Abstract: A communication device includes a primary communication unit and an auxiliary communication unit. The primary communication unit is operable between an operational state in which a primary communication channel is able to be established for communication with a remote control station and a non-operational state in which the primary communication unit is unable to communicate with the remote control station and the auxiliary communication unit is configurable in an operational state for establishing an auxiliary communication channel for communicating with the remote control station. The primary and auxiliary communication channels include primary and auxiliary radio links respectively.

Abstract: Communication apparatus comprising a plurality of mobile communication devices arranged for peer-to-peer communication using TDMA, the arrangement being such that a said device wishing to transmit uses a time slot in each TDMA time-frame used for transmission, the time slot in each frame being the same and wherein the communication devices include means for synchronization to the same TDMA time frame using a synchronization signal, the synchronization signal being transmitted by a said communication device or a GPS satellite.