently found in the 700-800 MHz band today.

One big drawback to APCO 16 trunked systems is that they were not interoperable; radios on a Motorola system, for example, would not work on a GE system. Thus began another APCO project effort to define a standard by which multiple manufacturers could adhere to when building trunked radio systems.

This Project 25 (or “P25”) standard incorporates the use of a device called a vocoder to convert voice radio traffic into a digital signal for transmission through the system architecture. This formed the basis for what is known as the P25 Common Air Interface (CAI). A radio using the P25 CAI should be able to communicate with any other P25 CAI radio, regardless of what manufacturer produced the radio.2

The final P25 standards were presented in 1994, with most of the manufacturers adopting the standard for use in their systems. These included Motorola, EF Johnson, Kenwood, and Daniels Electronics. One notable exception was Ericsson, which had purchased GE’s radio manufacturing division. This company is known today as M/A Com. This is significant, as many cities in the core of the Denver Metro area use a trunked radio system known as EDACS, manufactured by this company.

In the late 90’s, the State of Colorado developed a proposal to construct a statewide trunking radio network. The state purchased and began development of the statewide DTRS in 2001.

In 2002, the Consolidated Communications Network of Colorado (CCNC) was incorporated as a users group encompassing multiple jurisdictions and governmental layers. This group serves as the standards setting and system coordination arm of the DTR, which is maintained and monitored by the state.

I am DTR of Borg…not.

The arguments are compelling for a public safety entity or local government’s participation in CCNC and transitioning their operations to the DTRS. There is a distinct advantage to a trunked radio system’s ability to leverage multiple repeated channels, connected and coordinated through multiple transmitter sites, to providing wide-area coverage for even portable radios.

The state, along with other public safety organizations and the commercial sector, has touted the economies of scale and interoperability benefits associated with a statewide radio infrastructure to encourage local governments and special districts to move their operations to the DTRS. This is true even with the increased end user costs associated with such a move. DTRS mobiles and portables can cost nearly 5 times more than conventional VHF or UHF units.

Some of this encouragement has been less than subtle. The state Department of Local Affairs (DOLA), which administers many grant programs to local governments using funds such as Energy Impact fees, will only approve grant requests for radios that operate on the DTRS, regardless of what system is used by the local jurisdiction. Additionally, funding for communications upgrades from the Department of Homeland Security usually requires migrating to a P25 system.3

Even with this, there are jurisdictions committed to other radio technologies, and there are still very valid uses for legacy VHF and UHF radio systems. Many smaller agencies, even using grant funding, are having a hard time affording the cost of new field units. This is likely what is keeping most of Mesa County’s fire departments on VHF for the foreseeable future.

Some limitations are technical; the DTRS cannot be used for over-the-air paging, and cannot be accessed by airborne aircraft. Other factors include interfacing with federal resources, such as wildland firefighting crews and aircraft, which use a national VHF radio system for coordination.
There are now statewide and nationwide
common calling channels allocated for use in an analog, simplex mode which can be used to accomplish some of these user needs.

Technology has also played a role in the diminishing of the non-proprietary, common-across-manufacturers component of the P25 standard. While the P25 CAI is a non-proprietary ‘open’ trunking standard, some manufacturers have been marketing technology that incorporates proprietary components for use on these systems.

An example is encryption protocols, which provide another level of security for discreet communications. While there are forms of encryption which can be used in any P25 radio, Motorola markets a proprietary form of encryption, which when used requires any user needing to use encrypted talk groups on the system to use a Motorola radio.

A key development in the years following P25 is Software Defined Radio (SDR). This technology has facilitated the development of radios that can transmit and receive over multiple frequency bands, in either conventional or trunked modes. Radios from newer players in the public safety marketplace such as Harris Corp. and Thales are capable of communicating over VHF, UHF and 800 Mhz frequencies and trunked systems. The cost of these units are roughly double that of the currently available P25 equipment, often exceeding $5,000 per radio.

Concerns about safety in certain environments has also led to the development of alternative simplex channels using analog modulation, which can be contained in the same radio. An exhaustive study conducted by the Phoenix Fire Department concluded that “simplex channels provide incident commanders and firefighters a safe and consistent communications system that is not dependent on infrastructure in order to speak to other units on the

Despite these challenges, it made good sense for our local communications system to begin a transition to trunking. The obvious benefits outweigh a simple dollars and cents argument. While as a taxpayer I would have preferred an objective assessment of available technologies when there is big money involved, the DTRS was a common sense path of least resistance.

Right now there are eight transmitter sites providing coverage of the 3300 square miles of Mesa County, with more to come. These sites are part of a network of nearly 200 across the state, all accessible by the end user using the same radio. Every radio on the system is registered, its
usage monitored, and can be disabled remotely if malfunctioning or compromised.

By combining this robust technical resource with effective utilization protocols and consistent use of proven Incident Management strategies, our public safety responders are poised to provide a better coordinated response to all manner of emergency situations.

Growing Pains…and the Future.

As much as this technology brings to the potential effectiveness of public safety response, it is still 20 year old technology, and portions of it are showing their age. The development of improved means of transmitting digital voice has resulted in the establishment of a second phase of P25 digital standards.

The Colorado DTRS has been feeling the effect of some of these factors as their system has continued to grow in popularity and usage. This past February, a letter from the CCNC Executive Board detailed a moratorium on new users of the DTRS until specific goals pertaining to technical and administrative capabilities were met. These included, for example:

System Infrastructure Additions: As the DTRS has grown over the past 10 years, many entities have joined without adding the infrastructure necessary to support their traffic load. Applications to the CCNC must be more thoroughly scrutinized to ensure additional users do not negatively impact the system resources provided and used by current members.

Additionally, the development of Voice over Internet Protocol (VoIP) technology, and the ability to effectively use broadband networks to carry voice traffic, has led to a new push for broadband communications systems for public safety that incorporate the secure digital transmission of both voice and data.

This was most recently reflected in the National Broadband Plan released by the FCC for public review last month. Part of this plan advocates for the establishment of a broadband public safety network using radio spectrum in the 700 MHz band, recently allocated to public safety after the transition of broadcast TV to digital transmission.

However, the nature of public discourse in the form of some of the finest minds in technology implementation and consulting are already creating doubt as to the effectiveness of broadband communication versus channelized systems, given the nature of public safety operations. One of the most respected consultants in this area, Andrew Seybold, put it right out there last week in an email to an FCC commissioner:

Channelized communications for voice is one-to-many, which is a critical component of first responder communications…It is vitally important for all units in a given area to hear what is happening so they can prepare to provide additional coverage or assistance.

It is not possible to provide the level of voice communications required by public safety within the confines of commercial wireless systems or using commercial wireless technologies…It can be difficult to understand how different channelized devices are from cell phones. They must be able to communicate directly with each other no matter where they are, and with those around them so everyone knows what is happening. A delay of only a few seconds can mean the loss of life or property.

Scannerheads Unite.

What do the development and deployment of these rapidly evolving technologies mean for the average citizen who enjoys listening to public safety in action? From what I’ve heard, many have been converging on places like Radio Shack, trying to figure out why they can’t hear the GJPD anymore.

It’s possible that the scanning hobby may find itself fading out of popularity as these digital technologies make for more sophisticated and expensive equipment to monitor them. For the casual hobbyist, most of today’s scanners require a computer and software to program them with any degree of efficiency. Monitoring these communications may eventually become impossible.

If/when that day comes, I will regard it with some sadness. I remember the first police scanner I ever owned, a little handheld Bearcat that you had to buy crystals for. This was followed rapidly by a programmable Bearcat 210XL, which I took to work on the night shift and learned a lot. This eventually translated itself into a career.

There are several fellow hobbyists in the GJ area with a lot more experience and technical knowledge than I. They’ve kept ahead of the curve, and thanks to the Internet the fruits of their labor are available to anyone interested. Enjoy it while you can.

The times they are indeed a changin’.

Have a great week ahead.

Photo Credits:



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