Interoperability

When it comes to public safety radio communications, you’ll be hard pressed to find a concept that receives more attention than “interoperability.”

During radio’s Stone Age, when the first few public safety radio systems all used VHF lowband, analog FM and single-channel systems, interoperability meant having a crystal (a frequency-controlling component) and a channel switch that would allow one agency’s radios to be used to communicate on another agency’s frequency.

As new systems were built to use increasingly higher frequency bands, first VHF highband, followed by UHF and then 800MHz, most agencies on different bands lost interoperability. Some compensated by using scanners to listen to each other’s frequencies and communicate cross-band or by installing multiple radio units.

Emulating long-distance telephone switching (remember “trunk lines?”), manufacturers developed “trunking” radios that automatically select from a pool of assigned channels to boost system capacity. A public safety trade group developed a trunking standard, but standard and proprietary systems have proliferated. The difficulty of achieving interoperability increased with multiple frequency bands, multiple trunking protocols and conventional-to-trunked infrastructure incompatibility — offset by mutual aid channels.

Since the introduction of digital radio, representatives of local, state and federal agencies have worked together to develop a standard protocol (Project 25) for digital radio interoperability within a given frequency band (absent multiband radios) in North America. Alongside those representatives’ work, manufacturers developed other digital radio protocols, including another standard, TETRA (sold outside North America). Also included are proprietary protocols, OpenSky and EDACS ProVoice, chosen for use in several statewide, countywide and municipal systems in the United States.

Here in radio’s Migraine Age, public safety agencies face a bewildering choice of technologies.

Let’s not forget where interoperability begins. It starts with public safety workers (not to mention political leaders, sworn officials, emergency center managers and union chiefs) cooperating, within and among agencies and jurisdictions, to serve the public in the best possible way. It moves forward with organizational tools, such as the Incident Command System, that facilitate coordinated inter-agency emergency responses. It can fail without adequate radio communications.

Some agencies take the lead; others follow. Windows of funding opportunities open, and then close. The age, condition and relative obsolescence of radio systems varies within a geographic area of possible consolidation. Personal and professional rivalries may interfere. Through all this, public safety agencies advance toward interoperability.

Remember when the interoperability of wireless telephone systems was challenged by the development of multiple standards, including one analog and several digital standards on two frequency bands? At no small technical challenge, handsets were developed that operate on two frequency bands with more than one protocol.

As this column was being written, a radio manufacturer announced a similar development for public safety communications: a portable radio that works conventionally, trunked, analog or digital, with SmartNet, SmartZone, Multi-Net and Project 25 protocols, not to mention Project 25 DES-OFB encryption.

Where agencies otherwise do not achieve interoperability, console cross-connects, over-the-air interfaces and multiple-protocol radio units fit as pieces of a puzzle that may never be completely assembled.

Various interoperability definitions

1. The use of a standard digital radio protocol, trunked or conventional, so equipment from various manufacturers for a given frequency band would work on a standard system — such as Project 25 in North America and TETRA elsewhere.
2. The use of a common frequency band so that radios using a common trunking protocol, a common digital radio protocol or both (standard or proprietary), or the conventional analog mode could communicate.
3. Operational cooperation among agencies inside and outside a given jurisdiction.
4. The use of interchangeable equipment, including accessories, so workers providing mutual aid can share resources.
5. The common use of the same manufacturer’s proprietary trunking protocol, digital radio protocol or both.
6. The ability to spontaneously and immediately talk with a dispatcher or public safety worker from another agency on that agency’s frequency, whether using multiple, non-compatible radio units or standardized units.
7. The use of over-the-air cross-band, cross-protocol interfaces, such as the JPS ACU-1000, to allow otherwise non-compatible radio units or systems to communicate when the interface is activated.