Site hand off operation in a SmartZone system

In recent years, trunked land mobile radio system technology has grown from commercial Specialized Mobile Radio (SMR) applications into very sophisticated private system applications. Many of these private trunked radio systems provide communications over very large geographic areas such as entire states. Some wide area communications systems, as designed by Motorola, allow nearly seamless communications between sites within the total geographic area and are marketed by Motorola under the trademark SmartZone. Subscribers in a SmartZone multi-site trunked communication system have the ability to accomplish site hand offs without needing the fixed end equipment to notify them when to switch to another site. The subscriber units accomplish this by utilizing Received Signal Strength Indications (RSSI) in the hardware and with software algorithms to smooth out the raw RSSI data collected by the radio from the control channel. Preferences can be placed on specific sites which will cause the subscriber units to switch towards/away from specific sites. This process of having the subscriber units determine when it will be beneficial to switch to another site eliminates the additional signaling on the control channel which would be needed to keep the subscriber units at the optimal site if the site switching decision was performed at the fixed end