Background

Trunked radio system operations background

The system uses a central computer and a dedicated control channel to dynamically assign available frequencies from a shared pool of users which increases efficiency compared to conventional systems where frequencies are dedicated to specific groups. All radios listen on a control channel which has a dedicated frequency that is used as the central point of communication for setup and management. When a user presses their push to talk button, the radio sends a request to the control channel for a specific talk group. It is then dynamically assigned by the system’s controller which determines which frequency is communicated to all radios in the requested talk group, sometimes known as the voice channel. The radio’s frequency then switches to the assigned frequency and the user’s transmission begins. When the radio finishes the transmission, the radio then returns to the control channel frequency, and awaits the next call. An overview of how the system works is shown below.

The benefits of this system are the efficient use of channel frequencies so that a large number of users can share a smaller pool of frequencies. The automated assignment of frequencies by the controller is fast and minimizes delays that can occur when waiting for a channel to become available. It also supports an increase in capacity compared to conventional systems with the same number of available channel frequencies because it can support more users and groups. Most importantly, the system provides interoperability that allows for easier communication between different user groups, such as fire, police, and utilities, on the same system.

Added LTE and Wi-Fi capabilities

In order to complement the mission-critical communication paths, Wi-Fi and LTE/5G capabilities can be added to the system using interoperability gateways. The primary goal is to extend communications beyond conventional means, native range, and add broadband data services. The gateways connect to a broadband network, allowing standard mobile and portable radios to communicate with users Push-To-Talk (PTT) apps on smartphones, tablets, or PCs. This allows agencies to integrate existing radio communication systems with newer broadband technology, expands communication coverage to users outside the radio communication network, and provides a lower cost option for adding PTT services on existing smartphones, offloading non-critical traffic and freeing up capacity.