U.S. Department of Justice 

Office of Justice Programs 

National Institute of Justice 

IN 

NCJ 214331 

SHORT 

➡TOWARD CRIMINAL JUSTICE SOLUTIONS www.ojp.usdoj.gov/nij MAY 07 

Public Safety Communications 

and Interoperability 

Key Points 

■ Challenges to achieving interoperability include 

incompatible radio equipment, lack of a common 

language, and the use of different frequency bands 

by different agencies. 

■ Radio technologies that promote interoperability 

include simplex or line-of-sight systems and conventional and trunked radio repeater systems. 

■ To promote interoperability, agencies should— 

❑ Optimize their internal communications systems. 

❑ Agree on basic requirements, set realistic goals, 

and collaborate to achieve a common goal. 

❑ Use low-cost solutions, such as preprogrammed 

radios, shared radio frequencies, and plain 

language (instead of agency-specific coded 

language). 

INTEROPERABILITY CHALLENGES

Public safety agencies cannot communicate seamlessly 

for three primary reasons: incompatible frequencies, 

incompatible equipment, and lack of common language. 

Incompatible frequencies.The Federal Communications Commission has authorized multiple bands of 

the radio spectrum for use by public safety agencies. 

Four primary public safety bands exist: 

■ VHF Low or Low Band (30–40 MHz) 

■ VHF High (152–162 MHz) 

■ UHF (406–512 MHz) 

■ 700 or 800 MHz1 

Because agencies do not all operate on the same band, 

their communications devices are not interoperable. For 

example, a radio operating on a VHF Low radio system 

can communicate only with other radios in the same 

range with pre-programmed common frequencies. 

Incompatible equipment. Even when agencies do use 

radio systems in the same frequency range, differences 

in equipment often prevent interoperability. Agencies 

that have different equipment can use a bridging device 

or gateway to connect the different systems or purchase 

a cache of radios to use in emergencies.2 Using alternative radios for emergencies, however, requires first 

responders to carry and operate a second radio and 

requires agencies not only to pay for the additional 

radios, but also to monitor whether the batteries are 

charged. 

Lack of a common language.The third barrier to 

interoperability is the lack of a common language 

among agencies. Many agencies now use numbered, 

coded language, such as “10-4,” which in one jurisdiction can mean “I understand” and in another jurisdiction 

can mean “Man down! Send backup!” Interoperability is 

more likely to be effective when public safety agencies 

use plain language radio communications, allowing first 

responders to accurately relay information from one 

agency to another. 

Office of Justice Programs ■ Innovation • Partnerships • Safer Neighborhoods ■ www.ojp.usdoj.gov 
2 RADIO SYSTEMS AND FEATURES

Public safety agencies rely on three main types of radio 

systems to overcome interoperability barriers: 

■	 Simplex or line-of-sight systems 

■	 Conventional radio repeater systems 

■	 Trunked radio repeater systems 

Simplex or line-of-sight systems. Simplex communication systems allow communication to flow in only one 

direction at a time. This type of radio communication 

does not rely on costly infrastructures such as tower 

antennas or repeaters—devices that regenerate or replicate a signal. Instead, first responders communicate 

using radios preprogrammed to common frequencies 

(commonly referred to as talk-around mode). 

The drawback of a simplex or line-of-sight system is that 

it gives radio coverage only in a limited area, such as 

one city block. Such a limited coverage does not work 

for dispatchers, but it is used by firefighters and law 

enforcement special operations when they need their 

signals to penetrate a specific building or when operational security is critical. 

Conventional radio repeater systems. A conventional radio repeater system uses a repeater installed in a 

place with a line of sight to a large geographic area, 

such as the top of a building or hill. A radio repeater 

system can be digital or analog and typically consists 

of one or more channels made up of input and output 

frequencies. Users select frequencies by changing channels. A conventional radio repeater system extends the 

operating range beyond what users on the ground can 

achieve. The drawback to the conventional system is that 

it is inefficient when used by large numbers of public 

safety personnel. 

Trunked radio repeater systems. A trunked radio 

repeater system operates on the same principles as a 

conventional system. The difference is that a computer 

connected to a control channel sets the operating frequencies. When users press the push-to-talk button, they 

are requesting permission to transmit to a group of people who have the same privileges to use the channel. A 

group of users with common privileges is referred to as 

a trunk group. The control channel conveys a request to 

participate in a trunk group to the system, which recognizes the radio and assigns the correct privileges. If permission is granted, the system automatically directs the 

radio to the frequency that is assigned to the trunk group. 

Trunked radio systems support many more users than 

conventional systems. The drawback is that they are 

generally much more complex and costly. 

RECOMMENDATIONS TO IMPROVE INTEROPERABILITY

When choosing a system for a public safety agency, 

radio system planners need to conduct comparative 

analyses to determine which type of system is most 

appropriate for the environment and requirements 

imposed by their mission and operations. 

The following are important tips to improving 

interoperability: 

■ 	 Make sure your agency’s communications systems 

work smoothly before attempting to be interoperable 

with another communications system. 

■ 	 Sharpen your collaborative working relationships 

with other agencies before embarking on interoperability solutions. 

■ 	 Get agreement from all stakeholders on a set of 

basic requirements and acknowledge that all systems 

need to be maintained, upgraded, and eventually 

replaced. 

■ 	 Set realistic goals that fit the resources available and 

provide an achievable level of interoperability. 

■ 	 Keep in mind these three low-cost interoperability 

solutions: 

❑	 Preprogram all mobile and portable radios with 

national interoperability channels and frequencies 

(found at www.fcc.gov), a step that usually requires no additional infrastructure. 

❑	 Share radio frequencies with neighbors on
 

compatible radio systems. 


❑	 Adopt plain language communications for 


day-to-day transmissions.
 

FOR MORE INFORMATION

■ 	 NIJ’s Communications Technologies (CommTech) 

Web site: www.ojp.usdoj.gov/nij/topics/commtech 

■ 	 Regional National Law Enforcement Technology 

Centers: www.justnet.org 

NOTES

1.The 700 MHz band is allocated to public safety and 

will be available upon completion of the digital television transition on February 17, 2009 (see ”Digital 

Television Transition and Public Safety,“ National 

Telecommunications and Information Administration, 

http://www.ntia.doc.gov/otiahome/dtv/). 

2. For more information about implementing gateways, 

see NIJ InShort, Interoperability Gateways/ 

Interconnects, NCJ 217105, March 2007. 

*NCJ~214331*
 

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