09-07-2011, 03:46 PM
Terrestrial trunked radio (TETRA) is the modern digital private mobile radio (PMR) and public access mobile radio (PAMR) technology for police, ambulance, fire, transport and security services. It is use by utilities, the military, public access, fleet management, closed user groups, factory site services, mining, etc. In short, TETRA is digital radio.TETRA uses Time Division Multiple Access (TDMA) technology with four-user channels one radio carrier and 25 KHz spacing between carriers. A TETRA trunking facility provides a pooling of all radio channels, which are then allocated on demand to individual users, in both voice and data modes. By the provision of national networks, countrywide roaming can be supported, the user being in constant seamless communications with his colleagues. TETRA supports point-to-point and point-to-multipoint communications both through the TETRA infrastructure and by use of direct mode without infrastructure. New features and essential parts of the TETRA standard have been approved by all European nations and are widely adopted in most other countries than US and Japan. The services will continue to be standardized to TETRA for years to come, just has been the case with GSM
