From The RadioReference Wiki
iDEN™, short for Integrated Digital Enhanced Network, is a proprietary trunked radio system format developed and marketed by Motorola.
Nextel and the Southern Company's SouthernLINC radiotelephones use iDEN networks. ARINC also uses iDEN technology for it's AviNet Wireless Dispatch service covering major airports in the United States.
iDEN is based on an older all-digital trunking format called MIRS. There is an iDEN system operating in Israel under the name MiRS.
A smaller version of the iDEN system is available, the Harmony Wireless Communications System, with support for a maximum of 192 sites as of Small System Release 5.0. With the introduction of Small System Release 6.1, Harmony gains the ability to interface with a full iDEN system.
iDEN channels are 25 khz wide and carry a 16QAM modulated signal in a 6 slot TDMA configuration. Dispatch calls occupy one TDMA slot while duplex (eg. telephone or PSTN) calls occupy 2 slots. According to Motorola brochures, the vocoder is VSELP.
Synchronization: Each EBTS Base Site requires precise timing and location information to synchronize data across the network. To obtain and maintain this information each EBTS uses GPS satellites obtain a precise, timing reference pulse.(about Synchronization discussion:firstname.lastname@example.org)