Local radio communications frequencies often are taken into consideration when deploying interoperability solutions for interagency or local jurisdictional communications that operate in different bands or have technical limitations. In other cases, they are used to add additional functionality, such as extending push-to-talk communication to PC or PSTN users.

But an agency's interoperability solution also should include the capability to communicate with other agencies beyond its normal jurisdiction in the event of a large-scale incident, when resources may be deployed from anywhere in the country. Maintaining the ability to communicate with these resources can greatly aid in their usefulness.

The FCC has set aside a set of frequencies in each of the bands for this particular use. By including these frequencies in its interoperability solution, an agency will increase its capability of being able to communicate with other agencies that may be deployed into its jurisdiction during a disaster.

Most new radios have the ability to program many more frequencies into the radios than the jurisdiction requires. Thus, the first step for agencies programming radios is to include the proper interoperability frequencies.

Even if an agency is not deploying an interoperability solution, this extra effort of adding the public-safety pool frequencies into end-users' radios could still be done to give first responders the capability to communicate on TAC frequencies if they are deployed to another jurisdiction to fulfill a mutual-aid request. These frequencies also can be an excellent alternative if an agency's primary system experiences an outage, becomes overburdened during a disaster or the users are outside their normal coverage area.

If an agency also deploys an interoperability solution, including a set of radios with the capability to operate within the frequencies of the public-safety pool could greatly increase the odds of being able to communicate with radio users from other jurisdictions that may be deployed.

The diagram at right depicts an interoperability solution. In this example, the local UHF police radio and VHF fire radio are linked into the interoperability solution via the LMR gateway.

When required, both radios can be added to a virtual talk group during incidents that may require the two first response agencies to communicate with each other. To ensure the deployed solution also has the capability to communicate on the FCC-designated, multidiscipline interoperability channels in the public-safety radio bands, an additional set of radios would be added to the solution.

These additional radios ensure that the interoperability solution is capable of communicating with other radio users operating on a frequency from the pool. Using the virtual-talk-group capability and patching one or more of the pool radios with an agency's standard jurisdiction frequencies/talk groups gives visiting agencies the ability to communicate with jurisdictional radio users without actually having to reprogram radios.

This approach has an added benefit to the host agency. While reprogramming or swapping radios can make them difficult to control once they are deployed, the host agency remains in full control of a virtual talk group by maintaining the ability to activate or deactivate it as needed.

For example, let's say your local jurisdictional radio system is a Project 25 (P25)-compliant trunk radio system operating in the 800 MHz band, and you have an assigned talk group on that system that your radio users tune to for incident command. When a large-scale incident occurs, your local authorities request mutual-aid assistance.

A fire department from a neighboring state agrees to send a pumper truck and a five-person crew for two weeks to assist. When the pumper truck arrives and is briefed at the emergency operations center (EOC), it is discovered that the pumper truck and crew have VHF radios that have been preprogrammed with the VHF TAC set of frequencies from the interoperability pool as part of their jurisdiction's radio frequency plan.

Having deployed an interoperability solution with the capabilities shown in the diagram, including a set of radios capable of operating on each of the public-safety pool bands, the EOC had created a virtual talk group that includes the local 800 MHz trunked radio talk group for incident command, V-TAC 1, U-TAC 1D, and I-TAC 1D.

By adding the local P25 radio tuned to the incident talk group and each of the interoperability pool radios into a virtual talk group, the pumper truck and the crew's portable VHF radios can communicate with the incident-command talk group on the P25 800 MHz radio system by simply setting their radios to V-TAC 1.

With both parties having this capability to use the FCC interoperability frequency pool, the pumper truck and five-person crew can use their existing radios during the mutual-aid assignment and communicate with incident command on the P25 800 MHz trunk system. Without this capability, the local jurisdiction may have had to assign up to six P25 800 MHz radios to the truck and crew.

To make this vision a reality, the following needs to be in place:

  • It is important that a separate radio and antenna be dedicated for each of the frequency band pools. This will ensure that, should the need arise to create a virtual talk group with users on two separate bands simultaneously, you will have that capability.
  • Your local jurisdiction should determine which TAC channels will be considered the default. Often, this decision has already been made at a state level, so check with officials in your area.
  • It also is important to ensure that your agency meets all the FCC requirements as authorized users. The FCC allows mobile operation on these interoperability channels without an individual mobile license, provided the user is otherwise licensed under Part 90 of the commission's rules. Complete requirement details can be found on the FCC website and searching for document 00-348.

Technology can be used to solve interoperability issues. In fact, it may make sense that technologies from different vendors be combined to enhance the capabilities of different solutions — there is no one magic solution that meets everyone's needs.

However, deploying technology is not the only option, because some interoperability communications capabilities can be achieved with little or no technology. For instance, adding the proper TAC frequencies from the public-safety pool to your radio programming plan can be accomplished with no additional technology, if your radios have open programming slots.

But when you have chosen to deploy technology as a solution for interoperability, you can get a better return on your investment by adding the additional radios that are able to operate on each band of the public-safety pool.

Mark Vitosh is a network consulting engineer with Cisco Systems. He has worked in the communications industry for 25 years and currently specializes in integrating radio systems into VoIP environments for both interoperability and push-to-talk communications.